Knowledge Adventure: Space & Undersea Adventure & Speed

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»Ñ#`$╚*X/v7╘AOL╫RÅ[ej╨vê╘ï7ì∙ù╗ƒ¬º¡┼»∙▓ ╖{║ε┬Q╧╘╫ß,Θ6∩p∙╞√ùk ⌐ε∩EL ╨,·.ï3"<╨@òK√P¬Y¥]b₧eÖgâos▐v┐~äåêaöΦí>Ñ╫¿┴µ┴╤╟╒╙µ╛÷¥T╘xi M){28Å<F≥HNFS╘Wåg yWüúâ₧ëdï▌ÄΦÉíÆ█ÿ_¢¬│░o└Ü┬┘╟ò╔≥╬T╙█τ▄éΓ÷µ±╗⌠Ω∙ ╞├$¼dÉ) <.l2ê7½@≤CiM1P-UÿWó_êgâj¥rε}≥ä°çgïVÅÆ∩ôÇùΓÜ┤º=¬%¼ç¡Æ┬ ─é╟Q╥⌠╫ì▄▀¿σ╚µnΦ╣Ω@±@⌡ °85╛╨Ω≤b#&ÿ2t4┼6K9\A@H(M╔RBV┴Vx['] _τlªtσçkîBô^ª ▓k┴¡╚0╦d╠░▄ä▀ƒτ}∞≡ª÷U∙ƒ√öå ^ +@-<7pD╟HaJILòPUU~\üddh1l┴u└x|Hé~å[ë#ò£¢]º⌐á«<▒°╝j└p┼s╟╢▀.µ>Θ2≈Æ√Θµ ╦=e$ß$½'D*û/l1┼8╧<uBFK≈P·Z/^▓cïf╝lps zûæfÖ╒¥?íFº╧½Ä│T╝/┴⌐┼╠╦ë█@ßlµΣ∞íε╛≥t≈╞√φⁿ╛&~ X╪ìì$6*▌0ëA╛K⌠PjSJUP_ƒdpox╩~+åRìτæ┤ûhÜâí│Ñ1╡^╜ç┐╞┬┘╚c╓M▄9σô∞Kε`≥²3 i∞Space Adventure Quiz To play Space Adventure Challenge, choose a level of difficulty from the buttons to the right. A question will be displayed in this window. Then begin searching for the screen that answers the question. Every time you use the globe, the time line, or any other method of interaction with Space Adventure, your score will increase. It will keep increasing until you get to the screen that answers the question. Try to keep your score as low as possible. If you need help, return to this screen and select the Hint button. This will cost you some points, though! When you land on the right screen, Space Adventure will let you know! ▌Using Space Adventure If you need help using Space Adventure, read the following information. When necessary, click on the down button at the bottom of this text box to continue reading. KEYBOARD USERS: Move the cursor to a down button using the arrow keys or tab key, then press Enter. Tab and Shift-Tab move the cursor to various clickable areas. PICTURE WINDOW By moving the cursor over the picture window, you can often see additional information about objects in the picture. By clicking you can travel to a time and place somehow related to the object you click on. If nothing happens, try clicking elsewhere in the picture. TEXT WINDOW You are now using the text window. Move forward or backward in the window by using the up and down arrow buttons below. For faster forward and backward movement, use the double up and double down arrow buttons. By clicking on a word in the text window, you can access the index to find other references to that word in other screens. TIME LINE The time line below the picture window changes to reflect the date of the current screen. To travel to a specific time in history, click anywhere on the time line. To move forward or backward one screen at a time, click once on the right or left arrowheads at either end of the time line. You can also pick up the slider by holding down the mouse button and dragging it to any other time in history. KEYBOARD USERS: Press the Plus key to move forward in time or the Minus key to move back in time. GLOBE WINDOW Click on any point in the globe window (in the upper left of the screen) to travel to the nearest point geographically. Move closer to or further from the Earth using the slider bar. You can click anywhere on the slider or on the arrowheads at either end of the slider. You can also pick up the slider by holding down the mouse button and dragging it. KEYBOARD USERS: Press CTRL-PGDN to move closer to the Earth and CTRL-PGUP to move further from the Earth. You can rotate the globe using the four arrow buttons below the window. Or, you can rotate it by holding down the mouse button at any point on the globe. KEYBOARD USERS: Hold down CTRL and press the up, down, left, or right arrow keys. To see the globe in full-screen size, press the expand button just below the globe slider. To return the globe to normal size, press the expand button again. CATEGORY BUTTONS The seven upper-row buttons are category buttons. From the left, they are: Rockets, Human Exploration, Robotic Exploration, Science, Solar System, Universe, SETI-Science Fiction. You can move sequentially through the history of a category by clicking repeatedly on a category button. Or, you can lock in one or more categories (or unlock them) by holding down the Shift key and clicking on them. When a category is locked in, a yellow box appears around the button and your travels using the globe and time line will be limited to that category, or categories. FUNCTION BUTTONS Function buttons are those buttons just below the category buttons. They are Help, Retrace, Game, Zoom, Sound/Movies, Print and Library. Help takes you to this screen. Retrace takes you to the previous screen. Game lets you take a quiz to test your space knowledge. Zoom shows you a full-screen picture. Sound/Movie (when active) plays a sound associated with the picture, or shows a film clip. (Only one of these buttons is active at a time.) Print prints the contents of the text window. Library lets you look up information alphabetically and lets you quit Space Adventure. dExit - Salida - Sortie If you really want to quit your current adventure click on Quit, otherwise click on Continue. A Molecule Is Born 4 Billion BC EARTH We humans are made mostly of a few kinds of common, everyday atoms like hydrogen, oxygen, nitrogen and carbon. The atoms stick together in more complicated groups called molecules, of which water (H2O) is one of the simplest. Atoms are like the letters of the alphabet; molecules are like words formed from those letters. A few letters can make an endless variety of words. Many scientists think that after the Earth formed, the atmosphere consisted mainly of the simple gases found on today's giant planets such as Jupiter: hydrogen, ammonia, and methane. Hydrogen gas (H2, two hydrogen atoms) is found in water (H2O, two hydrogen atoms with one oxygen). Ammonia is the sharp-smelling gas found in many household cleaners (NH3, one nitrogen and three hydrogen atoms). Methane (CH4, one carbon and four hydrogen atoms) is natural (cooking) gas and swamp gas. These, dissolved in the ocean, were the basic ingredients that were available to form life. The chemicals mixed in the water, forming a soup of more complicated molecules. Sunlight provided the energy to cook the soup. Lightning accelerated the process, helping more complex chains of carbon atoms to form. Carbon is very special. Most atoms can only stick to themselves in small clusters (like hydrogen gas, H2, nitrogen gas, N2, and oxygen gas, O2). But carbon is unusual in that its atoms can stick to each other in endless chains, like sticky marbles. For example, ordinary sugar (which chemists call sucrose) is C12H22O11, meaning that a dozen carbon atoms (C) are stuck to each other, together with 11 water molecules (H2O). This unusual stickiness of carbon means that it can form incredibly complicated molecules. This is probably the single most important fact that allows life to exist. Without the ability to make complex molecules, life would be impossible. Scientists duplicated the conditions of early Earth in the lab. Chemists Stanley Miller and Harold Urey did the first such experiment. They put ammonia, methane, hydrogen, and water in a flask and used an electric spark to serve as "lightning." They found that a brown goop formed, made up of many of the same complex organic (carbon) compounds that we humans are made of. Other scientists have done similar experiments with different conditions and have found even more organic chemicals. However, scientists are still far from creating life in the laboratory. Some scientists think that the first atmosphere may have been quite different from the hydrogen-ammonia-methane theory. They suspect it was mostly carbon dioxide (CO2), like Venus's atmosphere. The early chemical reactions would have been different, but such an atmosphere would probably still have produced the organic chemicals of life with the aid of the water in our oceans. When complicated molecules formed in the early seas, they collided with each other. Sometimes they would break apart in the collision, but other times they would stick together to form even more complex molecules. With perfect conditions such a molecule may have formed that broke in two in a special way. The two pieces were identical, and when the right molecules ("food") stuck on them, they formed identical copies of their parent molecule. This would have been the first self-reproducing molecule, meaning that it made identical copies of itself, like a tiny photocopy machine. Each of those copies could then split in two and form more copies. The copies could make more copies. They then spread throughout the oceans, feeding on other molecules and multiplying like rabbits. This was the beginning of life. CSeven With the Right Stuff 1961 AD CAPE CANAVERAL, FLORIDA These were the first Americans chosen to go into space. In NASA's Mercury program, these seven astronauts were the pioneers. Shortly after Yuri Gagarin's first Soviet flight into orbit in 1961, Alan Shepard, Jr. became the first American to fly into space, although he did not go all the way into orbit. Virgil "Gus" Grissom flew the next Mercury flight, also sub-orbital. All of the Mercury astronauts landed in the ocean, and this nearly killed Grissom. His space capsule filled with water and sank. It still sits on the bottom of the Atlantic Ocean. Fortunately, Grissom was rescued by a helicopter. However, in 1967, he was killed in an Apollo space capsule by a fire during a test on the ground. In 1962, John Glenn became the first American to orbit the Earth. He became a hero to the American public. Like aviation pioneer Charles Lindbergh, he was given a ticker-tape parade in New York City. Glenn went on to become a US Senator. Scott Carpenter was the next American to orbit the Earth, followed by Walter "Wally" Shirra. The last Mercury flight was by Leroy Gordon "Gordo" Cooper in 1963. Only one of the original Mercury astronauts never flew in that program. Donald "Deke" Slayton was grounded by a doctor for a slight heart irregularity. He continued to work for NASA, waiting for the doctors to allow him to fly again. Finally, in 1975, the doctors decided he didn't have a real problem after all. His years of hard work were rewarded by rocketing into orbit on the Apollo-Soyuz flight, when American astronauts rendezvoused with Soviet cosmonauts. _Aldrin: First Men on the Moon July 20, 1969 AD MOON Nineteen minutes after astronaut Neil Armstrong became the first man to set foot on the Moon, Buzz Aldrin stepped out of the two-man lander Eagle. There, he joined his fellow explorer on the lunar plain called Mare Tranquillitatis (Sea of Tranquillity in Latin). Armstrong had uttered his famous phrase, "That's one small step for a man, one giant leap for mankind." As Aldrin emerged, he said: "Now I want to back up and partially close the hatch -- making sure not to lock it on my way out." "Good thought," Armstrong replied. It was the dream of the centuries fulfilled. For years people had imagined what it would be like to go to to moon, and finally it had been accomplished. While on the surface of the Moon the two astronauts performed various experiments, planted a US flag and explored the area around their landing site. Meanwhile, Michael Collins orbited the moon in the Apollo 11 Columbia command module. The two men gathered 23 kilograms of Moon soil and rocks, a treasure more precious than gold to scientists, and returned safely to Earth on July 24, eight days after their launch. ÷Jansky's Accidental Telescope 1930 AD HOLMDEL, NEW JERSEY This unlikely looking antenna was one of the revolutionary breakthroughs of 20th century astronomy. In 1930, engineer Karl Jansky was working for Bell Telephone Laboratories. He made this antenna capable of rotating on four Model-T wheels on a circular brick track, so he could aim it to locate radio sources on the Earth. The antenna operated on a short-wave radio wavelength of 14.6 meters (a frequency of 21 megahertz), between today's AM and FM radio bands. To Jansky's surprise, he found radio noise coming from the sky. He studied it for months and discovered that the source moved with the stars. He realized that it had to be a signal from beyond the solar system. By 1932 he had pinpointed the location to the constellation Sagittarius, which happens to be at the center of our Milky Way Galaxy. This was the first proof that the universe broadcasts radio signals that can be detected from the surface of the Earth. It made front page news in the New York Times. Jansky had created an entire new field called radioastronomy. Amazingly, astronomers ignored his discovery for many years. Only an amateur astronomer, Grote Reber, continued to follow up Jansky's discovery. Much later, after World War II, some astronomers began to build on the pioneering work of Jansky and Reber, and found that radio astronomy is one of the most powerful tools we have for studying the universe. Many of the most fascinating objects in the universe emit radio signals: the Sun, Jupiter, galaxies, pulsars and quasars. In honor of Jansky, the International Astronomical Union created the "jansky," a unit of measurement to describe the strength of radioastronomical signals. It also turned out that radioastronomy is the best way to study the structure of our Milky Way Galaxy, because nature's radio signals pass through the gas and dust that absorb starlight. By reading these radio signals, astronomers have been able to map the Milky Way's spiral arms, allowing us to "see" the galaxy as if from the outside. 7 Last Men on the Moon Dec. 7, 1972 AD MOON "As we leave the Moon at Taurus-Littrow, we leave as we came, and, God willing, we shall return, with peace and hope for all mankind." With those words, Apollo 17 Mission Commander Eugene Cernan ended an era. The Apollo lunar program had come to an end and never since has a human being been on the Moon's surface. The last men on the Moon had -- thankfully -- an uneventful mission. Apollo 17's landing site was on the rugged southeast edge of the Mare Serenitatis (Sea of Serenity in Latin), a rugged mountain valley called Taurus-Littrow. The lift-off from Kennedy Space Center on Dec. 7, 1972 was the first night launch of a Saturn V rocket, a dramatic event seen as far away as Georgia. Another first of the mission was a lunar auto repair (the Moon rover had its fender fixed). Also, after several successful Moon trips, NASA felt it was okay that two crewmen (lunar module pilot Harrison Schmitt and command module pilot Ronald Evans) had never been in space before. None of the other Apollo missions had included a scientist. All the astronauts who had been to the Moon previously were test pilots. But under pressure from scientists, NASA assigned to Apollo 17 an astronaut who was an experienced geologist, Harrison Schmitt. He would be the best possible astronaut for the last Moon visit. He could recognize the most important rocks that should be brought back to Earth for analysis in the lab, to help us understand what the Moon is made of and how it formed. When the lander blasted off the Moon, it left behind its descent stage. On it was a plaque showing Earth's two hemispheres with a picture of the Moon in between, and the inscription: "Here man completed his first exploration of the Moon, December 1972. May the spirit of peace in which we came be reflected in the lives of all mankind." In all, 12 astronauts walked on the Moon, spending 170 hours roaming over 60 miles of lunar surface and bringing home 400 kilograms (850 pounds) of soil and rock, 50 core samples, and 30,000 photographs. From their explorations, scientists have determined that the Moon has most of the same elements as are found on Earth, but higher levels of some rare elements, such as zirconium, chromium and titanium. Hydrogen is rare, and water is missing, not even found in rocks, although some scientists suspect there may be ice in the unexplored poles of the Moon. They found that the Moon is about as old as Earth, which suggests that they were born at about the same time. Most likely, the Moon formed when a Mars-size planet smashed into Earth, and the leftover debris became our Moon. U The Apollo Tragedy Jan. 27, 1967 AD CAPE CANAVERAL, FLORIDA It was the worst tragedy in the United States space program prior to the Challenger space shuttle disaster in 1984. On Jan. 27, 1967, astronauts Gus Grissom (the second American in space), Edward White (the first American to walk in space), and Roger Chaffee were strapped in their Apollo capsule for a rehearsal of the first manned Apollo flight. Suddenly, at 6:31 p.m., Grissom screamed, "We've got a fire in the cockpit!" Moments later Chaffee said, "We've got a bad fire, let's get out, we're burning up." They were the last words anybody would hear from the three astronauts. Within seconds the pressure from the fire cracked the capsule and black smoke began rolling out. If the escape rocket on top of the capsule was ignited, the entire rocket might blow up. Despite the danger, technicians rushed to get the astronauts out. After five minutes they were able to remove the hatches, but it was far too late. All three astronauts were dead and badly burned. An investigation determined that the fire probably started as a result of a short circuit in the wiring. In a normal situation, a short circuit would not have resulted in such a calamity, but the situation in the Apollo capsule was not normal. The capsule contained materials that could burn, including the astronauts' pressure suits. To make the situation worse, the cabin was filled with pure oxygen at full atmospheric pressure. The air we breathe is 80 percent nitrogen, which doesn't burn, and makes it harder for oxygen to burn things. In space, there would have been no nitrogen, but a much lower pressure of oxygen would have been used. A flame in the dense oxygen used in this test burns ferociously, and the astronauts had almost no time to react. Perhaps, despite all this, they could have escaped, but the capsule hatch took ninety seconds to open -- far too long. So they died. The tragedy brought the Apollo program to a halt for about a year while the capsule was redesigned. The wiring was changed, the interior was redesigned using fireproof materials and the astronauts' suits were changed to a non-flammable material. And the redesigned hatch took just five seconds to open. At the time of the tragedy, it looked as if solving the problems would delay the Apollo program so much that the United States would not reach the Moon by the 1969 date set by President Kennedy. But the disaster resulted in improved safety of the redesigned spacecraft, and the next Apollo missions were so successful that they were able to make up for lost time. As a result, Apollo 11 made it to the Moon and returned safely in 1969. VArmstrong: A Life of Adventure July 16, 1969 AD WAPAKONETA, OHIO Neil Armstrong will forever be remembered as the first man on the Moon, but for sheer hair-raising adventure, it probably pales compared to his earlier experiences. Armstrong, who was born in the little town of Wapakoneta, Ohio, in 1930, became a Navy pilot, flying 78 combat missions from the aircraft carrier USS Essex during the Korean War. On one occasion while flying through a valley, a cable (put there exactly for that purpose) clipped off part of the wing of his jet. He coaxed it back over safe territory and parachuted to safety. After the war he returned to school and in 1955 received an aeronautical engineering degree from Purdue University, then spent seven years as a test pilot at Edwards Air Force Base in California, where he flew the experimental X-15 plane at about 6,000 kilometers per hour (4,000 miles per hour). In 1962 Armstrong became the first civilian admitted to the astronaut corps. In March 1966, he commanded the Gemini 8 mission, and began the first successful docking in space. But then, everything went haywire. After docking with the upper stage of an Agena rocket, Armstrong attempted to maneuver, but a bad thruster caused the spacecraft to tumble crazily. After a wild ride, Armstrong managed to disengage Gemini from the Agena, and, having used 75 percent of the spacecraft's fuel, was told to return to Earth. By contrast, the July 20, 1969 Moon landing went right according to plan, except for an overloaded computer during the final seconds. Finally, there was an incredible moment, a dream of the ages fulfilled: a man setting foot on the Moon. ë"We've Had a Problem Here" April 11, 1970 AD LUNAR ORBIT "Houston, we've had a problem here," astronaut John Swigert radioed Mission Control. Indeed Apollo 13 did have a problem. Two days after the April 11, 1970 liftoff the mission was 300,000 kilometers (about 200,000 miles) from home and hurtling towards the Moon. Suddenly there was a bang. Astronaut James Lovell knew that one of the valves made that sort of noise, and he thought Fred Haise, Jr., the lunar module pilot, had turned it on without announcing it as a joke. "We didn't really get concerned right away," he said, "but then I looked up at Fred, and Fred had that expression like it wasn't his fault. We suddenly realized that something else had occurred." In fact, a liquid oxygen tank had exploded, destroying the fuel cells that supplied electricity for the service module. While the command module had a back-up battery, it was needed for re-entry into Earth's atmosphere, and in any case, it only had a 10-hour life and they were 87 hours from home. The crew's salvation was in the lunar lander. For three days they relied on its limited power supply and oxygen. Then, instead of going into orbit around the Moon, the crew fired the lunar module's descent engine to swing Apollo 13 around the Moon and head back to Earth. The maneuver was successful, though the trip home was unpleasant as the temperature dropped and carbon dioxide built up. On April 17 the crew moved into the command module and cut loose the dead service module. As it drifted off they could see the whole side had been blasted away. Finally, they made a successful re-entry, landing just six kilometers (3.5 miles) from their recovery ship in the Pacific Ocean. Despite the near-disaster, the mission was not a complete failure. As planned, the crew managed to crash the third stage of their rocket on the Moon so the impact could be picked up by a seismometer (earthquake detector) placed on the Ocean of Storms by the Apollo 12 crew. The impact gave geophysicists additional information about the composition of the Moon. Also, though they couldn't land, the crew did take pictures of the Moon during their swing around it. All other Apollo flights were successful. P Around the Moon Dec. 24, 1968 AD CAPE CANAVERAL, FLORIDA It was a delicate maneuver, putting a spacecraft into orbit around the Moon, but one that was critical to the success of a human landing there. The problem is that if you don't put on the brakes at the right moment for the right length of time, you'll fly away from Earth for eternity. The crew of Apollo 8 got to give this maneuver a try. The mission set off from Kennedy Space Center at 7:51 a.m. on Dec. 21, 1968, launched into a parking orbit around the Earth. After about two loops around Earth to make sure everything was working properly, Commander Frank Borman, Command Module Pilot James Lovell, and Lunar Module Pilot William Anders struck out for the Moon at 39,000 kilometers per hour (24,000 miles an hour), with the Earth -- a beautiful pearl against the blackness of space -- growing small in the distance. On Christmas Eve the spacecraft began its move into lunar orbit. The critical firing of the retro (backwards-shooting) rockets had to come when the craft was behind the Moon, and therefore out of communication with Earth. Anxiously, Houston Control waited while the radios went silent for about 35 minutes. Suddenly, to a great sigh of relief from the ground, Lovell's voice came over the radio: "Please be informed," he said, "there is a Santa Claus." During their orbits, the astronauts described what they saw. Lovell described the Moon as "sort of grayish sand;" Borman more poetically called it "vast, lonely and forbidding;" while Anders said, "All you really need is black and white film." They were the first humans ever to gaze upon the back side of the Moon. And since it was Christmas Eve, Borman (a lay reader in his church) read a prayer to be recorded and broadcast from the ground. Later, in one of the most moving moments of the flight, Anders said the crew members had a message they would like to send home. "In the beginning," came Anders' voice over the radio, "God created the heavens and the Earth..." Then the rest of the crew took turns reading through the creation story from Genesis in the Bible. Early Christmas Day, having successfully moved into lunar orbit and scouted potential landing sites, the crew fired the main rocket to head home. Fifty-seven hours later the command module splashed down in the Pacific Ocean, concluding one of the most amazing journeys in the history of mankind. τApollo Goes to the Moon July 16, 1969 AD CAPE CANAVERAL, FLORIDA The Saturn rocket stood tall on the launch pad that summer day in 1969. President Kennedy, long dead, had set the goal of putting a man on the Moon by the end of that year. Now we were to see if it was possible. The Mercury and Gemini programs had sent men into orbit around the Earth. Three Apollo astronauts had died on the ground during a test. Two Apollos, 8 and 10, had orbited the Moon without touching down. But no one in 5 billion years of Earth's existence had ever landed on the Moon. Three men sat in their capsule atop the gigantic Saturn V rocket with its 3,000 tons of explosive fuel. Apollo 11 astronauts Michael Collins, Buzz Aldrin and Neil Armstrong did their final check-offs, testing that every system was "go" for liftoff. The countdown sounded through the loudspeakers, echoing around the world. Satellites carried the television pictures to 700 million people, one-fifth of the population of the human race. At last the word came: "Ignition!" Kerosene and liquid oxygen flowed into the rocket's five massive engines, generating a thrust of nearly 4,000 tons. With a deafening roar that could be heard for miles, the rocket rose slowly off the launch pad. Apollo 11 was on its way to the Moon. ¢Throw-Away to the Moon 1961 AD WASHINGTON, DC How would humans get to the Moon? In 1961 President John F. Kennedy ordered NASA to devise plans to do it by 1969, but how? For years many ideas had been discussed, but to meet Kennedy's goal scientists had to decide which one to use. The straightforward way would be to use a giant spacecraft that would turn as it neared the Moon so its main rocket engines faced the Moon, and then fire them to slow it for a soft landing. To return, the astronauts would board the spacecraft, fire the rockets to take off and head back to Earth, then fire the rockets again to slow the spacecraft for re-entry into Earth's atmosphere. The problem with this method is that it takes an enormous amount of fuel to get even a small object to the Moon. A rocket not only has to lift the payload (humans), it has to lift all the fuel needed to lift the payload. Was there any way to cut down on the amount of fuel? After studying many alternatives, this is the answer NASA came up with: break the trip down into a series of steps and throw away as much of the space ship as possible without endangering the mission. So the plan was to launch a four-part Apollo spacecraft on top of a giant Saturn rocket. The first of these parts was the Command Module, in which the three astronauts spent most of the trip. Directly behind it was the Service Module, which contained bulky equipment and fuel tanks for the mission. The third and fourth parts were the two sections of the Lunar Module, which would actually make the landing. The lunar module was tucked beneath the other two modules during lift-off. Once the rocket reached orbit, the Command and Service Module (CSM) would separate, rotate, and dock with the Lunar Module. They would then travel together to the Moon. Once in lunar orbit, two astronauts would transfer to the Lunar Module, which would separate from the CSM and land on the Moon. In this way the massive CSM, including the weight of one astronaut, would not have to be carried. This meant that much less fuel would be needed for landing and lift-off at the Moon. After the Lunar Module landed and the two astronauts had explored, they would return to the module. The Lunar Module itself had two parts. The bottom part, called the Descent Stage, would remain on the Moon. It served as a launch platform for the upper part, known as the Ascent Stage. When it was time to leave the Moon, the Ascent Stage fired its rocket and blasted off, leaving the Descent Stage behind. The Ascent Stage, which weighed five tons, rendezvoused with the Command and Service Module. The Moon-walking astronauts then transferred back into the CSM, abandoning the Lunar Module forever. Using the rocket on the Service Module, the CSM then returned to Earth orbit. Abandoning the Service Module, only the Command Module, with the three astronauts in it, re-entered the Earth's atmosphere. Using first friction with the air, then parachutes, the Command Module landed in the ocean, where it was recovered by the Navy. By abandoning parts of the spacecraft, the amount of fuel needed to get to the Moon was enormously reduced. Even so, the main rocket, the Saturn V, was the largest ever made in the US space program. Message to the Stars November, 1974 ARECIBO, PUERTO RICO In November, 1974 the giant Arecibo radiotelescope transmitted a signal designed to be understandable to any alien civilization that might pick it up. The radiotelescope is a giant dish antenna normally designed to receive signals from Mother Nature's radio transmitters, such as clouds of gas in space or from quasars. But it also has a radar transmitter on it, which sends out radio signals that bounce off the Earth's upper atmosphere (the ionosphere), the Moon, and planets. The telescope was aimed at a cluster of stars known as the Great Cluster in Hercules, Messier 13. This is a globular cluster containing about 300,000 stars. The scientists and engineers at Arecibo designed a message that could be interpreted by another scientific civilization. They sent a picture consisting of 1,679 zeros and ones. The number 1,679 was chosen because it is equal to 73 x 23. These numbers, 73 and 23, are known as prime numbers because they are not evenly divisible by anything except one and themselves. So any civilization that picks up these 1,679 bits will be able to figure out that it is designed to be broken up into either 73 rows of 23 bits or 23 rows of 73 bits. The 23 rows arrangement of bits doesn't give a useful picture -- it's just a bunch of dots randomly spaced. But if you arrange them in 73 rows of 23 bits, you get a picture -- a cartoon of our civilization. The scientists packed as much information into these bits as they could. The first row shows how to count in the binary numbering system that computers use. There is one addition, though. There is an extra dot at the bottom of each of these numbers that shows the position of the number. So the first line shows how to count 1, 2, 3, 4, 5, 6, 7, 8, 9, and 10. That is the key to the rest of the picture. The next line has the atomic numbers of the most common chemical elements in our bodies. Chemists number the elements in the order of the number of protons in each atom -- the same as the number of electrons. Hydrogen is number 1, carbon is 6, nitrogen 7, oxygen 8, and phosphorus 15. The next three lines, then, describe the organic molecules from which life is made. Each molecule is represented by the number of atoms of hydrogen, carbon, etc., that it contains. Other information in the picture shows the population of Earth, a little cartoon of a human being, and the spiral structure of the DNA molecule. There is a picture of the nine planets and the Sun, with the Earth shifted slightly toward the human being to indicate that's where the message came from. The large shape at the bottom of the picture is a cross section of the Arecibo radiotelescope, showing the signal starting at the center and bouncing off the radar dish and traveling into space. The last line is the size of the dish, measured in units of the wavelength of the radio signal, 12.6 centimeters (five inches). The signals were aimed at the Hercules Cluster, which is 25,000 light years away. This means that we'll have to wait a long time to get a reply, assuming that there is anyone there to pick up the signal. Radio signals travel at the same speed as light, so it will take 25,000 years for the signal to get to the star cluster. If any aliens reply, it will take their signal another 25,000 years to get here, which means that we have to wait 50,000 years before we can have any hope of a possible reply. This is why most people in the search for extraterrestrial intelligence (SETI) don't want to transmit signals, but want to search for other civilizations' signals. If there was a civilization in this star cluster 25,000 years ago, then we might be able to receive their signals today. A British astronomer, Sir Martin Ryle, warned that Earth should not give itself away by broadcasting signals to other civilizations, which he felt might be hostile. However, we have already announced our existence through our radar and television signals. These are the strongest signals that Earth broadcasts, and they have been traveling into space for much of this century. If there are any civilizations with very sensitive radiotelescopes around nearby stars, they could already be receiving "I Love Lucy" and television news programs. Scientists sometimes joke that, if aliens are receiving our signals, they may think there is no intelligent life on Earth. ▓The Ariane From Guiana 1986 AD KOUROU, FRENCH GUIANA One of the most important rocket launch sites is neither in the United States nor Russia. It is in South America. It is often useful to launch rockets near the equator. If you want to get a satellite into an equatorial orbit, where most communication satellites fly, then launching from the equator in the right direction gives you the benefit of our planet's spin. So when the European Space Agency (ESA) decided to set up its own spaceport, it chose French Guiana, in South America, very close to the equator. Most European rockets are now launched there. ESA has also developed a series of rockets, called Ariane, powerful enough to take communication satellites into high Earth orbit. This has created major competition for the United States, Russia and China in the satellite launching business. Guiana was also the launch site for the Giotto spacecraft, which successfully flew into Halley's Comet in 1986. ?Ariel: Uranus' Sooty Moon 1986 AD URANUS ORBIT Ariel is a medium-sized moon of Uranus that orbits 191,000 kilometers (119,000 miles) from the planet. It is 1,160 kilometers (720 miles) in diameter. It is probably a mixture of ice and rock. Like all of the major moons of Uranus, it is very dark, as if coated with some carbon material, like soot. É Armstrong: The First Footprint July 20, 1969 AD MOON In all of history, not one human being had ever stepped foot on the Moon. For nearly 5 billion years, no footprints of any Earth creature had dented the dusty lunar surface. "You're asking for the Moon" had been a way to describe a goal impossible to reach. For billions of years, meteorites and comets had crashed violently into the Moon. Cracks opened, lava flowed, craters formed. Tiny micrometeorites had battered the mountains, flaking off dust that drifted like snowflakes downhill into the valleys and plains. Down on Earth, continents formed, volcanos cooled, oceans arose, life began. Millions of species came and went. Many of them could fly, but not one of them could leave the atmosphere. Until one day, an apelike creature came along. For billions of years, fire had been a terrifying accident of nature, caused by volcanos or lightning. This new creature was smarter than anything that had come before. With its powerful mind and skilful hand, this one learned to trap the fire and use it to keep warm, make light, cook food and scare away dangerous animals. Fire was just one of many tools the new creature had invented. Stone and wood had been turned into weapons and cooking utensils. Much later, someone else discovered that fire could melt metal rocks. The way was set for the Bronze Age, the Iron Age and, eventually, the Space Age. In 1969, about half a million years after the first creature harnessed fire, its descendents used that same flame to get to the Moon. With the fiery blastoff of the most powerful rocket ever successfully launched, the astronauts of Apollo 11 traveled to lunar orbit. Neil Armstrong, Buzz Aldrin and Michael Collins were in the Command and Service Module, orbiting around the Moon. Armstrong and Aldrin then entered the tiny Lunar Module, barely large enough to seat two men. After sealing the hatches, they separated from the larger module containing Collins. While Collins sat alone in the universe, Armstrong and Aldrin fell toward the surface of the barren Moon. With a burst of that ancient fire, the spacecraft slowed and landed softly in the perfectly dry Sea of Tranquillity. Earth shined brightly in the sky, and hundreds of millions of humans all over the home planet watched on television. Neil Armstrong opened the hatch. He climbed down the short ladder and jumped off the last rung, landing gently with a puff of moondust in the feeble gravity. He made the first footprint ever seen on that airless world. "That's one small step for a man," he said, "one giant leap for mankind." Humanity had arrived. Forevermore, a new catch phrase replaced the old one: "If we can get to the Moon, we can do anything." ¢Asteroids: Riches in the Sky 1801 AD SOLAR SYSTEM At first glance, asteroids (sometimes called "minor planets") are not very attractive; they are just huge hunks of barren rock orbiting the Sun. But someday they may become a source of great riches. The first asteroid ever found was Ceres, discovered by the Italian monk, Giuseppe Piazzi, in 1801. Since then 4,000 asteroids have been found. The four largest are Ceres, Pallas, Juno, and Vesta. Their diameters range from 247 kilometers (154 miles) for Juno to 1,003 kilometers (623 miles) for Ceres. Most asteroids are found in a great belt between the orbits of Mars and Jupiter, right where there's a big gap between the planets. The asteroid belt orbits the Sun like the rings orbit Saturn. Some scientists once speculated that asteroids were left over when a planet exploded in a collision with another object. But today we think there never was a full-size planet, but rather a few moon-size objects. Jupiter's huge gravity would have prevented them from forming a complete planet. As these mini-planets smashed into one another and shattered, some of the fragments were swept up by planets or got shot out of the solar system by the gravity of the giant planets. Some even hit the Earth (and still do). The fragments that survived are the asteroids. Though most asteroids are in orbits that keep them between Mars and Jupiter, a few get closer. Those that just cross the orbit of Mars are called Amor types. Those that cross Earth's orbit are called Apollo types (not to be confused with the Apollo Moon-landing program). From meteorites found on Earth, we know that some asteroids are made mostly of metal. One estimate is that a 1 kilometer (.6-mile) asteroid could have around $1 trillion worth of iron, nickel, cobalt, and platinum. The Apollo asteroids are the easiest ones for spacecraft to reach, because they cross Earth's orbit. Astronauts may one day explore them, and perhaps mine them for minerals. > Astrology's Endurance 1800 BC EGYPT In ancient times it was widely believed that stars could predict the future. Some people still believe this, but they are wrong. It was natural for the ancients to have this belief. They could see that the Sun controlled their lives, rising in the morning and bringing with it warmth and light. The ancient Sumerians and Babylonians developed math and astronomy as they studied the skies. The Egyptians, shown here, knew that the constellations rose and fell in the sky over a period of a year. Certain constellations meant winter was coming; others meant spring was on the way. Farmers knew they could plant their seeds when certain stars were visible, and could harvest when they saw others. We now know that the stars are essentially fixed in the sky, but as the Earth travels around the Sun, the Sun blots out half the sky. Since it takes one year for Earth to go around the Sun, it also takes a year for the constellations to return to their positions. Because the stars controlled farming, it seemed reasonable that they controlled people's lives as well. Furthermore, the constellations seemed to tell stories. There were great warriors, gods, goddesses and terrible monsters up in the sky. We now know that these are just random collections of stars that happened to look like some picture in the human mind. Most of the stars in a given constellation are not even near each other -- they are just accidental collections of stars that happen to be in the same part of the sky when viewed from Earth. Different cultures put the stars into different arrangements in their minds, seeing different pictures, in Egypt, China, India and the Americas. It was inevitable that superstitions would arise. Astrologers studied the stars and claimed that by simply knowing the date and time of someone's birth, they could predict which constellation would control his or her life. Some early astrologers made careful measurements of the positions of the stars and other astronomical events, such as the appearance of comets. Over thousands of years, astrologers laid the groundwork for a real science -- astronomy. Today's astrologers carry on these ancient superstitions. However, careful scientific tests have shown that astrology cannot predict the future. For example, when leading astrologers are given the birth dates and times of people whose names are kept secret, their predictions about the lives of these people are wrong in most cases. In the few cases where there is some resemblance between the prediction and the real person, the results are no better than predictions based on chance. hOne-and-a-Half-Stage Rocket 1951 AD WASHINGTON, DC One of the workhorses of the space program was a rocket originally designed to carry a hydrogen bomb. In 1951 the US Air Force planned to build the Atlas, an intercontinental ballistic missile (ICBM) designed to carry a hydrogen bomb from the United States to the Soviet Union. The original design was unusual in that it was neither a one-stage nor a two-stage rocket, but was sometimes called a "one-and-a-half-stage" rocket. In addition to its regular engine, it had booster engines on either side fed by the same fuel tank. After the rocket had flown some distance, the booster engines dropped off to save weight. Eventually, for the space program, additional rocket stages were added to allow scientific satellites to be sent to the Moon and into interplanetary space. The Atlas was used to launch the Ranger and Mariner series of space probes. The Northern Lights NORTH POLE The long nights at the North and South poles are often lit up by strange, waving curtains of color in the sky, called the aurora, also known as the Northern and Southern Lights. The Vikings thought these lights were the gods at work. We now know that when there's a storm on the Sun -- a solar flare -- a wind of electrons and protons (very hot hydrogen gas) blasts out with full fury. Some of its particles make their way through Earth's magnetic field, hitting the poles and causing the air to glow. Spying on Mother Nature July 31, 1990 AD PASADENA, CALIFORNIA At the Jet Propulsion Laboratory (JPL), an instrument has been designed to spy on Mother Nature. Called AVIRIS (pronounced AV-er-riss), it looks at Earth through hundreds of color filters. Using both visible and infrared light, it can tell the difference between types of crops, and even find out whether they are healthy or diseased. It can also tell the difference between types of minerals, and allow prospectors to search for needed resources. NASA plans to use similar instruments in its EOS (Earth Observing Satellite) program. The space agency plans a series of satellites that will study Earth's resources, atmosphere, oceans, plant life, and pollution. This will help us understand our ecology, and how civilization is altering the planet. αAXAF: X-Ray of the Universe 1997 AD EARTH ORBIT Scientists are now building a satellite that will take an X-ray picture of the universe. Explosions in the universe often make X-rays. Supernova explosions, quasars with explosive events inside of them, and black holes with their terrific energies all generate X-rays. But X-rays are hard to detect, because our atmosphere protects us from them. NASA has designed a large satellite called AXAF (X-Ray Astrophysical Facility). Scientists have used other rockets and other satellites to do X-ray astronomy, but AXAF will be the most advanced X-ray telescope ever launched. Black holes are probably the most fascinating of all the objects that X-ray astronomers study. They are places where the familiar laws of physics break down. No one knows for sure what happens in a black hole, though it appears that matter from space flows into the black hole, heats up, and radiates X-rays and the even higher-energy gamma rays. AXAF should give us a much improved idea of what goes on within black holes. Even our own Milky Way Galaxy seems to have a black hole at its center. This black hole radiates radio waves, X-rays, and gamma rays. AXAF will give us a much better idea of what is happening at the very center of our own galaxy. \Poor Soil, Good Banks 1973 AD BAHAMAS The picture you see below you is a view of the Bahamas taken in 1983 during a Challenger Space Shuttle mission. The first European to set eyes on the Bahamas was Christopher Columbus, in 1492. The Spanish held the islands until 1629, when the British took over. The Bahamas, with a population of about 245,000, became an independent country on July 10, 1973. Made up of 13,868 square kilometers (5,353 square miles) of islands, the Bahamas have poor soil, so there is little agriculture. Instead, the country relies on tourism, its liberal tax laws, banking, and to some extent, fishing. SThe Universe Explodes 1929 AD PASADENA, CALIFORNIA In 1929, Astronomer Edwin Hubble noticed something interesting. Light from the galaxies he was examining was slightly reddened. This seemingly trivial discovery was the basis for a revolutionary theory of the universe -- the Big Bang. To understand his discovery, you need to understand the Doppler shift. A Doppler shift occurs when an object emitting waves (of sound or light) moves towards or away from us. For example, a car horn has a higher pitch as the car approaches and a lower pitch as it drives away. The speed of the car makes the waves come at you more rapidly when the car is approaching, and more slowly when it's going away. Though difficult to detect, the same effect occurs with light. A light that is moving toward you has a higher frequency (pitch) than one that is moving away. A higher frequency of light means blue; a lower frequency, red. The effect is only important when moving at speeds approaching the speed of light, 300,000 kilometers per second (186,000 miles per second). On Earth, we don't see anything in normal life moving anywhere near this speed. But everywhere Hubble looked, he found reddened galaxies. They were all moving away from us at high speed. Not only that, the fainter they were, the redder (faster) they were. But the fainter the galaxy, the farther away it must be. So the farther they were, the faster they were moving. What could explain this? An explosion! If the universe had exploded like a hand grenade, the fastest bits would have flown the farthest. This was the simplest explanation of what Hubble had found. Does this mean the Sun is at the center of the universe? Not at all. Instead, it shows that about 15 billion years ago the universe was all together at a single point, and then blew up in an explosion scientists call the Big Bang. Exploding parts all move away from each other, so no matter which galaxy you are in, all other galaxies seem to be moving away from you. Since Hubble's discovery, thousands of galaxies have been measured, and they all fit this pattern. Most astronomers now accept the theory of the Big Bang. 4How Heavy Elements Were Formed 15 Billion BC UNIVERSE When the universe was born in the Big Bang explosion, it started a sequence of events that led to the formation of Earth. For the first three minutes, the universe was almost inconceivably hot and concentrated. Most fundamental particles of nature formed then: quarks (the building blocks of protons and neutrons), electrons, protons, neutrons and so forth. A proton is the nucleus (center) of the simplest atom, hydrogen. Some of the protons and neutrons formed into the nucleus of the next-simplest atom, helium, which is just two protons and two neutrons stuck together. The universe quickly formed vast amounts of hydrogen and smaller amounts of helium, but it could not yet form significant amounts of heavier atoms. The universe was very hot. Heat is just the random motion of particles; when a gas is very hot, the particles bounce off each other without sticking; when it cools enough, the particles may stick together. The universe expanded and cooled. Opposite electrical charges attract each other, so when it got cool enough, electrons (negatively charged) finally could stick to protons (positively charged). An electron orbited the proton nucleus like the Moon around the Earth. Two electrons orbited each helium nucleus with its two protons and two electrically neutral neutrons. As the universe expanded and cooled still more, clouds of atoms formed, like the clouds in our sky. Attracted by gravity, these clouds compressed into giant swirls of gas, the beginnings of galaxies and quasars. Within these huge clouds, smaller concentrations the size of stars formed like raisins in a pudding. Gravity brought particles closer and closer together. Stars were born. Stars became hotter as gravity heated up the collapsing gas. They became hot enough that their hydrogen nuclei -- protons -- fused together into helium, just as happens inside a hydrogen bomb or the Sun. Fusion converts a tiny bit of matter into energy, and the heat produced keeps a star from cooling off. But this early universe was poor in the ingredients of our common experience on Earth. Only hydrogen and helium were present in large quantities. There were almost no atoms heavier than that. No carbon, or oxygen, or nitrogen, out of which life could form. But those first stars continued to "cook" the matter inside of them, fusing the hydrogen into heavier and heavier atoms, including carbon, oxygen, nitrogen, and all the rest. Eventually, some of the stars exploded as supernovas, and filled space with these heavier atoms. Those atoms traveled around the galaxy until they, too, formed into clumps that became stars again. Only this time, the heavier atoms were available, so that when planets formed, they could have some of the carbon, oxygen, and nitrogen that we see today. Life as we know it could not have existed during the early years of the universe. But now that the universe has been cooking for 15 billion years, the matter from stars has been "recycled" and processed into the heavier atoms out of which we are made. Most of the atoms of which you are made were once inside a star. áAstronomy Self-Taught 1791 AD WASHINGTON, DC Benjamin Banneker, the first black American astronomer, lived through the American Revolution and helped plan Washington, D.C. Working on his own from an astronomy textbook that had been lent him, Banneker became skilled at astronomical and tidal predictions, producing an almanac between 1791 and 1796 that impressed Thomas Jefferson so greatly that he sent it to the Royal Academy of Sciences in Paris as evidence that blacks were capable of scientific pursuits. Banneker, a free-born black in Maryland, briefly attended a school open to both blacks and whites, where he showed a real ability in mathematics. However, his schooling was brief and for the most part he was self-taught. In 1753, when he was about 22 years old, Banneker examined a pocket watch and a picture of a clock, then made a completely wooden clock, each gear carved by hand. And it worked! It kept good time for about 50 years. Though he spent most of his life as a tobacco farmer in his native Maryland, from February to April 1791 he served as scientific assistant for Major Andrew Ellicott, helping survey what became the District of Columbia for the United States' capital city. ∞The Great Barrier Reef GREAT BARRIER REEF, AUSTRALIA This satellite view shows just a small stretch of the Great Barrier Reef, which winds 2000 kilometers (1,250 miles) along the northeast coast of Australia, following the continental shelf from the Torres Strait (separating Australia from New Guinea) to the Tropic of Capricorn. The Great Barrier Reef is the largest coral reef in the world. It, like other coral reefs, was created by ages of secretions by a small marine animal called the madrepore coral. The Barrier Reef is bright with animal life, including tropical fish, sea urchins, giant clams, star fish and oysters. In some places it has formed rings, which fill up with sand to become little islands inhabited by sea birds and salt-resistant plants. ╧ How to Become an Astronaut 1992 AD HOUSTON, TEXAS How do you become an astronaut? First, you need to study math and science. The more courses in these areas that you take, the more likely that you will be astronaut material. Every astronaut needs to have a college degree in one of these areas: math, physical science (such as physics or chemistry), biological science or engineering. There are two main types of NASA astronauts: pilots and mission specialists. Pilots are usually former or current military jet pilots. They must have 1,000 hours of flight time as a jet pilot. Test pilots are preferred. Mission specialists are scientists or engineers who will operate the experiments in space. It helps to have an advanced degree (a masters degree or a doctorate) in math, science, medicine, or engineering. It also helps if you've had experience working on a team under difficult conditions similar to spaceflight, such as on an oceanographic research ship or at an Antarctic research base. NASA looks for evidence that you can work well with other people. You have to be in good physical shape. Pilots need to pass the strict Class I flight physical; mission specialists need only pass the easier Class II. All astronauts need 20/20 vision in each eye, with lenses. Without lenses, pilots have to have at least 20/50 vision, and mission specialists 20/100, in each eye. Your height must be between 163 and 193 centimeters (five feet four inches to six feet four inches). If you pass the preliminary weeding-out of the application forms, then you will go to Houston for a week of intensive interviews and medical tests. Typically, there are hundreds of applicants for every astronaut position available, so the competition is fierce. Those selected are called candidates, and must go through a year of training. Only if they pass this training do they officially become astronauts. As NASA describes their ideal candidate, "Astronauts are expected to be team players and highly skilled generalists with just the right amount of individuality and self-reliance to be effective crew members." For an application to the astronaut program, write to this address: Mail Code AHX, Johnson Space Center, Houston, TX 77058. There is also a third route to becoming an astronaut. That is to work for an aerospace company or a foreign space agency. Occasionally, people are selected by a corporation or agency to accompany an experiment into orbit. These are called payload specialists, and they usually fly just one shuttle mission. Flights of Fantasy 1657 AD PARIS, FRANCE Cyrano de Bergerac is best known as the big-nosed hero of a fictional play and movies, but he was a real man who was himself an early science-fiction writer. His original name was Savinien de Cyrano, but he's best known as Cyrano de Bergerac. Cyrano was born in Paris in 1619 and became a soldier. After being severely wounded, he retired to Paris and became a poet and writer. He wrote two stories that can be considered as science fiction, although the term did not yet exist. These were "Voyage to the Moon" (1656) and "The States and Empires of the Sun" (1662). In these, he envisioned trips to the Moon and Sun by a variety of techniques, including rockets. This was the first known case in which rockets were used for space travel in fiction. These works influenced later writers of early science fiction such as the Irishman Jonathan Swift and the American Edgar Allen Poe, as well as the satires of another Frenchman, Voltaire. Jonathan Swift built on the idea of voyages to alien cultures in his classic novel, "Gulliver's Travels." In that book, not only did he explore the idea of non-human beings such as intelligent horses, but he even invented the concept of the mad scientist. His purpose was to satirize the human race, but in doing so, he created many of the techniques used by later generations of science-fiction writers. Edgar Allen Poe not only invented the mystery story, but also wrote many stories that can be considered science-fictional. In his poem "Al Aaraaf" (1829) and story "The Conversation of Eiros and Charmion," (1839), he described the destruction of Earth. His essay on a chess-playing machine, "Maelzel's Chess Player" (1836) and story, "The Man That Was Used Up" (1839), are really early robot stories. And "The Unparalleled Adventures of One Hans Pfaall" describes a journey to the Moon. Among Poe's many admirers was the Frenchman Jules Verne, who went on to write many science-fiction novels such as "From the Earth to the Moon" (1865) and "20,000 Leagues Under the Sea" (1870). σWorld-Changing Gunk 3.5 Billion BC PLANET EARTH Roughly three and a half billion years ago an incredible event occurred that changed the face of the Earth -- blue-green algae appeared. Blue-green algae? It hardly seems world-changing. It is, after all, virtually the same gunk that clogs ponds and rivers today. Nevertheless, it is amazing. As far as scientists can determine, blue-green algae was one of the first living things on Earth, appearing quite early in our planet's history. But how it came to life amid a swirl of non-living compounds is still a mystery. Scientists simulating an early Earth environment have managed to reproduce the basic chemical building blocks of life -- amino acids -- but how those building blocks came to be organized in such an incredibly complex manner has not yet been determined. One of the systems introduced to the world by blue-green algae is photosynthesis. This sophisticated electro-chemical process is still not fully understood, though in 1957 biochemist Melvin Calvin advanced a reasonable outline of how the process works, and won the 1961 Nobel Prize for chemistry for his effort. However, for human beings and animals, the appearance of photosynthesis was critical. Prior to blue-green algae, the Earth's atmosphere probably contained little oxygen. But because photosynthesis releases oxygen, that scummy pond slime that sticks to your ankles made it possible for you to breathe. Understanding where it came from helps us to figure out how life might arise on other planets. No-Escape Holes in Space UNIVERSE Imagine a place where gravity is so strong that nothing can escape from it -- not even light itself. These places, called black holes, apparently do exist. On Earth, gravity keeps us stuck on this planet, except when we use a rocket to escape. Our gravity is so strong that it takes a speed of 11 kilometers per second (seven miles per second) before the rocket can escape from the Earth. This number is called the escape velocity. The Sun is about 300,000 times as massive as the Earth. That is so much matter that if you were standing on the surface of the Sun, you would weigh nearly 30 times as much as you do on Earth. To escape from the Sun, you would have to move at 600 kilometers per second (400 miles per second). But this is still much slower than the speed of light, 300,000 kilometers per second (186,000 miles per second). Newton's law of gravity says the gravitational force of an object depends on its size and mass. In particular, if you take an object and squeeze it into a smaller size, you'll have a stronger gravity at its surface. The smaller you make it, the stronger the surface gravity will be. So if you were to squeeze the Sun down into a little ball, its gravity would be much greater. If you could make it into an object just 6 kilometers (4 miles) in diameter, the escape velocity from the surface would be a little bit greater than the speed of light. So not even light could escape. Nothing escapes from a black hole. Black holes are not really black. Even though light cannot escape from them, gas and dust in nearby space fall down into the black hole and are sucked in. As they are falling, they bang into other particles and are heated up enormously and glow. They are so hot that they emit not just light, but even stronger electromagnetic waves such as X-rays and gamma rays. Real black holes should be surrounded by glowing clouds of gas and dust. A number of places have been found in our Milky Way Galaxy that seem to contain black holes, including the very center of the galaxy. In fact, black holes are suspected to be at the centers of many galaxies and quasars. One evidence for their existence is that these holes emit X-rays and gamma rays that have been detected by spacecraft and rockets. Nevertheless, some scientists are not convinced that black holes exist. They think that the X-rays and gamma rays may be produced by some other fierce, but more normal, processes. Still, the evidence keeps mounting up in favor of black holes. The best bet is that they do exist, but what goes on inside of them is a mystery. 7It Won't Be an Island Atoll BORA BORA, SOCIETY ISLANDS This is an orbital view of several beautiful South Pacific islands, including Bora Bora, the little island on the left. Bora Bora is slowly becoming an atoll, which means it is being worn away by the sea and will someday just be a ring of coral reef around a lagoon. The island is located northwest of Tahiti and is a member of the Society Island Chain, an overseas French territory. Both Tahiti and Bora Bora are popular tourist attractions. The islands export copra, pearls, coconuts, precision instruments and mother of pearl. ¡Rockets for War and Peace 1960 AD HUNTSVILLE, ALABAMA Following the defeat of Germany in World War II, the United States Army captured many of Germany's V2 rockets, along with many of the German scientists who developed them. Chief among these scientists was Wernher von Braun, aristocratic son of an agricultural minister and an early convert to the idea of space travel. Von Braun, born in Wirsitz, Germany, in 1912, was early fascinated with the problems of rocketry and space travel. In 1931, when he was 18, he wrote a science fiction story called "Lunetta," an account of what a space station might be like. He later became a member of the German Society for Space Ship Travel, a frequently poverty-stricken club with the dream of going into space. The little group experimented with liquid-fueled rockets and in one case dropped one on top of a police station. It caused little damage, except to relations with the police chief. The society's work, and particularly that of von Braun, attracted the attention of the German Army, and in 1932 von Braun became the first of the society's members to accept an offer by the German Army to do secret rocket-development work. He began working in the town of Kummersdorf, and later at Peenemuende. Though involved in building weapons, von Braun said the reason he accepted the offer was that "It seemed that the funds and facilities of the Army were the only practical approach to space travel." When he surrendered to the Americans as the war was ending, von Braun was sent to White Sands, New Mexico. There, he and fellow German scientists refurbished and fired many of the leftover V2s. Later the team was sent to Redstone Arsenal in Huntsville, Alabama, where they formed the core of the 4,000-member Army Ballistic Missile Agency. In Alabama, von Braun's team developed the Redstone and Jupiter missiles, which launched the first US satellite, Explorer 1. In 1960, when NASA took over the Army's missile program, von Braun became head of the United States space program. He resigned from NASA in 1972 and from 1975 until his death in 1977 he served as president of the National Space Institute (now the National Space Society), an organization devoted to promoting space exploration. ║Cosmic Rays All Around MILKY WAY The universe is filled with cosmic rays. The very room in which you are reading this is filled with these rays from space. Cosmic rays are mainly very fast electrons, protons and other elementary particles that move at almost the speed of light. Some cosmic rays are gamma rays, electromagnetic waves at much higher frequencies than light waves, that move at the speed of light. Cosmic rays are very similar to the particles emitted by radioactive rocks, so cosmic rays can be thought of as the "radioactivity" of the Milky Way Galaxy. Cosmic rays travel throughout our galaxy. Some of them hit our atmosphere, causing a shower of lower-energy elementary particles that can be detected with instruments like this bubble chamber. Electrically charged cosmic ray particles, like electrons and protons, are bent by magnetic fields, and in a bubble chamber or cloud chamber they can be seen traveling along a curved path. Uncharged cosmic-ray particles such as neutrons or gamma rays, on the other hand, travel in straight lines. For a long time, it was a great mystery where these rays came from, but now we are pretty sure that they come from supernova explosions, pulsars, and black holes. A supernova, for example, is a star that explodes with such force that its very matter is thrown out into space at nearly the speed of light. Some of the cosmic rays passing through you at this moment may have been born in the explosion of such a star. Buzz Aldrin: Space Advocate 1992 AD SOUTHERN CALIFORNIA Buzz Aldrin, lunar module pilot of the first flight to the Moon, was born in Montclair, New Jersey, in 1930, the son of a retired Air Force colonel. He was christened Edwin, but picked up the nickname "Buzz" because his little sister Fay had a tough time pronouncing "brother." It came out "buzzer." Later he had his name legally changed to "Buzz." In 1951 Aldrin was graduated third in his class from the United States Military Academy. He became a pilot, flying a Sabrejet in the Korean War and shooting down two MIG-15 jets. In 1963 he received a Ph.D. in astronautics from the Massachusetts Institute of Technology and then became an Air Force representative at the Manned Spacecraft Center. Later he became an astronaut. Together with astronaut James Lovell, Aldrin concluded the Gemini space program, setting a five and a half hour record for space walking, performing a successful docking with an Agena rocket stage and using the Agena's engine to bump the Gemini 12 spacecraft into an 850 kilometer (530 mile) high orbit to take the first pictures from space of a solar eclipse. Previously, astronauts found they quickly became exhausted from their space walks. But Aldrin solved that problem by moving as slowly as he could. At the end of one of his three space walks, Aldrin had enough energy to carefully wipe the Gemini's window before coming back inside. His partner, James Lovell, joked: "Check the oil, too." Since retiring from NASA, Aldrin has been one of the foremost advocates for continued space exploration. Welcome to Space Adventure 1992 AD Hello. I'm astronaut Buzz Aldrin. Welcome to Space Adventure. You are about to enter a universe of wonders. You will see sights that no one until our era had even dreamed of. You will share the struggles that the pioneers of astronomy and spaceflight endured. Come visit the Moon with me. See what pulsars and black holes are. And encounter the mysteries whose answers we still do not know. Perhaps you will be the one to solve them. You will find a universe filled with possibilities: space colonies, trips to Mars, maybe even extraterrestrial beings. See places where you yourself may one day explore if you have the courage and wisdom. I was privileged to visit the Moon. Would you like to follow in my footsteps and walk on Mars? Take the first step and explore the universe with me. ╪Callisto: Last of the Big Four 1610 AD JUPITER ORBIT Callisto is the last of the four large moons of Jupiter as you move away from the planet. Like the other three, it was discovered by Galileo in 1610. It's 1,883,000 kilometers (1,170,000 miles) from Jupiter. Like Ganymede, it is a large ball made of about 60 percent rock and 40 percent ices of water and methane (CH4). It is 4,800 kilometers (3,000 miles) in diameter, or almost 40 percent larger than our Moon, and is heavily cratered by meteorites. /Canadian Space Contributions 1962 AD TORONTO, CANADA While the United States and the former Soviet Union have launched most of the world's spacecraft, other countries have also played an important role in the exploration of space. One major contributor has been the United States' neighbor Canada. Probably the Canadian contribution is most visible -- as this photograph suggests -- through its development of the space shuttle's Remote Manipulator Arm, better known as Canadarm. The 15-meter (50-foot) arm, shown here in its stored position on the left side of the shuttle, is designed to load and unload the shuttle's payload bay. It was built by Spar Aerospace of Toronto and can handle up to 65,000 pounds of payload. Its most notable achievement was rescuing the disabled Solar Max satellite from orbit in 1984. But Canada was involved in space exploration long before the space shuttle. In 1962 a 145-kilogram (320 pound) Canadian-built satellite called Alouette was launched from Vandenberg Air Force Base in California atop a Thor-Agena B rocket. The satellite, which studied the top side of Earth's ionosphere, was as advanced as any US satellite of the time. In 1984, Marc Garneau became the first Canadian astronaut in space. He rode into orbit on October 5 aboard the Space Shuttle Challenger. And currently, Canada is participating in the international Space Station Freedom project. The project is a joint effort of Canada, the European Space Agency, Japan and the United States. The first sections of the station should be in orbit by 1995 and it should be complete by about the year 2000. µCassini: Probing Titan 1995 AD SATURN ORBIT One of the most exciting of upcoming space missions is a joint European/NASA mission called Cassini. Cassini, now being built and due to be launched in 1995, will do for Saturn what the Galileo spacecraft will do for Jupiter. But while Galileo will orbit Jupiter and drop a probe into the atmosphere of the planet, Cassini will orbit Saturn and drop the probe into the atmosphere of its biggest Moon, Titan. Titan is one of the most fascinating places in the solar system. It's the only Moon with a thick atmosphere. Titan probably has lakes or even oceans of liquid organic chemicals. Conditions there in some ways resemble those from which life first formed on Earth. It is, however, much colder than Earth, and most scientists do not think that life is likely to exist there now. Nevertheless, Titan is a fascinating world that may show us a great deal about the kind of chemistry from which life first evolved. The Cassini probe will arrive at Saturn in the year 2004. SChallenger: The Deadly O-Ring Jan. 28, 1986 AD CAPE CANAVERAL, FLORIDA In 1986, tragedy struck the American space program. On a cold winter morning, the space shuttle Challenger blasted off. A few seconds after launch, while the world watched on television, the shuttle exploded, killing seven astronauts: Francis Scobee, Judith Resnick, Ronald McNair, Michael Smith, Sharon Christa McAuliffe, Ellison Onizuka, and Gregory Jarvis. It was the worst disaster in the history of the American space program. It threatened to bring the entire American astronaut program to an end. All of the shuttles were grounded for more than a year while investigators studied the evidence. The cause turned out to be in the solid rocket boosters. When a space shuttle takes off, it uses both solid and liquid fuel rockets. The main part of the shuttle -- the orbiter with the crew -- uses liquid oxygen and liquid hydrogen as fuel. These liquids are contained in the enormous tank strapped on the bottom of the orbiter. But for an extra boost, solid rocket boosters (SRBs) are strapped on the outside of the shuttle. The two SRBs are similar to rockets used in fireworks. They contain a solid fuel. And the walls of these rockets are cylinders stacked on top of one another like long pipes. The two cylinders are joined by a circular rubber ring, called an O-ring. The O-ring is supposed to prevent the rocket fuel from burning through. But on the morning of the Challenger launch, the temperature was below freezing. The rubber O-rings were hard, and did not flex during the stresses of the lift-off. Ordinarily, the boosters would fire for two minutes, and then be released, parachuting down to the ocean to be recovered and reused. Tragically, before the shuttle reached the point where the boosters would be let go, one of the rockets burned through its O-ring. The flames shot out like a blow torch and touched the spacecraft. This caused the shuttle to explode. Investigators found that on previous flights, flame damage had occurred to the O-rings. This was a warning sign that a serious problem could occur, but the astronauts were not informed and the problem was ignored. As a result of the Challenger investigation, a major shake-up took place within NASA. Parts of the shuttle were redesigned and safety procedures were greatly improved. If any problems were seen by the ground crew, they were required to tell the astronauts. Any engineer or technician who found a serious problem was encouraged to report it to NASA managers. NASA had been through a similar tragedy before. In the early days of the Apollo program, a fire broke out during an Apollo ground test. Three astronauts died in the Apollo fire. This threatened to seriously delay the Apollo program, but as a result safety procedures were greatly improved, and not only did Apollo get to the Moon on schedule, but there has never been a loss of life in space. Since the space shuttle started flying again after the Challenger disaster, there has never been another serious accident. But it is important to remember that it is always dangerous to explore a new frontier. All of the astronauts know the risks, and accept them. Chicago: Central City 1825 AD CHICAGO, ILLINOIS In this view from the Skylab space station, you can see Chicago, the great hub-city of the midwestern United States, along with the south end of Lake Michigan and the roads radiating from the center of town. Chicago was founded when the Erie Canal was opened in 1825. With the arrival of the railroads, it grew rapidly, becoming the grain and livestock processing center for the surrounding agricultural areas. The Great Chicago Fire destroyed much of the city in 1871, but it was quickly rebuilt. oChina's Great Invention 1200 AD CHINA Rockets already existed when Isaac Newton described how a cannon could theoretically fire around the world. They were invented most likely by the Chinese in the thirteenth century. The early Chinese rockets were essentially arrows with a small rocket tube attached to the side. They had a range of about 200 meters (200 yards). Between 1300 and 1800 there were advances in rocketry, but even greater advances in gunnery left rockets behind and almost forgotten. But then, in India, the Prince of Mysore bombarded the English with 12-pound rockets made of iron. This spurred the English to create the British Rocket Corps and brought rockets once more to the attention of the West. During the War of 1812, Francis Scott Key witnessed British rockets firing on Ft. McHenry, and wrote a song about "the rockets' red glare" that became the American national anthem. In 1970, the Chinese returned to the frontier of rocketry by becoming the fifth nation to launch a satellite. Today, their Chang Zheng -- "Long March" -- rockets are important competitors in the international marketplace for launching commercial satellites. yStars With Halos 1983 AD UNIVERSE Many stars have rings around them, like the rings of Saturn, but much bigger. In 1983, astronomers using the IRAS infrared-satellite telescope discovered that a nearby star called Vega has a ring around it. The ring looks much like Saturn's rings, but is far larger -- bigger than the whole solar system. The next year, astronomers Richard Terrile and Bradford Smith discovered that such rings could be seen with telescopes on Earth by using special techniques to block out the bright light of the star. Working with a telescope at Las Campanas Observatory in Chile, they photographed a huge ring around the star Beta Pictoris. It's a disk of glowing dust about ten times the diameter of Pluto's orbit. Since then, astronomers using both Earth-based and space-based telescopes have discovered many more of these rings around other nearby stars. What are they? Astronomers believe these rings are junk left over from when the star formed. The solar system was originally just a big cloud of gas and dust that collapsed as gravity pulled its parts together. The greatest concentration of matter was at the very center, which became the Sun. The leftovers continued to orbit around the Sun and, gradually, small clumps formed into planets, moons, asteroids and comets. Astronomers suspect that these rings around nearby stars -- called circumstellar rings -- are the leftover debris from the formation of these stars. We don't know for sure if planets have formed inside these rings. But the fact that these discoveries fit our theory so nicely suggests there's a good chance that planets also formed there. Or that they may form in the future. One estimate is that at least 10 percent of the ordinary stars in our galaxy have these disks, or rings, around them. This suggests that there's a good chance that planets may be a common byproduct of the formation of stars. If so, the odds that life may arise elsewhere in the universe are improved. PICTURE CREDIT: Reprinted from The Decade of Discovery in Astronomy and Astrophysics. Copyright 1991 by the National Academy of Sciences. Published by the National Academy Press, Washington, DC. ïFlying the Space Shuttle 1981 AD CAPE CANAVERAL, FLORIDA This is where the space shuttle is piloted. The commander and pilot of the shuttle sit on the top (flight) deck. Just behind them are seats for additional astronauts. Below is a middle level called the mid-deck, where more astronauts can sit. Either the commander or the pilot can fly the space shuttle. They can control when the solid rocket boosters are dropped and when the external tank is released. In orbit, they can control the small thrusters, called the reaction control system (RCS) and the vernier (smallest) thrusters, to fine-tune their orbit and rendezvous with other spacecraft. When they return to Earth the space shuttle flies much like an airplane. The flaps on the wings, called elevons, act like the flaps of an airplane to allow the shuttle to maneuver so it can land at an airport. However, when it re-enters Earth's atmosphere it can no longer use its rockets and it becomes a supersonic glider. Only by using the flaps on the wings and tail can the pilot control the shuttle. The landing approach has to be good because the shuttle cannot repeatedly turn around and try again if the first approach is bad. ñ The Cold War For Space 1946 AD SIBERIA, SOVIET UNION The modern space program is, to a large extent, the result of the Cold War. During World War II much of the basic technology had been developed, especially in Von Braun's V-2 rocket. But after the war ended, the world split into two major camps, and the old wartime allies became potential enemies. On one side you had Joseph Stalin's Soviet Union and the countries of Eastern Europe that had fallen under his dictatorship. On the other side you had the United States and its allies, especially Western Europe and Canada. The free world feared the dictatorship of Stalin, and Stalin feared the nuclear weapons of the free world. This began a tremendous arms race leading to the development of hydrogen bombs and intercontinental ballistic missiles (ICBMs), along with many other weapons. For decades, each side developed more powerful weapons for fear that the other side would be able to dominate militarily. Both sides took advantage of the captured German rockets and their engineers to improve on the German designs. In 1957, this led to the Soviets firing into space the most powerful rocket up to that time, which launched the Sputnik satellite. This was the first time anyone had succeeded in launching an object into orbit around the Earth. The Space Age had begun. Sputnik came as a great shock in the West. Those who thought the Soviets were not capable of advanced technology were rudely awakened. This began a race to catch up with the Russians in space. The United States then began to build rockets to launch their own satellites, finally succeeding with Explorer I in 1958. This also inspired President Dwight Eisenhower to create NASA (the National Aeronautics and Space Administration) out of the former NACA (the National Advisory Committee for Aeronautics). He wanted to create a civilian space agency to keep the space program from being completely dominated by the military. NASA then worked with private companies and the military to develop more powerful rockets, with the goal of sending humans into space. In 1961, Soviet cosmonaut Yuri Gagarin became the first human being to orbit the Earth. This was a resounding proof of the superiority of the Soviet space program, and led to John Kennedy's decision to send a man to the Moon. The Cold War finally ended in 1989, when Mikhail Gorbachev introduced freedom into the Soviet Union and the former dictatorships of Eastern Europe. The space programs of both the United States and the former Soviet Union are now reshaping themselves to survive in a post-Cold War world. They are searching for commercial and scientific reasons to continue space exploration now that the military/political competition is gone. 6Collins: Watching From Above July 20, 1969 AD LUNAR ORBIT While Neil Armstrong and Buzz Aldrin dropped down to the lunar surface to become the first men on the Moon, astronaut Michael Collins remained in orbit, waiting in the Command Service Module, Columbia, for the others to return and observing below him this strange and somewhat frightening new land. Collins, born in Rome, Italy, to an American Army family on Oct. 31, 1930, was graduated from the US Military Academy at West Point and served as an Air Force test pilot. He became an astronaut in 1963 and was copilot of the Gemini 10 flight, in which he and John Young docked with an Agena rocket stage and used the Agena to jump to a 763 kilometer (474 mile) high orbit, the highest ever for a Gemini mission. Also on that trip, Collins spacewalked to an upper stage of an Agena rocket to retrieve a micrometeorite package. But on the Moon trip, Collins watched while others got the glory. In his book, "Carrying the Fire," he gave this astronaut's-eye comparison of the Moon and Earth: "The Earth from orbit is a delight -- alive, inviting, enchanting -- offering visual variety and an emotional feeling of belonging 'down there.' Not so with this withered, Sun-seared peach pit out my window. There is no comfort to it; it is too stark and barren; its invitation is monotonous and meant for geologists only." ÅA New Home in the Sky 1969 AD PRINCETON, NEW JERSEY Future space colonists may look back on a science class at Princeton University as the place where their orbiting city was born. In 1969, physics professor Gerard O'Neill was teaching a class. It was two months before the Apollo astronauts had landed on the Moon for the first time, and it had become very popular at universities to question the need for technology. So O'Neill proposed that the class study the question "Is a planetary surface the right place for an expanding technological society?" Some scientists were talking about the limits of growth, the idea that humanity would have to live with limited natural resources, and could not expect to improve living conditions. This professor did not expect to come up with any breakthroughs, but to his surprise, he and his students were able to solve every problem they could think of that would face a space colony. Without using any technology beyond what would soon be available they calculated that it would be possible to build large colonies orbiting the Earth, powered by solar energy. They designed a colony with artificial gravity, air, sunlight, trees, animals and plants. O'Neill was not the first to think about colonizing space, but he was one of the most clever and dedicated. As he began to understand the possibilities of space colonization, and as he began to solve the technical problems, he tried to convince others that this is what we should be doing. As a very successful physicist, he had the scientific reputation to support his ideas, and gradually people began to listen. By writing many scientific papers and books, and by helping NASA studies on space colonization, O'Neill has continued to stimulate thinking in this area. He went on to found the Space Studies Institute in Princeton, New Jersey, which is dedicated to supporting space colony research. O'Neill realized that there are limits for humanity only as long as we stay on one planet. As soon as we leave Earth there is an entire universe of resources. It is up to us to take advantage of them. Someday, millions of people may live in space, and many of them may live in colonies inspired by Gerard O'Neill. ▀A Speck of Comet SOLAR SYSTEM This picture is probably of a tiny piece of a comet. To capture comet dust NASA sends up special high-altitude airplanes with sticky collection trays. Up high, some of the dust that it picks up comes from space. This particle is about .1 millimeters (.004 inches) in size. Chemically, it resembles some meteorites found on Earth but it has a fluffy structure made of millions of tiny crystals stuck together, quite different from any meteorite we have seen. The gases trapped inside the speck prove that it comes from space. This one probably came from a comet. Comets are basically dirty snowballs, and when they come close to the Sun, they are heated. Bits of comet vaporize, forming a giant tail. Gas and dust are spread throughout the tail, and sometimes the Earth passes through the tail. The larger dust particles burn up in the atmosphere, forming streaks we call meteors, but sometimes little dust grains like this one can survive entry into our atmosphere. =Red Glare Courtesy of Congreve 1804 AD BALTIMORE, MARYLAND When the British bombarded Ft. McHenry with rockets during the War of 1812, Francis Scott Key watched "the rockets' red glare" and wrote a poem about the attack that became the American national anthem. The red glare was provided courtesy of British Colonel William Congreve. Congreve, interested in reports of Indian rocket attacks on British troops in India in the late 1700s, set about experimenting with rockets and improving them. In 1804, he realized that rockets have a particular advantage over guns -- they don't have a recoil. This meant they could easily be fired from a lightweight platform, such as a ship. Congreve's rockets came in various sizes, but some could fly up to 2,000 meters (roughly 2,000 yards), twice as far as the Indian rockets that inspired him. His rockets were essentially pointed iron tubes filled with propellant and stabilized by a long stick trailing behind. Before long, most European countries developed rockets, and many were used during the 1800s. But as artillery became better, interest in rockets tapered off. uYou're Floating on Hot Rock 1912 AD EARTH Ever since Africa and South America had been mapped, people could see they looked like two pieces of a jigsaw puzzle, but it wasn't until 1912 that German geologist Alfred Lothar suggested they really had at one time been linked. But the idea was mocked because nobody could figure out why great sections of the Earth would slide around. But after scientists discovered a chain of undersea mountains and valleys that divides Earth into large plates, American geophysicist Harry Hess came up with the solution that is generally accepted today. He suggested in 1960 that molten magma pushing up between the plates could shove them apart, causing them to drift. And it is a good thing that the plates do move. If it wasn't for their drifting and buckling and for volcanoes erupting, we wouldn't have new mountains to replace the old ones that are constantly being worn away. █Corona: Space on Fire 1973 AD SOLAR SYSTEM During an eclipse, when the Moon blocks out the Sun, you can still see a bright glow surrounding the Sun and Moon, as if space itself were on fire. This is called the "corona," from the Latin for crown. The corona is an incredibly hot, thin gas from the Sun's outer atmosphere. It is millions of degrees hot, making it glow, but the brightness of the Sun normally outshines it, making it impossible to see from the Earth's surface except during an eclipse. ┼Earth Is Really Off Center 1543 AD KRAKOW, POLAND The ancient Greek astronomer Ptolemy had taught that the Earth is the center of the universe, and the Christians had picked up this pagan belief and made it their own. It would be centuries before Polish astronomer Nicolaus Copernicus challenged this belief. He had a tough job: After all, it's obvious that the Earth is the center of the universe. The Sun goes around us, doesn't it? You can see it every day. The Moon does likewise, and so do all the stars and planets, right? But science was just beginning to show that the "obvious" is frequently wrong. Copernicus dared to claim that Earth was not the center of the universe. If you assume the planets revolve around the Sun, he said, the solar system is vastly easier to understand. The complicated, slow motions of the planets in the sky become simple consequences of the way the Earth and the other planets move around the Sun. This was dangerous thinking. How dare he claim that Man was not the center of the universe? How humiliating! Many religious leaders were upset by this idea, and Copernicus withheld publication of his great theory for thirteen years. Finally, he arranged for it to be published. He called it "De Revolutionibus Orbium Coelestium" ("On the Revolution of the Celestial Spheres" in Latin). He almost waited too long. One of the first copies was handed to him on his deathbed. It was one of the most important books in the history of civilization. It shocked intellectuals throughout Europe. It had an effect much like Darwin had 300 years later when he said man was was the byproduct of evolution. Copernicus' theory eventually became generally accepted, though it was fought violently for a century. Copernicus created a revolution in human thinking which was still afire when Halley and Newton were born a century later. Not only did Copernicus's own Catholic Church put his work on its Index of Forbidden Books, but even the Protestant reformer Martin Luther denounced it. tNot Off to a Comet 1992 AD SOLAR SYSTEM NASA hoped to launch CRAF (Comet Rendezvous with Asteroid Flyby) in the 1990s to visit an asteroid and a comet. Comets are especially interesting because they are leftovers from the formation of the solar system, and give us clues to how the planets formed. CRAF would have first flown past an asteroid, taking close-up pictures. Then, it would have traveled on to meet a comet and match speed with it. It would stay close to the comet, following it as the comet approached the Sun and got brighter. It would even have dropped probes into the comet, to see whether it really is the ball of dirty ice that astronomers believe. Unfortunately, CRAF was killed by the US Congress because of budget problems. Still, as space travel becomes cheaper and available to more nations, it's likely that someday, someone will send a similar probe to actually land on a comet. «No Volcanoes on the Moon THE MOON Most of the craters we see on the Moon were created by meteorites. For a long time, though, geologists thought they were caused by volcanoes, because that is what causes most craters on Earth. However, we now know that it is often inappropriate to apply knowledge from Earth to other planets because the universe behaves in many different ways. We now understand craters much better and can see that lunar craters were formed by objects from space. Most likely, these objects were comets and asteroids (large mountains of rock from the asteroid belt), which also gave the Earth its meteorite craters. On Earth, however, most meteorite craters were worn away by the weathering of the atmosphere and water. Our planet has a molten interior, so most of the craters we see here today are not from meteorites, but were caused by volcanoes. The Moon is probably largely solid inside, so it apparently cannot have volcanoes today. ╣Dear Earthlings, How Are You? 1960 AD GREEN BANK, WEST VIRGINIA How do you send a message to someone on another world who doesn't speak your language? Frank Drake, one of the leading pioneers of SETI (Search for Extraterrestrial Intelligence), tried an experiment in the 1960s. He created a message as if it were from another civilization, sent it to fellow scientists and asked them to figure it out. It was a long series of ones and zeros -- binary bits. There were 551 numbers in this series, and that number was designed so that it equaled 19 x 29. These are called "prime numbers," meaning they can only be divided evenly by themselves and one. This was Drake's clue that the scientists were supposed to arrange them in 19 rows of 29 numbers or 29 rows of 19 numbers. One arrangement produces nonsense, but the other produces a cartoon. So when you arrange the bits in 29 rows of 19 bits, you get a little picture telling something about the "alien" civilization. On the left side is a crude picture of that civilization's solar system, with a big Sun, four little planets and four big planets, and then a little planet. The upper right hand corner shows pictures of carbon and oxygen atoms, with their six and eight electrons, showing they have a chemistry similar to ours. There is a stick figure showing that the aliens have two arms, two legs and a head, just like us. If it is hard to understand the diagram, that's because so few bits of information were used. A real civilization could use as many bits as they want and make pictures as high a quality as anything you see on television. It would take a committee of scientists to figure out the meaning of Drake's message, but high quality pictures might be understood even without assistance. The most important point is that Drake showed that you can communicate to other beings by using pictures, math, chemistry and physics. Some of the scientists were able to figure out the message. PICTURE CREDIT: Picture courtesy of Frank Drake. &A Map of Chlorophyll 1978 AD EARTH ORBIT One of the most important chemicals for life on Earth is chlorophyll, the chemical that makes plants green. This satellite image of the world shows chlorophyll on land and in the sea. From 1978 to 1986, NASA operated a satellite called Nimbus 7, which provided measurements that scientists have been refining ever since. They have also been combining that information with other observations to produce this world's first satellite picture of the entire chlorophyll of the planet. On land, chlorophyll is found in grass, trees, and other green plants. In the oceans, it is found in microscopic plants called plankton. (Strictly speaking, plankton comes in both animal and vegetable form. The plant type of plankton is called, technically, phytoplankton. These are single cells, primitive plant forms that ocean fish feed on. Those fish that don't feed directly on the plankton eat other fish that eventually, in the food chain, wind up eating plankton.) Since all life directly or indirectly depends on eating plants, we are all dependent on chlorophyll. That chlorophyll converts the carbon dioxide that animals exhale into the oxygen that they breathe. Satellites are now allowing us for the first time to monitor the whole planet's production of this most important chemical -- chlorophyll. ΓPlankton and Pollution 1978 AD MEDITERRANEAN This dramatic false-color satellite picture of the Mediterranean Sea shows concentrations of plankton. The bright reds and oranges represent regions of high concentration of these microscopic plants of the sea. The picture shows how the plankton tend to cluster along the shore, enriched, in some cases, by pollution, oddly enough. As you can see, plankton does not flourish in the Mediterranean -- but notice how abundant it is on the Atlantic side of Spain. █Winter-Spring Plankton Jan.-March 1979 AD EARTH ORBIT This satellite image of the plant-type plankton in the Earth's oceans shows how we can monitor the health and activity of our oceans from space. Using NASA's Nimbus-7 satellite, scientists plot the location and concentration of the plankton, the microscopic plants on which ocean life depends. The bright reds and oranges are the regions of largest concentration of the plankton. This picture shows the first three months of the year, January through March. .Where's the Rest of the Universe? UNIVERSE Ninety percent of the universe is missing, and nobody knows where it is or what it is. One of the greatest mysteries of science today is that we can measure the amount of matter in galaxies, but we cannot see it. How do these measurements work? Well, it's a lot like whirling a ball on the end of a string. If you whirl the ball very fast, you will feel a strong force on your arm, the centrifugal force of the ball trying to escape. Your arm, acting like gravity, has to pull harder on the ball to keep it from flying away. On the other hand, if you spin the ball slowly, you hardly feel it, because it doesn't take much force to keep the ball from flying away. So, by watching someone swing a ball, you can tell something about the strength of the forc e on the ball. Similarly, by watching a moon orbit a planet, an astronomer can tell the strength of the planet's gravity and the mass of the planet. For example, we can measure the mass of the Earth from watching our own Moon. We know it takes the Moon about one month to go around the Earth, and that the Moon is 384,000 kilometers (239,000 miles) away. Using these two numbers and Newton's law of gravity, we can calculate that the mass of the Earth is six thousand million million million tons. If the Earth were more massive than that, the Moon would have to orbit faster to keep from falling. If Earth were less massive, the Moon would orbit more slowly because Earth's gravity would be less. Similarly, we can tell how massive the Sun is. We know that it takes Earth 365 days -- one year -- to orbit it, and that the Sun is 150 million kilometers (93 million miles) away. From this, we can calculate that the Sun is 300,000 times as massive as Earth. Similarly, astronomers can look at galaxies and measure how far away they are and how fast the stars are orbiting around the center of their galaxy. Stars orbit their centers very much like planets around the Sun. From these measurements astronomers can calculate how much matter there is in the galaxy. In this way, they find that a typical galaxy, like the Milky Way, has an amount of matter roughly equal to 100 billion Suns. But here's the mystery: When astronomers add up all the matter they see, using all their telescopes on Earth and in space, with visible light, infrared, ultraviolet, and everything else, they come up with only about one-tenth of the matter that they measured by the gravity trick. In other words, there is ten times as much matter present in a typical galaxy as we can see with all of our astronomical tools. Ninety percent of the universe is missing! We call this missing matter dark matter. We don't know what it is. It could be objects like undersized stars that are too small to burn. It could be planet-sized objects. Or it could be elementary particles that physicists have predicted but that have never been proven. As astronomers build more telescopes on Earth and in space, and physicists conduct exotic experiments in labs, perhaps we will figure out what the dark matter is. Until then, we are amazingly ignorant about the universe. ^Darwin: Lots of Little Changes 1858 AD DOWN, ENGLAND How did life get here? The credit for the simplest scientific answer to that question must go to one of the most admired and hated of all scientists in history: Charles Darwin. Darwin was born in England in 1909, from a line of doctors. While he dithered between a career in medicine and the church, he decided to join an expedition. He signed up as the ship's scientist on a sailing vessel called the H.M.S. Beagle, which began its journey around the world in 1831. He traveled in exotic lands and studied the many life forms he encountered. He found fossils in unexpected places, such as the puzzling remains of tropical lifeforms on the tops of mountains. This started him thinking about how these creatures and plants came to be. He also noticed little variations between the same species of animal. In Galapagos finches, for example, he noticed some with longer beaks, or bigger claws. Each variation was specially suited to the particular food and environment the bird encountered. Darwin concluded that over the countless years life had been on Earth, many variations of animals had arisen, and in each generation there would be little changes, like the differences between the children of two parents. The ones that were not well adapted would have a harder time getting food and surviving to have offspring. The ones that were better suited to the resources available would be more likely to survive, and would flourish. In addition, fossils showed that very different life had once existed on Earth. Dinosaurs, flying reptiles and enormous beasts in the ocean were quite unlike anything found today. Yet they had flourished in the distant past. Darwin decided that the whole vast array of life on Earth could have originated in some very simple form. Then, as history progressed, those lifeforms had changed to fit the changing climate and the available environments. Simple organisms, breeding generation after generation, could become more complex. This led to his most revolutionary conclusion, and the one that caused his misery. Humanity itself could be descended from animals. Darwin knew this was a revolutionary claim and one that would cause a lot of emotional disturbance among those who felt that human beings were created directly by God. He held off publishing his theory for more than 20 years, until he learned that another English scientist, Alfred Russell Wallace, had independently come up with the same theory, and was about to publish it. In science as in sports, no one remembers the also-rans. The first person to publish his or her result is the one who gets the credit in the history books. Darwin knew if he delayed publication of his theory, Wallace would get the credit. Fortunately, in this case, both scientists shared the credit, presenting their results at a joint meeting in 1858. Darwin went on to write several lengthy books about his theory, and presented vast amounts of evidence supporting it, so he wound up with the lion's share of the credit. Certainly he deserves to be considered the originator of the Theory of Evolution, but increasingly today, scientists refer to it as the Darwin-Wallace Theory of Evolution. Darwin had come up with his ideas before Wallace and had discussed them with other scientists even though he had not yet published them. Today, Darwinian evolution is accepted by most scientists as the basis of biology. 1Death Valley: Deep and Dry 1849 AD DEATH VALLEY, CALIFORNIA As you can see from this false-color space image of Death Valley, California, its name is well chosen. The computer has colored the small amount of plant life red. There is a bit of red in the mountains surrounding the valley, and a few cultivated areas within the valley, but on the whole, it is a dry, hot and forbidding place -- though fascinating. It is so unearthly that it is sometimes used to test spacecraft designed to land on Mars. The canyon is 225 kilometers (140 miles) long and varies from 6 to 26 kilometers (4 to 16 miles) wide. Badwater, the lowest point in the valley, is also the lowest spot in the Western Hemisphere, 86 meters (282 feet) below sea level. Death Valley was named in 1849 by a party of immigrants, who became lost in the valley and suffered badly. sDeimos: Solar Watering Hole 1976 AD MARS ORBIT Deimos is the smaller of the two Martian moons, the other being Phobos. The two are probably asteroids that passed close enough to Mars that its gravitational field caught them. Both are tiny compared with our own Moon. Deimos is about half the diameter of Phobos, an irregular object roughly 12 kilometers (7 miles) in average diameter. Deimos is 23,000 kilometers (14,000 miles) from the center of Mars (more than twice as far as Phobos). It takes 1.26 days to orbit the planet. The first close-up photographs of Deimos were taken by the Viking Orbiter spacecraft in 1976. Deimos, like Phobos, is probably a type of meteorite known as carbonaceous chondrite -- carbon-rich rocks, similar to coal. If so, they are potentially very valuable to human explorers because they contain water and other chemicals that might someday be used by expeditions and colonies. What Killed the Dinosaurs? 65 Million BC BERKELEY, CALIFORNIA What killed the dinosaurs? It's like a classic Sherlock Holmes mystery. Bodies have been found. There are all kinds of clues. Something killed a great many victims. But what? The murders occurred 65 million years ago. The victims included the dinosaurs. In fact, not only were the dinosaurs killed off, but so were most other animals and plants. Fortunately, science often produces a Sherlock Holmes to solve its greatest mysteries, and one of them seems to have solved the mystery. This modern detective was Nobel prize-winning physicist Luis Alvarez. His theory seems to explain many of the clues the killer left behind, buried with the dinosaurs in the rocks beneath our feet. Alvarez' theory is highly controversial, but it seems to be the best theory around. Luis Alvarez's investigation of the case of the dead dinosaurs began several years ago, when his son, Walter Alvarez, a geologist, pointed out a puzzle. There was an unexpected rare metal, iridium, found in some rock samples. Iridium, a whitish-yellow metal, is the Latin word for "rainbow," and was named because of the colors it gives to liquids. Iridium is quite rare on Earth, yet was strongly present in the geologist's samples. Why? The samples had been taken from the thin slice of Earth that occurs right above the layer where the dinosaurs died. Over Earth's billions of years, soil and rocks have rolled down mountains, been blown by wind and been carried by streams, depositing layer upon layer in valleys. They found that, all over the world, the story seems to be the same: Below the iridium layer, dinosaurs and many other kinds of life flourished. Just above it, most of them are gone. Something weird must have happened when the iridium layer formed. Something that killed off most life on Earth. But what could have done it? Many theories have been proposed over the years. Some scientists think that Earth's climate turned cold, killing off most life. This was the most popular theory prior to Alvarez. But why did the climate change? Some think there was a tremendous eruption of volcanos that polluted the air and water. Luis Alvarez proposed a radically different theory. When his son discussed the iridium layer with him, Alvarez pointed out that there is one place where iridium is fairly common. It's not on Earth -- it's in space. How do we know iridium is more common out there? Because meteorites have lots of it. Earth rocks usually have little. Most geologists are used to dealing with normal rocks, not space rocks. But Alvarez was used to thinking about space, so like Sherlock Holmes seeing the one clue that all the other detectives had overlooked, he deduced a connection between the dinosaurs and outer space. Not only that, he was used to the idea of big explosions. He worked on the atomic bomb during World War II. If a meteorite killed off dinosaurs all over the world, it had to have been a big one. He knew that space is littered with big ones. Many of them are far bigger than the one that created Meteor Crater in Arizona, 1.2 kilometers (almost a mile) in diameter. He, his son and other scientists began thinking about the details. How big would the meteorite have to be? What are the odds against such a big rock hitting the Earth in 65 million years? What would be the effect of the explosion? And suppose it hit the ocean instead of land? What would it do to the atmosphere? How would it kill -- by heat, poisoning or some other way? Above all, they had to compare the theory with the facts. Were there any known facts that contradicted the theory? If so, might the "facts" be wrong? The scientists sat down and computed the effects of the biggest explosion the world had ever seen. The blast must have been big enough to throw dirt thousands of miles. They figured that any meteorite much smaller than about ten kilometers (6 miles) in size would probably not be big enough to do the job. They estimated that there are enough ten-kilometer asteroids -- about the height of Mount Everest -- so that one of them ought to hit us every hundred million years or so. Asteroids much bigger than that are far rarer, so are not likely to have done the dirty deed. What would happen if Mount Everest came crashing to Earth as fast as a typical meteorite (around 40 kilometers per second or 90,000 mph)? It would be like millions of hydrogen bombs going off at once. Whether it hit land or water, it would shoot millions of tons of debris high into a high layer of the atmosphere, the stratosphere, where lighter particles float for years. Sunlight would be cut off as on a badly overcast day. The world would turn cold. Since plants use sunlight to make food that animals eat, the plants would die and animals would starve to death. So that is how the dinosaurs probably died: Starvation. The mighty brontosaurus, the fierce tyrannosaurus, the armor-plated stegosaurus -- they all died in a cold, dark world, their bellies crying for food. Why didn't all life die out? Some seeds remained in the ground, waiting for the Sun to return. Some animals survived by eating the carcasses of other creatures. In 1980, the Alvarez group published their ideas in the journal "Science" and triggered a storm of controversy. Many geologists, who normally ignore astronomy, thought it was ridiculous. Astronomers, on the other hand, welcomed the theory with open arms. They're always happy to find that their research applies to Earth. The debate has continued. More and more evidence has been found supporting the Alvarez theory, and now even many geologists accept it. Astronomers have come to prefer the idea that comets killed the dinosaurs, rather than meteorites. They would have roughly the same effect, but Earth has probably been hit by more comets of this size than meteorites, so it's still basically the Alvarez theory. Where's the crater? There's evidence that it's in the Yucatan province of Mexico, largely covered up by dirt and jungle. This is often called the "smoking gun" of the Alvarez theory -- the evidence that could convict the astronomical dinosaur killer. ┼Dione: Saturn Moon 1979 AD SATURN ORBIT Dione is one of Saturn's medium-sized moons. It is 377,000 kilometers (234,000 miles) from Saturn and is 1,118 kilometers (694 miles) in diameter. It is a mixture of rock and ice. ┼A Slow Message to the Stars 1977 AD CAPE CANAVERAL, FLORIDA The most sophisticated messages we have ever sent to an extraterrestrial civilization are also some of the slowest. In 1977, Voyagers I and II were launched on trips to Jupiter, Saturn, Uranus, Neptune -- and beyond. Scientists knew the spacecraft would leave the solar system eventually, so they attached a kind of video disk with pictures and sounds from Earth. This picture shows the cover of the disk. On it are instructions on how to play the disk and a map of where we are in the Milky Way. The disk contains samples of Earth's languages, and some of our greatest music (from Johann Sebastian Bach to Chuck Berry). It also contains still photographs showing life on Earth. There are photographs of Earth's citizens living in the Arctic and the tropics, eating and playing and engaging in normal human activities. The problem with this set of messages is that it travels at the speed of the spacecraft, which is much slower than the speed of light. If the spacecraft were aimed at a nearby star, it would take hundreds of thousands of years to get there. But, in fact, it's not aimed at any particular star, so it is likely to wander in the galaxy for billions of years, and only a very advanced civilization would have a chance of detecting it in the vastness of space. But perhaps, billions of years from now, some civilization may find the two Voyagers and discover a treasury of sights and sounds from the human beings who made it. The Little Plan of You CAMBRIDGE, ENGLAND There is a tiny set of plans for your body in every cell you have. It's a chemical called DNA. DNA, which stands for deoxyribonucleic acid, comes in long strands that inhabit the nucleus of your cells, and the cells of every other living thing. These strands of DNA are connected by pairs of four small organic (carbon) molecules called bases: adenine, thymine, cytosine, and guanine, abbreviated A, T, C, and G. Organic chemicals behave very much like jigsaw-puzzle pieces. Certain pieces will fit into other pieces but not into ones that are shaped differently. Just as you cannot fit a square peg into a round hole, two organic molecules that don't have the right shapes won't stick together. Because of this, A always goes with T, and C with G. The DNA is like a long spiral staircase in which each rung is made up either of an AT or CG combination. Your DNA is a unique sequence of these four letters, A, C, T, G. There are three billion pairs of these letters in the rungs of your DNA. But here's what's truly amazing about them. They are a secret code. They represent the instructions for building the molecules out of which you are made. These three billion pairs of A, T, C, and G molecules told your mother, when you were one cell old, how to build you. Half of your letters were from your father and half were from your mother. They came together in a unique pattern that was a mixture of your two parents' blueprints. The exact sequence determined whether you had blue eyes, or brown hair, or have a flair for languages. Although DNA is often called the blueprint for life, because it is like plans from which a building is made, it's more like the computer program of life. Computer programs consist of line after line of simple statements: move X to Y, subtract T from Z, erase W, jump to line 17. The DNA is just like this. Each pair of A's and T's, and C's and G's is a step in the code. It's something like the Morse code that is used for the telegraph. Individually, each part looks pretty simple, but put it all together and it spells "human." Most of the sequences of letters in your genes are the same as mine. That's what makes us human. In an ape, the sequences are a little bit different. In a turtle they are quite a bit different. In a rose they are very different. But they are all built out of the same chemical building blocks, and they all have the same general twisted step-ladder shape, called the double helix. Just as many scientists have seen physical similarities between species as evidence for evolution, now many see evidence for evolution in the similarities between DNA of various species. For example, when we look at apes we find that, indeed, we share most of their DNA. The genetic program in a human being is almost identical to that of a chimpanzee. It varies by only one percent or so. 99 percent of us is chimp. The more distant the animal is in relation to us, the more different is its DNA. The overall structure is still the same, but the number of differences in the detailed arrangement of the letters in the computer program of the DNA is different. Would life on another planet have the same DNA molecule as its foundation? We don't know. If we ever find life somewhere else, however simple, even in the form of fossils, we might have the answer. ╢A Formula For SETI 1960 AD GREEN BANK, WEST VIRGINIA Frank Drake, the man who conducted the first modern search for radio signals from other civilizations, developed a way of thinking about how many civilizations there could be in our galaxy. It's now known as the Drake Equation. What he did was to break up the big problem into a number of little ones. In the equation, N is the number of advanced civilizations existing in our Milky Way Galaxy right now. R is the average rate at which stars form. There are about 400 billion stars in the galaxy, which have been around for about 10 billion years. So, 400 billion stars divided by 10 billion years is 40 stars per year. In other words, something like 40 stars are born every year in the galaxy. Fs is the fraction of stars like the Sun. Stars that are much bigger than the Sun burn out more quickly, and wouldn't last long enough for life to form. Fortunately, the Sun is a very common type of star. There are many such stars in the galaxy that are not much hotter or colder than our own Sun -- just about the right size. So a reasonable estimate for this term is one-tenth. Fp is the fraction of those good stars that have planets. We don't know for sure, but there is some indirect evidence that planets are a natural result of the formation of stars. It looks like the junk that is left over when a star forms tends to condense into planets. So a reasonable guess here is that perhaps one-tenth of the stars that are good can have planets. Ne is the number of planets around the good stars where life could exist. In our own solar system, we only know of one planet where life exists -- Earth. However, there are other places where, theoretically, it might exist, or might have existed in the past, such as Mars. Still, to be conservative, a reasonable guess is that there could be one Earth-like planet in a system, where life could exist. Fl is then the fraction of those Earth-like planets that life actually does arise on. Here the question becomes very controversial. No one knows how easily life can form if you have a nice planet near a good Sun. Some scientists think Earth is the only place with life. Others think that once you have a reasonable planet near a decent star, it's almost automatic that the chemicals that are widespread in the universe will form more and more complicated molecules, and before long some of those molecules will start reproducing themselves -- life is born. So some scientists say that this fraction is approximately zero, and others say that it's close to one. We just don't know. Fi is the fraction of those planets with intelligent life. This is even more uncertain. We have no idea whether -- once life starts on a planet -- it may become intelligent. It could be that, if we humans had not come along, no other species on Earth would have become intelligent. Or, it could be that, if we hadn't arisen, some other animal, such as the chimpanzees, or the bears, or the dinosaurs, might have developed intelligence. Again, the answer could be anything from zero to one. Fc is the fraction of those planets with intelligent life that are capable of communicating across space. It could be that there are planets of intelligent dolphins that don't have the ability to use radio, in which case, we can never detect them. Or it may be that any species smart enough to be considered intelligent will sooner or later discover the laws of electricity and magnetism that make radio communication possible. L is the lifetime of the communicating civilization. In other words, how long does a civilization last once it starts being able to communicate across the distance between the stars? The bottom line is that some scientists are pessimists and think life rarely gets started, and, if it gets started, it rarely develops intelligence. If they are right, there may be no intelligent civilizations in our galaxy today. A few think there may not even be any other civilization in the whole universe. However, optimists think that life could be widespread in the universe. There could be thousands, or even millions, of civilizations in the Milky Way today. So the Drake equation is a fascinating way of analyzing the question of whether we're alone in the universe. But there are too many unknowns. The only way we can know for sure is to look. This is why some scientists believe in SETI (the search for extraterrestrial intelligence). If we look for astronomical signs of another civilization, we may find that we have neighbors in our galaxy. ╩DSN: The Link to Space 1986 AD PASADENA, CALIFORNIA The Deep Space Network (DSN) is NASA's link with all American spacecraft beyond the Earth. It's a system of antennas around the world with radio receivers designed to pick up the faint signals from spacecraft going to the distant planets. There are three main locations for DSN antennas: Southern California, Spain, and Australia. These are roughly equally spaced around the Earth, so as the planet rotates, there is always at least one antenna able to pick up the signals of a distant spacecraft. At each location, there's one large antenna, 70 meters (230 feet) in diameter, together with a number of smaller ones. These antennas are similar to the satellite dishes used by many people to pick up television signals from orbiting satellites, but much larger. They are the ears of the space program. The larger the antenna, the more sensitive it is, because a larger area can collect more of the faint radio waves. If you cup your hands behind your ears you can hear fainter sounds because you've made a larger collecting area to bounce the sound into your ears. Similarly, a dish antenna bounces radio signals to a receiver. The headquarters for the Deep Space Network is at the Jet Propulsion Laboratory (JPL) in Pasadena, California. This is where mission controllers monitor distant spacecraft and transmit signals to them. At each antenna there is a transmitter and receiver. Using the same antenna, a powerful transmitter can send a signal to tell the spacecraft to turn instruments on or off, or to aim them in a particular direction. Sensors on the spacecraft measure the temperature and check the instruments. If the spacecraft starts to get too hot because it's facing the Sun constantly, a signal is sent to Earth. The engineer monitoring that signal can then send a signal telling it to rotate so the shadowed part of the spacecraft faces the Sun and vice versa. When the spacecraft approaches a planet, ground controllers send a complex set of commands to tell it how to aim its camera and other instruments so that it will look in the right direction during the fly-by or orbit. Each spacecraft carries a small computer that has a detailed program of how the instruments should be turned on and off, and where they should be pointed. New programs can be transmitted from DSN antennas to modify the existing ones. Spacecraft usually have back-up systems -- spare radios and other critical components that can be switched on if the main one fails. The spacecraft is usually smart enough to automatically switch to a back-up if the main instrument fails. It then radios Earth for more instructions. One of the most important uses of these antennas is to track the spacecraft, measuring its position precisely. To do this, scientists apply the Doppler effect. This says that if a transmitter is moving away from you, then its frequency drops, just as a train whistle falls to a lower pitch as it moves away from you. By keeping the spacecraft's transmitter on constantly, scientists can monitor slight frequency changes as the craft leaves Earth and accelerates due to the rocket and to the gravitational pull of the Sun and planets. It's as if the spacecraft were trailing an enormous tape measure. A spacecraft at the distance of Mars can be located to within a meter (a yard) by this method. In the future, some of these antennas will be used in the search for extraterrestrial intelligence (SETI), looking for radio signals from other civilizations that may exist in space. In particular, the 34-meter (112-foot) dish in Southern California will be used regularly to scan the skies for such radio signals. In recent years, the Deep Space Network has also helped the Russians track spacecraft. In 1986, when the Soviets sent a probe past Halley's Comet, NASA measurements enabled them to precisely adjust their spacecraft's orbit, so that it flew very close to the comet and returned high-quality pictures. Future Russian robotic Mars explorers will also use DSN help to receive data. ╢ A Universe Made for Man? The Beginning UNIVERSE Is the universe designed just for us? Today, one of the most fascinating questions on the frontier of science is called the anthropic principle, from the Greek word "anthropos," meaning "man." This question involves the laws of physics and the remarkable way they fit together to allow life to exist. We know many of these laws, though not all of them. The remarkable thing is that at the bottom of these laws there are just a few numbers, called the constants of physics, that control our universe. One of these numbers, for example, is the strength of gravity. This is the number that determines how strong gravity is here on Earth, but it also determines how strong it is on the Sun and in other galaxies. If this number were just a little bit larger, then gravity would be stronger everywhere, and stars would burn up much faster, and life would not have had time to arise. Another of these numbers controls the speed with which atoms fuse in the Sun to heavy atoms. Stars are basically great fusion reactors, turning hydrogen into helium and into heavier elements like oxygen and carbon. Some of the stars explode as supernovas and splatter these heavier atoms throughout the universe, where they are then part of the raw materials out of which other stars are made. This is where the carbon that is essential to life on Earth comes from. The remarkable thing is that there is a coincidence in some of these numbers that allows carbon to be made in great quantities. If this coincidence of different constants had not existed, then carbon would be very rare, and life, as we know it, would probably be impossible. There are several other such constants that seem to be critical, as if they were fine-tuned to allow life to exist. Some people interpret these coincidences as signs that the universe was designed for life to exist by some super-intelligence. Others think there may be a better explanation. For one thing, if life could not exist in our universe, we wouldn't be here to talk about it. Some scientists think there may be other universes separate from ours, where the constants are different. Some of those universes would have no life in them, and so there would be no one around to ask these questions. The anthropic principle is one of the open questions that is causing scientists to probe the very nature of the universe. As our understanding of physics and astronomy gets better, we may one day have the final answer to this question. éGalileo: No Intelligent Life Here Dec. 11, 1990 AD EARTH These are some of the first pictures ever taken of Earth by an interplanetary spacecraft. The Galileo spacecraft, after flying by Venus, flew by Earth and the Moon in 1990. This was the first spacecraft ever to take pictures of Earth after visiting another planet. These pictures were taken as Galileo flew away from Earth, from distances of 2 to 2.7 million kilometers (1.2 to 1.7 million miles). They show Earth rotating over a one-day period, and let us see our planet as an alien coming from another star would see it. They would see a blue planet covered with vast oceans. Only a fairly small part of its surface is land. The picture also shows a very cloudy world, with water clouds covering roughly half the planet. The Galileo spacecraft even looked for signs of intelligent life on Earth, but found almost nothing, so scientists joked that there's no intelligent life here. _When Midday Turns Dark 2000 BC MESOPOTAMIA In ancient days, it was terrifying when the Moon covered up the Sun, making the daytime black. It seemed as if the gods were punishing humanity by taking away the Sun. Nowadays, we don't get so flustered because we understand this natural phenomenon, called a solar eclipse. A solar eclipse occurs when the Moon blots out the Sun. We live at a time in history when the Moon is the same diameter as the Sun, as seen from the Earth. A couple billion years ago, the Moon was closer, and would have looked much bigger than the Sun. Several billion of years from now, the Moon will be much farther and will be too small to completely cover up the Sun's disk. But right now, the Moon is just the right size to neatly cover up the Sun during an eclipse. For scientists, eclipses are valuable because they allow us to see the faint outer atmosphere of the Sun, called the corona -- "crown" in Latin. This tells us about the flares and other conditions in the outer part of the Sun that may affect our weather and climate. Ordinarily, the Sun is so bright that we cannot see the corona. Amazingly, the corona is actually much hotter than the surface of the Sun that we see. The Sun's surface that you normally see is about 6,000 degrees Celsius (10,000 degrees Fahrenheit). But the corona has a temperature of millions of degrees. We don't completely understand how this happens, but apparently the magnetic field of the Sun heats the very thin hydrogen gas out of which the corona is made, especially when it is stirred up in solar storms. If you ever watch a solar eclipse, never look at it directly. Your eye becomes adapted to the darkness during the eclipse, and when the Sun reappears, it can burn the retina of your eye, damaging it permanently. Eclipses should only be viewed through very thick, dark filters, or by projecting a telescope image onto a white card. Einstein's Two-Part Theory 1905 AD BERNE, SWITZERLAND Albert Einstein was the greatest scientific genius of the 20th century. He was born in Germany, but moved to Switzerland. He was not a good student, and had trouble getting a job. He wound up working in the Swiss Patent Office, where he did much of his revolutionary research. He is best known for the theory of relativity, which came in two versions, called the special and the general theories of relativity. The first one was the special theory, which is what most people mean when they just say "relativity." The special theory of relativity says that nothing can travel faster than light (300,000 kilometers per second or 186,000 miles per second). If you got into a spaceship that had all the fuel in the world, and accelerated as long as you possibly could, you would still never go faster than light. The faster you move, according to relativity, the more massive the spaceship becomes. At the speed of light, it would become infinitely massive, so you can never have enough fuel to reach the speed of light. In the special theory of relativity was Einstein's famous equation, E=mc². Here E means the energy of a piece of matter, m is the mass of the matter, and c is the speed of light. What this means is that every piece of matter has some energy inside of it. Matter can be thought of as made of energy. Normally this energy just stays there and doesn't do anything, but occasionally, as in nuclear reactions, some of that energy is released. For example, in the atomic bomb, some of the energy in the atoms of uranium or plutonium is released. The first atomic bomb dropped in war, which destroyed the Japanese city of Hiroshima, resulted in converting about one gram of matter into an amount of energy roughly equal to that of 10,000 tons (10 kilotons) of TNT explosives. This equation also helps us understand how the Sun works. For a long time it was a mystery that it hadn't burned out. It should have burned out long ago, according to 19th century scientists. Instead, when the Sun's hydrogen fuses into helium, the resultant helium weighs around 1 percent less than the hydrogen that formed it. What happened to that tiny 1 percent? The matter was converted into energy by the E=mc² formula. That 1 percent conversion of matter into energy is enough to keep the Sun burning for billions of years. This is basically the same thing that happens in a hydrogen bomb. Some of the hydrogen's matter is converted to energy by fusion. So the Sun is like a giant hydrogen bomb continually exploding. But its gravity is so powerful that most of the explosion is contained. The Sun is really a giant fusion reactor in the sky. Einstein's other theory of relativity is called the general theory of relativity. This is his theory of gravity, starting where Newton left off. Einstein modified his special theory of relativity to cover very massive objects. The general theory of relativity views gravity as the warping of space. A small body, like a planet, makes a small dent in space. If a beam of light shines past it, the beam is only slightly affected. A big body, like a star, makes a bigger dent in space and light is bent a little bit more. A huge concentration of mass makes a very big dent. The ultimate case is a black hole, a kind of rip in space, from which even light cannot escape. The general theory of relativity allowed scientists to calculate the overall structure and history of the universe. When it was combined with Hubble's discovery of the expanding universe, the result was the best theory that we have today of the universe. Today's physicists look for something even better than Einstein's theory, but so far none has been found. ╨Enceladas: Saturn Moon 1980 AD SATURN ORBIT Enceladas is one of Saturn's medium-sized moons. It is 238,000 kilometers (148,000 miles) from Saturn and is 502 kilometers (312 miles) in diameter. It is probably a mixture of rock and ice. qEarth's Microwave Radiation Jan. 1979 AD EARTH All warm objects, including Earth itself, emit microwaves. These microwaves are the similar to waves used by microwave ovens to heat foods, and by satellite dishes to communicate with Earth-orbiting satellites. When an object glows, it emits radiation, that is, electromagnetic waves like light waves. Most of those waves are concentrated around one region of the spectrum. Measuring that region gives the object's temperature. For example, a red-hot piece of iron radiates most of its energy in the red region of the visible spectrum of light. But it also "glows" at the longer wavelengths of infrared, and at the even longer wavelengths of microwaves. When the Earth is heated by the Sun, it too "glows," mostly with infrared light, but also at microwave wavelengths. Special satellites can detect these microwave signals. This picture shows a satellite's view of what you would see if you could see Earth's microwave glow. Different kinds of surface materials (rocks, ice, water) absorb sunlight differently and radiate at different wavelengths. Scientists use the information to better understand how Earth operates. ) To the Moon -- Again 2012 AD MOON One day, humans will again walk on the Moon. It is full of resources that people can use. As the human population continues to grow rapidly, metals and other materials will be desperately needed, and the Moon may be the best place to find them. The next step will probably be to send a lunar polar orbiter to the Moon. We still do not know what lies on the poles of the Moon. All the previous spacecraft orbited near the lunar equator. Is there ice on the poles of the Moon, as some geologists have suggested? Water, even in the form of ice, would greatly reduce the cost of living on the Moon. Otherwise, water would have to be imported from Earth. The discovery of ice on one of the poles of the planet Mercury makes it more reasonable to think that ice may indeed be found in the lunar poles. The Moon is a great place to set up experiments. The far side of the Moon is particularly outstanding for astronomers. This part of the Moon never sees the Earth, because the Moon continuously keeps one face towards the Earth. The Moon would act as a gigantic shield to protect instruments from interference by Earth. Radiotelescopes, cosmic-ray detectors and other experiments could be operated with much greater sensitivity than on Earth. Also, the Moon is a good place to test the effects of low gravity on human beings for long periods of time. If people fly to Mars, it will probably mean at least two years spent in space. If the trip is spent in weightlessness, the astronauts might be too weak to endure the shock of landing and takeoff, or to walk around on the surface of Mars. It may be that the Mars spacecraft will have to be spun, creating artificial gravity for the astronauts. If so, perhaps spinning it at a slow rate, to simulate the one-sixth gravity of the Moon, might be a good compromise over the faster spin needed to simulate the gravity we feel on Earth. Setting up a research base on the Moon would help us discover whether lunar gravity is strong enough to avoid the medical problems that zero gravity causes. The desire for freedom, for living space, and for resources has led the human race to spread throughout Africa, Asia, Europe, the Americas and Australia. This expansion may someday continue to the Moon. One day there may be cities on the Moon, outgrowths of these small research stations. Taking Earth's Temperature January 1979 AD EARTH The best place to take Earth's temperature is from space. Satellites can monitor the entire planet, whereas scientists on the ground can only make measurements at local places. Also, cities and roads change the temperature by the way they absorb and reflect light, so that temperatures measured too close to them are often not accurate measurements of what's going on over a large area. Then, too, it's hard to get regular measurements from the middle of the ocean or from vast wastelands of desert. The technology that produced this picture took advantage of the fact that warm objects radiate infrared light. Infrared is similar to visible light waves, but has longer wavelengths. Generated by heat, infrared can be detected by instruments orbiting Earth. This map shows our planet's heat as measured in January, 1979. The computer uses blues to represent cold temperatures and reds to represent hot ones. Notice that the Arctic and Antarctic regions are blue (cold), while the equator is red (hot). Also, notice that it is colder in the Northern Hemisphere than in the south. Much of Europe, Asia and North America are covered with blue, because January is wintertime. When it's winter in the Northern Hemisphere, it's summer in the Southern Hemisphere. The seasons are caused by the tilt of Earth's axis. If Earth had no tilt, that is, if Earth's rotation was perpendicular to its orbit, there would be almost no seasons. (There would be slight seasonal effects caused because Earth's orbit is slightly elliptical, so part of the year Earth is closer to the Sun and slightly warmer than at other times. However, this is a tiny effect compared with the tilt.) Because Earth's axis is tilted 23 degrees, the North Pole faces more toward the Sun during half of its orbit, making it warm during that half of the year. The other half of the year, the North Pole is tilted away from the Sun, making it colder in the Northern Hemisphere. Then, the Southern Hemisphere points more nearly toward the Sun, making it summer there. Satellite measurements are the best way to tell if the whole planet is really heating up, as claimed by the theory of the greenhouse effect. If it is getting warmer, the ice caps will eventually start to melt, the oceans will rise, and cities will be flooded. rIs There Life in Europa? 1979 AD JUPITER ORBIT Europa is a Moon of Jupiter that may have an ocean inside of it. It's the second of the four large moons of Jupiter, after Io and before Ganymede as you move away from the planet. It's a bit smaller than our Moon. It is 671,000 kilometers (417,000 miles) from Jupiter and its diameter is 3,138 kilometers (1,950 miles). Europa is mostly rock, but it is covered with a thick layer of ice, perhaps 100 kilometers (60 miles) thick. The same gravitational process that heats Io and causes its volcanoes must also heat Europa. But Europa is farther away from Jupiter, so the gravity cannot affect Europa as strongly. Furthermore, Europa appears to be very icy, like many of the moons of other planets. But there is evidence to suggest that while the surface of Europa is frozen, there could be a layer of warm water beneath the surface, something like the Arctic on Earth. This has led some scientists to speculate that life might exist in the under-ice ocean of Europa. And just as we have exotic life forms such as tubeworms living near warm vents in the bottoms of our oceans, perhaps it is possible that some life forms could be swimming inside of Europa. The Galileo spacecraft will be flying by Europa in the near future and making much better measurements. It may be able to tell whether there is an ocean inside Europa. If so, one day, we may send a submarine there. QFrom Dust Cloud to Our House 4.6 Billion BC EARTH Way out in the boondocks of the Milky Way Galaxy about 4.6 billion years ago, a cloud of gas and dust began to come together into a rotating disk, attracted by its own gravity. As this disk formed, the large lump of gas at the center experienced pressure so great that the hydrogen atoms began to fuse together, creating a nuclear reaction and igniting the fires of our Sun. Orbiting the Sun, other clumps formed, eventually becoming planets, one of them the Earth. Those close to the Sun, namely, Mercury, Venus, Earth and Mars, became small and rocky planets. Those farther away mostly became large gas-covered planets: Jupiter, Saturn, Uranus and Neptune. When Earth was first formed, you couldn't have lived on it. It was extremely hot and there was no oxygen to breathe. It took a long time for our planet to be ready for plants, animals and people. Though Earth was once very hot on its surface, today it has cooled. But the natural radioactivity of rocks keeps the insides of our planet hot. Large sections of the Earth's surface drift around slowly, as you see illustrated here. c Life: How Did It Happen? 4 Billion BC EARTH In this illustration, you can follow what might be the history of life on Earth. In the sky, you see the development of galaxies similar to the Milky Way. There are the comets, planets and moons that formed in the solar system. And the rays of our star, the Sun, send us the energy that life depends on. In the ocean at the far left, the molecules that were the original building blocks of life are forming. As you look to the right you can see the bacteria that were the first cells of life, followed by more sophisticated sea life. Amphibians were able to climb out of the sea and walk on land, and finally they led to land animals like dinosaurs and humans. This is the story of life that fossil rocks show us, but how did it happen? For a long time there was only the religious explanation -- "God made it." It wasn't until naturalist Charles Darwin published his book, "The Origin of Species," that anyone came up with a convincing explanation that used only the laws of nature. Darwin proposed that life evolved by a series of accidental little changes, called mutations. Most of them didn't help the plant or animal survive. Some even hurt. But some of them were beneficial. So, for example, giraffes might have evolved their long necks because those that were born with longer necks were better adapted to eating from the tops of tall trees. They would be better able to survive, and so they'd have more babies. If a mutant short-necked giraffe was born, he'd have a hard time getting enough food. He'd be more likely to die before he had a chance to breed. There are plenty of examples around of these little changes. Think, for instance, of all the sizes and shapes of dogs you know. Think of the many kind of birds, each adapted for a different type of tree or kind of food. One result of this evolution over billions of years was to produce humans -- creatures able to make telescopes and rockets, computers and television sets, satellites and movies. From lowly little single-cell bacteria swimming in the sea, we became the creatures we are today: Colonies of billions of cells able to travel to the Moon or send a spacecraft to Mars. And perhaps there are more worlds where this sort of thing has happened. There could be other stars with other planets around them, where extraterrestrial beings are wondering if there are creatures like us in the universe. │Universe at a Glance 15 Billion BC UNIVERSE In this artist's illustration you can follow scientists' current understanding of the steps that occurred in the formation of the universe. At the far left is the Big Bang, the explosion that marked the beginning of the universe. Why the bang occurred and where the material came from that exploded is still unexplained by science, but what follows is more clear. To the right of the Big Bang you can see the great stretches of hydrogen that made up the early universe, and following it, the condensation of hydrogen into large clouds, and then into an early star -- one of billions. In the next image you can see our solar system begin forming, and then, finally, Earth. ▐America's First Space Success Jan. 31, 1958 AD HUNTSVILLE, ALABAMA The Russians had launched the world's first orbiting satellite, Sputnik. America's Vanguard program tried to launch its own space probe, but had met with some embarrassing delays. The US government was anxious to get something into space. Finally, the Army Ballistic Missile Agency at Redstone Arsenal, in Huntsville, Alabama, and the Jet Propulsion Laboratory in Pasadena, California, were told to get something flying. And just 84 days later, on Jan. 31, 1958, they did it. The United States successfully launched Explorer 1, its first satellite. Explorer 1 was 2 meters (80 inches) long and 15 centimeters (6 inches) around. It carried 5 kilograms (11 pounds) of instruments, batteries and radios. The instrument package was developed by scientists, engineers and students at the State University of Iowa under direction of James Van Allen. Explorer 1 sent back some curious Geiger counter readings. They showed strong radiation, similar to that of radioactive rocks. This was the discovery of a radiation field surrounding the Earth that would be called the Van Allen Belt. Energetic electrons from the Sun are trapped and concentrated in the Earth's magnetic field. The space race now had real competition. #Florida: America's Launch Site FLORIDA Florida is the launch site for America's space exploration program. Though there are two other US launch sites -- at Vandenberg Air Force Base in California, and at White Sands, New Mexico -- all human flights and planetary probes take off from Cape Canaveral, Florida. For a number of years, the cape was called Cape Kennedy, after President John Kennedy. Then it was changed back to its old name, Cape Canaveral. Astronauts simply call it "The Cape," or "Kennedy," short for NASA's Kennedy Space Center, located there. In addition to Cape Canaveral, Florida has a number of other attractions, including Disney World, the Everglades National Park, and the luxury hotels in Miami Beach. As you can see from this space picture of Florida, the state is a long peninsula jutting south between the Atlantic Ocean and the Gulf of Mexico. The peninsula is about 500 miles long and quite flat. The highest point in the state is only 345 feet above sea level. The first European to explore Florida was Ponce de Leon, who came in 1513. In 1564 France established a colony on the St. Johns River, which Spain destroyed. The Spanish established St. Augustine in 1565. It is the oldest city in the United States. In 1818, as an outcome of the Seminole War, Florida came under control of the United States. yHow the Fly Flies EARTH Life on Earth is amazingly diverse, even though it is also surprisingly similar. All life springs from a set of chemical blueprints, called DNA, and though the blueprints are different for each species, they are organized in essentially the same way at the molecular level. Insects, in particular, show this diversity spectacularly. There are more than a million known species of insects on Earth, and around ten thousand more are discovered every year, mostly in jungles. Insects all have six legs as adults. The fly is a good example of this group. Though flying is a tremendously complex process, the fly is not the only creature with that capability. There are flying squirrels, flying fish, flying snakes, birds, and there once were the flying reptiles of the dinosaur age. These have all arisen independently to take advantage of Earth's atmosphere as a means of travel. The diversity of life on Earth, and the ability of creatures to perform such tremendously complex processes (such as flying) is a good measure of the power of evolution. Life has adapted to take advantage of almost every possible environment on Earth. ÿSpace For Sale 1990s AD EARTH ORBIT The "For Sale" sign the astronauts are displaying here was meant as a joke, but it demonstrates a real truth -- space is of great commercial value. So far, the most important economic contribution of space has probably been to stimulate miniaturization. Almost as important was the idea of communications satellites, conceived by science fiction writer Arthur C. Clarke. Today, communications satellites are a multi-billion dollar, international industry. Telephone and television communications rely heavily on satellites to provide almost instant access between any two points on Earth. There are many ways in the future that space may become economically important to human civilization. One possibility is to have solar power satellites in orbit. These satellites could collect sunlight, convert it to electricity, and beam it down to the Earth as microwaves. In space the Sun is available twenty-four hours a day, unlike on Earth, where clouds and night interfere. One day, recreation in space may be of great economic importance. Hotels and hospitals in space would take advantage of zero gravity. Hotels would allow people to have fun orbiting the Earth, watching the planet revolve below them, and playing games in zero gravity. Hospitals would allow people with crippling diseases to enjoy the comfort of weightlessness. Probably the most important economic benefit of space exploration will be using the resources of the solar system. As Earth's resources become increasingly expensive to extract, or the environmental costs become ever more politically unacceptable, we will have to turn to space. Fortunately, there are vast stores of minerals throughout the solar system. The Moon is one of the most promising places, being filled with useful metal ores. Also, there are many asteroids that pass close to Earth that are fairly easy to get to and are rich in all the metals that civilization needs. The moons of Mars, and Mars itself, may also be harvested. The Moon may also become important in scientists' attempts to produce controlled thermonuclear fusion, producing energy by fusing atomic nuclei, the way the Sun does. Using powerful magnetic fields, atoms stripped of their electrons are smashed into each other, fusing into bigger nuclei and releasing energy. So far none of the existing systems can generate energy economically. One possibility is to use an unusual form of helium called helium 3. Ordinary helium has two protons and two neutrons in its nucleus, but helium 3 has two protons and only one neutron. It would be an excellent fuel for a fusion reactor but is extremely rare on Earth. But the Moon has helium 3 right in its surface soil. For billions of years the solar wind has been spraying the Moon with helium 3. If this helium 3 could be harvested, it could become the most important source of energy in the future. Right now, these resources would be very expensive to obtain, but as the cost of going into space keeps falling, and the cost of extracting minerals on Earth frequently rises, there will probably come a day in the 21st century when it is cheaper to harvest resources in space than on the Earth. Furthermore, we can locate industries in space where they will not pollute our planet. Another advantage of having industry in space is that metal alloys can be formed in zero gravity that cannot be made on Earth. Some metals that will mix when molten in zero gravity are like oil and water on Earth -- one will just float on top of the other. Scientists have made such zero-gravity alloys in orbit, and it may be that one day these will be economically important. Many experiments have been conducted and others are planned to see what can be done to process metals and medicines in zero gravity. Finally, history suggests that the most important discoveries are often those we cannot predict. Merely by having people living in space, we will probably make discoveries that turn out to be indispensable. RThe Theory of Evolution 1 Billion BC EARTH Astronomy, geology and the theory of evolution tell us the overall history of life on Earth, although some of the details are unclear. In the beginning, the solar system formed out of gas and dust in the Milky Way Galaxy. The biggest clump of stuff became the Sun, and nine smaller lumps of dirt and ice became planets. The Earth happened to be at just the right distance from the Sun so that it was neither too hot nor too cold, just like the bowl of porridge in the fairy tale of Goldilocks and the Three Bears. This meant that water could exist in liquid form over most of the planet. Water was essential. As long as you have liquid water, the chemicals from dirt and air can dissolve and make a soup, where they bump into each other randomly. Gradually more complicated molecules form. Lightning seems to speed up this process, helping to make complicated molecules, as does ultraviolet light from the Sun. If you're trying to cook up life, remember that the secret of success is time. Earth had all the time in the world. The planets started almost five billion years ago, so there was a long time for the atoms to meet each other and get friendly, and to form more complicated molecules until the first living cells arose. Actually, though, it didn't take five billion years. The first life happened fairly quickly, as geologists measure time -- within a few hundred million years. Then, over billions of more years, those simple cells turned into increasingly complex life forms. This building up of complicated organisms from simple ones is called evolution. It was the basic idea of British naturalist Charles Darwin. Although most scientists accept the idea of the evolution of life, there is still a lot of debate about how easy that first step was. Some think life occurs almost automatically when the conditions are right. Others suspect that it's difficult to go from non-living molecules to even the most primitive cell, in which case life may be rare in the universe. The early atmosphere was something we would call poisonous. We could not breathe it. But the first life forms took advantage of it. Some of the oldest organisms were plants, which took in air and exhaled waste products, of which the most important was oxygen. After a while there were so many plants that they began polluting this atmosphere by turning it into oxygen. Oxygen may well have been poisonous to early life forms in the ocean, but eventually the oxygen reached such a level that it became useful to other creatures that then took advantage of it. This allowed animals to use the oxygen that the plants produced. Swimming, microscopic, one-celled animals came first, followed by ones made of groups of cells. About half a billion years ago, nature invented sex. With sex, two different cells joined together to produce offspring. Until then, cells had reproduced by splitting in two. The offspring were clones -- identical copies -- of the parents. After sex came into being, there were male and female cells. When they mated, they could pass on the best qualities of both parents. This may have sped up the process of evolution. If it weren't for that one invention so long ago, you would probably not exist. All this time, the oceans were sloshing around due to tides and storms, mucking up the shores with scum and the occasional odd fish tossed unhappily onto the beach. Some of the fish grew accustomed to living in the shallow water, where they were protected from their bigger enemies of the open ocean. The tides rose and fell, creating little pools. Some creatures, like the lungfish of today, learned to live partly in the world of water and partly on land. Similarly, plants from the ocean began to take up root along the shores. Eventually, some of these beach life forms found that they liked the land enough so that they moved farther and farther inland. Their skins contained a tiny, portable ocean, in the form of blood and other liquids. One of the nifty little clues about this history is a fact contained within our own skins. Our blood is like sea water. In fact, the concentration of salt in our blood is about half that in sea water. The reason? It may be that when our ancestors came out on the land, the oceans were less salty. After all, why are oceans salty? It's because rains wash the salts from the land down into the sea. They add salt to the ocean soup. So there is a continual increase in the amount of salt in the sea. Generation upon generation of creatures evolved. Reptiles such as the dinosaurs came and disappeared. Birds and flowers arose. Apes evolved, and one branch of these may have become your ancestors. 3First American Spacewalker 1965 AD CALIFORNIA COAST In 1965, the first American walked in space. Just three months earlier, a Soviet cosmonaut, Aleksei Leonov, had become the first human being to walk in space. Being able to get out of a space capsule and float was of great importance if human beings were to be of any use in space. NASA had been planning a spacewalk, and despite being beaten by the Russians they were determined to have one of their own. Gemini 4 would be the longest American space flight yet, a four day mission carrying astronauts James McDivitt and Edward White. Some people at NASA were worried about spacewalking, but tests on the ground showed it was ready to be tried. On their second orbit, the astronauts sealed their pressure suits and depressurized the cabin, leaking the air into space in preparation for the walk. Then they opened the hatch, a first for the American space program. The danger was that if the hatch did not shut properly, it could endanger the spacecraft when it re-entered the atmosphere. Later, three Soviet cosmonauts lost their lives when their hatch failed to close properly. White was attached to the spacecraft by a line called a tether and a hose called the umbilical, which provided him with oxygen. He was also equipped with a handheld maneuvering unit, an oxygen gun that would allow him to maneuver in space. White floated out of the hatch. The Earth was overhead, with the coast of California approaching. He found himself tumbling slowly, and fired his oxygen gun. The gun worked beautifully, allowing him to maneuver. But it soon ran out of fuel, and he had to tug on his tether to move around. "This is the greatest experience", said White. "It is just tremendous." Tragically, White and two other astronauts perished in 1967 when a fire destroyed their Apollo spacecraft during a ground test. &Gagarin: First Man in Space 1961 AD TYURATAM, KAZAKHSTAN, SOVIET UNION The first human being to fly into space was a Russian. Yuri Gagarin was launched on April 12, 1961 from the Soviet Union. Flying a Vostok spacecraft, he went around the world once completely and then landed back in the USSR. Gagarin was born in 1934 in the Smolensk region of the Soviet Union. He trained in the Soviet air force as a pilot and engineer, achieving the rank of colonel. He died in 1968 in an airplane training accident. In his memory, a crater on the far side of the Moon was named after him. αOur Home: The Milky Way MILKY WAY We live in a galaxy called the Milky Way. In the city the Milky Way is hard to see because the lights reflect from the sky. But if you get away from the city on a clear night you can see it, a band of white running across the sky. The Milky Way is made of about 400 billion stars. Our Sun is just one of those many stars. It's a very ordinary star, like most of the stars in the Milky Way. Some of the stars are much bigger -- giants and even supergiants. All of them orbit a point called the Galactic Center, like the planets orbit the Sun. The galaxy is like an enormous spinning pancake, 100,000 light years in diameter. (1 light year is 10 trillion kilometers or 6 trillion miles.) But because we live inside the pancake, when we look out, we see the edge of the pancake as a strip of stars in the Milky Way. The nearby stars are close enough so that they are spread all over the sky and don't seem to be in the pancake, though they really are. Our Milky Way is just one of many galaxies in the universe. Astronomers can see many others. One of the closest is the Andromeda Galaxy. But even it is two million light years away. There are around 100 billion galaxies in the universe and each one of them has roughly 100 billion stars. So there is roughly one galaxy for every star in the Milky Way. Because the number of stars in the universe is so enormous, many scientists think that some of the stars have planets with life, and some of those planets may have civilizations. úJupiter's Third Big Moon 1610 AD JUPITER ORBIT Ganymede is one of the large moons of Jupiter discovered by Galileo in 1610. It's the third large moon out, 1,070,000 kilometers (665,000 miles) from Jupiter. Its diameter is 5,262 kilometers (3,270 miles), making it half again the size of our own Moon. It's probably about 60 percent rock, with the rest a mixture of frozen water ice and methane (CH4) ice. Its surface is cratered by meteorite hits. ZThe Middle of the Milky Way MILKY WAY GALAXY The Milky Way is a spiral galaxy with several hundred billion stars orbiting its center like planets around the Sun. But instead of there being a big star at the center of the Milky Way, there is probably a gigantic black hole with as much matter as a million suns. This mysterious region is called the Galactic Center. Though dust -- like dirt on a window -- prevents us from seeing it directly, radiotelescopes can see through the dirt. They take advantage of the galaxy being full of hot gas that broadcasts radio noise that penetrates the dust. By aiming the radiotelescope's antenna at the Galactic Center, we can "see" through the dust. What we see are huge lines, light-years in length. These are probably caused by magnetic fields that make the very hot gases (called plasma) flow almost like iron filings near a toy magnet. ∞The Other Great Spot 1989 AD NEPTUNE Just as Jupiter has its Great Red Spot, so, too, Neptune has its Great Dark Spot (GDS). This was one of the discoveries of the Voyager 2 mission, when it flew by the planet in 1989. Neptune, being much farther from the Sun -- six times farther than Jupiter -- is much colder. The chemistry of its atmosphere mainly makes blue clouds, instead of the reds and oranges of Jupiter. The Great Dark Spot of Neptune seems to be a large storm, much like the Great Red Spot of Jupiter. ªSwarms of Stars MILKY WAY Globular clusters are swarms of stars, containing as many as several million. There are about a hundred of these clusters known in our Milky Way Galaxy. If we lived there, the night sky would be brilliant, and it would be easy to visit the nearest star. Occasionally, one star passes too close to another, and it is spat out by the gravity. The orphaned star then wanders the galaxy like an ordinary star. Father of American Rocketry 1935 AD WORCESTER, MASSACHUSETTS Robert Goddard, the founder of American rocketry, was born in Worcester, Massachusetts in 1882, the year naturalist Charles Darwin died. In 1914, the New York Times learned of Goddard's ideas for space travel and wrote an editorial denouncing the scientist's ignorance of physics. (Half a century later, after spacecraft orbited the Earth, the Times admitted its error.) In 1919, the Smithsonian Institution published Goddard's classic scientific paper, "A Method of Reaching Extreme Altitudes," describing the results of his rocket experiments. In it, he explained how rockets could reach the Moon. Goddard was able to shoot rockets far faster than airplanes could go. In 1935, he shot one that went at least 1,100 kilometers per hour (700 mph) and may have gone faster than the speed of sound, the first time a human had sent a rocket that fast. Much of the money for his research came from the US Navy, which was interested in the military uses of rocketry. However, Charles Lindbergh, the first human to fly solo across the Atlantic, was intrigued by the possibilities of rocket flight. Lindbergh arranged for a private foundation to support some of the early rocket experiments. German rocket scientists followed Goddard's work closely, and added their own ideas. When World War II arrived, they built the V-2 rocket, incorporating some of Goddard's techniques. Goddard lived to see the V-2 rocket used in World War II against his country's allies. He died in 1945, too soon to see his followers reach the Moon. ZGrand Canyon: A Geologic Record 1919 AD GRAND CANYON, ARIZONA The vast Grand Canyon you see here is located in northern Arizona. It is as much as 29 kilometers (18 miles) wide and 1.6 kilometers (one mile) deep. Along the sides of its deep gorges can be seen different colors of rock layers that reveal changing conditions during vast spans of Earth's history. Scientists believe the canyon was cut over millions of years by the Colorado River, which flows through it. The first Europeans to see the canyon were members of Spanish explorer Francisco Coronado's expedition in 1540. The Grand Canyon was made a national park in 1919. ëMelted Icecaps, Flooded Cities 2000 AD EARTH One of the bleaker possibilities scientists have recently been considering is that Earth's climate will become so hot that the icecaps will melt and flood coastal cities around the world. They worry that a process called the greenhouse effect could cause such a catastrophe. Oddly enough, this effect was first clearly understood as it applies to Venus, showing the importance of planetary research in understanding our own world. The way the greenhouse effect works is this: Most of the Sun's energy is in the form of visible light. This energy passes through our atmosphere, except where clouds reflect it. Sunlight heats the Earth, and the heat generates infrared light. Infrared light is much redder than red light (longer in wavelength), and it's invisible to the human eye. But like visible light, infrared light contains energy. Normally this energy travels out into space, passing through the atmosphere. If it didn't go off into space, Earth would get hotter and hotter as the Sun continuously pumped energy into Earth. So the average temperature of Earth is the result of the energy coming in from the Sun being balanced by the energy going out to space in the form of infrared waves. But some gases, such as carbon dioxide, absorb infrared light. Our civilization produces a lot of carbon dioxide by burning fuels. Nature also produces carbon dioxide -- animals and people inhale oxygen and exhale carbon dioxide. Plants, on the other hand, inhale carbon dioxide and release oxygen. But civilization adds carbon dioxide to the atmosphere faster than plants can get rid of it. So there is a steady build-up of carbon dioxide on Earth. This carbon dioxide traps some of the infrared light that Earth radiates, and acts like a blanket over the whole planet. On Venus, where the atmosphere is mostly carbon dioxide, and is almost one hundred times the pressure of Earth's air, there is a very strong greenhouse effect. Venus is much hotter than it would be if it had a thinner atmosphere or less carbon dioxide. Earth may now be getting warmer because of the greenhouse effect. However, Earth is more complicated than Venus. We have plants converting carbon dioxide into oxygen, which Venus does not have, and we have oceans where carbon dioxide can be dissolved, and where ocean plants live. And we have clouds which sometimes form, reflecting some of the sunlight away. Because Earth is so complicated, and nature often adjusts conditions to keep the planet in balance, we don't know for certain that Earth really is going to get warmer. But not only does the possible temperature change worry scientists, but there may also be weather patterns and climate changes as a result of this carbon dioxide. So even if the world doesn't warm up, there could be great changes damaging crops and making it tough to feed the world's rapidly growing population. In a sense, Earth's carbon dioxide production is performing an experiment on our planet, and we don't know what the result will be. During the next few years, one of the most important projects of civilization will be to monitor our atmosphere and climate. NASA is designing an Earth-Observing System (EOS), a system of satellites to make careful measurements of the changes on our planet. And many other scientific experiments all over the world will be conducted to see what is really happening and to understand, with powerful computer simulations, how the weather, climate and ecology of Earth interact. Earth's rapidly-growing population, combined with the widespread burning of fuels such as gasoline, make it extremely important for us to understand what is happening, and what we can do to prevent dangerous climatic changes. éPendulum to Gyroscope 1852 AD PARIS, FRANCE One of the least appreciated inventions that was necessary for rocketry came about by studying Earth's rotation. In 1851, French physicist Jean Foucault discovered that a pendulum could show the motion of the rotating Earth. By suspending a weight from a rope in the ceiling, the motion of the pendulum, like a schoolyard swing, would go back and forth. But if this pendulum were made very carefully, so that there was very little friction in it, the pendulum could swing for days. As it swung its path slowly rotated. Foucault realized the pendulum was not actually rotating, but the Earth was rotating under it. The pendulum moved in a straight line when viewed from the stars, but on the Earth, the rotation of our planet made it seem to turn. The next year, Foucault extended this idea and invented the gyroscope. A gyroscope is basically a wheel in a frame, like a bicycle wheel. If you spin the wheel and allow the frame to move freely, the wheel will continue to point in one direction as long as it spins. With a well-designed frame -- with as little friction as possible -- the frame can move in any direction, but the axis of the wheel continues to point in one direction as long as it spins. This is much like a magnetic compass, which always points north. But the gyroscope points in whatever direction you started it at. Today, gyroscopes are powered by electric motors and are used in rockets to serve as compasses. They were used as far back as World War II for aircraft navigation and in military rockets such as the German V-2. Without gyroscopes it would not be possible to send rockets over long distances accurately. ûHalley: Man of Many Talents 1656 AD LONDON, ENGLAND The man who first understood comets was an Englishman, Edmond Halley. (Many people say "HALE-ee," but the name was probably pronounced "HAL-ee," and this is the way most astronomers pronounce it.) Halley was born in 1656 at his parents' country house in Haggerston, near London, when his future friend Isaac Newton was a teenager. Halley's father was a fairly wealthy man who earned a good living as a soap-boiler and meat-salter. This was only 40 years after Shakespeare's death and 36 years after the Pilgrims landed at Plymouth Rock in the New World. It was more than a century before the American Revolution. Halley met Isaac Newton at Cambridge University, at a time when Newton was not yet well known. Newton was a crusty man with few friends, but Halley became one of them. As a result, Halley learned that Newton had solved the problem of planetary orbits. Newton had discovered the laws of gravity and motion. Put together, they explained why the German astronomer Kepler had found that planets move in elliptical orbits around the Sun -- like circles, but a bit squashed. Halley realized that this could explain the mystery of the comets. Comets were strange glowing white lights that would appear mysteriously at night and hover in the sky for weeks at a time. They had been seen for thousands of years, but they came at random times, so were thought to be completely unpredictable. Superstitious people believed that comets were signs of wars, plagues and other disasters. They were terrified of comets. The Danish astronomer Tycho had proven that comets were outside of our atmosphere. So Halley had a brilliant idea: Suppose comets were orbiting around the Sun like distant planets, but in a more elliptical -- stretched out -- orbit? If so, they would come back again and again over a period of many years. But comets were hard to identify. Each one seemed to be different. So Halley went through every recorded appearance of a comet in history whose positions had been measured by an astronomer. He laboriously calculated the shape of each comet's orbit, how long it would take to go around the Sun, and other numbers. To his delight, he found three comets about 76 years apart, that had approximately the same set of numbers, He suspected that they were really one comet coming back three times. If he was correct, this comet orbited the Sun every 76 years. In 1705, Halley predicted that the comet would return in 1758. Unfortunately, he didn't live to see the comet's return. He died in 1742, 15 years after Newton. But in 1758, the comet did appear. The world was amazed. This omen of terror had been predicted! It was, in fact, not an omen. It was just a heavenly body, orbiting the Sun like clockwork. The forces of superstition were pushed back. The comet became world-famous as Halley's Comet. We now know that it has been recorded in history on almost every appearance for about 2000 years. And for its 1986 return, several spacecraft flew out to meet the comet: the European spaceprobe Giotto, two Japanese spacecraft, Sakigake and Suisei, and the Soviet VEGA probe. Halley was well-known in his own time for other work: He mapped the stars of the southern hemisphere. He sailed as a captain in the Royal Navy on astronomical expeditions. He served as a diplomat, much like that later scientist-diplomat, Benjamin Franklin, who was born when Halley was 50. Halley invented a diving helmet for underwater salvage. He created the first systematic tables of life expectancies, laying the foundation for the entire life-insurance industry. Although he is most famous today for his comet work, its importance was so unrecognized in his own lifetime that it was not even mentioned in the newspapers when he died. Even if he didn't live to see the return of his comet, he had in fact once seen it with his own eyes, long before he'd solved its mystery. He had seen the comet of 1682, which we now know as Halley's Comet. Hawaii: Pearl of the Pacific 1898 AD HAWAII Notice the volcanic mountains in this space picture of Hawaii. Eons ago hot magma began erupting from the ocean floor in the mid-Pacific, slowly building up undersea mountains that eventually became the Hawaiian Islands. The volcanic soil of Hawaii is tremendously rich, and ideal for flowers, sugarcane, pineapples, macadamia nuts, fruits, melons, and other crops. Hawaii was once an independent country, but was annexed by the United States in 1898. It became the United States' 50th state in 1959. Giotto's Suicide Ride 1986 AD SOLAR SYSTEM This is one of the best pictures ever taken of history's most famous comet, Halley's Comet. This comet spends most of its time out near the orbits of Uranus and Neptune, but every 76 years it passes Earth's orbit. When Halley's Comet returned in 1986, the European Space Agency (ESA) was ready. It sent a space probe called Giotto, named after an Italian Renaissance artist who had seen Halley's Comet and painted it as the Star of Bethlehem. The Giotto probe was shot from the European launch pad in French Guiana, in South America. It was the first time the Europeans had launched a probe beyond Earth without using American or Russian rockets. Giotto was sent on a kamikaze mission right past the heart of the comet. It was badly battered by ice and dust particles from the comet, but it survived. The Giotto data proved that many of the comet's particles are made of a fascinating material called CHON, which stands for carbon, hydrogen, oxygen, and nitrogen. What makes CHON so interesting is that these are the main atoms that Earth life is made of. This suggests that the ingredients of life may be common in the universe. In 1992 Giotto flew by another comet, called Grigg-Skjellerup, and sent back useful information, although its camera had been destroyed by Halley's Comet. ÿJapanese Comet Spacecraft 1986 AD JAPAN When Halley's Comet returned in 1986, the Japanese wanted to meet it, so they designed two space probes to fly past the comet. The two, called Sakigake (Pioneer) and Suisei (Comet), were launched from a base in Japan. This was the first time the Japanese had launched spacecraft to a target beyond Earth. Both were successful, returning measurements that helped scientists understand the comet. 6Halley's Comet and Leftovers 1986 AD SOLAR SYSTEM One of the most beautiful sights in the solar system is a comet, as you can see from this picture of Halley's Comet taken in 1986. Many comets take thousands of years to go around the Sun, but Halley's Comet makes the trip around the Sun every 76 years. Furthermore, it is a fairly young comet. We can tell it's young because it hasn't burned out by going around the Sun too many times. It still has lots of ice left to evaporate and form the beautiful trail of gas and dust that we see in the sky. When Halley's Comet returned in 1986, after being gone since 1910, it was greeted by five spacecraft: two from the Soviet Union (called VEGA), two from Japan (Suisei and Sakigake) and one from the European Space Agency (Giotto). Twice a year, you can see meteor showers that are probably leftover pieces of Halley's Comet. This is because bits of dust from the comet's tail form an orbit around the Sun, an elliptical trail. Twice a year we pass through one part or the other of this trail, and those tiny pieces of comet become meteors, glowing streaks in the sky. The first meteor shower is between March 2-7, and is known as the Eta Aquarid shower. The second is between October 16-26, and is called the Orionid shower. The next time that Halley's Comet will fly close to the Earth will be in the year 2061. BSoprano to Astronomer 1782 AD BATH, ENGLAND Caroline Herschel was the first major woman astronomer. At a time when women scientists were almost unheard of, she began her career as an astronomer as an assistant to her astronomer brother William, to whom she was deeply devoted. When William moved to England from Hannover, Germany, she followed him, and became a soprano soloist in performances he conducted, because he was a musician before he became an astronomer. When he became interested in astronomy, Caroline assisted him, often staying up all night with him. Later she began searching the heavens herself, and between 1786 and 1797 discovered eight comets. However, Caroline was deeply hurt when William got married, and unfortunately destroyed ten years of her journals, from 1788 to 1798, which must have contained a great amount of information about the work of the brother-sister team. Caroline returned to Hannover when William died, and compiled a catalog of nebulae and clusters her brother had observed. For her work on this catalog, the Royal Astronomical Society awarded her its gold medal. ûBigger, Better Telescopes 1782 AD BATH, ENGLAND The first person in history to discover a planet was the remarkable William Herschel. He was a German who came to England as a military bandmaster, probably the least likely background for a great astronomer imaginable. Astronomy was originally just a hobby to him, which he pursued with the help of his sister Caroline, who herself became an important astronomer. William became obsessed with building bigger and better telescopes, and before long, he was making the best in the world. He and his sister observed tirelessly until they became so good that they could no longer be called amateurs. They were real pros. Then one night he observed a faint blur that he thought was a comet. He reported it as such, but when he calculated its orbit, he found it had the nearly circular orbit of a planet, but beyond the known worlds of the solar system. He was the first human ever to set eyes on a new world. Like Halley, he knew which side his bread was buttered on, so he named his planet Georgium Sidus, George's Star, after the king of his adopted England, George III (the same George whose ineptitude led to the American Revolution). The name didn't stick, but it did not hurt his reputation in the palace. The name of Uranus was finally given to Herschel's planet. Ironically, it happens that Uranus is visible to the naked eye. However, it is about as faint as the eye can see, so it is not surprising that it had gotten lost among the thousands of other stars. (What other strange objects may lurk in the starry sky, perhaps just as visible to our eyes, but unrecognized?) After its discovery, other astronomical records were examined and Uranus was found in them, marked as a star. Several astronomers had blown their chance to be the first with a new planet. Herschel was knighted and made Court Astronomer, which gave him a salary and freed him from the necessity of giving music lessons to earn a living. ¡Himalayas: Stark From Space April 1981 AD HIMALAYAN MOUNTAINS The stark scene before you is an overhead view of the great Himalayan mountain range taken during the first space shuttle mission in April, 1981. The tallest of these mountains is Mt. Everest on the Tibet-Nepal border. It is known to the Nepalese as Sagarmatha and to the Tibetans as Chomolungma. The mountain was first scaled in 1953 by Sir Edmund Hillary of New Zealand and Tenzing Norgay, a Nepalese. }Venus: Probe Killer 1975 AD VENUS The Soviet Union sent probes to Mars and Venus, but while their Mars probes were usually failures, their Venus probes were remarkably successful. The Soviet Venus probes were called Venera, Russian for Venus. The Soviets have sent more than a dozen Venus probes during the last 30 years, most of which were successful. They've been increasingly sophisticated, even ejecting capsules into the atmosphere and using parachutes to slow the descent of the probes. Venera 7 had a capsule that survived to return measurements from the surface in 1970, although it did not have a camera. It found Venus has a temperature of 475° Celsius (900° Fahrenheit), hot enough to melt lead. The hellish environment of Venus is the main obstacle to a lander. The heat destroys the probe's electronics, allowing it to last only for an hour or so on the wickedly hot surface of the planet. Nevertheless, the Russians landed Venera 9 on the surface of Venus in 1975, complete with a television camera. It was the first time pictures had ever been sent from the surface of another planet, and they showed sharp rocks littering the surface of the planet. The above photograph was taken by this probe. Later Soviet probes landed on the surface of Venus and sent back color pictures, which information was used to colorize some of the American Magellan spacecraft radar images taken from orbit around the planet. NThe Largest Space Telescope 1990 AD CAPE CANAVERAL, FLORIDA It's long been the dream of astronomers to have a telescope in space. There, no atmosphere interferes with the "seeing." Telescopes on Earth have to fight the bubbling air currents that cause stars to twinkle. In the vacuum of space, there is no air to interfere. To make that dream come true, the Hubble Space Telescope was launched by space shuttle in 1990. It is by far the largest optical astronomical telescope ever put in space. Its main mirror is 94 inches in diameter, about half the size of the Mt. Palomar telescope mirror. Unfortunately, there was a manufacturing error in the mirror, and pictures taken by it are not as sharp as they should be. Nevertheless, computers on Earth can correct for the error in certain types of objects, such as stars. Some of the corrected pictures are still better than the best Earth-based telescope pictures. A new camera lens has been designed to correct the mirror's error. In 1993, a space shuttle will take it up, and astronauts will replace one of the current cameras. This should result in the best possible pictures. Edwin Hubble Sees Red 1929 AD MT. WILSON, CALIFORNIA The modern view of the universe was revolutionized by a lawyer. Edwin Hubble, born in Marshfield, Missouri, in 1889, became a Rhodes Scholar, studying law at Oxford University in England. For a short time he practiced law in Kentucky, but he was drawn to science. He was attracted by astronomy, and accepted a post at the Yerkes Observatory in Illinois. After serving in the infantry in World War I, he accepted a position at the Mt. Wilson Observatory in Southern California. At that time its 2.5 meter (100 inch) telescope was the world's largest. In 1929, Hubble was studying galaxies, measuring how fast they move. He analyzed the light from these galaxies with a spectroscope, which shows the spectrum of light emitted by the stars in the galaxy. Each of the different kinds of atoms in these galaxies create particular bright and dark lines in a spectrum. Hubble found that they were shifted slightly from where they were in the laboratory. They were reddened -- which meant that they were moving away from us. This is because when an object emits a signal, such as a light wave, the frequency of the signal changes if the object is moving. This is known as the Doppler effect, the same one that causes the sound of a railroad whistle to change as it moves towards you or away from you. Hubble was not the first person to use the Doppler shift to measure the speed of galaxies, but he went one step beyond where other astronomers had gone. He found that the faster a galaxy was moving, the fainter its light. But (assuming most galaxies are similar) faint galaxies are farther away, just as a street light at night is generally brighter when close and dimmer when more distant. So he realized that the farther away a galaxy was, the faster it was moving away from us. After thinking about it, he realized that this is what you would expect if there had been a great explosion and all the galaxies were moving away like the fragments of an explosion. So Hubble discovered that the universe was expanding. The galaxies were all moving away from each other. And if this was true, that meant that the explosion had to start at some particular point in time. Today we call this the Big Bang theory. Our best measurements are that the Big Bang occurred about 15 billion years ago. Most astronomers think the universe started out as an incredibly dense point of matter that exploded. Hubble changed our view of the universe as much as Copernicus had. In his honor, NASA named the Hubble Space Telescope after him. ÇIapetus in Black and White 1979 AD SATURN ORBIT Iapetus is one of the strangest moons in the solar system. It is a medium-sized moon made of rock and ice; it is 1,436 kilometers (892 miles) in diameter and is located about 3,561,000 kilometers (2,213,000 miles) from Saturn. What makes it strange is that it is basically black on one side and white on the other. It is the only moon we know of that has such a tremendous difference in brightness from one side to the other. Astronomers are not sure what causes this, but it may have to do with meteorites hitting other moons in the Saturn system. Debris from these strikes could land on one side of Iapetus. Since Iapetus, like most moons, keeps one face pointing toward its planet -- as our own Moon keeps its face toward Earth -- this could lead to a build-up of a different type of material on one side of the Moon from the other. Iapetus is a mixture of rock and ice. Storehouses of Knowledge c300 BC ALEXANDRIA, EGYPT Welcome to the Space Adventure Library! You can use the card catalog in the library picture to find any topic you wish. Just click on the card catalog drawer containing the topic you want to find, then click on the topic itself. Space Adventure will take you right to a screen on that topic. Though electronic libraries such as this one are new, other types of libraries have been around for ages. One of the earliest libraries was a collection of about 10,000 clay tablets discovered in Nineveh (an ancient city in what is now Iraq) during an archaeological excavation in 1850. But perhaps the greatest storehouses of knowledge in the ancient world were the great libraries at Alexandria, Egypt. These libraries were greatly expanded by Ptolemy Philadelphus, the son of one of Alexander the Great's generals and the ruler of Egypt. They were frequented by many great scholars from throughout the Mediterranean world. The Alexandrian libraries held a huge collection of volumes from throughout the Hellenistic world. Various estimates put the collection at anywhere from 400,000 to 700,000 volumes. But as Alexandria declined in political importance, it appears the libraries also declined, and in 640 AD were completely destroyed in a fire of unknown origin. Herschel Discovers Invisible Light 1800 AD SLOUGH, ENGLAND William Hershel, the discoverer of Uranus, was also the discoverer of an important tool in the exploration of space -- invisible light. Herschel, a German bandleader who moved to England and became an amateur astronomer, was using a glass prism to study the light from the Sun. Passing sunlight through a prism casts a rainbow of colors on a wall. It works this way because a prism bends different colors by different degrees, so it separates white light into a rainbow, called a spectrum. In 1800, Herschel measured the temperature of the different colors in the Sun's spectrum. To his surprise, he found there was heat not only where there was color, but even where there was nothing. If he put a thermometer beyond the red end of the spectrum, it still got hot. He realized there was some kind of light there that was invisible to the human eye, which had enough energy to heat the thermometer. This is what we call infrared light. We now know that all warm objects give off infrared light. Today, infrared astronomy is one of our most important tools for finding astronomical bodies that do not glow visibly, since they still glow with infrared light. In fact infrared is often the only way we have of seeing the dust out of which stars and planets form. çThe Gemini Space Program 1964 AD JOHNSON SPACE CENTER, HOUSTON, TEXAS NASA's Gemini Program was the successor to the Mercury Program. The Gemini craft held two astronauts -- instead of the Mercury's one -- in a maneuverable space capsule. Built in three sections, the Gemini craft had a crew section that resembled the earlier, smaller Mercury capsules, but with thrusters and control functions. The next two sections were cylindrical housings for the retro (reverse) rockets and their fuel supply, which were jettisoned after firing. The third section, jettisoned minutes before retro-fire, held thrusters, fuel, power supply, and items to sustain the crew for up to two weeks. The entire Gemini weighed up to four tons and required more lift than the Atlas rocket used for Mercury capsules could provide. So NASA converted a missile booster (renamed the Titan 2) that developed 180,000 kilograms (400,000 pounds) of thrust. There were ten manned Gemini missions, Gemini 3 through Gemini 12. Astronauts on these missions took more than 2,400 photos from heights of 160 to 1400 kilometers (100 to 850 miles). These photos showed the distribution of air and water pollution, city development, weather patterns, and geological formations. In addition, the Gemini program proved that two spacecraft could dock, that astronauts could walk, work and test equipment in space. The first American to spacewalk, Ed White, was so thrilled by the experience that he didn't want to come back in, and had to be ordered in by astronaut James McDivitt. Houston's Mission Control became operational for the first time during Gemini 3. Missions 6 and 7 performed the first space rendezvous between two spacecraft. Prior dockings had been with special Agena boosters. While the astronauts made their work appear easy, Gemini 3 crewman Gus Grissom, when asked what would be the most difficult part of the flight, answered "the part between lift-off and landing." Io: The Volcanic Moon 1979 AD JUPITER ORBIT Of all the objects in our solar system, Jupiter's moon Io is surely one of the most unusual. (Some people call it "EYE-oh"; others say "EE-oh." Both are okay.) Discovered by Italian astronomer Galileo, Io is the biggest of Jupiter's four main moons and is the closest to the giant planet. It is 3,640 kilometers (2260 miles) in diameter, slightly larger than our Moon. The amazing thing about Io is that it has more erupting volcanoes than any body in the solar system. Why? Just before the first Voyager flew by Io, scientists had predicted that Jupiter's gravity would cause Io to heat up. The reason is this: Io moves pretty much in a circular orbit around the planet, but the slight gravity of another Moon, Europa, sometimes tugs on it a little. This disturbs Io's orbit slightly, so it's not quite a circle. This causes Io to move slightly in and out around Jupiter. But Jupiter's enormous gravity squeezes Io, in just the way that our Moon's gravity squeezes Earth's oceans to make the tides. This squeezing makes Io heat up, like a piece of metal bent again and again. The heat causes volcanoes to erupt. In 1979, when the Voyager 1 spacecraft flew by Io, a volcano was seen erupting. Between the Voyager 1 and 2 flybys of Io, eight erupting volcanoes have been detected. ÿIon Drives: A Long Little Push 1964 AD JET PROPULSION LABORATORY, PASADENA, CALIFORNIA One of the best ways to travel around the solar system has never been used in practice, except for brief tests. It is called an ion drive. The idea is to use electricity to accelerate electrically charged particles -- ions -- instead of using chemical reactions. In a chemical rocket, the fuel is burned rapidly, and is gone in a few minutes. In an ion drive, the fuel is produced one atom at a time, and can be fired for months on end. Though the thrust is much smaller than in a chemical rocket, if the spacecraft is already in orbit, a tiny thrust fired for a long time will accelerate it to a very high speed. The fuel for an ion drive would be a metal such as cesium. Cesium is easily vaporized, and can be accelerated by electrical fields. Solar panels would convert sunlight into electricity, which would then be used to power the ion drive. This picture shows an ion drive designed by NASA to take a spacecraft to Halley's Comet. Unfortunately, Congress did not provide the money for the project, so it has never flown. But the idea is excellent. Experiments on ion drives have been conducted in laboratories in several countries, but the first space test was done by the Soviet Union in 1984 by a Vostok spacecraft. Because ion drives have such small thrusts, you cannot use them to get from the surface of the Earth into space. But if you use a conventional rocket to get into orbit, you can then launch an ion drive craft to the Moon, Mars, or anywhere else in the solar system. There continues to be interest in ion drives and it is likely that spacefaring nations will use such drives before the decade is out. @Our Neighboring Galaxy 1983 AD ANDROMEDA The nearest large galaxy to our own Milky Way is Andromeda. It is similar to our own galaxy, but even larger, with about twice as many stars. This is an infrared picture taken by the IRAS (Infrared Astronomical Satellite), showing what you would see if your eyes could see the infrared glow of heat waves. \Jets That are Really Rockets Aug. 8, 1929 ELBE RIVER, GERMANY Sometimes there isn't much room for an airplane to take off. Or, perhaps, the plane is heavily loaded and needs a boost to get airborne. One way to give a plane a boost was with a Jet Assisted Take Off device, or JATO. JATO, which the British more accurately called RATO, for Rocket Assisted Take Off, was developed in the decades before World War II, and boosted planes into the air both during and after the war. Actually, the JATO concept was invented in the 1880s by Englishman T.J. Bennet, who attached gunpowder rockets to a model airplane. The earliest known piloted jet-assisted takeoff was August 8, 1929, when a German airplane was propelled off the Elbe River by six solid-fuel rockets. The United States made its first successful jet assisted take off on August 23, 1941, and thousands of the devices helped planes get into the air in World War II, mostly using solid-fuel 12-second rockets. They were particularly useful in launching overloaded planes, helping seaplanes take off in restricted areas, and rescuing aircraft forced down in areas without a lengthy airfield. óThe Biggest Planet JUPITER Jupiter is by far the largest planet in the solar system. It's three times as massive as its nearest competitor, Saturn. It was one of the planets known to the ancients. It takes 12 years to orbit the Sun. Jupiter is five times as far from the Sun as the Earth is. It's mostly made of hydrogen (H2) gas, the same as the Sun, but with substantial amounts of ammonia (NH3, as in household cleaner), methane (CH4, natural gas) and helium (He). Four spacecraft have flown by the planet: Pioneer 10 and 11 and Voyager 1 and 2. A spacecraft called Galileo is now on its way to Jupiter. Galileo will orbit the planet and drop a probe into its atmosphere. The "surface" we see is nothing but clouds. The temperature and pressure of these clouds is similar to those in your room. Some scientists have suggested that conditions there could have allowed living creatures to evolve, floating high in Jupiter's clouds. Jupiter Dwarfs Earth JUPITER/EARTH Jupiter is about 11 times the diameter of Earth and has about 300 times as much mass. Here they are shown side by side at the same scale for comparison. In fact, Jupiter is five times farther from the Sun than Earth, and takes 12 years to go around the Sun. vJupiter's Invisible Ring 1973 AD JUPITER ORBIT Jupiter has an enormous, doughnut-shaped ring of gas around it. Jupiter's moon, Io, has many erupting volcanoes that spew forth gas into space. These atoms of sulfur, hydrogen, and sodium are then trapped by the planet's strong gravity and orbit the planet like a big doughnut. This ring is invisible to the naked eye, but can be detected by instruments on Earth and in space. This is quite different from Saturn's famous rings, which are made mostly of ice. Jupiter has such a ring, too, close to the planet. But it's much fainter than Saturn's rings, and wasn't discovered until spacecraft flew by Jupiter. ÷Jupiter: Mysterious Giant JUPITER Jupiter is by far the largest planet in the solar system. All four of the large outer planets, Jupiter, Saturn, Uranus, and Neptune, are called giant planets, or Jovian planets (after the Roman god Jove, or Jupiter). But Jupiter is the most gigantic of them all. It is three times as massive as the next largest planet, Saturn, and 300 times as massive as the Earth. Jupiter is so much larger than any other part of the solar system that it has been said that the solar system consists of the Sun, Jupiter and junk. It takes Jupiter 12 years to orbit the Sun. It is five times as far from the Sun as Earth, which means the Sun would be 25 times dimmer. It spins very rapidly, about once every ten hours, compared with our planet's twenty-four hour day. This creates a centrifugal force that causes the equator of Jupiter to be noticeably larger than its pole, so it is slightly squashed as a result. Jupiter has four large moons (Io, Europa, Ganymede and Callisto) that were first seen by Galileo, and are called the Galilean satellites. It also has about a dozen small moons. One of the most remarkable features of Jupiter is its Great Red Spot, an enormous storm that has been observed for centuries. It also has very distinctive belts of storms that are parallel to the equator. Jupiter is mostly made of hydrogen, the most common atom in the universe. This makes it very different from the Earth and the other inner planets. Whereas the inner planets are mainly made of rock, the giant planets are made mostly of gas, like little stars. So Jupiter is mostly gas, although if you go down deep enough, there must be a place where the gas is a liquid. And there is probably also a rocky core a little bit bigger than the Earth at the very center of the planet. One of the most astonishing discoveries about Jupiter is that it actually radiates more energy than it receives from the Sun. A planet like Earth receives energy as visible light from the Sun, which heats it up, causing it to radiate infrared waves. But the amount of energy leaving the Earth in the form of infrared energy equals the amount of energy from the Sun. Jupiter, on the other hand, radiates twice as much energy as it gets from the Sun. This came as quite a shock to astronomers. It meant Jupiter was something like a star, in that it radiated more energy than it received. But this seemed to be impossible. A star would have to be much larger -- around one-tenth the mass of the Sun -- in order to allow the fusion reactions of hydrogen that create the heat. But Jupiter is only about one-thousandth the mass of the Sun. How to explain this mystery? The answer is probably that Jupiter is still contracting from its original formation. When the solar system formed, gas and dust orbited the Sun and formed clots that became planets. Gravity caused these planets to form by attracting gas and dust into concentrations. Jupiter is so big, and so full of gas, that apparently it is still contracting, and the contraction causes it to heat up. In addition to the overwhelming abundance of hydrogen, there are other important gases in Jupiter: helium (as in party balloons), ammonia (as in household cleaner), and methane (as in swamp gas and cooking gas). Jupiter has the strongest magnetic field of any planet, almost ten times as strong as Earth's. One of the effects of Jupiter's magnetic field (especially as it interacts with the moon Io) is to accelerate solar wind electrons to great energies, causing them to emit radio waves that can be detected from Earth. Pioneer: First Beyond Mars 1973 AD SOLAR SYSTEM This is a historic picture from the first spacecraft ever to travel beyond the orbit of Mars, Pioneer 10. Pioneer 10 was the first spacecraft to reach Jupiter. It was soon followed by Pioneer 11, which later also flew by Saturn. These were then followed by more advanced spacecraft, Voyagers 1 and 2, which visited not only Jupiter and Saturn, but also (in the case of Voyager 2) Uranus and Neptune. Pioneer 10 took better pictures of Jupiter than the best Earth-based telescopes ever had. The picture above shows the Great Red Spot, the shadow of the Moon Io and the belts of Jupiter (clouds and storms in the atmosphere of the planet). The picture was taken at a distance of 2,500,000 kilometers (1,580,000 miles) from Jupiter. The two Pioneers also measured the very strong and complicated magnetic field of Jupiter for the first time. Both Pioneers have now left the solar system, carrying an interstellar message known as the Pioneer plaque, in the hopes that some day a distant civilization may find it. φGalileo: Soon to be Squashed Dec. 7, 1995 AD JUPITER The Galileo spacecraft is now on its way to Jupiter. When it gets there, part of it, called the orbiter, will circle the planet forever, sending back television pictures. On December 7, 1995 another part -- the entry probe -- will fall into the planet's atmosphere. As the Galileo probe enters Jupiter's atmosphere, it will be slowed by a parachute and by friction. Its transmitter will radio back measurements to the orbiter until the probe is crushed by Jupiter's tremendous atmospheric pressure. It will probably survive about an hour during its exciting ride through the incredibly windy atmosphere. Unlike the orbiter, the probe does not have a television camera, so we will not get pictures from within Jupiter's atmosphere. However, the probe does have instruments that will tell us much about the atmosphere, including its temperature and pressure. Currently, there is a serious problem with the orbiter's main antenna. It's stuck like a broken umbrella, and cannot completely unfold. However, there is a smaller antenna that will be used if the main one cannot be unstuck. We will not get back as much data that way, but we will still get many pictures of the planet and its largest moons, and we will still get the entry-probe data. √The Biggest Optical Telescope 1992 AD MAUNA KEA, HAWAII The world's biggest optical telescope is found on a mountain top in Hawaii. Known as the W. M. Keck Telescope, it is equivalent to four Mt. Palomar telescopes in the size of its mirror. For decades, the Mt. Palomar telescope was the most powerful optical telescope in the world. With a mirror five meters (200 inches) in diameter, it was able to pick up fainter light than any telescope on Earth. The larger a telescope mirror, the more light it collects, so scientists are forever trying to build bigger telescopes. In 1974 the Soviet Union completed an even larger telescope, with a six meter diameter mirror. But it is extremely difficult to make mirrors this large. The slightest imperfection can ruin it. Also, as the telescope is pointed at different parts of the sky, stresses can distort it. For the Keck telescope, a very different design was chosen. Instead of having a single giant mirror, it was built of 36 smaller mirrors. Each mirror is 1.8 meters (5 feet, 11 inches) wide. Using lasers, the mirrors are precisely adjusted so they act as one giant mirror. Operating together, the 36 mirrors are equivalent to a single 10 meter mirror. This is twice the diameter of the Mt. Palomar mirror, but since area goes as the square of the diameter, it has four times the area. So it's got four times the power of the Mt. Palomar telescope. Furthermore, it's on the mountaintop of Mauna Kea, Hawaii, the best location in the world for an optical telescope. The air is unusually steady there, and the sky is free of interference from city lights, which cause problems for Mt. Palomar. An identical copy of the Keck telescope is being built a few feet away from the original, which astronomers sometimes call the "Bride of Keck". This will double the collecting area of the telescope system. It will also allow the two to be used together as what astronomers call an interferometer, which makes the telescope pair act in some ways as if it were an even bigger telescope, 85 meters (93 yards) in diameter. With it, astronomers may be able to detect Jupiter-sized planets around nearby stars and see galaxies that formed a billion years after the universe began. Such galaxies are so far that it takes their light approximately 14 billion years to get here. Kennedy: Shoot for the Moon! May 25, 1961 AD WASHINGTON, DC In 1961, President Kennedy made the decision to take humanity to the Moon "before the decade is out." Perhaps in part because of embarrassment over the failure of his Bay of Pigs invasion of Cuba, he chose a program that the entire country could rally around. He announced that the US would put a man on the Moon by 1969. In a speech to Congress, before the United States had even sent a man into orbit, Kennedy proposed a bold and ambitious goal: "I believe," he said, "that this nation should commit itself to achieving the goal, before this decade is out, of landing a man on the Moon and returning him safely to the Earth." Even though he did not live to see it happen, his program succeeded on July 20, 1969, when Neil Armstrong and Buzz Aldrin landed on the Moon. ^ Kepler's Laws 1571 AD WEIL DER STADT, GERMANY Johannes Kepler was a German astronomer born in 1571, a time of great religious turmoil. Protestants battled for the separation of their church from the Roman Catholic Church. Because he was a Lutheran, he had to frequently leave the cities where he lived in order to move to a place where he would not be persecuted. At one point, Kepler's mother was arrested for witchcraft, although several years later she was freed. Back then, most people thought the planets moved around Earth, and that Earth was the center of the universe. However, Copernicus had shown a few years earlier that the Sun could be considered the center around which the planets moved. Kepler wanted to analyze the motion of the planets. By carefully using the painstaking measurements that Danish astronomer Tycho Brahe had made, Kepler found patterns in the movements of the planets. Kepler deduced three laws of the motion of planets. His first was that planets move in ellipses around the Sun. The ancients believed that the planets moved in very complicated paths centered on Earth. Copernicus had assumed that the planets moved in circular orbits around the Sun, which was a good approximation. But Kepler discovered that the planets actually move in an ellipse, a somewhat squashed circle. Kepler's second law was that if you draw a line from the Sun to a planet, the area swept by that line in a given time is the same, no matter where the planet is in its orbit. This means the planet moves fast when it's close to the Sun, and slowly when it is far from the Sun. So the line from the Sun to the planet sweeps the same amount of area in one day. Kepler's third law relates the time it takes the planet to go around the Sun -- its year -- to its average distance from the Sun. He found that if you take the length of the planet's year and square it (multiply it by itself), the number is the same as the distance of the planet from the Sun cubed (multiplied by itself three times). This law let astronomers calculate how far a planet was just by knowing how long it took to go around the Sun. Kepler also wrote the first true science fiction story ever, Solemnium, in which he imagined the voyage of a man to the Moon. Kepler's work laid the foundation for the revolutionary theories of Isaac Newton, who then explained Kepler's laws with his own laws of gravity and motion. ªKohoutek: The Shy Comet 1973 AD CZECHOSLOVAKIA In 1973, a Czechoslovakian astronomer discovered a comet while it was still far from the Sun, and it was named Kohoutek after him. Some astronomers expected it to be very bright when it got close to Earth. The average citizen heard a lot of talk about "the comet of the century" and expected a spectacular light show when it got close to Earth. Unfortunately, comets can brighten and dim unpredictably, and Comet Kohoutek chose to stay dim. Scientists, however, weren't disappointed. This was the most thoroughly observed comet in history prior to the 1986 return of Halley's Comet. Skylab astronauts watched it from space, and to them, it was spectacular. ╙Korolev: The Russian Von Braun 1933 AD MOSCOW, SOVIET UNION Just as Wernher Von Braun, more than any other person, made the American space program a success, so rocket designer Sergei Pavlovich Korolev drove the Soviet space program to success. Korolev, born in Zhitomir, USSR, in 1906, was inspired by the ideas of Russian rocket pioneer Konstantin Tsiolkovsky. In 1931, he helped organize a Russian rocket-study group and helped launch the first Soviet liquid-fueled rocket, GIRD-09, in 1933. During World War II, Korolev designed JATO rockets to help military aircraft take off from short runways. After the war, he organized the development of military and scientific rockets. He led the team that designed Sputnik, the first artificial satellite, which began the Space Age. Later he helped develop the Vostok and Voskhod spacecraft. The Vostok was used to make the first human flights in space, and the Voskhod to make the first spacewalks. Under his leadership, the Soviet Union sent spacecraft to the Moon, Mars, and Venus. One of his spacecraft, Luna 3, was the first to take pictures of the far side of the Moon, which had never before been seen. Appropriately, the largest feature on the hidden side of the Moon was named Korolev. He died in 1966. @Los Angeles: Look Quick, No Smog 1975 AD LOS ANGELES, CALIFORNIA This view of a smog-free Los Angeles was snapped by astronauts during the joint US/Soviet Union Apollo-Soyuz Test Project in 1975, when an American spacecraft docked with a Soviet spacecraft. The city was founded by the Spanish in 1781, was taken over by the United States in 1846, and has grown to be one of the largest cities in the country. Though it is known for its movie industry (not to mention smog and urban sprawl), the Greater Los Angeles area actually has a very diverse economy, ranging from aerospace industry to Pacific shipping. πEight Million Year Satellite 1976 AD EARTH ORBIT One of the most unusual Earth satellites ever launched was called LAGEOS (Laser Geodynamics Satellite). It went aloft in 1976 to help scientists precisely measure movements of the Earth's continents. There are no electronics on board, just reflectors. At the heart of the satellite is a heavy brass mass, put there so traces of atmosphere high above Earth will not slow the satellite down. For the same reason, it was placed in a high orbit -- about 6,000 kilometers (4,000 miles) above Earth's surface. But even at this high altitude, atoms from Earth's atmosphere will drag on the satellite, causing it to crash in about eight million years. Because it is going to be up there so long, it also contains a message to the future, designed by astronomer Carl Sagan. The message shows the drifting of the continents, past, present and future. Surrounding the brass is an aluminum sphere about 60 centimeters (2 feet) in diameter to which 426 silicon reflectors are attached. The idea is for scientists on Earth to bounce laser light off the satellite. They carefully measure the time it takes the light to travel from Earth to the satellite and back again, thereby allowing them to precisely measure its distance. In this way, as Earth's continents drift across the planet, causing Earthquakes and volcanoes, LAGEOS can help measure exactly how fast the Earth's crust is moving over the liquid interior. The continents typically move only a centimeter or two (an inch or so) per year. But over billions of years these very slow movements are enough to cause continents to drift all over the planet. Geologists believe that at one time all of the continents were one gigantic continent that was then broken up by this slow drift. This is why South America seems to fit into Africa like a jigsaw puzzle piece. Many other parts of the Earth similarly match. ASI, the Italian space agency, has built the next generation of such satellites, LAGEOS II. It will be launched by NASA in late 1992. ╡Volcanoes: Krakatoa to Mars August 27, 1883 AD KRAKATOA, INDONESIA Krakatoa, a volcanic island in Indonesia, had slept peacefully since it last erupted in 1681, more than two centuries before. Then, in 1883, a series of minor eruptions began. Steam and ash clouds formed over the island once again. On August 26, a series of huge explosions began. But that was nothing compared to the next day. Sea water flowed into the volcano and mixed with the hot magma (molten rock), creating a bomb of magma and steam that exploded on August 27, destroying virtually the entire island and causing tidal waves that sank ships and killed about 36,000 people. It was the worst volcanic eruption in recorded history. The melted rock called magma forms where the Earth's crust meets the mantle, the huge gooey rock mass that makes up 80 percent of our planet. It tends to make its way to the surface near the edges of the Earth's 12 huge continental plates, where the crust is weakest. When the magma reaches the surface it is called lava, and generally is about 900 to 1,200 degrees Celsius (1,650 to 2,200 degrees Fahrenheit). Many of the world's volcanoes are located around the giant Pacific Plate, which roughly encircles the Pacific Ocean. This circle of volcanoes is often called the Ring of Fire. Obviously, volcanoes can be terrifying and extremely dangerous, and thousands of people are killed by them. But on the positive side, volcanoes bring minerals such as potassium to the surface of the Earth that greatly add to its fertility for crops. The most common volcanoes are the well-known cone variety with a single vent at the top, but there are also shield volcanoes and fissure volcanoes. Shield volcanoes often have several vents that spew forth runny lava that makes a low, flat shield shape. Fissure volcanoes are made up of a series of vents along a crack in the Earth's surface. In fact, scientists have even located volcanoes on other planets, such as Venus and Mars, and on Io, a moon of Jupiter. ╓Leonov: First Space Walker 1965 AD TYURATAM, KAZAKHSTAN, SOVIET UNION The first human to walk in space was a Russian, Alexei Leonov, who flew into space in 1965 on board the Voskhod 2 spacecraft with cosmonaut Pavel Belyayev. Leonov, a graduate of the Soviet air force flying and engineering schools, emerged from the hatch and floated into space. He wore a backpack containing air, similar to the pack worn by scuba divers. For twelve minutes he "walked" -- or floated, really -- in space. The success of his spacewalk was another embarrassment to the American space program, which was still trying to catch up to the Russians. It prompted NASA to accelerate its Gemini schedule so American astronaut Edward White could walk in space three months later. ±Lifting Body: Power by Pontiac 1963 AD EDWARDS AIR FORCE BASE, CALIFORNIA In the 1960s, NASA was thinking ahead, even beyond the Apollo Moon landing. One thing they decided was that they wanted a reusable aerospace plane. They came up with the "lifting body" concept. This is a stubby airplane in which the body of the plane is itself a wing, able to generate enough lift to keep it flying. The idea was to have a vehicle that could take off like a rocket but then land on a runway. At this time, all spacecraft -- US and Soviet -- landed with parachutes, either in the ocean or on land. None of them could land like an airplane. None of them had wings. The problem in designing such a craft was that any vehicle re-entering Earth's atmosphere from space would be traveling far faster than sound, which would destroy an ordinary airplane. So they began to experiment with model airplanes, and graduated to the design you see here, a lifting body towed by a Pontiac automobile. NASA had the Pontiac souped up, extensively modified to make it powerful enough to tow this lifting body into the air. Eventually, NASA and the Air Force studied a variety of lifting body designs from various aerospace companies. The more advanced models were carried up by an airplane and dropped to see how well they could be flown by a test pilot. If you have seen the television series, "The Six Million Dollar Man," the opening sequence of an accident is actual film of a lifting body that crashed on landing. The pilot was injured, but survived. These designs eventually evolved to become the space shuttle. That design, in turn, has inspired the next generation, known as the National Aerospace Plane (NASP), which NASA hopes to fly in a few years. It would have the ability to take off like an airplane as well as to land like one, but would travel into space as a true rocket. The French, British, Germans and Japanese have all come up with their own designs for aerospace planes, but it is not certain whether the money will be available for any of these to be built. *LIGO: Gravity Wave Telescope 1998 AD HANFORD, WASHINGTON There must be waves of gravity filling the universe, but we have never seen them. For decades, scientists have looked. The best theory of gravity that we have is Einstein's general theory of relativity, which goes beyond Newton's theory of gravity. Einstein's theory predicts that gravity ought to form waves something like light waves. While light waves are waves of electricity and magnetism, gravitational waves would be ripples on the very fabric of space and time. According to Einstein, gravity is a distortion of space itself. A star distorts space a great deal, whereas a planet distorts it only a little bit. A gravitational wave would be an even tinier distortion. Just as an electron can generate radio waves by moving, so a massive object can generate gravity waves by moving. Though never detected directly, gravitational waves have been detected indirectly, thanks to a binary pulsar. A binary pulsar is a pair of neutron stars (pulsars) that orbit each other. By measuring the pulsars' signals, we find that they are getting closer and closer. Their orbits are shrinking. The two neutron stars are spinning around each other in a cosmic dance as they move toward their eventual merging. When an object is found to have a shrinking orbit, that means it is losing energy. But the only way we know that they could lose energy at this rate is through gravitational waves. Astronomers would love to be able to detect gravitational waves with some kind of a telescope. The problem is that gravity is very weak and gravitational waves are extremely difficult to detect with any kind of instrument. For decades, scientists have tried to find these signals, building massive detectors that would be shaken slightly by a passing gravitational wave, but no one has succeeded. Now scientists are building a huge pair of gravitational telescopes called the Laser Interferometer Gravitational-wave Observatory (LIGO). The two-part LIGO is being built in Hanford, Washington and Livingston, Louisiana by scientists from the California Institute of Technology (Caltech) and the Massachusetts Institute of Technology (MIT). These will be the largest gravity telescopes ever made. They will be in the shape of an "L", in which each arm is four kilometers (2.5 miles) long. Lasers will be used to measure changes in the movement of one-ton masses. Movement as small as one one-thousandth of the diameter of the nucleus of an atom will be measured! It is important to have two telescopes at different locations, to rule out interference from earthquakes and passing trucks. When the telescopes are completed, scientists expect to see gravity waves from black holes crashing into each other. LIGO will hopefully give us a whole new view of the universe, similar to when Galileo first turned his telescope on the heavens. ┌Blasting Into Space With Lasers 2010 AD RENSSELAER POLYTECHNIC, TROY, NEW YORK One of the most revolutionary ideas for getting into space is to use a laser to blast spacecraft into orbit. It would work like this: A specially-designed spacecraft would be built with a surface that vaporizes when hit by laser light. Then, a powerful ground-based laser weighing many tons would be focused on the back of the craft. As the light hits the surface, the surface would erupt, causing a rocket-like effect that would boost the spacecraft into orbit. The huge lasers that would be needed have already been developed for the Strategic Defense Initiative (SDI or "Star Wars") program and for controlled thermonuclear fusion power-generation programs. The idea is to convert these tremendously powerful lasers into space drives. Researchers such as Jordin Kare at the Lawrence Livermore National Laboratories and Leik Myrabo of the Rensselaer Polytechnic Institute (RPI) have already designed such drives on paper. Ideally, engineers would first build small units to launch little payloads. Even this would be enormously valuable, because if you launch a lot of small payloads, the cost per payload is very small. You could use these "lightcraft" to resupply orbiting astronauts with fuel, food, and other necessities. Then, if this system worked, you could add lasers and make a more powerful system capable of taking a human being into orbit. Even if you could only take one human being up, this could tremendously reduce the cost of getting into space. It would be like having a space elevator, lifting one person at a time into orbit. In this way, any number of people could be brought up to or down from a space station. Laser propulsion could greatly reduce the cost of space travel. █A Lunar Civilization That Wasn't 1835 AD NEW YORK CITY, NEW YORK In 1835, a newspaper reporter for the New York Sun decided to have some fun with his story about an astronomical expedition in Africa. He wrote that the astronomer's powerful telescope showed him a civilization on the Moon. The picture shows what the Lunarians were supposed to look like. He described the civilization in such detail that many New Yorkers were convinced it was real. Eventually, he confessed his Moon hoax. Today, other writers follow in his footsteps. "Reporters" sometimes write stories in sensationalist newspapers about aliens visiting the President or finding airplanes on the Moon. It's easy to make up such stories and to fake photos. And they still sell a lot of newspapers. PRussian Lunar Robots 1970 AD MOON Most people have forgotten it, but the Russians sent roving robots to the Moon. When they realized they were not going to win the race to put humans on the Moon, they devised robotic lunar landers, perhaps in the hopes of retrieving some lost glory. In 1970, a year after the first Apollo landing on the Moon, Luna 17, also known as Lunokhod 1, landed softly on the Moon. This eight-wheeled robot roamed the Moon's surface for ten months. It "slept" during the two-week long lunar night, shutting down in the cold. It "awakened" during the two-week-long lunar daytime to continue its roaming. It traveled a total of ten kilometers (6 miles) and made photographs of the Moon's surface and took other measurements. In 1976, Lunokhod 2 was sent to the Moon on a similar mission. It lasted only four months, but covered 37 kilometers. ╛Apollo Blastoff From the Moon July 21, 1969 AD MOON Six Apollo Lunar Modules (LMs) landed on the moon, each bringing two men. After exploring the moon, they would climb into their LM and close the hatch. The LM had two parts. The bottom part, called the descent stage, contained the rocket that braked their landing. The upper part, the ascent stage, was their capsule. It also had a rocket, but this one was fired to get them from the Moon to lunar orbit. The descent stage served as their launch pad. When they were ready to go, they fired the ascent stage and blasted off the Moon, leaving the descent stage behind. A television camera they'd set up on the Moon broadcast pictures of their takeoff back to Earth. After the astronauts reached lunar orbit, they rendezvoused with the Command and Service Module (CSM), in which a lonely third astronaut waited. They then abandoned the ascent stage. The CSM had its own rocket, and with that, they blasted out of lunar orbit and back to Earth. êLifting Off From the Moon July 21, 1969 AD MOON When Apollo 11 astronauts Buzz Aldrin and Neil Armstrong were ready to blast off from the Moon, they fired a rocket on the Lunar Module (LM). The LM left its base behind, reducing the amount of weight the rocket needed to get into orbit. Once launched, the LM went into orbit around the Moon, where it rendezvoused with the Command Module, piloted by Michael Collins. Aldrin and Armstrong transferred from the LM into the Command Module. They released the LM and fired the thrusters of the Command Module. The three astronauts slowly drifted away forever from the little vehicle that had taken two of them to the surface of the Moon. ┬Venusian Meteor Craters 1991 AD VENUS This Magellan radar image of Venus shows three dramatic meteorite craters. They range from 37 to 50 kilometers (23 to 31 miles) in diameter, and the picture shows an area of 550 by 500 kilometers (342 by 311 miles). The bright areas around the craters are rough areas of boulders and debris created when the meteorites smashed into the planet. They are bright because they reflect the radar very strongly. The dark areas are very smooth. pGiant Venusian Spiders 1991 AD VENUS Venus has strange features found nowhere else in the solar system. They look like spiders with their webs, and are called arachnoids, from the Latin word for spider. These arachnoids range from 50 to 230 kilometers (31 to 140 miles) in diameter. They may be caused by volcanic activity. Lava, in flowing up from the interior of Venus, may have caused the surface to crack. There are bright areas in the center of this picture that are lava flows that have frozen. Some of the spider-web features cross these lava flows, indicating that the arachnoids occurred after the lava had flowed. Because Venus is so close to the Sun, it is very hot. And because it has a tremendously thick atmosphere -- almost 100 times the pressure of our own -- the conditions on Venus are very different from those on the Earth. This is probably why we do not have arachnoids on Earth. AVenus' Great Lava Flow 1991 AD VENUS ORBIT The Magellan spacecraft sent back dramatic pictures of past lava flows on Venus. The images show a large part of Venus -- 5.5 million square kilometers (3.4 million square miles) -- called Lada. Lava flowed across a long ridge belt and spilled into an open plain, covering 100,000 square kilometers (40,000 square miles). In looking at the radar image of Venus (or even of Earth), remember that bright and dark are not exactly what the eye would see. Bright means the surface is highly reflective to radar; dark means very little of the signal came back. Generally speaking, rough surfaces reflect a lot of the radar energy and smooth surfaces reflect very little. So bright means rough and dark means smooth. The source of the lava flow is a volcanic crater about 300 kilometers (200 miles) outside this picture. ▒The Force of Magnetism 1855 AD UNIVERSE The universe is filled with magnetic fields. Anyone who has ever used a pocket compass has experienced Earth's magnetic field. Albert Einstein, for example, was fascinated by a toy compass he received as a gift from an uncle when he was a little boy. He was amazed at the invisible force that controlled the needle, and spent the rest of his life trying to understand the forces of nature. A much larger magnet is Earth itself. There are electrical currents flowing deep inside the hot interior of our planet that generate a strong magnetic field all over the world. A pocket compass, like the one that fascinated Einstein, consists of a little bar magnet with two poles, called north and south. With magnetic poles, opposites attract. The north pole of one magnet attracts the south pole of another. (Similar poles repel: north repels north and south repels south.) Conveniently, Earth's magnetic poles are arranged so one is near the North Pole, and one is near the South Pole. So one end of a compass needle will point north and the other will point south, except if you are at the north or south magnetic poles, in which case the needle becomes inaccurate, or points to the ground if you turn the compass on its side. Electricity and magnetism are related, as was first fully understood by the 19th century Scottish physicist, James Clerk Maxwell. One proof is that a wire moving through a magnetic field generates electricity, as happens in an electric generator. Another piece of evidence is that electrically-charged particles passing through a magnetic field are pushed sideways by the magnetic force while neutral -- uncharged -- particles are unaffected. Also, an electric current running through a wire creates a magnetic field, which causes a compass needle to move. The Sun provides a continuous stream of electrically-charged particles: electrons (negative) and protons (positive). If Earth did not have a magnetic field, this solar wind would crash directly into our atmosphere and we would see the night sky glow as these particles hit the air. But Earth does have a magnetic field, which pushes aside the solar wind so it mostly flows around the Earth without touching it. However, at the North and South Poles, electrons and protons can leak into the Earth's atmosphere. When this happens, the sky glows at night: a process called the aurora (the Northern Lights and the Southern Lights). Earth is the only planet of the inner solar system with a strong magnetic field. Neither Mercury, Venus nor Mars has a strong field. But the giant planets, Jupiter, Saturn, Uranus, and Neptune, all have powerful magnetic fields. The Sun also has a strong magnetic field, but a very complicated one. The field is strongest at the sunspots, relatively cool areas of the Sun where magnetic fields occur that are much more powerful than Earth's. The Sun's magnetism bends the electrons and protons of its atmosphere into huge arcs along the magnetic field lines. Today, we know that magnetic fields are found in many places in the universe. In the center of our galaxy, and in distant quasars, magnetic fields accelerate electrically-charged particles to great energies, generating radio signals that we can detect. iThe Pancakes of Venus 1991 AD VENUS These are Venusian geologic features that scientists have nicknamed "pancakes." They are on a part of Venus known as Alpha Regio, shown here by the Magellan probe's radar. There are seven strange, dome-like hills, 25 kilometers (15 miles) in diameter. These circular features are thought to be very thick lava flows that came through openings in fairly flat ground, allowing the lava to flow out evenly. The domes are up to 750 meters (2,475 feet) above the ground and resemble some volcanic domes on Earth. Another theory is that the domes may simply have been pushed up from molten rock inside Venus. ╞Seeing Through to Venus 1990 AD VENUS ORBIT Because Venus is permanently covered with thick clouds, we can't see its surface with light. But radio waves pass through the clouds easily, and so radar lets us map the surface. The Magellan spacecraft uses radar to take images of Venus so fine that they look like photographs. Rough areas of Venus reflect the radar strongly. Smooth areas tend to reflect the radar away from the spacecraft, and therefore look dark in Magellan images. EVolcanoes on Venus 1992 AD VENUS Radar on the Magellan probe reveals volcanoes on Venus such as this one, Maat Mons, the second highest mountain on the planet. Here, the computer has exaggerated the height (eight kilometers or five miles) for clarity. Volcanoes have now been found on Venus, Mars, and Jupiter's moon Io, as well as on the Earth. µMars: How We Can Get There 2010 AD MARS Perhaps the most exciting project of the 21st century will be a human expedition to Mars. Ever since the 19th century, when some people thought Mars held an advanced alien civilization, Mars has excited the imagination like no other planet. And while we now know that there is no civilization on Mars, we have discovered intriguing facts about the planet that places it on the top of the list of planets to explore. Mars was once very wet, with vast riverbeds and canyons produced by flowing water, which means that life might have existed there. Even today, it's possible that primitive life exists on Mars. There is water frozen under the ground and in the ice caps, and the temperatures are not so extreme as to prevent life from existing there. The atmosphere is thin, about one percent of the pressure of the air we breathe here. It is carbon dioxide, but this is a perfectly good gas for plants to breathe. Some scientists have suggested that life might have arisen during Mars' first few hundred million years, when the planet was wet. There might be fossils of this ancient life on Mars. There is even a slight possibility that life might have continued to evolve as conditions became more hostile on the planet, while the water evaporated into space and the atmosphere thinned out. President George Bush has made a human expedition to Mars one of the goals of the American space program for the next three decades. Humans have been to the Moon, so we have solved many of the problems needed to go to Mars, but other problems remain. The main problem is that Mars is far away. Even at its closest, it is about half the distance to the Sun. To get to Mars, astronauts would have to travel for many months. Most missions that have been designed on paper involve a year-long trip from Earth to Mars and another year-long trip back. Depending on how much time the astronauts spend on Mars, they would be in space from two to three years, though some new technologies might cut the travel time somewhat. It will be a long journey, requiring the astronauts to bring all their food, water and other supplies. They will be completely on their own except for radio and television communications. If anything goes wrong, they will have to take care of it themselves. One of the problems is that weightlessness weakens astronauts, unless they are careful to exercise a lot. We don't know for certain that human beings would remain strong enough on a one-year flight to survive the landing and then walk around on the planet, even though the gravity is only one-third that of Earth. We do know, however, that the Soviets have had experience with cosmonauts in orbit for as long as a year, simulating Mars trips. The cosmonauts came back in a weakened condition, but were basically healthy. It may be that the best way to go to Mars is with artificial gravity. By spinning the spacecraft, perhaps using a wheel design, any amount of gravity can be simulated. Astronauts could feel as if they were walking on Earth and would be in excellent condition by the time they got to Mars. Another hazard is radiation. The Sun puts out many kinds of radiation, most of which is sunlight, which is no problem. But sometimes, during solar storms, the Sun also sends out large bursts of X-rays and gamma rays, similar to those produced by radioactivity. Without shielding, the astronauts might suffer from radiation sickness. One way to protect against this would be to have a shield, but that would require mass, which costs a lot of fuel to take along. On Earth, laboratories use lead to shield against radiation, but lead is a very heavy metal, and it would be a waste of huge amounts of rocket fuel to get it into orbit. One solution is to have a small compartment which would serve as an emergency radiation shelter. It would just take a small amount of shielding to protect a single room, and the astronauts could crowd into the room whenever there is a solar storm. Once the astronauts reach Mars, they may be able to replenish some of their supplies from the Martian moons, or from the surface. A lander would take them down to some flat area on the planet. They could then emerge and set up huts on the surface, where they could live for months and explore the surrounding areas, including those too dangerous to land on. The carbon dioxide atmosphere of Mars could be converted to oxygen for the astronauts, perhaps using plants. There is even a design for a rocket that could use carbon monoxide as a fuel, converted from the Martian atmosphere. When they were done, the astronauts would take a rocket back into orbit, much as the Apollo astronauts did to get from the surface of the Moon to the orbiting command module. Then the entire expedition would leave Mars and return to the Earth. Eventually we may set up a permanent colony on Mars. It would start as a research station, and perhaps grow into a Martian city. Some scientists even believe that, over centuries, humans could convert the carbon dioxide atmosphere of Mars into an oxygen one, perhaps with the aid of plants. The resources of Mars and its moons may turn out to be of commercial value. And Mars is a geological treasure trove that would help explain the history of the solar system. It may even contain clues to the formation of life on Earth. OLanding Like a Leaf 2000 AD PASADENA, CALIFORNIA One of the most ingenious ideas for space exploration is a spacecraft that could be shot like a cannonball from Earth to Mars and float down through the atmosphere like a leaf. James D. Burke, of the Jet Propulsion Laboratory (JPL), has patented this design. Just as a maple seed flutters down from a tree, its helicopter-like blade slowing its fall, this proposed spacecraft could spin through the Martian atmosphere, taking television pictures as it fell. A simple light-sensor would scan the scene, taking advantage of the spinning to make a panoramic picture. bFirst Martian Close-up 1965 AD MARS Mariner 4 was the first spacecraft to take close-up pictures of Mars. Flying by the planet in 1965, it showed a heavily cratered surface -- to the surprise of many scientists. It looked amazingly like our Moon. Because it was so Moon-like, with very little air, and only frozen water, many researchers decided life could not exist there. However, later spacecraft took better pictures of Mars and found signs of ancient riverbeds. Mars began to look less like the Moon. Billions of years ago, there was water on Mars, and there might have been life there. The lesson: Don't jump to conclusions. ╡ Mars: Is Anybody Home? MARS If there is life elsewhere in our Solar System, Mars is the place to find it. Mars has been known as the "red planet" since ancient days, because its reddish color makes it distinctive in the sky. Perhaps because it is the color of blood, the planet was associated with the ancient god of war, called Mars by the Romans. As a result of the Viking landers on Mars in 1976, we know that the reddish color is due to iron oxide, similar to rust. Mars is red because it's rusty. The sky under Mars' two tiny moons, Phobos and Deimos, is very thin, about one one-hundredth the density of Earth's. You can see it in this Viking orbiter picture. It is mostly carbon dioxide, similar to Venus' atmosphere, but much, much thinner. Its size is also less than Earth's, 6,800 kilometers (4,200 miles) in diameter, or about half Earth's size. Because it is so much smaller, the gravitational pull of Mars is about one-third of Earth's. On Mars you would weigh one-third of what you do here. Though its gravity is less, the planet has a day which is very similar to our own, just 37 minutes longer. However, it takes about twice as long to go around the Sun -- 687 days. Mars has dark markings that change with the seasons. These led some 19th century astronomers to think there were canals placed there by ancient civilizations. We now know the markings change because of dust moved by wind. Mars is 228 million kilometers (142 million miles) from the Sun, 52 percent farther than Earth. Because Mars is farther away, the temperature is freezing everywhere on the planet except sometimes during a hot summer's day in the southern hemisphere, when it may rise a few degrees above freezing. The planet has ice caps of both water ice and dry ice (frozen carbon dioxide). These ice caps change with the seasons, too, as the ice evaporates or condenses. Spacecraft photographs show many signs of riverbeds and other hints of past water on the planet. Some parts of the surface look like permafrost regions of Siberia, where ice exists underground even during summer. This is one of the reasons why some scientists suspect life might have arisen on Mars. Many people would like to see humans explore Mars. One reason would be to look for fossils of past life. There is even a slight possibility that there could be some primitive form of life existing on Mars today, perhaps near the ice caps, or underground, living on water from the planet's permafrost. Something like the moss, lichens, or algae that are found in cold regions of Earth could conceivably exist there. Finding even one example of life on another planet would revolutionize our understanding of how life arose on Earth, and whether it can exist around other stars. Exploring Mars by Balloon 1996 AD MARS Scientists have long desired to send a robotic lander to Mars to make measurements of the surface. NASA did this with the Viking landers, but they each stayed in one spot. Ideally, we'd like to be able to have a robot roam all over the planet, exploring every interesting place. The Russians have sent a number of probes to Mars, and while they were mostly successful with their Venus probes, their Mars probes have generally failed. The French came up with another idea for exploring the red planet -- balloons. Balloons might work well because they are light and can travel great distances over a planet without using much energy. They proposed this idea to the Russians. A third group, a private organization called The Planetary Society, helped put the two ideas together, sponsoring design studies and experiments for a joint Soviet-French balloon mission to Mars. The society has sponsored balloon tests in the rugged Mojave Desert of Southern California, which resembles the Martian landscape in some ways. On Mars, the balloon (outfitted with a package of scientific instruments) would be heated by the Sun in the daytime, and rise like a hot air balloon into the Martian sky, to be carried along by the winds. At night, it would sink to the surface as its air cooled. In this way, a large area of Mars can be studied at low cost. In 1996, the balloons will be launched toward Mars. rThe Canals That Aren't There 1866 AD FLAGSTAFF, ARIZONA At one time some people thought there were canals on Mars, built by Martians. There weren't -- it was just a mistranslation. In 1866, Italian astronomer Giovanni Schiaparelli discovered the "canals" of Mars, though actually he called them "canali" -- channels in Italian. Channels can occur in nature, as in river channels, and are not necessarily artificial. However, the American amateur-astronomer-turned-pro, Percival Lowell, called them canals -- and canals are artificial. This meant there were Martians on Mars, or so he thought. Schiaparelli never agreed with Lowell about the Martians, and we now know that the canals were an optical illusion. Seeing the tiny disk of Mars in a telescope, and watching it dance at high magnification in our soupy, swirling atmosphere, causes dark spots to seem momentarily to be connected by lines. So Lowell's wonderful story of canals bringing water from the ice caps to the Martian cities has to go back into the pages of fantasy. The photos of Mars sent back in our time by the Viking orbiters and other spacecraft prove that the canals were an optical illusion. LMartian Clouds: Evidence of Water 1976 AD NOCTIS LABYRINTHUS, MARS This photograph shows one piece of evidence that there is water on Mars. This region is a high plateau known as Noctis Labyrinthus (the labyrinth of the night, in Latin). Taken at sunrise, the picture shows bright white clouds forming in canyons. Geologists suspect that the water condensed out of the atmosphere during the afternoon, when slopes of the canyon floor were in shadow and became cold. Then, when the Sun rose, the ice crystals -- frost -- vaporized and formed clouds. This picture covers about 10,000 square kilometers (4,000 square miles). èMars: Simpler Seasons MARS Mars has seasons, just like Earth, and for the same reason, the tilt of the planet's spin axis. Mars' spin axis is tilted at 24 degrees away from the perpendicular to its orbit, just one degree more than the Earth's axis. Because the tilt is almost identical to Earth's, the extremes of the seasons are very similar. Mars, however, takes about two years to orbit the Sun, so the change between seasons is more gradual. There are times when strong winds blow and cause dust storms far worse than any we have on Earth. Sometimes they cover the whole planet. This causes great changes in the light and dark markings of Mars that were thought, in the 19th century, to be canals and the seasonal growth of plants watered by them. One way Mars differs from Earth is that it has dry ice (frozen carbon dioxide) as well as water ice at its poles. So as the northern polar cap evaporates during the summer, the southern polar cap is experiencing winter, and some of the carbon dioxide that evaporated off of the north pole condenses onto the South Pole. Without great oceans of water, the Martian seasons are simple and uncomplicated compared to Earth. Here, our seas act as vast reservoirs of water, some of which enters the atmosphere as clouds. As a result, it's easier to predict the weather on Mars than on the Earth. By studying Martian weather, we can understand some aspects of Earth's weather, since the simplification avoids some of the confusion caused by other processes that take place on Earth. Even though there are temperature changes during the Martian seasons, you would have to go to the planet's equator on a hot summer day to avoid freezing. Simulated Mars Flight 1991 AD MARS Using radar images of the Martian surface manipulated with sophisticated computer mapping techniques, Jet Propulsion Laboratory (JPL) scientists in Pasadena, California, have created this fascinating simulated flight across the Martian landscape. àGroovy Place for Water 1976 AD MARS Viking Orbiter I took pictures of this strange grooved region of Mars, which covers an area 150 by 80 kilometers (93 by 50 miles). Geologists say the grooves in these valleys are similar to places on Earth where freezing and thawing of ice within the surface cause similar markings. This is one of many pieces of evidence for the existence of ice beneath the Martian surface. (Mars and Kermit the Frog 1976 AD MARS This Viking orbiter photo shows the region of Mars where some people claim to see a giant head on Mars, supposedly carved by ancient alien visitors. But most scientists are convinced that it's just a hill worn down by wind and other forces of nature. The problem is that, if you stare at the thousands of craters, mountains, volcanoes, and riverbeds on Mars long enough, you can see almost any shape you could wish for. Scientists with a sense of humor have even found Martian features that look like a happy-smile face and Kermit the Frog. dLayer Cake Martian Poles 1976 AD MARTIAN POLES The polar ice caps of Mars are like layer cakes of ice. They are so large, bright and white that they have been visible from Earth-based telescopes for more than a century. But in 1976 the Viking Mars-orbiters took close-up pictures showing they have a very strange structure. The ice caps are made of layer upon layer of ice, like terraces or staircases, and they are thick: up to six kilometers (four miles) deep. This suggests that the ice has been deposited regularly over a long period of time. One possibility is that the Sun brightened and dimmed occasionally over periods of thousands and millions of years. Or, it may be that the wobbling of Mars over these long periods of time caused these strange structures. The ice caps are mixtures of water ice and dry ice (frozen carbon dioxide). The water ice could be like snow on Earth, and the dry ice is similar to the dry ice that is sometimes used to keep ice cream cold on Earth. It is also white, but much colder than ordinary ice. Dry ice evaporates very easily when the temperature is raised. When it is summer in the northern hemisphere, the warmth causes much of the dry ice to evaporate, increasing the carbon dioxide in the atmosphere. Some of this carbon dioxide then freezes on the South Pole, where it is winter. So when the North Pole shrinks the South Pole grows. We know this because the Viking landers measured Mars' atmospheric pressure in the same way that weather-watchers measure it on Earth. They found a regular cycle from summer to winter that corresponded to the carbon dioxide being added to or subtracted from the atmosphere. ▀The Next Martian Probe 1992 AD MARS In late 1992, the United States will launch its first Mars spacecraft since 1976. Following the success of the two Viking landers and their orbiters in 1976, the US concentrated on analyzing the data from those missions and investigating other planets. But scientists began to study the possibility of launching a Mars Observer and, over the years, constructed one that uses as many parts from other spacecraft as possible, to keep the cost down. The Mars Observer will orbit Mars, taking far better close-up pictures of the surface than were possible from the Viking orbiters. Those orbiters took excellent pictures, but with today's camera technology it's possible to take images that will show far more detail than could be done with the Viking equipment. The Mars Observer is designed to survey virtually the entire surface of the planet over a period of years. It will answer many of the questions that geologists came up with after the successes of the Viking orbiters. ¡River Beds on Mars 1976 AD MARS Though there is no liquid water on Mars now, there must have been tremendous amounts in the past to make the huge riverbeds you see in this dramatic picture taken by Viking Orbiter 1. Much of the water evaporated into space, and the rest is either in the icecaps or frozen underground. Geologists believe there was a massive flood of water during the early days after Mars was formed, creating these temporary rivers. In some cases, we see water channels through craters -- which means the crater was there before the river. In other cases, the crater obliterated part of the river bed -- meaning the crater occurred when a meteorite hit Mars after the riverbed had formed. Russian Mars Probe Problems 1989 AD TYURATAM, KAZAKHSTAN, SOVIET UNION The Russians have had terrible luck with Mars. Most of the spacecraft they have sent there have failed. By contrast, they've been mostly successful with their Venus probes. But something almost always seems to go wrong when they send a probe to Mars. They've had some success with fly-bys of Mars, but none of their attempts so far to land a probe on the planet has been successful. The most successful one started to broadcast for a few seconds and then died. Their most ambitious probe was called Phobos, named after the larger Martian moon. There were two Phobos probes. One died on the way to Mars; the second reached Mars successfully and began to orbit the planet. It took some useful measurements and photographs for a few days, but failed in its main mission: to rendezvous with the moon Phobos and to blast its surface with beams to find out what it's made of. It would be valuable to know more about Phobos. Astronomers suspect that it's a captured asteroid. It's probably a type called a carbonaceous chondrite (pronounced KON-drite), made of carbon and water, that looks much like coal. If it is this type, it could someday be a useful resource for a human expedition to Mars. In October, 1994, the Russians will launch their Mars 1994 spacecraft. It will plant small observational stations on Mars and shoot penetrator probes deep into the soil. It will arrive at Mars in September, 1995. In November, 1996, the Russians will launch their Mars 1996 spacecraft. This will include a balloon designed by French scientists in cooperation with The Planetary Society. Mars 1996 will also land rovers on Mars, wheeled robots that will roam the surface and conduct experiments. This spacecraft will reach Mars in October, 1997. There's a lot of cooperation between the Russian projects and NASA's Mars Observer satellite that will be launched in 1992. With the help of European and American scientists and engineers, there's a good chance these will be the most successful Russian Mars missions ever. ┌The Grander Grand Canyon 1976 AD MARS One of the most amazing features on Mars is a canyon so big it makes the Grand Canyon look like a ditch. This is the Valles Marineris -- a valley named after the Mariner Mars probe. The canyon stretches 4,500 kilometers (2,800 miles) across the face of Mars. Earth's Grand Canyon would fit into one of the smaller branches. It was probably formed as a result of the movement of water, perhaps as ice froze and thawed. This picture was taken by Viking Orbiter 1. aArsia Mons: A Martian Volcano 1976 AD MARS This is a Martian volcano, though to the non-geologically-trained eye, it looks about the same as a meteorite crater. This picture, taken by Viking Orbiter 1, shows a caldera (volcanic crater) called Arsia Mons, sometimes called "South Spot." It's located in the Tharsus region of Mars. It is 100 kilometers (60 miles) in diameter and 27 kilometers (17 miles) high, three times higher than Mauna Loa in Hawaii, if measured from the bottom of the ocean. (When measured from the ocean floor, Mauna Loa is the highest mountain on Earth.) There are traces of active lava flows surrounding the crater. (Mapping With Radiotelescopes 1991 AD JET PROPULSION LABORATORY, PASADENA, CALIFORNIA One of the least-known ways astronomers explore the solar system is with radar. Not just radar on spacecraft, but radar that sits on the Earth and transmits a powerful signal -- so strong that it can bounce off a planet and still be detected on Earth. A very large antenna is necessary, such as the giant Arecibo radiotelescope in Puerto Rico, which can be used not only for radioastronomy but also for radar astronomy. This picture shows a map of the planet Mercury made by such radar. Before astronomers were able to bounce radar off of Mercury, they relied on optical telescopes to tell them about the planet. They thought Mercury constantly kept one face toward the Sun and one face away from the Sun, much as the Moon keeps one face toward the Earth. This led to a lot of wonderful science-fiction stories that took place on a Mercury where one side was incredibly hot and the other side horribly cold. But then radar showed they were wrong. Mercury actually rotates slowly. It takes Mercury 88 days to go around the Sun, but 59 days to spin around its axis, just two-thirds of its year. The most amazing radar discovery occurred in 1991, when scientists made the best radar pictures ever of the planet. They were surprised to discover a region at the pole that strongly reflected the radar signal. They were forced to conclude that Mercury has an icecap. No one had ever expected that this planet, so close to the Sun, could possibly have an icecap like our own Arctic or Antarctic regions. Apparently, the ice is from comets. Occasionally, a comet must crash on Mercury. Its ice vaporizes. Some of the water molecules then freeze out at the cool poles. This lends support to scientists who have suggested that there could be ice at the poles of our own Moon. ¢Mercury: Running Hot and Cold 1974 AD MERCURY If you didn't know you were looking at Mercury, you might think this was a picture of the Moon. Mercury, the closest planet to the Sun, is covered with craters and looks very much like our Moon, but has no moons of its own. It rotates slowly, taking 59 Earth days to spin once on its axis, compared with just 88 days to go around the Sun. Because it is so close to the Sun, Mercury is extremely hot. The planet may reach 450 degrees Celsius on the hot side when it is closest to the Sun, and can get as cold as -180 degrees Celsius on the night side. Mercury has essentially no atmosphere. There are faint traces of helium and argon, but for all practical purposes, it is airless. It is the second smallest planet in the solar system, just behind Pluto, measuring only 4,880 kilometers (3030 miles) wide, about 40 percent of Earth's diameter. Amazingly, Mercury seems to have an icecap. At the poles, the Sun is very low on the horizon, and there are shadows in craters and mountains where it can get cold and stay that way. Astronomers using radar in 1991 discovered strong reflections from one of Mercury's poles, and were forced to conclude that it was icy. ∙The Amazing Shrinking Mercury MERCURY The only spacecraft that has observed the planet Mercury closely is the Mariner Venus/Mercury mission. During three fly-bys, Mariner took pictures of one side of Mercury and revealed a surface very similar to our own Moon. But it did find one very interesting difference from the Moon: Mercury appears to have shrunk. Mercury, being the closest planet to the Sun, gets very hot, and was once bombarded powerfully by meteors. As it cooled, cracks formed, which you can see in this picture. ∞ Bombs From Space 50,000 BC METEOR CRATER, ARIZONA About 50,000 years ago -- if there were any Native Americans in what is today the state of Arizona -- they must have been shocked by a devastating crash. A huge nickel-iron meteorite, 40 to 50 meters in diameter and weighing about a million tons, smashed into the Earth with the energy of a 15-20 megaton hydrogen bomb. It left a gigantic hole in the ground that is still visible today. The hole, 1.2 kilometers (4,000 feet) in diameter, is now a tourist attraction near Flagstaff, Arizona. Officially, it is called Barringer Crater, but it is widely known as Meteor Crater. (It really should be called Meteorite Crater, because a meteorite is a meteor big enough so that it doesn't burn up in the atmosphere and manages to hit the ground.) Also, while meteors are thought to often be tiny pieces of comets, meteorites are usually pieces of asteroid, which Barringer probably was. There are about 100 meteorite craters on Earth, many of them so old that they are worn down and covered with vegetation, making them difficult to see. The reason Earth is not as heavily cratered as the Moon is that our atmosphere allows erosion to take place. Water and wind and plant life wear away the surface of the Earth. On the Moon, with no air, water or life, the surface doesn't change except when the occasional meteorite hits. The solar system is swarming with dangerous objects such as the one that hit Arizona. Astronomers estimate that one meteorite makes a crater ten kilometers (six miles) in diameter every hundred thousand years. But even smaller ones can be dangerous. In 1908, for example, something from space hit Siberia. The region known as Tunguska was struck by a fireball. It was probably only about 15 meters (16 yards) across, but it flattened much of a forest and was heard hundreds of miles away. It was probably a piece of a comet, perhaps the comet known as Encke. Its explosive force was about equal to a huge 12-megaton hydrogen bomb. Fortunately, that part of Siberia had no people living in it, so there was no human loss of life. Some scientists worry that we may receive a hit like this someday. We may not be so fortunate to have it land in an isolated area. Even medium-sized objects like these can be devastating. Unfortunately, these objects are very difficult to find. In a program called Spaceguard, NASA scientists have proposed monitoring the skies for such dangerous meteorites. If we detect them far enough away, we might be able to deflect them with rocket-launched bombs. oMimas: Saturn Moon 1979 AD SATURN ORBIT Mimas is one of Saturn's medium-sized moons. It is a mixture of rock and ice that is 199,000 kilometers (124,000 miles) from Saturn and 394 kilometers (244 miles) in diameter. It has a huge crater in it from a past meteorite hit. If that meteorite had been a bit bigger, it would have smashed Mimas into smithereens, forming another Saturn-like ring. ┐World Peace Space Station 1986 AD TYURATAM, KAZAKHSTAN, SOVIET UNION There is a space station orbiting the Earth, and it is Russian. After many years of experience with Salyut space stations, the Russians launched a new generation of space station, called Mir (meaning "World" or "Peace"), in 1986. Mir has four ports for docking with spacecraft and other modules. It also has more windows, two private rooms, and is longer than the old Salyut space station. It's 17 meters (56 feet) long, compared with the previous 13.5 meters (44 feet). It is four meters (13 feet) wide, the same as Salyut. In 1987, the Soviets attached another unit to the Mir called Kvant (Quantum) 1. This made the space station twice as large. Cosmonaut Musa Manarov set many world records for length of time in space, living for about a year in orbit. (The most that American astronauts have lived in space was no more than three months in the old Skylab back in 1974). Today, with the end of the Soviet Union, the space program is in the hands of the Russian Republic. Money to operate the program is in short supply and it is not clear what its future will be, though NASA is investigating the possibility of purchasing some of the ex-Soviet space technology. ïMiranda: The Weirdest Moon MIRANDA Miranda is one of the weirdest moons in the solar system. It is a medium-sized moon of Uranus, 130,000 kilometers (81,000 miles) from the planet and 484 kilometers (300 miles) in diameter. What makes Miranda strange is that it's a hodge-podge of different shapes and features. It's as if Miranda were a jigsaw puzzle assembled from many different pieces. One possibility is that Miranda may have actually been destroyed in a collision with another moon, and then the debris could have gathered by gravity to form a new moon as it orbited the planet. Miranda is a mixture of ice and rock, with a very dark surface, perhaps of carbon. hEarth Orbiter Goes to Moon 1991 AD JAPAN In 1991 the Japanese launched their first spacecraft to the Moon. Called Hiten, after a Buddhist spirit, the spacecraft had two parts. The large part was designed to orbit the Earth; the small part was designed to break away from the main ship and travel to the Moon, to orbit it and make measurements. This was a major event because no countries except the United States and Soviet Union had ever sent spacecraft to the Moon. It was the result of steady progress in the Japanese aerospace industry. For years they have been developing ever more powerful rockets for commercial satellites and have been designing a series of satellites to be put in lunar orbit, and eventually to land there. Hiten had a problem, though. After the small part was launched toward the Moon, it broke down and could not be controlled. The larger part continued to orbit the Earth, but it was not designed to go to the Moon. The Japanese, however, decided to see whether it would be possible to send the large part to the Moon anyway. Mathematicians at the Jet Propulsion Laboratory (JPL) in California and the University of Barcelona in Spain had developed advanced techniques to save rocket fuel by using the gravitational fields of the Earth and Moon in a clever way. JPL mathematician Edward Belbruno and Jaume Llibre of Spain pioneered the study of what is called the gravitational four-body problem. Astronomers talk of the motion of spacecraft and moons in terms of the number of objects involved. When a satellite is launched around the Earth, it is said to be a two-body problem, with the two bodies being the Earth and the satellite. The Moon and Sun are so far away that they have little effect, and therefore can be ignored in most calculations. When a spacecraft goes from Earth to the Moon, it is often called a three-body problem, because the main factors are the gravity of the Earth and the Moon on the third body, the space probe. In fact, however, it is really a four-body problem because the Sun's gravitational field is also strong enough to have an effect. For decades, computers have been used to solve the four-body problem, but it is very complicated. Belbruno and Llibre came up with ways of analyzing the problem to determine better orbits for spacecraft. They found there are certain types of orbits that can take advantage of the gravity of the Earth, Sun and Moon to give the spacecraft a boost with no fuel. Working with Belbruno, the Japanese were able to devise an orbit that would take the large, working Hiten spacecraft, and slowly spiral out away from the Earth toward the Moon. In a complicated, unique set of movements using a small amount of rocket fuel, the Japanese succeeded in moving the spacecraft from Earth orbit to lunar orbit. It is now permanently orbiting the Moon. Japan thus became the first country other than the US and USSR to get to the Moon. This is a very important event, because it means that countries with smaller rockets can accomplish interplanetary missions. Similar techniques to those used to get Hiten to the Moon can be used to get to other planets. PICTURE CREDIT: Painting (c) Edward Belbruno. ┤Orbiter Takes Crater Close-up 1966 AD LUNAR ORBIT In 1966, the American Lunar Orbiter spacecraft took this photograph. It shows the huge lunar crater Copernicus, which had been seen from the Earth from time immemorial. However, this is the first close-up picture, and the first to give people a feeling of what it would be like to fly over the Moon. It was reproduced on the front pages of many newspapers around the world, and was called "the picture of the century." -Mare Orientale: Lunar Bull's Eye MARE ORIENTALE, MOON One of the most remarkable features on the Moon is this cosmic bull's eye, a crater called Mare Orientale. Mare Orientale is visible on the edge of the Moon, but no one prior to the space program had ever seen it directly overhead. When a spacecraft finally took such a picture, astronomers discovered it was a series of circular craters, one inside of the other. Geologists suspect that it was created by a giant meteorite that hit almost squarely into the Moon, and ripples in the molten rock formed the craters within craters. dDune Buggy for the Moon 1971 AD MOON As the Apollo astronauts returned to the Moon for longer stays, they needed a way to get around, so NASA developed the Lunar Roving Vehicle (LRV), an electrically powered dune-buggy. It weighed about 200 kilograms (400 pounds), used open-mesh wire tires and traveled at around 13 kilometers per hour (7-8 miles per hour) on the Moon. It was stored folded up on the side of the Lunar Module, then unfolded after landing. The rover was brought to the Moon for the last three landings (Apollo 15-17), and the astronauts were able to travel much farther from their lunar module than they could on foot. πApollo 12 Meets Surveyor 3 Nov. 14, 1969 AD MOON On Nov. 14, 1969, Apollo 12 lifted off from Cape Canaveral, and though the Saturn V booster was hit twice by lightning, the mission continued. Charles (Pete) Conrad, Richard Gordon, and Alan Bean would go to the Moon and back in just over 10 days in the Command and Service Module (CSM) Yankee Clipper and the Lunar Module (LM) Intrepid. Gordon stayed in the CSM, which made 45 orbits of the Moon, and performed survey and spectral photography tests, while Conrad and Bean landed near the old Surveyor 3 Moon probe in Oceanus Procellarum (Ocean of Storms), a large and very young area of the Moon. This is the same general area where Luna 9, 13, and Surveyors 1 and 3 landed. The mission was designed to land near Surveyor 3, to see if they could bring back pieces of it to tell what effects the space exposure had had. The Intrepid had to land within 2,000 feet of Surveyor 3 so the astronauts, not having a rover to ride, could walk to it. This was not easy. Apollo 11 had missed its target by four miles, and the Surveyor was sitting in a crater only 600 feet across. Nevertheless, they decided to aim for the Surveyor. The calculation for the landing was produced by hand, because the computers at Mission Control couldn't handle the math quickly enough. The astronauts' calculations and flying brought them right over the Surveyor, too close to land, so they had to land across the crater. Conrad and Bean walked to the Surveyor and brought back the television camera, the scoop shovel, aluminum tubing and electrical cables -- about 11 kilograms (25 pounds) worth in all. The astronauts brought them back home for tests for exposure to radiation and micrometeorites. The astronauts also set up a science experiment package that included a solar wind test, radiation tests, and moonquake tests, performed a number of other geological tests. They collected 34 kilograms (74.7 pounds) of rock and soil, and photographed everything in sight. They stayed on the Moon for 31 hours and 31 minutes. ╝The Message of the Moon Rocks 1972 AD MOON This is a piece of Moon rock brought back by the last men to land there. It's Apollo 17 sample number 70017, sliced thin and viewed under a microscope using special lighting conditions (polarized light) that bring out colors. This type of rock is known to geologists as basalt, one of the most common types of rock on Earth. Geologists are able to tell how old the rocks are by studying traces of natural radioactivity in them. By "age" of a rock, geologists mean the time when it was last molten. When it cooled and froze, the ingredients were fixed, and the natural radioactivity in them began to decay. By measuring how much the material has decayed -- atoms transforming into different atoms by radioactivity -- they can tell how long the rock has existed as a solid. By examining the various rocks from the Moon, geologists concluded that it was formed 4.6 billion years ago. That's probably also approximately the time that Earth formed. The Apollo samples helped us understand the formation of the Moon, which, in turn, gives us clues about how Earth began. There are still many unanswered questions, but the best theory is that the Moon was formed when a Mars-sized planet hit the newly formed Earth about 4.6 billion years ago. The tremendous collision caused debris to orbit Earth much like the rings that encircle Saturn. After millions of years, gravity brought much of the debris together to form the Moon. Before the Apollo landings, astronomers and geologists were groping in the dark for explanations about the formation of the Moon and planets. Now we have actual pieces from the Moon and are beginning to unravel the complicated and exciting history of the early days of the solar system. ║The Soviet Lunar Program October 4, 1959 AD TYURATAM, KAZAKHSTAN, SOVIET UNION This picture is from Luna 3, a Soviet lunar probe that was the first spacecraft ever to take a picture of the far side of the Moon. No human being in history had ever seen the other side of the Moon. Locked by Earth's gravity, the Moon has throughout history kept the same side toward us. Luna 3 revealed a heavily-cratered surface, even more than the side of the Moon that faces us. The Soviets sent two dozen spacecraft to the Moon between 1959 and 1976 as part of their lunar exploration program. The first probe, Luna 1, missed the Moon, but became the first spacecraft to leave the Earth's gravitational field completely. It went into orbit around the Sun. The second probe crashed into the Moon. The third one orbited the Moon and took photographs of the far side. Following Luna 3, the Soviets sent other Luna probes, some of which landed on the Moon. Two of them, known as Lunokhod, had robots that wandered around the surface of the Moon taking pictures. And three of them actually picked up soil samples from the Moon and shot them back to Earth. However, this happened in the year after the Apollo 11 lunar landing and was hardly noticed by the public. ~First Lunar Soft Landing 1966 AD MOON NASA's Surveyor Program, which lasted from 1966 to 1968, was the last step in unmanned lunar exploration. Surveyor's mission was to "soft land" and investigate the surface of the Moon to see if it would hold up astronauts and their lander, to check the composition of the soil, to survey and return television pictures of possible landing sites for the Apollo Manned Lunar Program. The Surveyors had robot claws to dig up soil samples, a conveyor belt to a panel of sensors, and a spectrograph to measure light. In addition there was a camera pointed at the "Moon claw" (which looked like a toy dump shovel) and cameras to provide a 360-degree view of the landing area. The mechanical scoop dug small trenches to check the lunar soil. One of the Surveyors was sent with extra fuel so that after it had landed, it could take off and test the lunar surface for launch strength. Here is a summary of the Surveyor missions: May 30, 1966: Landed, sent back more than 11,000 pictures. September 20, 1966: Tumbled in orbit and crashed on the Moon. April 17, 1967: Landed, sent back pictures and used a mechanical scoop. July 14, 1967: Retro-rocket exploded and the mission failed. September 8, 1967: Landed and again successfully used the Moon claw. November 7, 1967: Landed, sent back pictures and performed a small jump. January 6, 1968: Landed and was successful in its mission. TAround the Sun to the Moon 1990 AD EARTH ORBIT In 1990, the Galileo spacecraft that had already flown around the Sun and passed Venus was flying by Earth. This was part of a complicated orbit to take advantage of gravitational tugs from Venus and Earth to boost Galileo to Jupiter. Since Galileo had to fly close to the Earth, scientists used the opportunity to test its equipment by aiming its cameras at both the Moon and Earth. This was the first time an interplanetary spacecraft had taken pictures of the Earth and Moon while approaching them. Galileo took these four pictures of the Moon using special filters to reveal different chemicals in the lunar surface. (The chemicals are highlighted with false colors by computer.) Studying the chemical differences helps us better understand the history of the Moon, and may pinpoint resources that we may be able to use one day. hGoing to the Movies Here is a list of the movies in Space Adventure. Click on the movie name to view one of these movies. ÅShepard: Flea Jump Into Space 1961 AD CAPE CANAVERAL, FLORIDA More than 30 years ago, millions of Americans sat in fascination to watch a brief historical event on their black and white television sets. On May 5, 1961, Astronaut Alan Shepard -- shoehorned into the little Mercury capsule Freedom 7 atop a Mercury-Redstone rocket -- blasted 185 kilometers (115 miles) into the sky. At the top of his orbit Shepard was briefly weightless, but immediately the capsule began its descent, falling back toward the Atlantic Ocean. Freedom 7's parachutes lowered the capsule gently into the sea, just 15 minutes after the flight began. Shepard was preceded into space by a chimpanzee named Ham, who made a successful suborbital flight on January 31, 1961. On July 21, Virgil Grissom, in Liberty Bell 7, made a similar flight. Americans were thrilled with Shepard's exploit, even though he hadn't gone around the world. But the Soviets were not impressed. Premier Nikita Khruschev sneeringly called it a "flea jump." While it wasn't a very diplomatic remark, he had some justification for making it, since Soviet cosmonaut Yuri Gagarin had flown Vostok 1 around the world on April 12, three weeks earlier. ÄMississippi: Building a Delta MISSISSIPPI RIVER DELTA In this view from space of the Mississippi River Delta, you can see how the river has pushed its way out into the Gulf of Mexico over the ages. As the Mississippi approaches the ocean it spreads out and slows to a crawl. Slowly-moving water cannot hold as much soil as quickly moving water, so it drops much of the dirt it's carrying, slowly building up a vast delta. ╔Namib Desert: Not Mars NAMIBIA Though this picture may look like the surface of Mars, it is actually the Namib Desert in Namibia, a sparsely populated country on the southwest coast of Africa. The Namib Desert is known for its huge dunes, the biggest on Earth. Some of these are three kilometers (two miles) wide and 300 meters (1,000 feet) high. Water is rare here, but it does flow from time to time, as you can see from the dry stream bed in the middle of the picture. ╕For Further Information... 1992 AD EARTH These are organizations and publications of interest to people who want to know more about space exploration. All are in the United States, except where noted: "Air & Space," NASM, P.O. Box 51244, Boulder, CO 80321-1244. Beautiful aerospace magazine published by the Smithsonian Institution. Astronomical Society of the Pacific, 390 Ashton Ave., San Francisco, CA 94112. For amateurs and pros, even those far from the Pacific. "Astronomy," P.O. Box 1612, Waukesha, WI 53187-9950. A beautifully illustrated magazine written at a popular level. British Interplanetary Society, 27/29 South Lambeth Rd., London SW8 1SZ, England. For amateurs and pros. California Museum of Science and Industry, 700 State Drive Exposition Park, Los Angeles, CA. Has an excellent aerospace museum with many spacecraft and demonstrations. Campaign for Space, Box 1526, Bainbridge, GA 31717. Political action committee. Committee for the Scientific Investigation of Claims of the Paranormal, P.O. Box 229, Buffalo, NY 14215-0229. Critically investigates UFOs and such. Those in Southern California should contact Southern California Skeptics, P.O. Box 5523, Pasadena, CA 91107, to learn about frequent fascinating lectures on such subjects, held at California Institute of Technology and other locations. Jet Propulsion Laboratory, 4800 Oak Grove Drive, Pasadena, CA 91109. A branch of NASA run by the California Institute of Technology. The Public Education Office can arrange tours for educational groups. National Aeronautics and Space Administration (NASA) Headquarters, Washington, D.C. 20546. National Air and Space Museum, Smithsonian Institution, Washington, DC 20560. Located on the Mall in front of the Capitol Building, this is the most popular museum in the world. Has many original spacecraft, airplanes, and numerous other exhibits. National Space Society, 922 Pennsylvania, SE, Washington, DC 20003. Among other things, sponsors Dial-a-Shuttle, a number to call when a space shuttle is flying. Ohio State University Radio Observatory, Department of Astronomy, Ohio State University, Columbus, OH 43210. The world's longest-running SETI system. The Planetary Society, 65 N. Catalina Ave., Pasadena, CA 91106. In the US call 1-800-969-6277. Supports planetary exploration and SETI. Largest private space group in the solar system. Royal Astronomical Society of Canada, 136 Dupont St., Toronto, Ontario M5R 1V2, Canada. SETI Institute, 101 First St. #410, Los Altos, CA 94022. Sponsors SETI research, including work on the NASA project. "Sky and Telescope," Sky Publishing Corp., 49 Bay State Rd., Cambridge, MA 02238-1290. A magazine for advanced amateur and professional astronomers. Space Coalition, c/o Dickstein, Shapiro & Morin, 2101 L St., NW, Washington, DC 20037. Political action committee. Spacepac, Suite 201-S, 3435 Ocean Park Blvd., Santa Monica, CA 90405. Political action committee. Space Studies Institute, Box 82, Princeton, NJ 08542. Founded by space-colonization leader Gerard O'Neill. Supports colonization-oriented research projects. US Space Education Association, 746, Turnpike Rd., Elizabethtown, PA 17022. International nonprofit, nonpartisan group promoting peaceful space exploration. World Future Society. Publishes a magazine about trends and future possibilities of society. 4916 St. Elmo Ave, Bethesda, MD 20814-5089. World Space Foundation, 11631 Clark St., Suite 101, Arcadia, CA 91006. Supports asteroid search and solar-sail research. ¢The Military and Rocketry 1950 AD HUNTSVILLE, ALABAMA Almost from the start, the military has been interested in rocket technology. Rockets were introduced to the West by the British military, which was bombarded by them during campaigns in India. A British officer, Colonel William Congreve, improved them and his rockets were used against Britain's foes, including the United States during the War of 1812. During the 20th century, the scientific work of Herman Oberth, Klaus Reidel, Rudolf Nebel, and young Werner von Braun was taken over by the German Army under Adolf Hitler. The Germans developed the V-1 (ram-jet cruise missile) and the V-2, a liquid fuel rocket that could hit London with high explosives. At the end of World War II, Von Braun gave himself up to American soldiers. The US Army took him and other German rocket scientists and engineers to White Sands, New Mexico, where they modified the V-2 for scientific experiments. By 1950 the Army's Rocket Team moved to Huntsville, Alabama, where the Redstone and Jupiter rockets were developed. These rocket engines were used for ballistic missiles, mostly carrying nuclear warheads. Control of the intercontinental ballistic missile (ICBM) programs, the most advanced systems, was given to the US Air Force. Meanwhile, the Soviets, having captured their share of German rocketeers, were hard at work producing missiles for the Soviet military. On Oct 4, 1957, they launched the first artificial Earth satellite, Sputnik 1. By May 1958 the Soviets were able to launch a payload of nearly 1.5 tons. The US was startled, and fearing a threat to their national security, began a large space program, both military and civilian. During the 1980s the military in both nations helped create their respective shuttle programs. In fact, even though the Soviet Union collapsed in 1991, the US is still spending billions of dollars for Strategic Defense Initiative (SDI or "Star Wars") antimissile research. Stars that Blink Radio Waves 1967 AD CAMBRIDGE, ENGLAND In 1967 astronomers thought they had detected an extraterrestrial civilization. British astronomer Antony Hewish, at Cambridge University, had designed a radiotelescope to look for rapidly changing radio signals. He expected to see fluctuations in natural radio signals from the universe caused by interference from the solar wind. Until then, astronomers using radiotelescopes normally averaged their signals over long periods of time, automatically filtering out rapid changes. One of Hewish's students, Jocelyn Bell (now Burnell), used the radiotelescope to discover strange pulses -- like a heartbeat -- coming from a point in the sky. The first possibility was that it was some kind of noise from our own civilization. No one had ever seen regular radio pulses from the sky. But we have transmitters that make all kinds of noise. So they studied the signal for months and found three more sources like it in the sky. They found the sources were fixed in the sky with respect to the stars, so they were not moving like a satellite. This proved they really were sources from the galaxy or beyond and not signals from our own civilization. But what could produce such signals? Nothing was known in nature that could produce radio bursts pulsating around once a second, like the ticking of a clock. The astronomers began to wonder if this could be another civilization signaling to us. They even nicknamed the four objects they had found "LGM" objects, for "little green men". Should they announce to the world that contact had been made with extraterrestrials? Like good scientists they decided to be cautious and study the signals more carefully. After months of analysis they decided the signals were probably some kind of pulsating star. They then announced their discovery to the world. Astronomers all over the planet eagerly searched for more of these objects, which became known as "pulsars." There is a good lesson here for those interested in SETI (the Search for Extraterrestrial Intelligence): Don't be fooled by Mother Nature. It's very easy for a new astronomical phenomenon to be mistaken for another civilization signaling to us. If we ever detect what appears to be such a signal we need to be certain we have first ruled out all natural sources. We now believe the best explanation is not pulsating stars but another strange object that had been predicted but never detected before -- neutron stars. A neutron star is the core of a star, which sometimes remains when a large star blows up in a supernova explosion. This core develops because when the star uses up all its hydrogen and other atoms -- its fuel, in other words -- there is not enough heat left to keep the core from collapsing, so it is crushed down into a tiny object. A star that starts out bigger than our own Sun winds up as a tiny sphere around 20 kilometers (12 miles) in diameter. Scientists now believe the reason these stars pulsate is because of their magnetic field in combination with very rapid spinning -- typically, about one revolution a second. Many stars have magnetic fields, and scientists believe that neutron stars have extremely strong fields. These magnetic fields sweep up electrons and accelerate them to enormous energies. Electrons that move rapidly in magnetic fields generate radio signals, a principal that is used to generate microwaves in microwave ovens. The pulsar and its magnetic field turn about once a second, and produces a radio signal that sweeps the sky like a lighthouse beacon. This is why the astronomers see pulses of radio signals every second. Since 1967, more than 400 pulsars have been discovered in the Milky Way and astronomers estimate there could be as many as 100,000 more in our own galaxy. Most of them pulsate around once a second; some pulsate as slowly as once every four seconds, and others as fast as every two thousandths of a second. For this discovery, Antony Hewish received the Nobel Prize in physics. Some think his graduate student, Jocelyn Bell, should have shared the award with him, although it is a tradition that the Nobel Prize is given for a body of work. Hewish was the designer of the radiotelescope and Bell was a student using it under his supervision. Pulsars are one of the strangest objects we have yet found in our exploration of the universe. In these neutron stars, matter is compressed to such high densities that it is completely beyond the ability of any laboratory on Earth to reproduce. In fact, if the density were just a little higher -- if there were just a bit more matter in the neutron star -- it would collapse completely and could never stop collapsing. It would become a black hole. One of the most exciting results of the discovery of pulsars was the realization that if pulsars exist, then neutron stars exist, and black holes ought to exist. fNebulas: Tombstones in Space UNIVERSE After the invention of the telescope, people sometimes found what looked like planets in the sky -- but weren't. They were "fixed" in space -- they didn't move, compared with the stars and the planets, which wander slowly in the sky. These objects looked like fuzzy disks, and astronomers named them planetary nebulas, from the Latin word "nebula," meaning "cloud." But actually, they have nothing to do with planets. They are great clouds of gas and dust, produced by dying stars. When a star like the Sun runs out of its fusion fuel it does not explode in a supernova the way a more massive star would, but turns into a red giant as the outer layers of the star expand. A red giant star can be larger than the entire solar system, but most of the material is just a hot gas, not a dense object like our present Sun. As the star cools and dies, it turns into a tiny star about the size of the Earth, called a white dwarf. During this dying phase, stars often throw off this cloud of gas, which forms a roughly spherical shell around the star. This is the planetary nebula, the tombstone of a dying star. ┤The Planet Beyond Uranus 1989 AD NEPTUNE The next planet beyond the orbit of Uranus is Neptune. (Strictly speaking, Pluto happens to be closer to the Sun than Neptune right now. But this is due to Pluto's very elongated orbit. After 1999, Pluto will return to its normal place beyond Neptune.) In 1989, the Voyager 2 spacecraft that had previously flown by Jupiter, Saturn and Uranus completed its mission: It become the first probe ever to fly by Neptune. Neptune is very similar to Uranus in size and mass. Most likely, Neptune is largely made of water, with some hydrogen, helium, methane and rock. Like all of the giant planets, Neptune is completely covered with clouds. But where the cloudtops of Uranus had been essentially blank, Neptune had dramatic markings much like Jupiter's. Just as Jupiter has a huge storm called the Great Red Spot, Neptune has a region called the Great Dark Spot. All of the giant planets have rings around them, though only Saturn's are easily visible in a telescope. Neptune's rings are extremely faint and had only been indirectly detected from Earth before the Voyager 2 flyby. The spacecraft found them to be very faint, but they were successfully photographed for the first time. Neptune has one large moon, Triton. It's 2,700 kilometers (1,700 miles) in diameter, slightly smaller than our own Moon. Triton has a very thin atmosphere of nitrogen and is the coldest body in the solar system ever measured. Neptune also has a small moon called Nereid, about 340 kilometers (210 miles) in diameter. Nereid is in a cigar-shaped orbit that suggests that it's probably an asteroid captured by the gravity of Neptune. Voyager 2 also discovered six more tiny moons the size of Nereid or smaller. ■The Clue to Neptune 1845 AD ENGLAND Would it be possible to predict the existence of a planet never seen before? Edmond Halley had predicted that a comet (the one that now bears his name) would return in 1835, and it did. Then, several years later, the science of astronomical prediction he helped create began to flower and led to an even more extraordinary prediction. A French farmboy, Alexis Bouvard, working as an aide to the mathematician Pierre-Simon de Laplace, calculated where the newly discovered planet Uranus should be, but found it wasn't there. He concluded there had to be some unknown force altering its path. What could it be? Uranus is a big planet, four times the diameter of the Earth and 15 times as massive. It takes a heck of a force to nudge a planet that size. The only known force strong enough would be the gravity of another planet. Could there be another planet beyond Uranus? It was an intoxicating time to be a scientist. Science had given us the ability to predict the return of comets; could it allow us to predict the location of an unknown planet? It was a very sticky problem. While theoretically it would be possible to predict where the planet lay, then scan that part of the sky for it, Isaac Newton's gravitational theory involved extremely difficult equations. Two men tackled the problem: Urbain Jean Leverrier of France (who had most thoroughly developed Newton's theory), and at about the same time, John Couch Adams of England. It became a horse race: Who would finish the calculation first, Leverrier or Adams? To which nation would the glory go if the planet were found, France or England? In 1845, the 26-year-old Adams gave his result to the Astronomer Royal and to the head of Cambridge Observatory. He was greeted with slaps on the back and a bottle of champagne, right? Wrong! The two senior astronomers didn't think much of Adams, who was too modest to brag about his achievements. So they ignored his work. It was not published, and no one bothered to look for his planet. The next year, Leverrier published his own prediction. Did his countrymen sit up and take notice? He had no better luck than Adams -- except, ironically, in England. There, the two astronomers who ignored Adams read Leverrier's prediction and found to their horror that it agreed with Adams. So the head of Cambridge Observatory hustled off to his telescope. It is not possible to precisely predict where an unknown planet is. For one thing, you don't know how big it is. For another, you don't know how far away it is. A big planet, far away, can produce roughly the same effect as a little one nearby. Thus not even Adams and Leverrier could give the exact place in the sky where the planet would be. All they could do was narrow the search to a small piece of sky. But considering the size of the sky, and the millions of stars and star-like objects visible in a telescope, even an approximate position is extremely helpful. So the British astronomer measured the positions of all the stars in the predicted area over a two-month period to see which one moved -- the test of a planet. One of them did move and he had discovered the new planet! But he didn't know it! Unfortunately, he had other work to do and did not have time to look at his results. Meanwhile, back in France, Leverrier was becoming frustrated. Here he had made the first prediction in history of a new planet (he didn't know about Adams) and everyone was ignoring him! So he wrote to astronomer Johann Galle of the Berlin Observatory in Germany, who did pay attention. The very night he received Leverrier's letter, Galle looked at the sky as instructed and compared the stars to the new German star map he had just received. Lo and behold, he found the planet! It was named Neptune and it was even bigger than Uranus. At last, justice was done, at least in part. Galle announced the planet to the world and received the recognition he deserved for discovering the planet, while Leverrier received the recognition for predicting it. Unfortunately, they didn't know about Adams. Poor Adams. The English astronomers came to his defense and announced his work, but on the Continent they thought it was just English sour grapes after losing to a Frenchman and a German. Leverrier did all right. Just as had happened with Halley's comet, even non-scientists were amazed at the ability of science to predict the future. One historian writes, "This course of events made a deep impression on the world of scientists, but no less on the world of educated laymen. From all countries honours were showered upon Leverrier, and the discovery at a desk of a body never seen was the ruling topic for a long time." Happily, science eventually accepted Adams' work, and now Adams and Leverrier share the honor in the history books for the prediction of Neptune. ÖWhere Are the Other Neutrinos? 1967 AD LEAD, SOUTH DAKOTA Probably the last place on Earth you would think of putting a telescope is in a gold mine, but that's exactly where this one is. This is no ordinary telescope, but one designed to detect some of the most elusive particles in the entire universe -- neutrinos. Neutrinos are tiny particles given off in nuclear reactions. They are hard to detect because they have no electrical charge and pass through matter as if it were not there. A neutrino can sail through the entire Earth without difficulty. Almost any other particle would be absorbed in a collision with the nucleus of an atom or with an electron. Scientist Raymond Davis, Jr. knew that the Sun ought to emit a huge number of neutrinos since -- according to the current theory of its workings -- it generates its power by a nuclear fusion reaction similar to a hydrogen bomb explosion. Neutrinos are the automatic byproduct of such reactions. Even though neutrinos are extremely hard to detect, he figured that if he made a huge tank of the right chemical, the neutrinos would cause the radioactive transformation of a few atoms' nuclei, which could be detected. Since there is a constant rain of cosmic rays from space that would interfere with the detectors, he knew he had to put the telescope into a mine deep below the Earth's surface so that the rock would block most of the interfering particles. He built this tank 6 meters (20 feet) in diameter and 12 meters (40 feet) long. He filled it with 380,000 liters (100,000 gallons) of perchloroethylene, a chemical similar to the carbon tetrachloride used for dry cleaning. He put it 1,480 meters (4,850 feet) underground in the Homestake Gold Mine in Lead, South Dakota. The chlorine atoms in the tank are occasionally struck by neutrinos and converted into argon, an inert gas. This form of argon is radioactive, and can be swept out of the tank by flushing it with helium gas. The radioactive argon can then be detected with instruments similar to a geiger counter. He expected to see about one atom of argon per day produced. That is an incredibly small rate, but his instruments were sensitive enough to detect it. In fact he only saw about one-third of this amount. Since then, other scientists have done similar experiments and gotten the same result. This was an amazing mystery because we thought we really understood how the Sun worked. For years, physicists have been trying to figure out why neutrino telescopes do not see as many neutrinos as their theories predict. The best theory is that neutrinos can change form. There are three types of neutrinos, and it appears that two-thirds of those emitted by the Sun are in a form that cannot be detected by this experiment. The gold-mine experiment has improved our understanding of how Mother Nature works on the smallest scale, and of how our favorite star works. Understanding this star is of enormous importance, since it controls all life on Earth. #Newton: 17th Century Einstein 1687 AD CAMBRIDGE, ENGLAND Sir Isaac Newton was a genius's genius, the Einstein of the 17th century. A genius might be defined as someone who revolutionizes our understanding. A super-genius is then someone who revolutionizes our understanding in several profoundly different ways. Einstein and Newton were super-geniuses. Just as Einstein radically changed our understanding of space, time, gravity and light, Newton had a similarly profound effect on our knowledge of space, gravity, light and math. Newton and Einstein probably accelerated our comprehension of the universe by centuries. One of the key moments in Newton's life came when Edmond Halley paid him a visit in 1684. Halley had a problem that was puzzling him and he thought Newton's theory of gravity might provide the solution. Legend has it that Newton came up with his theory when he saw an apple fall from a tree. We don't know if this is true, but there were apple trees on his family's property, and one of them may well have inspired him. A cornerstone of Newton's theory of gravity was that the force of gravity weakened as the square of the distance. Thus, if the Moon were moved twice as far away from Earth, it would not feel one-half of Earth's gravity, but one-quarter (one divided by two, squared). This became known as the inverse-square law of gravity. Now the problem that puzzled Halley was that the German astronomer Johannes Kepler had proven that planets move in elliptical orbits around the Sun. Were these orbits the logical consequence of an inverse-square law of gravity? Several scientists had speculated that this was the case, but not one could prove it. It was a very difficult problem, and the mathematics of the day was not advanced enough to solve the difficulty. Halley visited the reclusive Newton to ask him about this, not expecting even he could shed much light on so intimidating a problem. To Halley's amazement, Newton said he had proved that, indeed, elliptical orbits were a direct consequence of an inverse-square gravity law. Halley asked him for the proof and Newton rummaged in his files but couldn't find it. One of the most important discoveries in the history of science, and Newton had misplaced it! Halley urged Newton to re-do the work. Reluctantly, over several years, with the frequent prodding and help from Halley, Newton did so. He expanded it into the book called "Philosophia Naturalis Principia Mathematica" (Mathematical Principles of Natural Philosophy, in Latin). Known as "Principia" for short, this book solved most of the outstanding problems of planetary motion. How did Newton solve the problem of the ellipse that had eluded so many scientists? It required the use of a new form of mathematics: calculus, which didn't exist -- so Newton invented it. Most people today find calculus difficult even though its principles are laid out in great detail in a thousand books. Newton didn't have those books; he just had problems that needed solving. So he not only invented calculus, he figured out how to use it cleverly to solve the very tricky mathematics that resulted from his particular theory of gravity. That's genius. Halley kept after Newton to publish "Principia." Reluctantly, Newton gave in and allowed Halley to take it to the Royal Society. Unfortunately, the Society had just published a book about fish that had bankrupted its treasury. It was so poor that the society had paid its officers' salaries in copies of the fish book. (How would you like to get paid in copies of a fish book?) On account of this fish book, a landmark of human thought was very nearly lost. Halley, who was usually well off but who was short of money at this point, scraped together the funds out of his own pocket and paid for its publication. And that is how one of the greatest works in the history of science reached the world. Newton Figures Escape Velocity 1687 AD CAMBRIDGE, ENGLAND Sir Isaac Newton laid the groundwork for the space program by discovering the fundamental laws of motion and gravity that are used to design spacecraft orbits and to calculate the flight of falcons. In 1687, Newton published a book called "The Mathematical Principles of Natural Philosophy." There, he spelled out his great discoveries of motion and gravity. One of his ideas, shown here, made space satellites possible. He showed that if you climbed to the top of a mountain and threw a ball, it would travel a certain distance and then hit the Earth. But suppose you could throw the ball twice as fast. It would travel farther. If you threw it three times as fast, it would travel even farther. If you kept increasing the speed, say by using a cannon, a point would come when the ball would be traveling part way around the planet. And if you shot it with just the right speed, it would travel completely around the Earth and hit you in the back of the head. If you shot much faster than that, the cannonball would travel off into space and never return. The slowest speed at which this happens is called the escape velocity. For Earth, the escape velocity is 11 kilometers per second (seven miles per second). Any rocket leaving Earth must travel at least as fast as the escape velocity, or it will fall back to the ground. Other planets have different masses. Their gravity may be stronger or weaker. For those, the escape velocities are different. On little Mercury, for example, the escape velocity is only four kilometers per second (2.5 miles per second). On giant Jupiter it is 61 kilometers per second (38 miles per second). On a tiny asteroid, the escape velocity can be so small that if you were standing there you could simply jump off and fly away into space forever. aInfrared New York February 1983 NEW YORK, NEW YORK This infrared (heat) photograph of metropolitan New York was taken by the thematic mapper on the LANDSAT 4 satellite in February 1983. The mapper uses colors to show different wavelengths (invisible "colors") of infrared light. In it you can see Manhattan Island and even Central Park (the square region in the middle of Manhattan), the west edge of Long Island, and part of New Jersey. New York was originally a trading post established by the Dutch, called New Amsterdam. Later it was occupied by the British and renamed New York. It's one of the largest cities in North America. Oberon: Uranus Moon 1986 AD URANUS ORBIT Oberon is one of the five medium-sized moons of Uranus. It is a dark object made of rock and ice, seen in this picture from the Voyager flyby of Uranus. Oberon is 583,000 kilometers (362,000 miles) from the planet and 1,550 kilometers (964 miles) in diameter. &Clouds of Organic Molecules 1968 AD MILKY WAY The Milky Way has many huge clouds of molecules similar to the ones from which living things are made. These are known as giant molecular clouds (GMCs). Astronomers once thought that complicated molecules could not exist in free space, out between the stars, because stars produce ultraviolet light, which breaks down most molecules. To their surprise, they discovered in these cold clouds (just a few degrees above absolute zero, the coldest temperature that anything can have) signs of very complicated molecules. The clouds are made of dust and gas. Most of the gas is hydrogen, but there are such huge quantities of gas -- typically 10,000 times as much matter as in our entire Sun -- that there is room for lots of other molecules. What allowed the astronomers to see these molecules was radioastronomy. Using radiotelescopes similar to large satellite dish antennas, they were able to detect the microwave frequencies emitted by complicated molecules. The discoveries started in 1968-69 when astronomers found the first complex molecules in the Milky Way: ammonia (NH3, one nitrogen with three hydrogens), water (H2O, two hydrogens with one oxygen), and formaldehyde (H2CO, two hydrogens with one carbon and one oxygen). Normally, we say that space is a vacuum, meaning that there's nothing there. But the universe is never a perfect vacuum. There are always atoms, electrons, protons, or dust floating around. On Earth, the air we breath has about three million million million molecules in each cubic centimeter, a volume about the size of a fingertip. In space, far away from planets and stars, there is usually around one atom in each cubic centimeter, and this atom is usually hydrogen. Interstellar clouds, the clouds of gas and dust that often float between stars, have densities ranging from around 100 molecules per cubic centimeter up to 100 million. So, even though these clouds are much more concentrated than in free space, they are still practically vacuums compared with the air we breathe. But the clouds are huge. Even a small cloud in interstellar space is almost a light year in size (a light year is 10 trillion kilometers or six trillion miles). The largest clouds, the giant molecular clouds, are up to 300 light years across. These sizes are so enormous that even this low concentration of molecules adds up to a huge amount of matter. The smallest clouds have around ten times as much mass as the entire Sun; the largest have masses up to ten million times the Sun. Most of the matter in these clouds is in the form of hydrogen molecules, and some in the form of helium, which does not form molecules. But a sizeable part of it is in the form of complicated organic molecules. In chemistry, an organic molecule is one containing carbon atoms. It's called organic because all organic matter consists mainly of carbon molecules, so the molecules out of which each of us is made are organic molecules. However, just because a chemical is called "organic" doesn't mean that it was ever living. More than 70 types of molecules have been found in these clouds, most of them organic. Molecular clouds are also where stars are born, so they are of great importance in the history of our own solar system. Our Sun and planets were probably born in such a cloud. One of the most detectable molecules found in these clouds is carbon monoxide (CO, one carbon and one oxygen), the same poisonous gas produced by incompletely burned fuel in a car. Alcohol, an organic molecule, is also found in these clouds. About one ten-thousandth of the matter in these clouds is organic. But even a small fraction is enough so that a typical cloud would have an amount of organic matter in it much greater than the mass of our own Sun. The fact that complicated organic molecules of the same kinds that are found in life on Earth occur in these clouds makes us suspect that the ingredients for life are widespread in the universe. So molecular clouds provide a clue to the possible existence of life on other worlds. They suggest that life may arise in other locations in the universe. ╢Orion: Birthplace of Stars ORION NEBULA The Orion Nebula, shown here, is the birthplace of a cluster of bright new stars known as the Trapezium. The nebula, most of which is hidden behind gas clouds, is about 1,600 light years away, located just below the three stars making the belt in the Orion Constellation. On a clear night you can see the nebula with a good pair of binoculars or a telescope. Its red glow is caused by light from the Trapezium and other stars illuminating a gigantic cloud of hot hydrogen about 10 light years across. There is enough hydrogen in this cloud to make thousands of stars. About five billion years ago our solar system may have formed out of a nebula very much like this one. ²The Hole in the Sky 1985 AD ANTARCTICA In 1985, scientist Joseph Farman discovered something strange about the atmosphere. In the stratosphere (the upper atmosphere), there is a layer of gas made of molecules called ozone. Ozone is an unstable molecule with three oxygen atoms stuck together, instead of the two atoms of ordinary air. Ozone is formed by ultraviolet light (light waves shorter than visible light) from the Sun. The ozone layer protects us from dangerous ultraviolet rays that can cause skin cancer. Farman noticed that the ozone above Antarctica had temporarily thinned every October, starting in the late 1970s. The amount of ozone fell by half. This became known as the hole in the ozone layer. Dangerous ultraviolet is called UV-B, where the "B" stands for "biologically active." This type of sunlight can cause skin cancer and cataracts -- a form of blindness. The ozone hole doubled the amount of UB-V reaching Antarctica. The main culprit turned out to be chlorine atoms from industrial chemicals known as chlorofluorocarbons (CFCs), found in refrigerators and some spray cans. CFC gases slowly rise through the atmosphere. After ten years, they start a series of chemical reactions that destroy ozone molecules. During November and December, some of this Antarctic air mixes with the air over countries such as New Zealand, Australia and southern South America. It may take years to see if this causes an increase in skin cancer, blindness and poorer crops. Clouds in the stratosphere are critical in this story. They keep chlorine atoms in their ozone-destroying form. Since such clouds are less common over the North Pole, it is less likely we'll see an ozone hole over the Arctic. However, humanity keeps dumping CFCs into the atmosphere. An international treaty is slowing that process, but the amount of CFCs is still expected to increase until about 2010. Furthermore, if global warming occurs, it would probably cause stratospheric clouds, which could help cause ozone holes in the Arctic that will threaten even more people. ├The 200-Inch Eye 1949 AD MT. PALOMAR, CALIFORNIA For decades, the Palomar telescope was the largest in the world. It was built thanks to the efforts of astronomer George Ellery Hale. He wanted to build the biggest telescope ever, one with a five meter (200 inch) wide mirror. Hale arranged for financing by the Rockefeller family, starting in 1928. But the telescope was not completed until 1949. Hale did not live to see the telescope in operation, but it was named the Hale telescope in his honor. It has played a major role in understanding stars, galaxies, quasars, and many other objects of our universe. For most of its history, the telescope mainly used photographs to survey the universe. But in recent years, it has been upgraded with modern, ultrasensitive electronic detectors known as charge-coupled devices (CCDs), which are much more sensitive to light than film. They act like supersensitive television cameras, and are used with computers to process the pictures to bring out subtle detail. Mt. Palomar has suffered from "light pollution" as the lights of the nearby city of San Diego have expanded with the growth of this part of Southern California. But it is still one of the most powerful telescopes in the world. nPatriot: Scud Killer January 1991 SAUDI ARABIA One of the heros of the Persian Gulf War with Iraq was the Patriot air defense missile, produced by Raytheon. The system relies on computerized radar to track incoming missiles. At the proper moment, the Patriot is launched so it will intercept its target at about 25,000 feet above sea level. During the Persian Gulf War, Patriot missiles were set up in Saudi Arabia, Israel and Turkey. They were used to shoot down Russian-made Scud surface-to-surface missiles launched by Iraq against Saudi Arabia and Israel. At the time, the Patriots seemed to have a high success rate, apparently shooting down most of the Scuds. After the war, it was revealed that the missiles, which were not designed for this type of combat, often failed to hit the Scud warhead. Many of the apparent hits were probably the result of badly made warheads exploding ahead of time. oPegasus: Cheap Route to Space 1989 AD EARTH ORBIT The Pegasus rocket is the most important breakthrough in years for getting small satellites into orbit cheaply. Several private companies had tried to develop small rockets to get into space inexpensively, but Pegasus was the first to be successful. The rocket was a private project developed by Orbital Sciences Corporation of Fairfax, Virginia and Hercules Aerospace Company of Wilmington, Delaware. The companies came up with the idea of a small, winged rocket that would be carried into the air under a B-52 bomber. This would allow it to get to high altitude without using any fuel. At 12 kilometers (40,000 feet), the rocket is released and its engine fired. Using three stages, the solid-fuel Pegasus then flies into orbit. The $45 million Pegasus is 15 meters (49 feet) long, 1.3 meters (50 inches) in diameter, and with a wing span of seven meters (22 feet). It weighs 20 tons and can carry a payload of up to half a ton. Potential customers include the military, which has been especially interested in using it to get Strategic Defense Initiative ("Star Wars") weapons and instruments into orbit; NASA, which would use it to send up small scientific instruments; and many nations that do not have rockets of their own. Thanks to miniaturization, a great deal of scientific instrumentation can be packaged into half a ton. Because of budget cuts in the space programs of most nations, researchers are increasingly looking at using this low-cost rocket to launch relatively inexpensive miniature spacecraft. Much of the space science of the future will be conducted with these small satellites and space probes. ìTip of the Persian Gulf 1990 AD PERSIAN GULF This stretch of water and land is a satellite view of the tip of the Persian Gulf. In it you can see the Tigris-Euphrates River Delta and the countries of Iran, Iraq and Kuwait. Roughly, Iran is the land on the top of the picture, Kuwait the area on the lower right, and Iraq the part in the lower left corner. All three of these countries have large oil reserves, but Kuwait, a small country about the size of New Jersey, is particularly rich in oil. On Aug. 1, 1990, Iraq invaded Kuwait and began a conflict that eventually led to an invasion by American and allied forces and the restoration of Kuwait as an independent country. &Phobos: A Diseased Potato 1976 AD MARS ORBIT Phobos is the larger of the two moons of Mars, about 30 kilometers (20 miles) in diameter. Described by astronomer Carl Sagan as looking like "a diseased potato," it's covered by tiny craters. There are also strange grooves that may have been caused by rocks orbiting Mars. Phobos is probably a captured asteroid, a huge rock flung out from the asteroid belt between Mars and Jupiter when the giant planet's gravity stirred up the swarm. It may be an important source of fuel and other resources for future astronauts visiting Mars. █ Galileo Recants 1630 AD PADUA, ITALY Galileo Galilei was the first astronomer to see the universe through a telescope, and he found proof of the revolutionary theory of Copernicus that the Earth was not the center of the universe. But before the invention of the telescope, Galileo had made another revolutionary discovery. The ancient Greeks such as Aristotle taught that heavy objects fall faster than light ones. It's obviously true, isn't it? But Galileo proved that it was wrong! According to legend, he climbed up to the top of the Leaning Tower of Pisa and dropped two weights, one large and the other small. Amazingly, they both hit the ground at the same time. Historians say that this experiment probably never happened at the Leaning Tower, but Galileo did conduct experiments and made theoretical arguments proving that all weights fall at the same speed, apart from air resistance. (A feather falls slower than a ball, but only because air resistance slows it down. A pea that weighs as much as the feather will fall just as fast as the ball. The pea doesn't have much air resistance.) This fact showed that the ancients were not to be believed. Just because Aristotle said something didn't make it true. This was a revolutionary idea. A few years earlier, another Italian, Giordano Bruno, had strongly supported Copernicus's idea that the Earth was not the center of the universe. Bruno was rewarded by being burned at the stake for this and other heretical ideas. Then, just nine years after Bruno's death, Galileo turned the newly-invented telescope on the sky. Galileo found that four moons revolved around Jupiter, proving that at least four heavenly bodies did not revolve around the Earth. He found that Venus had phases like the Moon, proving that it revolved around the Sun, not the Earth. He was rewarded for his brilliance by being shown the torture chambers of the Church's Inquisition. He was thereby encouraged to renounce Copernicus. He was placed under house arrest for the rest of his life. Galileo died in the year Newton was born, 1642. One genius left the world and another stepped into it. It was a world which was struggling to accept the new idea of science, the idea that it was not enough to rely on Recognized Authorities. Observations and experiments were needed. And when observations contradicted Authority, Authority was wrong, no matter how powerful they were or how many people believed it or for how many centuries it had been accepted. The Age of the Doubting Thomas had arrived. ╙A Message from Earth 1983 AD MILKY WAY The Pioneer 10 and 11 spacecraft were not only the first to go to Jupiter, but also were the first to leave the solar system. Since they would wander for billions of years throughout the Milky Way Galaxy, scientists thought that perhaps, in the distant future, an alien civilization might find one of these spacecraft. This led them to design a plaque to tell other civilizations about us. Since the aliens would probably not speak any Earth language, a different kind of "language" had to be invented. They used math, astronomy and pictures instead of words. The Pioneer Plaque shows a picture of two humans, so the aliens would learn that we have two arms, two legs, and one head. There's a little map of our solar system, showing the nine planets. Earth is bumped up towards the picture of the humans, to show where our planet is. The thing that looks like a spider is an astronomical map of where we are in the galaxy. The lines point to pulsars. In 1983, Pioneer 10 went beyond Pluto and Neptune and became the first man-made object ever to leave the solar system. Soon it was followed by Pioneer 11, and later Voyagers 1 and 2. These are our first interstellar spacecraft, wandering forever among the stars! ¬How the Solar System Started 4.6 Billion BC SOLAR SYSTEM Though the details are not fully understood, it appears our solar system started about 4.6 billion years ago as a whirling disc of hot hydrogen gas mixed with heavier atoms from ancient supernova explosions. Gravity pulled the hydrogen together, toward the center of the disc. The hydrogen became more and more compressed until a nuclear fusion reaction began, generating energy. The Sun was born. The remaining tenth of a percent of solar material condensed into smaller bodies that eventually became the planets. Leftovers became moons, comets, and asteroids. Violent collisions with the leftovers pockmarked the planets and tilted some of them, like Uranus. ÜA Planet Beyond Pluto? March 12, 1930 BEYOND PLUTO Which planet is farthest from the Sun? Usually, it's Pluto, but not right now. At this moment, Neptune is actually a bit farther than Pluto. Pluto's orbit is very elliptical, ranging from about 4 billion kilometers (3 billion miles) from the Sun all the way out to 7 billion kilometers (5 billion miles). Pluto is so far away that it takes 249 years to orbit the Sun. For 20 years of that orbit, it is closer to the Sun than Neptune. Pluto came closer than Neptune in 1979 and will become the most distant planet again in 1999. Then, for the next two centuries, Pluto will remain the farthest planet in the solar system, as usual. Pluto is the only planet in the solar system that crosses another planet's orbit. But there is no danger of collision because Pluto's orbit is tilted strongly compared to the rest of the planets, so the two never pass very close. Because of this unusual situation, some astronomers suspect that Pluto may once have been a moon of Neptune. Others think that there may have been hundreds of Pluto-size planets in the outer solar system, and most of them got thrown out by the gravity of the giant planets like Jupiter. Pluto was discovered in 1930 by Clyde Tombaugh. For years, astronomers suspected there might be a planet beyond Neptune, because the motions of Uranus and Neptune were slightly different from their calculations. It looked as if an unknown planet tugged on Uranus and Neptune. Astronomer Percival Lowell, the man who thought the Martian canals had been built by a civilization, had built an observatory in Arizona. He hired an amateur astronomer, Tombaugh, to look for the planet. Painstakingly, Tombaugh studied the images of 90,000,000 stars, looking for one that seemed to move in the sky against the background of stars. This could be the signature of a planet. In 1930 his patience was rewarded. He became the only person in the 20th century to discover a planet. Pluto is so far out that the Sun is just a very bright star in the sky, with about one-thirtieth the diameter we see from Earth. Even though it is now about as warm as it ever gets on Pluto, it is probably over 200 degrees Celsius below zero (300 degrees Fahrenheit below zero), the coldest planet in the solar system. For comparison, the coldest it ever gets on Earth is 88 degrees Celsius below zero (127 degrees Fahrenheit below zero). You couldn't even get a Pluto-like chill thrill by traveling to Antarctica on a cold winter's night -- not one of the more popular tours at your travel agency. Pluto is the smallest planet in the solar system, 2,300 kilometers (1,400 miles) in diameter. That makes it one-third smaller than our Moon. It also has a very thin atmosphere of methane (CH4) gas. It's only around 1/100,000th of the pressure of the Earth's atmosphere -- airless, for all practical purposes. It's the only planet in the solar system that has never been visited by a spacecraft, though scientists have ideas for space probe designs that could get to Pluto in a reasonable time. It's possible that within the next 10 to 20 years a Pluto probe may be launched. In 1978, astronomer James Christy of the US Naval Observatory noticed a bump in a photograph of Pluto. Being small and so far away, Pluto is very hard to photograph even in the best telescopes. Examining other pictures, he saw that the bump moved around Pluto. It was the first picture taken of what turned out to be a moon around Pluto. Called Charon (pronounced "Karen"), this moon takes six days to orbit its planet. Charon is about 1,200 kilometers (700 miles) in diameter, half the size of Pluto. No other moon in the solar system is so close in size to its planet. Another unique aspect of the Pluto-Charon system is that not only does Charon keep one face toward Pluto constantly, the way our Moon keeps one face toward the Earth, but Pluto also keeps one face toward Charon all the time. This is because they are close enough that the gravitational forces of the two objects are so strong that they drag on each other until they are "locked" facing each other forever. The two spin around like a dumbbell in space. There's one mysterious footnote to this story. It now appears that Pluto is too small to have moved Uranus or Neptune by itself, so the original calculation of where to look for Pluto was irrelevant. Pluto was found by a combination of luck and hard work. So there's probably something else out there, pulling on Uranus and Neptune. The search is on for a planet beyond Pluto, often called Planet X. It will be extremely difficult to find, because it would be very faint and easily confused with the billions of stars in the sky. Someday, it's likely that someone will find Planet X. It could be you. ╝ Roemer Calculates Light Speed 1679 AD PARIS, FRANCE White light consists of many colors, as this prism shows, but all the colors travel at the same speed in space. Light travels so fast that it took centuries before human beings could measure its speed. It was a clever observation by a Danish astronomer, Ole Roemer, that gave the first correct measurement. While working in France, Roemer noticed a puzzle in the behavior of the moons of Jupiter. They should have orbited Jupiter at very precise intervals. Jupiter's closest Moon, Io, in particular, takes six days to orbit Jupiter. When he looked at many observations, he found there were variations of a few minutes in this time. What could cause it? Then he had a brilliant insight. Perhaps light did not travel instantaneously. Maybe the light from Io takes a certain amount of time to get to Earth. Because Earth circles the Sun once a year while Jupiter takes 12 years, this means there are times in the year when Earth is close to Jupiter and times when it is far away. He noticed that Io was late when Earth was farthest from Jupiter. From this, he calculated that light traveled at 225,000 kilometers per second (140,000 miles per second). He announced a prediction in September 1679. He claimed that the eclipse of Io by Jupiter that astronomers expected for the 9th of November would be 10 minutes later than the astronomers expected. Sure enough, when November rolled around, his prediction proved correct. Many scientists were amazed, and others were skeptical. We now know that he was correct, even though he was slightly off in his calculation due to the inaccuracies in the astronomical measurements of that day. In fact, light travels at 300,000 kilometers per second (186,000 miles per second). Light is just one type of electromagnetic wave. Radio waves, infrared light, ultraviolet light, X-rays and gamma rays are all forms of electromagnetic waves. All of them travel at the speed of light in space. (When traveling inside a substance such as glass, they slow down.) When engineers send spacecraft to the planets they have to allow for the time delay caused by the speed of light. Even when Mars is close to Earth it still takes about a quarter of an hour for radio signals to get there. If a command is sent to change an instrument setting, it takes a quarter of an hour for that signal to get there and another quarter of an hour for the spacecraft to signal that the change was made. This is why robots on Mars will have to be highly intelligent. Because of the time delay we cannot sit back on Earth and control them remotely. If the robot is walking over a cliff, it needs to be smart enough to know the cliff is there and to react quickly. It can't wait half an hour for instructions. Ptolemy's Earth-Centered System 151 AD ALEXANDRIA, EGYPT In ancient Egypt, the Greek astronomer Ptolemy taught that Earth was the center of the universe. At least one Greek, Aristarchus of Samos, challenged that idea, suggesting that the Earth revolves around the Sun. But Ptolemy and his believers won the acceptance of most people. It wasn't until the 16th century that Copernicus convincingly presented evidence that the planets revolve around the Sun. But he and his followers such as Galileo had to fight more than a thousand years of belief in the old ideas. ▌ Pioneer Venus Probes 1978 AD VENUS The most sophisticated American probes to enter the atmosphere of Venus were known as Pioneer Venus. In 1978, Pioneer Venus 1 and 2 were launched. Pioneer 1 orbited Venus, using radar to map the surface. It also used ultraviolet and infrared instruments to study the clouds. Pioneer Venus 2 had probes to enter the atmosphere. The USSR had sent probes to Venus previously, and this was now the big American effort to go beyond what the Soviets had done. Pioneer Venus 2 had one large probe and three small ones. Each of them entered the atmosphere in a different location, and parachuted down to the surface. Only one of them survived the landing, but it transmitted data for an hour. They did not have cameras on board, unlike some of the Russian probes, but they did make precise measurements of the gases in the atmosphere of Venus. By comparing precise measurements of the atmospheres of Venus, Earth and Mars, you can learn a great deal about the history of the solar system. Venus is just inside the orbit of the Earth, and Mars is just outside. Yet Venus has an atmosphere roughly one hundred times the pressure of the Earth, and Mars has one roughly one one-hundredth that of Earth. Why are there such radical differences? We still don't know all the answers, but at least we are beginning to understand how atmospheres form, and how they leak away into space, despite the gravity of each planet. The Pioneer Venus probes also measured the temperatures of the different locations. They confirmed that the greenhouse effect keeps Venus hotter than it would otherwise be. The greenhouse effect says that an atmosphere of carbon dioxide such as Venus has can act like a blanket to keep the planet warmer than it would be if it did not have an atmosphere. The greenhouse effect was first detected on Venus, before it was suspected on Earth. One of the surprises of the Pioneer Venus probes was the detection of lightning. Venus has thick clouds of sulfuric acid, and scientists didn't expect these would form lightning. One possibility is that there may be active volcanoes on Venus which could generate lightning. The radar maps of Venus showed evidence of volcanic regions, and encouraged scientists to design an even better radar space probe, the Magellan orbiter, which later went to Venus. By studying Venus, we understand our own atmosphere better, and are beginning to understand the possible dangers of a greenhouse effect on our own planet, as our civilization produces carbon dioxide. A Message to the Stars 1963 AD ARECIBO, PUERTO RICO The world's largest radiotelescope fills a valley in Puerto Rico. Called the Arecibo radiotelescope, it's a giant dish antenna 305 meters (1000 feet) in diameter. Most radiotelescopes look like large satellite or radar dishes. The dish is a metal reflector that concentrates radio waves just like an optical telescope's mirror concentrates light waves. Instead of looking at the output with a lens or a camera, a radiotelescope uses a radio receiver to pick up the signals. Since many astronomical objects create radio noise, the radiotelescope can often detect the faint signals of a distant pulsar, quasar, interstellar gas cloud or galaxy. The Sun and Jupiter also broadcast strong radio signals. Most radiotelescopes are able to point anywhere in the sky, like a radar dish. Arecibo, however, has a unique design. Because of its huge size, the dish is rigidly fixed, held by towers much like a suspension bridge. Since the big dish can't move, to aim the radiotelescope, small movable radio antennas are suspended high above the center of the dish. The incoming signals bounce off the dish and are focused onto the small antennas. By aiming the small antennas in different directions, astronomers pick up signals that have bounced off the dish from different parts of the sky. There is also a powerful transmitter at the antenna that allows Arecibo to be used for radar. The antenna was originally built to study the upper atmosphere region called the ionosphere, which radio signals bounce off. The radio signals would start from the transmitter, bounce off the big dish, then bounce off the ionosphere (which has electrons knocked off atoms by the Sun's ultraviolet light). Some of the reflected radio waves return to the antenna and are detected. Measuring how long the signals take to come back tells how far the layer is. The strength of the signal tells how dense the ionosphere is at that level. But the transmitter can be tuned to higher frequencies that pass straight through the ionosphere and into space. The signals can be aimed at the Moon, Venus, Mercury, and other solar-system objects. Even though the reflections are extremely weak, supersensitive receivers can detect them. Sometimes another radiotelescope is used together with Arecibo. NASA's Deep Space Network (DSN) in Southern California is often used, with one antenna serving as the transmitter and the other as the receiver. One of the most exciting uses of the Arecibo dish is in the search for extraterrestrial intelligence (SETI). NASA's High-Resolution Microwave Survey (HRMS) project sometimes will use it to search for such signals. And the University of California at Berkeley has a project called SERENDIP III operating at Arecibo. (SERENDIP stands for the search for extraterrestrial radio emissions from nearby developed intelligent populations.) This project, under the direction of astronomer Stuart Bowyer, takes advantage of the fact that scientists already use the telescope to look at interesting astronomical objects. SERENDIP taps into the astronomers' signals and tunes four million radio channels, looking for signs of other civilizations. They search at frequencies from 424 to 436 megahertz, which are close to ones used on Earth for UHF TV, cellular phones and radar. SERENDIP will run until 1996. 9The Suicide Rangers 1964 AD MOON The first American spacecraft to get to the Moon was on a suicide mission. Before the Apollo spacecraft could send humans to the Moon, NASA wanted to send a series of robotic spacecraft there. First, they wanted to crash land a series of spacecraft to get close-up pictures. The spacecraft in this series were called Rangers. The first six Ranger spacecraft all misfired or went astray. Ranger 6 actually got to the Moon, but its camera broke down, so it didn't send pictures back. Ranger 7 was the first one to successfully crash into the Moon with all of its systems operating, landing within 16 kilometers (10 miles) of the point it was aimed at. It sent back 4,000 television pictures before it slammed into the Moon. This picture is one of those. It shows an area 420 kilometers (260 miles) wide. The failure of the first six Rangers caused severe strains within NASA, but the engineers learned from their mistakes. Starting with Ranger 7, the rest of the Rangers were successful. In all, three Rangers crashed successfully into the Moon, Rangers 7, 8 and 9. qThe Big Red Hurricane March 1, 1979 AD JUPITER Jupiter's Great Red Spot is so large that three Earths would fit inside it side by side. It's been seen for centuries with the help of telescopes. The spot is actually a huge storm, something like a hurricane. This picture was taken by the Voyager 1 spacecraft during its flyby of Jupiter from a distance of five million kilometers (three million miles). ├Rhea: Saturn Moon Nov. 12, 1980 AD SATURN ORBIT Rhea is one of the medium-sized moons of Saturn. It is 527,000 kilometers (328,000 miles) from the planet and measures 1,528 kilometers (950 miles) in diameter. It is a mixture of rock and ice. This photo was taken by the Voyager 1 spacecraft during its flyby, when it was 1.7 million kilometers (one million miles) from the moon. The colors here have been somewhat exaggerated by the computer to show the delicate surface features. /Robot Bugs to Mars 1989 AD CAMBRIDGE, MASSACHUSETTS This is a remarkable insect-like robot designed at the Massachusetts Institute of Technology (MIT). Engineer Rodney Brooks designed a six-legged robot as a way of overcoming some of the difficulties that a robot has in getting around. We humans have two legs, allowing us to walk over obstacles. But it's very difficult to make a two-legged robot, because it's hard to keep properly balanced. Our complicated brains and our sense of balance allow us to walk without falling over. Wheeled robots can get around fine on sidewalks and smooth hallways, but they cannot climb over obstacles. Brooks devised this robot to walk like an insect. With the ingenious use of artificial intelligence (on-board computers), he was able to make them climb effectively. One day, such robots may be sent to Mars. They could land at a safe spot where the surface is smooth. Then many small, insect-like robots could climb out and explore the dangerous places of Mars. If one or two were lost, falling over cliffs, it would not endanger the whole mission. ûCanada's Mechanical Arm August 1981 AD TORONTO, ONTARIO The Remote Manipulator System, originally nicknamed Canadarm, was built as part of Canada's commitment to NASA's shuttle program. Its purpose is to load or unload equipment and satellites from the shuttle cargo bay while in space. Normally stored on the left side of the shuttle, it's 15 meters (50 feet) long and 38 centimeters (15 inches) in diameter. The robot arm has six degrees freedom of movement and can handle up to the maximum 30 tons of payload. Run by an astronaut known as a mission specialist, the arm can be controlled from inside the shuttle with the help of a closed circuit television system or from a special "cherrypicker basket" attachment on the arm in the cargo bay. The mechanical arm has shoulder, elbow, and wrist joints run by electric motors, and mimics human movement with precision. The end of the arm can be fitted with special "end effecters" (tools) to perform specialized tasks. The astronauts have kidded each other about using the grasp attachment to scratch their backs during spacewalks. On Shuttle Mission 7, after successfully using the robot arm, Sally Ride and the crew reported, "We pick up and deliver." The Krazy Komet 1945 AD GERMANY The rocket-powered Messerschmitt Me 163B Komet was not for the faint-hearted. It was one of the most fascinating aircraft to emerge from World War II, but you had to have a strong sense of adventure and very little regard for your own life to fly the thing. Germany was getting desperate as the Allied armies closed in and as American and British bombers became increasingly bold. To counter the threat, scientists working for the Nazi regime came up with this blazingly fast little rocket-fighter, which was six meters (18.5 feet) long with a nine meter (30 foot) wingspan. The Komet's engine mixed two chemicals the Germans called "T Stoff" and "C Stoff." When the two touched each other, they burst into violent flame, so all the Komet had to do was pump the T and the C into the combustion chamber, where it ignited and propelled the plane. The problems with the Komet were numerous. First of all, it only had fuel for a little over four minutes at full throttle, so you couldn't launch it until the enemy was in sight. Pilots usually rocketed up to nine kilometers (30,000 feet), which only took two-and-a-half minutes. Then they dived on the Allied bombers, hoping to shoot one or two down as they sped through their formations. But the Komet was so fast that the pilot only had about three seconds to aim and fire. Then he was out of fuel and had to glide home and land on the plane's skid (the Komet dropped its wheels on takeoff). If it was a rough landing the pilot might be killed from the impact, or left-over fuel might get mixed together and explode the little craft. For that matter, Komets sometimes exploded just sitting on the runway. Of the 300 Komets that were made, most were destroyed by accidents. They were more dangerous to their own pilots than to the enemy. ▄Keeping the Planets in Place 1659 AD THE HAGUE, NETHERLANDS Rollercoasters show us an important principle you need in order to understand gravity -- centrifugal force. This is the force that keeps the people safe in their rollercoaster cars even when they are upside down. Centrifugal force is what you feel when you whirl a ball on a string around your head. It tugs on your hand. It was first described by a Dutch physicist and astronomer, Christian Huygens. But it took Isaac Newton to combine centrifugal force with the idea of force in general to describe the laws of motion and gravity. Newton realized that a body that moves in a straight line will tend to continue in a straight line unless something interferes with it. If you throw a ball, it would move in a straight line, if it weren't for gravity pulling it toward the Earth. If you take that ball on a string and swing it and let go of the string, it moves off in a straight line until gravity tugs on it. If you keep holding the string instead of letting go, the ball moves in a circle, but you have to continually pull on it to keep it from flying away. The pull that bends the ball away from a straight line path is centrifugal force. If it were not for gravity, the Moon would fly away from the Earth in a straight line. In fact, the Moon moves roughly in a circle around the Earth, and there has to be a force -- just like the force of your hand on the string -- to overcome the centrifugal force of its circular motion. Newton called that force gravity. He realized that all bodies in the universe attract each other with gravity, and he calculated precisely how strong that gravity is. It depends on the mass of the bodies doing the attracting, and the distance between that body and the one being attracted. On the Moon, where gravity is only one-sixth of Earth's gravity, you could make a rollercoaster go in slow motion, and the upside-down people would still not fall out. The smaller centrifugal force would still be stronger than the force of gravity. └The Expensive Moonmobile 1971 AD MOON It is one of the most unusual and expensive automobiles ever built. Called the Lunar Roving Vehicle, or just Rover, it looks like a backyard-built dune buggy. But looks can be deceiving. This special vehicle was built by NASA to extend astronauts' reach while on the Moon for the final three Apollo lunar landings. The buggy had no steering wheel or foot brake. It was operated using a hand device between the seats that could be controlled by either passenger. The controls also featured a gyroscope and computer that would calculate the direction and distance to the spaceship. After all, it wouldn't do to get lost on the Moon. On the front the rover had a television camera, and on the back containers for Moon rocks. Its fat, flexible wire-mesh wheels were covered with tread made of titanium, and each wheel was powered by its own quarter-horsepower electric motor driven by two 36-volt batteries. Top speed was about 7-8 miles per hour. £Sally Ride: Third Woman in Space June 18, 1983 ENCINO, CALIFORNIA The United States has had many "firsts" in space, but getting the first woman into orbit isn't one of them. Sally Ride, the first American woman in space, went into orbit on June 18, 1983, 20 years after the Soviet Union's Valentina Tereshkova became the first woman in space and less than one year after the Soviet Union's Svetlana Savitskaya became the second. Ride, a 32-year-old physicist from Encino, California, however, opened the door for American women to participate in space exploration, and several have been in orbit since her first journey. Ride, an expert in working the space shuttle's robot arm, was in charge of deploying and retrieving the SPAS-1 satellite, a task she successfully performed. It was the first time the robot arm had been used. Following the explosion of the space shuttle Challenger, Ride served on the presidential commission that investigated the disaster. j Salyut: Problems to Success 1971 AD EARTH ORBIT Though initially plagued with problems, the Soviet Union's Salyut space station program showed that persistence pays off, and that a permanent orbiting space station is an attainable goal. Salyut 1 was launched on April 20, 1971, followed three days later by three cosmonauts in the Soyuz 10 spacecraft, who successfully docked with the space station, but didn't enter Salyut. On June 6, 1971 Soyuz 11 brought Georgii Dobrovolsky, Vladislav Volkov and Viktor Patsayev to Salyut 1. They stayed 23 days, but when they returned to Earth a valve opened prematurely in their Soyuz craft, letting all the air out and killing the three cosmonauts. Before the Soyuz could be fixed, Salyut's orbit decayed and crashed into the atmosphere on Oct. 11, 1971. Salyut 2 failed to reach orbit, as did its backup, Cosmos 577. Salyut 3, 4 and 5 were successfully placed in orbit, but docking problems limited the number of times they were successfully occupied. But with Salyut 6, the Soviet Union began to benefit from its persistence. Salyut 6 was a newly-designed, long-duration space station. It had two docking ports, so the regular crew could attach its Soyuz spacecraft to one port and visiting crews (or unmanned cargo craft) could park at the other port. Salyut 6 was launched Sept. 29, 1977, and after one docking failure, was successfully occupied in December by Yuri Romanenko and Georgi Grechko of Soyuz 26. They hosted visiting crews and received Progress 1, an unmanned craft that brought food and fuel and took their garbage to a fiery crash into the Pacific Ocean. Romanenko and Grechko returned to Earth on March 16, having set a new endurance record for time in space: 96 days and 12 hours. It was just the first of several times over the next few years that Salyut cosmonauts would set endurance records. On April 19, 1982, the Soviet Union launched Salyut 7. Though its main oxidizer tank ruptured, the crew stayed to set another endurance record. The next crew to occupy the station fixed the ruptured tank. Then, on Sept. 27, 1985, the Soviet Union sent Cosmos 1686 aloft. Cosmos was like a room addition to Salyut 7. It docked at one end of the space station and increased its living area by about 50 percent and almost doubled its length. Salyut 7 was the last of the Salyut series, but not the end of the Soviet space station program, which continued with the Mir. ┘San Francisco: Not This Red 1849 AD SAN FRANCISCO, CALIFORNIA The San Francisco Bay Area in California isn't really this red. This is a false-color image taken by the LANDSAT 2 satellite from 925 kilometers (575 miles) up. The computer uses false colors to highlight different kinds of surfaces. For example, suburban areas and farmland appear as pink and red; desert areas as blue to light gray, and cities as light gray. Together with other local cities, San Francisco has become one of the largest metropolitan areas on the west coast of the United States. San Francisco was originally settled by the Spanish and became a major city during the California Gold Rush of 1849. Because of excellent harbor facilities, the area has become a major world port. %Europeans In Space 2000 AD EUROPE The Europeans are not content to let America and Russia send humans into space without competition. They have designed spacecraft they hope will one day carry European astronauts into orbit. The French, for example, have developed the Hermes design that they hope to launch on top of one of their Ariane rockets. The Germans favor an aerospace plane they call the Saenger, named after a pioneering German rocket engineer. It's designed to take off as a rocket and land as an airplane. But with the financial problems following the reunification of Germany, it's uncertain if this aerospace plane will be built. Still, in Germany there's a strong tradition of interest in sending humans into space, going back to the pioneering work of such Germans as Hermann Oberth and Wernher Von Braun. (Seeing Under the Sand 1990s SAHARA DESERT, EGYPT One of the most remarkable things you can do from space is to study the Earth with radar. Radar was developed during World War II to detect enemy planes by bouncing radio signals off them and picking up the echoes. Today, it's much more sophisticated. Synthetic aperture radar, for example, allows a small orbiting antenna to act like a huge antenna. As the satellite travels along its orbit, it regularly sends down radar signals. The signals bounce off the ground and are picked up by the satellite's antenna. The satellite then sends the information to Earth where a computer puts together all the signals from many minutes of observation. It's as if you had a huge antenna in space, and that allows you to see very fine detail. This is particularly effective in the desert. While moisture absorbs radio signals, in the desert the signals pass through the dry, soft sand to bounce off deeper layers. The result is that you can see ancient riverbeds that have been covered by sandstorms. This kind of radar can help find underground water in the desert, or detect lost cities of ancient civilizations. Already, archaeologists have used it in the Sahara Desert to find signs of ancient human life along lost riverbeds. It has also been used to find ancient Mayan canals in Central America. In 1994, Canada plans to launch such a spacecraft, called Radarsat, to study oceans, crops and the Arctic. The European Space Agency (ESA) now operates such a radar satellite. Called ERS-1, its pictures are being used to study crops and land use. Radar Mapping of Earth 1984 AD EARTH ORBIT Space-based radar can reveal aspects of our planet invisible to people on the ground. With such radar, the Earth can be studied as if it were not covered by vegetation. As long as the vegetation is dry, the radar peers right through it as if it were not there. In places where there is heavy jungle, the moisture sometimes prevents the radar signals from penetrating to the ground. In this way, geologists can see the true underlying rocks without being confused by the colors and shapes of trees, brush, grass and other plants that cover so much of the Earth. Furthermore, the brightness of the radar image tells much about the roughness of the ground. Very rough rocks reflect radar signals strongly and appear bright in such pictures. Smooth areas, such as much of the deserts of the world, reflect most the signal away from the spacecraft and tend to look dark. NASA is working with German and Italian researchers on the next generation of this type of radar for a mission called "SIR-C" to fly on the space shuttle. ╢The Clouds of Saturn August 19, 1981 SATURN This is one of the best pictures ever taken of Saturn. It is a close-up picture of the cloud tops of Saturn taken by Voyager 2. The computer has taken the browns and whites of the real Saturn and artificially colored them to make subtle differences clearer. All of the features we see are caused by clouds at different heights in Saturn's atmosphere. The color differences are due to chemical reactions that take place at different heights, where the temperatures are different -- higher levels being colder than lower ones. This picture was taken from a distance of seven million kilometers (four million miles), showing features as small as 130 kilometers (80 miles) across. úThe Make-Do Skylab May 14, 1973 AD EARTH ORBIT In the '70s, after the landing on the Moon, NASA's budget was tight. So instead of designing an orbiting laboratory from scratch, the space agency converted a rocket stage from a Saturn IB into orbital living quarters and a working area. The area originally intended for a liquid hydrogen tank was made into the living area, while a liquid oxygen tank was turned into a waste and trash disposal unit. On the upper floor of the two-story lab were storage facilities and experimental equipment. On the outside of Skylab there was supposed to have been a combination meteorite/Sun shield, but it wasn't there because it accidentally opened before the spacecraft was out of the atmosphere. The air ripped it off, and it, in turn, knocked off one of the giant solar panels and jammed another. Without the shield, Skylab was exposed to too much sunlight and began to overheat. As a temporary measure, NASA maneuvered it to expose less of its surface to the Sun. As a long-term solution, the first astronauts to inhabit the lab placed a reflective plastic "umbrella" between the lab and the Sun to cool it down. Astronauts Charles Conrad and Joseph Kerwin spent 28 days in the lab, performing experiments, before climbing back in the command module and heading home. The second crew to inhabit the lab stayed for 56 days, fixing the deteriorating Sun shield and the now failing gyroscopes. By the time the third crew arrived, Skylab was becoming a burden just to maintain. The cooling system was leaking and had to be fixed. Despite the maintenance problems, the crew spent a record 84 days aloft, still the American record for time in space. But Skylab was not to be a permanent space station. It was falling apart, and besides, it was slowly dropping closer to Earth because its giant solar panel was dragging against unexpected traces of atmosphere. It remained aloft for years, but finally, on July 11, 1979, it tumbled into Earth's atmosphere, breaking into a wild fireworks display over Perth, Australia. Amazingly, we now know a way that could have kept Skylab from falling. If the astronauts had only known about a concept known as tethers, they could have re-oriented Skylab. Using a weight and a tether (a long line), they could have tugged on Skylab so that it pointed horizontally instead of having its long axis pointing down towards the Earth. This would have reduced the air resistance that dragged it down, and kept it up longer. However, during the 10 months it was occupied, Skylab provided humanity with a wealth of information. Astronauts performed more than 250 experiments. They found they could create new alloys that can't be produced on Earth's surface and could grow crystals five times larger than on the ground. Spiders, they discovered, adapted quite well to life in orbit; their webs becoming just slightly disoriented. And Skylab accumulated a great deal of information about the Sun impossible to get on the ground. SSatellites on the Same Line 1992 AD EARTH ORBIT Sometimes when you are talking on the telephone you can hear two other people trying to carry on their own conversation. It's annoying and makes it difficult to understand the person you're trying to talk to. That is similar to a problem faced by scientists listening for radio signals that might be from intelligent beings from elsewhere in the universe. There is already plenty of radio noise from natural causes that complicates the search for extraterrestrial intelligence (SETI), but in today's high-tech world, there is also a man-made problem: satellites and more satellites. While satellites have made global communications relatively inexpensive -- which is great for just about everybody else -- for SETI scientists they are a real problem because they broadcast strong signals on the same frequencies they want to listen in on for weak signals. So, if E.T. was trying to call our house from space, who knows if he would be able to get through. Nobody, of course, really knows if there are extraterrestrials out there, and if there are, whether they are able to get in touch with us -- or even if they would want to. But if they are there and want to place a call to Earth, satellite broadcasts could drown them out. And even if they don't completely mask possible radio messages, satellite transmissions do make it more difficult to determine what might be significant. As more satellites are sent up, the problem will, of course, increase. In the 21st century, we may have to put a SETI system on the far side of the Moon to block out the interference from our own civilization. ÿThe Mysterious Rings of Saturn 1610 AD SATURN The rings of Saturn have mystified humans since Galileo first saw the strange oval shape of Saturn. He didn't know what he was seeing, and thought he might be seeing two moons. His telescope was not good enough to show the rings as we know them today. It wasn't until 1659 that a Dutch scientist, Christiaan Huygens, realized, with his excellent telescope, that Saturn was "surrounded by a thin, flat ring, nowhere touching." For centuries, astronomers wondered what the rings could be, and the public was struck by the beautiful and unique shape of Saturn. In the 19th century, the Scottish physicist, James Clerk Maxwell, concluded that the rings could not be solid, because they would be unstable -- they would crash into the planet sooner or later. Therefore, they had to be made of particles, a theory we now know to be correct. Scientists have actually bounced radar signals off the rings of Saturn all the way from Earth. Analyzing the signals tells us that the typical Saturn ring particle is probably a ball of ice about the size of a snowman one meter (one yard) in diameter. Saturn was first visited by the Pioneer 11 spacecraft in 1979. This was followed by the more sophisticated Voyager 1 in 1980 and Voyager 2 in 1981. For centuries it was thought that Saturn was the only planet with rings around it, but now we know that all of the giant planets have rings -- including Jupiter, Uranus and Neptune. Their rings, however, are very faint and can only be seen by spacecraft or with special astronomical equipment from Earth. What causes the rings? One likely source is collisions between moons. The moons, if they pass too close to each other, can crash, and the pieces then orbit the planet in the form of rings. One theory of the origin of our own Moon is that a Mars-sized planet crashed into the Earth, and the pieces of the shattered Moon formed a Saturn-like ring around the Earth. Eventually, the pieces collected into the present-day Moon, attracted by gravity. The Voyager spacecraft also found strange markings in the rings, called spokes. The spokes move around the rings like a solid bicycle wheel. This seemed to be impossible, because the rings are not solid. In fact, each ring particle is in a separate orbit. The ones closest to Saturn move the fastest, and the ones farther away move slower, so how could there possibly be a solid structure orbiting around Saturn? The answer is probably that the spokes are actually dust that is electrically charged by ultraviolet sunlight or by the electrons and protons bouncing around in the planet's magnetic field. Saturn has a strong magnetic field, like Jupiter, and the magnetic field sweeps up electrically-charged particles, causing them to rotate with the planet, as if they were attached to it. Studying the rings of Saturn and the other outer planets has helped us to understand how the solar system formed, and how the Earth and Moon probably came to be. ⌐Saturn and Satellites SATURN Beyond Jupiter comes Saturn, a giant planet famous for its brilliant rings. Saturn is similar to Jupiter, but 16 percent smaller in diameter and one-third as massive. It has many moons, but only one of them, Titan, is large. Titan is especially noteworthy because it's the only moon in the solar system with a thick atmosphere. Saturn was first visited by the Pioneer 10 spacecraft, and then by Voyager 1 and 2. ]The Most Beautiful Planet 1980 AD SATURN Seen through a telescope, Saturn is the most beautiful of the planets because of its rings. Even though Jupiter, Uranus, and Neptune all have rings, they are feeble and impossible to see from Earth under most circumstances. Saturn's rings, however, have been seen for centuries. They are so bright and broad that even a small telescope can sometimes detect them. As a planet, Saturn is very much like Jupiter, a gas world made mostly of hydrogen, with helium, ammonia, and methane gases as well. It is the next planet out beyond Jupiter, the sixth planet from the Sun. It has one-third the mass of Jupiter, but almost a hundred times the mass of the Earth, so it is another giant planet. Saturn is 120,000 kilometers (75,000 miles) in diameter, about ten times the size of the Earth. It is roughly twice as far from the Sun as Jupiter and ten times farther from the Sun than Earth. It takes 29 years for Saturn to orbit the Sun. It is has only one large Moon, Titan, but about two dozen smaller ones. Like Jupiter, Saturn has bands of clouds and raging storms, although the features are not as dramatic as on Jupiter. Also like Jupiter, Saturn has a strong magnetic field, although not as strong as Jupiter's. Saturn was first visited by the Pioneer 11 space probe in 1979, and then by Voyagers 1 and 2 in 1980 and 1981. This picture is a Voyager image. zSaudi Arabia: Just a Few Farms SAUDI ARABIA The curious green circles you see in this satellite picture show how dry the country of Saudi Arabia really is. These are farmlands irrigated with underground water, pumped through a sprinkler system that spreads the water in a circular pattern. Notice how brown the desert is by contrast. In fact, almost all of Saudi Arabia's 2.2 million square kilometers (840,000 square miles) is desert. Only about two percent is fit for agriculture, and much of that little bit is used to grow dates. Fortunately for Saudi Arabia, it owns about 30 percent of the world's oil reserves, so it does not need to rely on farming. ùSDI: The Star Wars Defense 1983 AD EARTH ORBIT In March 1983 US President Ronald Reagan announced the Strategic Defense Initiative (SDI, popularly known as "Star Wars"). It came as a major shift in defense policy. Prior to the speech the US and the USSR followed a policy of Mutual Assured Destruction (MAD), meaning any attack on the US or its allies would result in a swift, massive counter-strike. Both sides would not want to strike first because that would leave them open to destruction. The Star Wars proposal changed this concept by attempting to raise a shield against incoming missiles. The first part of this shield would be space based, with lasers, particle beam weapons, electromagnetic railguns, and mirror satellites. The beam weapons shoot particles: atoms, electrons, protons and neutrons, acting much like lasers. Railguns use electromagnetics to accelerate an object to very high speeds (32 - 80,000 kilometers per hour or 20 - 50,000 miles per hour). These weapons would probably be powered by nuclear reactors or by nuclear explosions. The mirror system would be powered by ground-based reactors and would use their mirrors to reflect laser or particle beams flashed to them for aiming. The entire system would be activated and guided by spy satellites watching for rocket launches. While these first-line weapons continued firing, the next layer of the shield, called Brilliant Pebbles, would be activated. This is essentially a string of explosive canisters strewn in the path of oncoming missiles, though some would be self-propelled and aimed at their targets. The final phase would include an updated version of the antiballistic missile (ABM) system of the 1970s, antisatellite missiles launched from aircraft, and ground-based laser and beam weapon installations. The program was criticized on a number of points. The Soviet Union said it was a first-strike system, meaning that whoever had it could hit the other side first, and be able to withstand a counter-strike. This would allow that country to hold everyone else hostage. Besides, the Soviets said, they could counter the defence by using multiple-warhead missiles and decoy systems. Financially, some estimate the SDI systems could cost more than a trillion dollars. With the end of the Soviet Union, the need for SDI is lessened, though some feel parts of the system could be used in antiterrorist operations. Technologically, critics said there is no hardware capable of withstanding the stresses of space war, no computer that can perform the necessary calculations and no software that can handle all the incoming data. They also complained that there is no way to really test it since a true test means someone would have to launch an all-out attack. Some of the ideas turned out not to work in tests. Other parts of the systems have been built, with mixed successes. The Star Wars program continues, but the end of the Cold War has caused more legislators to question the need for it. PMapping Earth's Surface 1978 AD EARTH ORBIT SEASAT (Specialized Experimental Applications Satellite) was a NASA satellite launched in 1978 to study the oceans. It pioneered the use of orbiting radar to measure ocean waves and currents. Its transmitter broadcast radio signals that bounced off the rough surface of the ocean. The amount of reflection depended on the ocean waves, so scientists could map the waves from orbit. It only lasted about three months on orbit. Then, a short circuit ended its broadcasts. However, it had taken enough data to provide oceanographers with much information about the seas. Radar techniques used on SEASAT helped inspire the use of radar on American and Soviet Venus orbiters such as NASA's Magellan spacecraft. TOPEX, a descendent of SEASAT, was launched in 1992. It uses a more advanced radar to continue the study of the oceans. αA View of the Ocean Bottoms 1978 AD EARTH ORBIT One of the unexpected results of looking at the Earth's oceans with radar was this picture of the bottoms of the seas. The SEASAT satellite had a very sophisticated radar that measured the precise height of the spacecraft above the ocean as it flew over. It found that the height of the ocean varied unexpectedly from place to place. This turned out to be because of the gravitational attraction of rock. Rock is denser than water, so it has a stronger gravitational attraction than water. The very slight gravitational attraction of the rock causes slight dips and pile-ups of ocean over underwater canyons and mountains. As a result, SEASAT was able to map the bottoms of the oceans in a way that no one had ever seen before. Previously, scientists used measurements made from ships, with probes and sonar laboriously measuring the depth at each point of the ocean. Now, from space, we can see islands rising out of the ocean, underwater mountains and deep canyons -- all from a global perspective. These underwater features are caused by the slow drift of the Earth's continents on top of the Earth's molten interior. SEASAT proved once again that often the results of exploration are unexpected insights into our world. ≡Stages to Space EARTH'S ATMOSPHERE One of the difficulties of getting into space is weight. The more something weighs, the more difficult it is to boost it into orbit. To overcome this problem, most rockets are built in sections, or stages. As the lower stages consume their fuel, they fall off -- as you can see here -- so they do not burden the rocket on its upward flight. Because of this, the portion of a rocket that actually makes it into space is just a fraction of what came off the launch pad. $SETI: The Big Search 1992 AD GOLDSTONE, CALIFORNIA NASA wanted to build the most powerful SETI (Search for Extraterrestrial Intelligence) system in the world. They wanted to look for radio signals from other civilizations. The scientists built on the ideas of SETI pioneers Frank Drake, Giuseppe Cocconi, and Philip Morrison, who believed the easiest way to detect another civilization in the galaxy, if it exists, is to find its radio signals. Several dozen such searches have been conducted since Frank Drake's first project Ozma in 1960, but all of them have been limited to small parts of the vast radio spectrum. Most of the electromagnetic spectrum (radio, light, X-rays, etc.) is not suitable for communication between stars because of noise at long and short wavelengths. But there is a nice region where the galaxy is fairly quiet. This is roughly from 1 to 10 gigahertz (1 to 10 billion cycles per second), the microwave region of the spectrum. Microwave ovens and communications satellites use these waves. NASA proposed surveying this entire region, though this would be an enormous task because there are billions of potential channels. For example, if the spectrum is divided into one-hertz-wide channels, then there are nine billion channels between 1 and 10 gigahertz. To search such a large number of channels within a few years, NASA wanted to build receivers able to see about ten million channels at once. Throughout the 1980s, engineers and scientists developed circuits, devised electronic chips, and studied the many difficulties of making the system. Another problem NASA had to face is our own noisy civilization. Automobiles often have noisy ignition systems that cause interference. There are thousands of different types of transmitters on Earth, from police radios to taxi drivers to military communications. Then there are communications satellites which sometimes broadcast signals that can be detected when the antenna points toward the satellite. And there are military satellites that broadcast on secret schedules. NASA scientists wanted to be sure they would not be fooled by a false alarm. It would be very embarrassing to announce that contact had been made with another civilization only to discover it was someone's spy satellite. So an important part of the development of the NASA system was to study Earth's radio noise and develop software to automatically reject it so the scientists would not be overwhelmed by false alarms. Another problem was designing computer software to automatically look for intelligent signals, taking into account that the signal may drift due to the movement of the sending transmitter. The analysis had to be quick because otherwise the SETI system would accumulate a huge amount of data that would pile up into a hopeless task. Next was the problem of where to look. Some scientists think we should look mainly at stars that are similar to our own Sun, because this is where life is most likely to be. Stars that are very different from our Sun probably won't allow life to exist -- they'll be too unstable or short-lived. Others think we should look over the entire Milky Way Galaxy, without assuming what kind of life might exist out there. NASA decided on a two-pronged approach. The group at the NASA Ames Research Center in Northern California chose a targeted approach, looking at a thousand nearby stars similar to our Sun. The other NASA group, at the Jet Propulsion Laboratory (JPL) in Southern California, chose to examine the entire sky systematically, called an all-sky survey. The whole two-pronged program is officially called HRMS (High-Resolution Microwave Survey). The targeted search is more sensitive because a particular star can be observed for a long time. The all-sky survey, however, takes in the entire sky, initially looking at the Northern Hemisphere and eventually moving down into the Southern Hemisphere. Initially, the targeted search will begin with the world's largest radiotelescope, the 305-meter (1,000-foot) Arecibo antenna in Puerto Rico. However, the time available on large radiotelescopes is very limited, due to competition with astronomers who want to observe other objects. So the search will be moved to different radiotelescopes. The system was designed to be portable, transported in a trailer, so it can be shipped to radiotelescopes around the world. The all-sky survey will look at the full 1-10 gigahertz spectrum using NASA's 34 meter (112 foot) diameter antenna at the Goldstone station in Southern California. This station is part of NASA's Deep Space Network (DSN), and is located not far from Edwards Air Force Base, where the space shuttle sometimes lands. The NASA system was scheduled to be turned on on the 500th anniversary of Christopher Columbus' voyage to the New World, October 12, 1992. This was meant as a tribute to the exploration of the world, and a symbol of the greatest search ever: The search for other civilized worlds that may be waiting for us to discover them. Both systems are expected to last at least five years, if Congress continues to provide the money needed. It will take at least that long to survey the universe at all of these frequencies. Unfortunately, politicians love to attack SETI on the grounds that it is a waste of taxpayers' money to look for "little green men." It only costs about $10 million a year for the program, peanuts by Washington standards. But it's politically easier to attack than some billion-dollar program with a large voting bloc behind it. So the future of NASA's SETI is uncertain. Until now, scientists had to guess what frequencies to monitor. The most popular, proposed by Cocconi and Morrison in 1959, is the frequency of hydrogen atoms, 1420 megahertz. However, the NASA system will not rely on such guesses, so it offers the best chance of receiving the first confirmed signal from another civilization. Even if NASA does not detect another civilization, there is a good chance that this unprecedented search will discover new astronomical phenomena, because the radio sky has never been so thoroughly searched before. The 1990s may become known as the decade of SETI. WMaybe ET is Down South 1990 AD BUENOS AIRES, ARGENTINA On Columbus Day, 1990, Argentine astronomers began the world's first long-term search for extraterrestrial intelligence (SETI) in the Southern Hemisphere. Years earlier, Argentine scientists and engineers had built two radiotelescope antennas near Buenos Aires. Each is 30 meters (98 feet) in diameter. They were designed to look at the universe, studying natural radio signals. Then the Argentine Institute of Radio Astronomy reached an agreement with The Planetary Society of Pasadena, California to allow Argentine engineers to construct a duplicate of a SETI system that had been built at Harvard University. There had been almost no searches of the southern sky for extraterrestrial civilizations. Most of the SETI work had been done on radiotelescopes in the Northern Hemisphere. But nearly half of the universe cannot be seen from the Northern Hemisphere. Also, the center of our own Milky Way Galaxy is in the Southern Hemisphere, and two of the closest galaxies -- called the Magellanic Clouds -- can only be seen in the Southern Hemisphere. For this reason, if an extraterrestrial civilization exists in the Southern Hemisphere, it might not have been detected by other SETI searches. To set up the program, two Argentine engineers traveled to Harvard and spent a year studying and duplicating physicist Paul Horowitz's SETI project called META. They then installed the electronic equipment at one of the Argentine radiotelescopes, and called the project META II. Since 1990, the Argentine scientists have been scanning the skies of the southern universe, looking for E.T. ≡SETI Around the World 1992 AD GOLDSTONE, CALIFORNIA The NASA Search for Extraterrestrial Intelligence (SETI) program will use antennas all over the world for its observations. To begin with, the NASA SETI systems will be used in California and Puerto Rico. A 34 meter (112 foot) diameter antenna at the NASA Deep Space Network (DSN) at Goldstone, in the Southern California desert, will systematically search the whole sky. And at Arecibo, Puerto Rico, the giant 305-meter (1,000-foot) dish antenna will be used for a month to look at some of the stars nearest the Sun. This targeted search uses equipment that will be transported to other observatories around the world. There is a possibility that some of the equipment may even be used on the Russian Deep Space Network. ┘SETI by Suitcase 1985 AD CAMBRIDGE, MASSACHUSETTS In 1981, the NASA Search for Extraterrestrial Intelligence (SETI) program was temporarily killed by Senator Proxmire, who thought it was a waste of money. As a result, scientists wishing to do SETI had to use money from private organizations. A Harvard scientist who had been visiting the NASA SETI scientists, Paul Horowitz, conceived a design that would be smaller and cheaper to build than the large NASA SETI system. It couldn't do everything the bigger system could, but it could be built for so much less money that it might be funded by a private group. A new organization, The Planetary Society, had recently been formed by astronomer Carl Sagan and other scientists. The society relied on private members to support its programs, and they agreed to provide money to allow Paul Horowitz to build his SETI system. With help from NASA scientists, Horowitz built a system called Suitcase SETI, and took it to the giant Arecibo radiotelescope in Puerto Rico. There, he tested the system, looking at some nearby stars similar to the Sun. It worked fine. When he got back to Harvard, he discovered a radiotelescope that was about to be mothballed. Located in a town called Harvard, Massachusetts, a few miles from the university, it had a 26 meter (85 foot) dish antenna. With more help from The Planetary Society, he installed Suitcase SETI permanently at this place and called it Project Sentinel. Suitcase SETI used computer-like electronic circuits to observe 131,000 radio channels. The antenna would be locked into one position for 24 hours while the Earth rotated. In this way, a strip of the sky, typically one-half a degree wide, would be scanned while the Earth rotated. During the scan, 131,000 different radio channels would be studied for artificial signals from space. Usually, the receiver is tuned to a frequency band that astronomers think another civilization would use if it wanted to be detected. A favorite choice is the frequency of hydrogen atoms, 1420 megahertz (often called by its wavelength, 21 centimeters). The universe is filled with hydrogen atoms that broadcast radio signals at this frequency, so any civilization with radio astronomy should know about these signals. It's a natural channel, then, on which to broadcast a signal if you want it to be noticed. Horowitz used 131,000 radio channels closely spaced around this 1420 megahertz channel. After observing with the system for some time, Horowitz realized it would be useful to search many more channels. There were various reasons why a civilization might broadcast a signal near the 1420 megahertz band, but not necessarily exactly within the frequency band he was observing with Sentinel. So he designed a system with 64 times as many channels, eight million channels in all. At this time, Steven Spielberg, director of the movie E.T., gave The Planetary Society $100,000 to turn Project Sentinel into the eight million channel system. The new system, using the same antenna, was then named Megachannel Extraterrestrial Assay (META). Steven Spielberg turned on Project META in 1985, and it has been observing 8 million channels ever since. So far, no signal from another civilization has been detected. As a result, Horowitz is now building a system that will have 160 million channels, and eventually this will probably be expanded to a billion channels. In the meantime, Argentine scientists are using their duplicate of META, known as META II, to observe the universe from the Southern Hemisphere. CThe Longest Search 1973 AD COLUMBUS, OHIO The world's longest-running search for extraterrestrial intelligence (SETI) has been operating since 1973 in Columbus, Ohio. Radioastronomers John Kraus and Robert Dixon have used the Ohio State University radiotelescope to search for intelligent signals from space. Despite the extreme difficulty in raising money for the search, these dedicated scientists and their colleagues have worked year after year, looking for that beep that might be the first proof of an alien civilization. Of the many difficulties encountered in searching for these signals, one of the greatest turned out to be completely unexpected, a golf course. After the Ohio State SETI system had been running for a number of years, the land on which the radiotelescope sat was sold to a golf course. The developers wanted to extend the golf course and obliterate the radiotelescope. But after a public outcry heard around the world, a compromise was reached, allowing the radiotelescope to continue its observations. The radiotelescope continues to do both radio astronomy and SETI to this day. 4SETI from the Land of Oz 1960 AD GREEN BANK, WEST VIRGINIA The first modern search for extraterrestrial intelligence (SETI) was named after the Wizard of Oz. In 1960, Frank Drake, a radioastronomer, turned his radiotelescope onto two nearby stars, Epsilon Eridani and Tau Ceti. He tuned the radio to the frequency of hydrogen atoms, 1420 megahertz. He was looking for signals from any civilization that might exist around these stars. He named his project "Ozma," for the queen of the imaginary land of Oz, which he described as "a place very far away, difficult to reach, and populated by exotic beings." The first star he looked at showed no signals. But when he turned the antenna toward the second star, he got some strange, strong artificial radio signals. And when he turned the antenna away from it, they disappeared. Had he detected another civilization? For days, he studied the sky thoroughly. Sadly, he discovered that, in fact, what he'd first detected was just an accident. He had unexpectedly picked up radio signals from a military experiment. People often wonder, why don't SETI scientists look for unidentified flying objects (UFOs)? The reason is that most scientists think that UFOs are incorrectly identified natural phenomena (airplanes, balloons, stars, planets) or hoaxes. There is no UFO report that is generally accepted in the scientific world as reliable. Scientists are skeptics. Science is all about doubting someone's claims, testing them. We need to see solid proof before we'll believe anything unusual. And this is what leads SETI researchers to look for astronomical proof of other civilizations. If SETI ever finds an artificial signal coming from another star, then every astronomer in the world can prove that it's real. Only then will scientists be convinced that there are other civilizations in the universe. Even though Drake did not discover a radio signal from another civilization, his experiment was the first in modern SETI research. It has served as the model for most of the SETI work that has followed. PHOTO CREDIT: Courtesy of National Radio Astronomy Observatory. ╤Science Fiction: An Amazing Story 1926 AD UNITED STATES The first American magazine to publish science fiction only was called Amazing Stories. And behind Amazing Stories is an amazing -- or at least interesting -- story. In 1926, Hugo Gernsback was the owner of a magazine called Modern Electrics. One day, he found that he had a blank spot in his publication, so he dashed off the first chapter of series called "Ralph 124C 41+." "Ralph" was an amazing success. The 12-part story was filled with all kinds of wild inventions unheard of in 1926, including television, fluorescent lighting, juke boxes, solar energy, television, microfilm, vending machines, and a device we now call radar. In fact, Gernsback described radar so precisely that when Sir Watson Watts of Great Britain applied for a US patent for radar, the Patent Office turned him down. Gernsback had, in a sense, already invented it. In "Ralph 124C 41+," Gernsback recognized a trend, so he began publishing a pulp magazine, "pulp" referring to the cheap paper made from wood pulp. He called it "Amazing Stories," and it was an instant success. Though "Amazing Stories" and its many imitators were popular, the paper shortage of World War II put many of them out of business. Some of them still survive, including "Amazing Stories," "Fantasy and Science Fiction," and "Analog" (originally called "Astounding"). These magazines reprinted 19th century science-fiction of such greats as Frenchman Jules Verne and Englishman H.G. Wells. But it went beyond them to introduce new writers who made the field so popular. They included Americans such as Edgar Rice Burroughs, Isaac Asimov (who now has a magazine named after him), Ray Bradbury, Frederik Pohl, and Robert Heinlein; and the Englishman, Arthur C. Clarke. Blast off to Nowhere 1978 AD HUNSTVILLE, ALABAMA The Marshal Space Flight Center in Huntsville, Alabama, was in charge of the space shuttle's main engines, called SSMEs. Rockwell Rocketdyne built them in the late 1970s and early 1980s. The engine design was upgraded after the January 1986 Challenger loss. A single engine stands 4.2 meters (14 feet) tall, is 2.4 meters (eight feet) in diameter at the flare of the nozzle, and produces 220,000 kilograms (488,000 pounds) of thrust. Unlike previous rockets, the engines are designed to be reusable for many missions. The engines burn a mixture of liquid hydrogen and liquid oxygen under high pressure (200 kilograms per square centimeter or 3,000 pounds per square inch). Three main engines are used together on the shuttle, capable of a total of 680,000 kilograms (1.5 million pounds) of thrust. Located in the aft section of the shuttle in a triangular pattern, the main engines can swivel up and down 10.5 degrees and side to side 8.5 degrees, thereby allowing the spacecraft to steer. The huge external tank strapped on the outside of the space shuttle orbiter (the airplane-like part in which the astronauts fly) contains the main engines' fuel. It is burned in two stages. First, it's pumped to special "sparkplug" igniters, where it is partially burned at low temperature in "pre-burners." Then under high pressure, it is turbine-pumped to igniters in the main combustion chamber (nozzle). The main engines burn for the two minutes of the assist from the two large external solid rocket boosters (SRBs), at which point the SRBs break away and parachute to the ocean for recovery. The main engines continue to burn for another six minutes, drawing more than 180,000 liters (47,000 gallons) of liquid hydrogen and 64,000 liters (17,000 gallons) of liquid oxygen a minute. Computer controlled, the engines' thrust can be varied from 65 percent to 109 percent of their rated (normal) power for controlling the flight to orbit. The three main engines generate enough energy to light Manhattan Island for seven minutes. Once the shuttle is orbiting Earth, the main engines shut down and are never fired again until the next launch from the ground. Instead, the two small orbital maneuvering system (OMS, pronounced "ohmz") engines are used to change orbit, and to re-enter the atmosphere. ïShuttle Piggyback 1980s-1990s AD EDWARDS AIR FORCE BASE, CALIFORNIA One little problem with the space shuttles is that after they re-enter the Earth's atmosphere, they are basically gliders. Big, heavy, supersonic gliders, perhaps, but gliders nevertheless. Their rockets are never fired after re-entry. The difficulty here is that once the shuttle lands at, say, Edwards Air Force Base in California, it cannot, under its own power, get back to Cape Canaveral, Florida, for another flight. NASA's solution is to fit an aerodynamic cowl (hood) over the shuttle's tail, hoist it atop a specially-modified Boeing 747 jet and carry it piggyback cross country to its launch site. HThe Shuttle Landing Site 1980s-1990s AD EDWARDS AIR FORCE BASE, CALIFORNIA As you can see from this photograph, the space shuttle lands just like an airplane. Nose up, rear wheels touching the landing strip first, then the front wheel, then the shuttle brakes to a stop. The landing site, Edwards Air Force Base in the Mojave Desert of California, is a good place to land. The base has long been home to experimental aircraft and the generally clear weather in the desert makes it fairly certain the shuttle will not encounter rough weather as it comes home. This is particularly important since the vehicle is a glider once it has begun its descent and the pilot cannot change landing sites at the last minute. After landing, the shuttle is hoisted onto the back of a special NASA Boeing 747 jet to be ferried back to Cape Canaveral, Florida, for another trip into space. The Flying Brickyard April 12, 1981 AD CAPE CANAVERAL, FLORIDA The first flight of the world's first reusable spacecraft was almost perfect: but not quite. At the conclusion of the mission, NASA found that 16 of space shuttle Columbia's heat-shielding tiles had fallen off and another 150 had been damaged. On the inside, the only problem was that the zero-gravity toilet broke: fortunately, just before re-entry. The critical point of the 54-hour mission was re-entry. How would the spacecraft's heat-shield tiles hold up under the extreme temperatures generated during first contact with the air? As Columbia hit the atmosphere after 36 orbits, the tiles on its underside glowed red and the resulting ionized air (electrons ripped off atoms) cut off communications for 21 minutes. Despite the lost tiles, it came through without a problem, and pilot Robert Crippen glided the space plane to a clean landing at Edwards Air Force Base on April 14, 1981. "What a way to come to California," he said. Columbia was a departure from previous spacecraft in that it could be used time and again. The American Rocket Society and the British Interplanetary Society had long before suggested such a vehicle, and NASA scientist Wernher von Braun had pointed out the advantages of a reusable space vehicle as far back as the 1950s. But it wasn't until March 1970 that President Richard Nixon announced plans for the shuttle program. To test the concept, NASA first built an experimental model for atmospheric tests called Enterprise, after the spacecraft in the television show "Star Trek." But the first real space shuttle was Columbia, and like many new technologies, Columbia at first had problems. On its flight from California to its launch site at Cape Canaveral, Florida -- flying piggyback on a 747 jet -- thousands of the tiles fell off. This delayed its launch and earned it the name "Space Lemon" from critics. The 30,000 tiles glued to the spacecraft also gave it the more affectionate nickname, "The Flying Brickyard." The Columbia should have flown in 1979, but because of the lost tiles, the launch date had to be delayed until the end of March 1981. But then a computer malfunction delayed lift-off again. Finally, on April 12, the Columbia roared off into the sky, its rocket engines -- the most efficient ever built -- generating the power of seven Hoover Dams. The trip began a new era, designed to make space flight routine. Columbia and its sister shuttles would soon be used as moving vans to deploy satellites, pick them up, or fix them right there in outer space. `Going to the Simulations Here is a list of the simulations in Space Adventure. To see a simulation, click on its name. ┤Sinai From On High SINAI PENINSULA The dry land far below you is the Sinai Peninsula, famous as the land through which Moses led the Israelites after their escape from Egypt. Among the mountains at the lower end of the peninsula is the famous Mt. Sinai, where the Bible says God gave Moses the Ten Commandments. In this space shuttle view, you can also see the Nile River on the lower left of the screen and the Mediterranean Sea in the upper left. The small inlet on the right is the Gulf of Aqaba, and the larger one is the Gulf of Suez. They connect with the Red Sea at the lower right. At the upper tip of the Gulf of Suez you can see the Suez Canal cutting across the desert to the Mediterranean Sea. uThe Milky Way by Infrared 1993 AD EARTH ORBIT Two spacecraft are being built that will study the Milky Way with infrared telescopes. The European Space Agency is building ISO (Infrared Space Observatory), to be launched in 1993. NASA is building an even more powerful one called SIRTF (Space Infrared Telescopic Facility), but it won't be launched until the year 2000. These two telescopes will use advanced infrared technology to study the Milky Way. Analyzing the heat-glow of the galaxy in infrared light will show us the concentrations of gas and dust in which stars are born. This will help us understand how our own star and solar system came to be. ;Light You Can't See EARTH ORBIT Though much of it is invisible to the human eye, the universe is filled with light. Much of this invisible light is called infrared, which means it is redder than red, with a longer wavelength than visible light. Warm objects give off infrared light that can be seen on Earth with special night-vision devices, such as those used by the military to detect enemy vehicles. In the galaxy, objects that do not glow brightly enough to be seen are frequently warm enough to create infrared. Moisture in our atmosphere absorbs much of the infrared light from space, and our own atmosphere glows with infrared. This makes it difficult to do infrared astronomy from the ground, except at a few wavelengths. The best way to do infrared astronomy is to use infrared telescopes in rockets or satellites. Using these, infrared astronomers have discovered that the Milky Way has many clouds of gas and dust that emit strong infrared light. Some of this infrared is from molecules floating in space. Other infrared is from particles of dust. Nearby stars heat up the clouds, making them warm, and then the dust glows with infrared light. Astronomers suspect that much of the galactic dust is made of carbon, very much like ordinary soot. Dust is very important because it's the first stage in the formation of planets like Earth. ╕Jupiter's Snakeskin 1979 AD JUPITER This is Jupiter's "snakeskin," the nickname for a series of Jupiter photos stretched out as a Mercator-projection map. The pictures are stored in a computer and then put together as a rectangular image. The top view shows Jupiter as it looked to Voyager 1, and the bottom, to Voyager 2. Notice the differences between the images. What we're seeing are the clouds and storms of Jupiter, moving in bands around the giant planet. :Supernova Light Ring 1987 AD LA SERENA, CHILE When a large star runs out of fuel, it often explodes in an incredible flash of energy. Such an explosion is called a supernova. A supernova can be as bright as an entire galaxy of hundreds of billions of stars, though only for a few days. Supernovas are rare. None has been seen in our Milky Way galaxy for four centuries, probably because there is so much dust in the galaxy that it blocks our view of many of the other stars. In 1987, astronomer Ian Shelton saw the next best thing. He was at the Las Campanas Observatory in Chile, where he discovered a brilliant new star in a nearby galaxy called the Large Magellanic Cloud. He knew that it is extremely rare to see a nearby supernova, but that's what it was. He'd become the discoverer of the star astronomers would call supernova 1987a. Although the supernova explosion was observed in 1987, the star actually exploded 160,000 years ago. But the Large Magellanic Cloud is located 160,000 light years from us, so it took all that time for the light to get here. This picture was taken by the Hubble Space Telescope, with a camera designed by the European Space Agency. The elliptical ring around the exploded star is not completely understood. Presumably, it is matter that is glowing in the light from the energy of the explosion. Astronomers expect debris from the explosion will reach the ring in a hundred years and destroy it. Presumably, a tiny neutron star has been left behind as the tombstone of the star that exploded. Astronomers are now looking for the signs of a pulsar that would help prove that our theory of supernovas, neutron stars, and pulsars is correct. Our own Sun is too small to ever become a supernova. It will end quietly, first turning into a red giant star, then collapsing down into a star the size of Earth, called a white dwarf. πSo Large and So Small 4.5 Billion BC RURAL MILKY WAY To send a spacecraft to the outer reaches of our solar system takes years, but a beam of light can cross the entire solar system in less than a day. To us the solar system is vast, but compared to our own galaxy, the Milky Way, it is microscopic, almost lost among the Milky Way's 100 billion other stars. The beam of light that crosses our solar system in less than a day would take a hundred thousand years to cross the Milky Way. The solar system is composed of the sun and all the objects that travel around it: mainly planets, asteroids, and comets. Most important of these orbiting bodies are the planets. From nearest the sun, they are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune and Pluto. There have been different theories about how the solar system was formed, but today most scientists believe it was formed about 4.5 billion years ago out of a disc of hydrogen gas and heavier materials that slowly condensed into the sun and planets. éSolar Flares and Radio Reception SUN We are all familiar with storms on Earth, but there are also storms on the Sun. At times, there are solar regions where magnetic fields release enormous amounts of energy, causing flares. These flares shoot very fast protons and electrons into space. When they reach Earth, they hit our magnetic field. Most of them are deflected by the field and never hit our atmosphere. But some slip in along magnetic field lines to collide with the air high above the north and south poles. During unusually strong solar storms, these particles sometimes hit the atmosphere in more temperate climates. Then they can disturb the ionosphere, the upper layer where electrons have been knocked out of atoms by ultraviolet light from the Sun. Free electrons reflect many radio waves, and the changes in the ionosphere can cause interference with long-distance radio communication. This also causes electric currents to flow in the ionosphere and electric currents generate magnetic fields. Sometimes these solar storms generate such large currents that their magnetic field becomes strong enough to interfere with magnetic compasses. Compass needles may point in the wrong direction for a while. On rare occasions, these changing magnetic fields even create electric currents in the vast electric-power grids of countries. This can play havoc with the carefully regulated electricity and cause power breakdowns. iNelson Rescues Solar Max 1984 AD EARTH ORBIT Astronaut George Nelson flies to the rescue! NASA had launched a satellite called the Solar Maximum Mission Satellite, or Solar Max. The Solar Max satellite was designed to observe the Sun during a period when it was very active, full of raging storms. But the satellite broke down, and only the space shuttle could repair it. In 1984, the space shuttle approached the Solar Max satellite and astronaut Nelson went on a space walk. He was unable to attach his tools to the satellite at first, so the space shuttle was maneuvered closer to the satellite. Using the shuttle's manipulator arm like a robot hand, the astronauts were able to haul the satellite in and make repairs. The satellite was successfully fixed, and released into space. Later on, in 1986, the satellite was used to observe Halley's Comet during its close approaches to the Earth. ΓSailing the Solar Seas 2000 AD SOLAR SYSTEM There's a way to travel around the solar system with no fuel at all! You need what's called a solar sail. Around the turn of the century, scientists began to realize that sunlight actually pushes against objects. This force, called radiation pressure, is too feeble to feel on Earth, but in space it is strong enough to push against light objects such as atoms and dust. Scientists have proposed taking advantage of this radiation pressure by building great sailing ships in space. A large sheet of reflective material could be launched folded up. Then, in space, it could be opened up. Once in free space, the solar sail would travel between the planets by using this gentle, steady pressure. Organizations such as the World Space Foundation of Arcadia, California, are actively building a solar sail to be put into space by a rocket. It will be stored rolled up, like an umbrella. But once it is in orbit around Earth, it will unfurl. The gentle push of sunlight will cause it to spiral out from the Earth. It could sail to the Moon or Mars. There's a very good chance that, by the year 2000, there will be a solar sail in space, traveling much like the sailing ships of old, but with the pressure of light instead of wind. └Buran: The Soviet Space Shuttle Nov. 15, 1988 AD TYURATAM, KAZAKHSTAN, SOVIET UNION For years, Western space experts knew the Soviets were building something like the American space shuttle. Scale models of their space shuttle had been launched by the Soviets and recovered from the ocean. Photographs showed these models strongly resembled the American space shuttle. Finally, the Soviets announced they had launched their first space shuttle, called Buran (Snow Storm). When the pictures were released, experts were amazed how closely the Soviets had copied the design of the NASA space shuttle. However, there are important differences. The Buran orbiter does not have large engines of its own. Instead, it was strapped onto the Soviet Union's powerful booster, the Energiya. The Energiya is currently the most powerful booster rocket in the world. By attaching the space shuttle orbiter to Energiya, the Russians were able to easily launch the shuttle and large payloads into orbit. And the Buran can be run completely automatically, without a crew on board. In fact, its first flight was without a crew. In 1988, Buran was launched into space. It did two orbits of the Earth and returned safely to the ground, all automatically. The American space shuttle is never launched into orbit without a crew. With the collapse of the Soviet Union, the Soviet shuttle is now a part of the Russian space program. With Russia's economic problems, it is not clear how often the Russians will be flying their shuttle. █ Cooperation in Space July 15, 1975 AD TYURATAM, KAZAKHSTAN, SOVIET UNION Though not as dramatic as a trip to the Moon, docking a United States spacecraft with a Soviet spacecraft presented some unique problems. First of all was language. If the Americans only spoke English and the Soviets only spoke Russian, the whole experiment would of course turn into a nightmare. Then, of course, they had to develop some sort of linking device to attach the two spacecraft together. And there was the problem of atmospheres. The Soviet Soyuz spacecraft used ordinary air, a nitrogen-oxygen mixture at sea-level pressure. But the American Apollo craft used pure oxygen at one-third atmospheric pressure. For three years before lift-off, Russians and Americans met 44 times, visiting each other's training sites and working out the details of the venture. This space cooperation had begun in the early 1960s with agreements to share scientific and medical data obtained from space flights. About 1970, the United States suggested the docking experiment, which was approved by President Richard Nixon and Soviet Premier Kosygin on May 24, 1972. On July 15, 1975 the spacecraft docked over Europe. The astronauts and cosmonauts had studied each other's language. During the exercise the Americans spoke Russian and the Russians spoke English. The craft were linked using a special docking module sent aloft with the Apollo. To complete the joining, American crewmen Thomas Stafford and Donald "Deke" Slayton climbed into the docking module, closed the door behind them and raised the pressure to two-thirds that of sea level, while the Soviets reduced the pressure of their spacecraft to the same level. Then they opened the door on the Soviet side, reached across and shook hands with Soviet cosmonauts Alexei Leonov and Valery Kubasov. The two spacecraft remained linked until July 19. After breaking apart, Soyuz made an uneventful landing on July 21, but Apollo's July 24 landing could have been tragic. As the command module descended into the atmosphere, the crew noticed yellow fumes which irritated their eyes and started them coughing. Astronaut Vance Brand passed out before his fellow crewmen could put a mask on him. It turned out to be nitrogen tetroxide from the maneuvering thrusters, which could have been deadly in larger quantities. It was the last Apollo project, and the end of America's disposable-spacecraft era. In all, the Apollos had made 15 Earth orbit flights and taken nine trips to the Moon, carrying 45 astronauts aloft. Floating Free, But Not Too Free 1965 AD EARTH ORBIT A key to the success of human exploration of space is the ability to leave a spacecraft to do work. Soviet cosmonaut Aleksei Leonov pioneered this "spacewalk" technique, followed shortly by American astronaut Edward White. For their safety, the astronauts were attached to the spacecraft by a long cord, and maneuvered using a small compressed-air thruster or, later, they wore a Manned Maneuvering Unit (MMU), a backpack device that allowed them to fly around to perform repairs or other tasks. One of the main problems encountered during these space walks was the stiffness of the space suit, caused by air pressure. To minimize this problem, NASA learned to keep the pressure to a minimum, although even today working in a pressure suit is hard and sweaty. [Experimental Station in Orbit 1983 AD EARTH ORBIT Whether you want it or not, on the surface of the Earth there is always an extra factor that enters into scientific experiments and processes: gravity. For example, some mixtures of metals (alloys) are impossible to create on Earth. When you melt and mix them, gravity undoes your work by separating them right back out again. Just as oil floats on water, some metals float on others when molten and just will not mix. But in a weightless environment, there is no "up" or "down" and these alloys are easily made. Spacelab, not to be confused with the Skylab of the 1970s, is a transportable space station built by the European Space Agency (ESA) in cooperation with NASA. Spacelab is designed to ride in the payload bay of the space shuttle, connected to the shuttle cabin by a tunnel. The laboratory gives scientists the room and equipment they need to perform space experiments. Spacelab 1, the first Spacelab mission, went aloft in the Columbia for a 10-day trip beginning Nov. 28, 1983. It carried 72 experiments as well as the first non-American to fly in a United States spacecraft, Ulf Merbold, a research physician from West Germany. Since then, there have been several other Spacelab missions, and more are planned. Spacelab is basically a small space station. But it's attached to the space shuttle, and cannot be left behind in orbit. ╢Aquanauts and Astronauts 1950 AD HUNTSVILLE, ALABAMA Sometimes astronauts have to be aquanauts. The only way to experience something like zero gravity for long periods of time without leaving the Earth is to do it underwater. Here, two astronauts work on a mock-up of a space station at the NASA Marshall Space Flight Center's Neutral Buoyancy Facility. The astronauts wear pressure suits similar to those they use in space, but they are carefully weighted so they neither float to the surface nor sink to the bottom, just like in weightlessness. In this way, they can learn to work where there is no up and no down. Here they practice repairs of a space station module using the space shuttle's remote manipulator arm. A Rocketship Built for One 1980 AD JET PROPULSION LABORATORY, PASADENA, CALIFORNIA The Manned Maneuvering Unit (MMU) was designed to allow astronauts to move around construction and repair jobs in space. The "Buck Rogers backpack" weighs 150 kilograms (330 pounds) on Earth. It's 1.2 meters (49 inches) tall, 81 centimeters (32 inches) wide and 66 centimeters (26 inches) deep, with the arms folded down. Its 24 gas jets have .77 kilograms (1.7 pounds) of thrust each, and are connected to twin tanks of nitrogen gas. The fingertip electronic controls complete this one-person spacecraft. The current backpack design comes from tests during the Gemini and Skylab programs with personal jetpacks. As a Gemini astronaut, Eugene Cernan had difficulty getting into and out of his maneuvering unit, as well as using it. The Skylab test showed the suit had to be water cooled because of the heat a working astronaut generates. The backpack now features two latches that secure the crewman, two D-rings to release it, an easily viewed fuel gauge, and other improvements that made one user say, "Hey, this is fun!" Other "backpack jocks" have talked about the sense of freedom the MMU gives, as well as the awesome view of the universe it lets them have. The usefulness of the backpack has been proved during the repair and retrieval of satellites. It allowed astronaut George Nelson to reach out and grab the Solar Max satellite, slowing the spin so that the robot arm could grab it. Because of the MMU, astronauts proposed the slogan, "We pick up and deliver, and fix it too!" ûThe Supercannon Man 1990 AD CANADA Isaac Newton would have been amazed by a man who almost made his thought-experiment of a world-orbiting cannonball come true: the incredible Canadian-American ballistics genius, Gerald Bull. He was inspired by a huge German cannon called the V-3 that was bombed by the Allies before it could be used much in combat. Bull went on to design some of the most advanced cannons on Earth. His ultimate goal was to build a gun so powerful that it could fire a shot into orbit. But gradually, funding in North America fell off and he began to work illegally for the South Africans. When he was caught, he was jailed in the United States for four months, which soured him on his previous customers. When released, Bull became a freelance cannon designer. He wound up working for a Middle Eastern client who was interested in long-distance shooting: Iraq's Saddam Hussein. He sold Hussein hundreds of his huge 155mm howitzers, the best in the world. And Bull set about designing a supergun for him capable of shooting 600 miles, which would have brought Israel into range. But in 1990, before it could be built, two assassins in Brussels, Belgium, with much smaller guns under their coats, killed Bull. It was an ironic ending for a gun designer. The supergun was never finished, and Hussein had to rely on the much-less reliable Soviet Scud missiles for long-range shooting in the Persian Gulf War. Coincidentally, while Bull was working for the Iraqis, the American Star Wars (Strategic Defense Initiative) program was designing superguns that could eventually allow super-cannons or electromagnetic guns to fire small, tough satellites into orbit, much like Bull's cannon. åThe International Space Station 1995 AD EARTH ORBIT Space Station Freedom is the first international effort to place a permanent workplace into orbit. NASA -- which is coordinating the joint United States, Canadian, European and Japanese effort -- plans to send the first sections of the station aloft in 1995, and to have the station completed by about the year 2000. The project will include four modules: a crew quarters module and three laboratories. Freedom will be built on a 353-foot-long framework by astronauts living temporarily in a space shuttle. The station will draw its power from solar panels when it is in view of the sun, and from batteries when it is not. It should be usable for 30 years or more. Many critics have attacked the space station. It was proposed as an $8 billion project by President Ronald Reagan in 1984, intended to be launched in 1992, for the 500th anniversary of Columbus's voyage to the new world. Since then, it has been redesigned and postponed many times, and its estimated cost has soared to between $30 and $40 billion. Some scientists criticize it on the grounds that the money could be better spent on other projects; others, because it duplicates much of the work done by the Russian space program with its space stations. NASA is studying the possibility of using the giant Russian Energiya rocket to launch parts of the space station, instead of the space shuttle. Its supporters argue that the station's labs will enable scientists to stay aloft for months on end, studying the effects of weightlessness on plants, animals, humans and various materials, examining Earth, and developing technologies for future human flights to the Moon and Mars. MSpectrum: Fingerprint of Stars 1704 AD CAMBRIDGE, ENGLAND How can you tell what something's made of if you can't touch it? The answer lies in the rainbow. We owe the roots of this method to Isaac Newton. Gravity was just one of Newton's fascinations. Light was another. Almost nothing was known about light before him. Philosophers and scientists speculated endlessly about what light really was, but very little was truly known. One thing that had been known from antiquity was that light sometimes breaks up into colors when passing through a transparent substance, like an odd-shaped piece of glass. Newton knew about lenses, as did Galileo before him, but nobody knew much about how they worked. The simple lenses used then created colored fringes around objects seen in a telescope or microscope. Today, we are so used to sophisticated optics that avoid this problem that we forget that the images seen by these great scientists were quite poor by our standards. Any white object would be surrounded by a colored fringe. Often the greatest progress in science comes from simplifying a problem to eliminate distractions. So Newton decided to study the simplest lens he could imagine: a prism, a piece of glass like a slice of pie, but with all flat sides -- a wedge. This would behave like the edge of a lens. He passed a beam of sunlight through the prism in a darkened room and saw pretty colors on the wall where the light hit it, colors we now call the spectrum of sunlight. They are the colors of the rainbow, for a very good reason: Rainbows are produced by water droplets in the sky that scatter sunlight like tiny prisms, as astronomer Edmond Halley proposed. Many scientists today think Newton discovered the spectrum of sunlight, just as they often think Galileo invented the telescope. Neither statement is true. Both took phenomena others had found, but used them with genius. Where others merely saw pretty toys, Newton and Galileo saw the universe. As Newton played with his sunbeam and prism he discovered that, contrary to what philosophers thought, white light, once it had broken into its rainbow spectrum, consisted of pure colors that could not be broken down further. Then he performed a brilliant experiment: He used another prism to bring the colors back together again. What happened? The light became white once more! He proved that the colors were present in white light. They were not created by some peculiar characteristic of the prism. White light consisted of a mixture of all colors. He published his results in 1704 in the book "Opticks." In the 19th century scientists took his discovery further. In 1814, the German physicist and astronomer Joseph von Fraunhofer found that, when looked at with higher quality instruments than Newton had, sunlight not only has the continuous rainbow of one color blending into another, but also has dark lines on top of the rainbow. This seemed a minor discovery, but was to have profound consequences, as scientists discovered when they looked at other light sources, such as candle flames. A flame also produced a rainbow spectrum, but they found that when they put a substance like salt into the flame, they would see lines like those in the Sun's spectrum. Scientists discovered each chemical had a different set of lines. They had learned to fingerprint chemicals. More than that, they could fingerprint chemicals at a distance. In 1855, the first substance was identified on the Sun. The French physicist Leon Foucault discovered two of Fraunhofer's lines were the same as those produced by sodium in the laboratory. This was one of the great breakthroughs in astronomy. Now we could identify the chemicals in the Sun, in stars, in planets and in comets. We could at last learn what the universe is made of without traveling the vast distances of space. The impact of this on science is hard to appreciate today, when we routinely measure the composition of galaxies millions of light-years away. Much of chemical research for industry as well as astronomy now depends on measuring the spectrum of a substance. But to Newton, though he began this whole business, it would have seemed as incredible as turning lead into gold. Consider these words, written by a Frenchman, A. Comte, around 1840: "We may speculate with some hope of success on the formation of the Solar System of which we form a part, for it presents to us numerous perfectly well-known phenomena, susceptible perhaps of giving proof of its true immediate origin. But what, on the other hand, could possibly form a rational basis for our conjectures on the formation of other suns? How confirm or disprove by the evidence of phenomena any [star-formation] hypothesis when no phenomena of such kind are known, nor, doubtless, are even knowable?" "Nor, doubtless, are even knowable." These words have probably been uttered in one form or another throughout history. Whenever you hear their echo, remember a law described by Arthur C. Clarke, the British science-fiction author of "2001: A Space Odyssey." Clarke's First Law says, "When a distinguished but elderly scientist states that something is possible, he is almost certainly right. When he states that something is impossible, he is very probably wrong." It was particularly shocking that Monsieur Comte made his statement a quarter century after Fraunhofer had discovered the lines in the Sun's spectrum. It should have been obvious that we would one day discover such lines in other stars, and that those lines would tell us something about the nature of stars. Today, analysis of these spectral lines tells us not only what an astronomical object is made of, but how hot it is, what the gas-pressure is, how fast it is moving, how rapidly it is spinning, and, sometimes, how old it is and how far away. It's as if a doctor could diagnose your temperature and blood pressure and the condition of your heart by just looking at you. And then tell you your birthday! ¬Fingerprint in the Spectrum 1814 AD MUNICH, GERMANY One of the most important discoveries in the history of science started in an optical shop in Germany. Joseph von Fraunhofer was a brilliant maker of optical glass. He knew that Isaac Newton had shown there were colors in sunlight after it passed through a prism, and he began to examine this rainbow of colors very carefully. He discovered there were dark lines in the rainbow. He then found that flames also created a rainbow effect when their light passed through a prism. And this rainbow also had lines in it. An English scientist, William Wollaston, had noticed a few of these lines earlier, but Fraunhofer, unlike Wollaston, studied them carefully. But it wasn't until two other Germans began to follow up Fraunhofer's discoveries that these lines became enormously valuable. Gustav Kirchhoff and Robert Bunsen discovered that the lines were different for different chemical elements. If you put carbon (soot) into a candle flame, this created one set of lines in its rainbow. If you used sodium (as in salt, which is sodium chloride), this produced a different set of lines. Today we call this rainbow the spectrum of the chemical. Each set of lines (called spectral lines) is a distinct identifier of a particular chemical element, like a fingerprint. When scientists looked at the Sun's spectrum with this knowledge they found they could identify many of the chemicals in the Sun by the lines in its spectrum. Today, we use the spectrum of stars and galaxies to tell us what they are made of. It is amazing to think that even though something may be a million light years away, you can still tell exactly what atoms it is made of. Using these techniques we can also tell what gases are present in the atmospheres of planets by studying the sunlight that is reflected off the planets. Much of astronomy today consists of taking measurements of the spectrum of astronomical objects, and figuring out what they are made of. TSpiders in Space 1973 AD EARTH ORBIT Can a spider weave its web without gravity? What would it do when there was no "up" and "down"? To find out, two spiders were taken aloft to an orbiting spacecraft. Three astronauts went up to the Skylab space station in 1973 with a miniature zoo. They carried two minnows, 50 minnow eggs, six pocket mice, 720 fruitfly pupae (babies), and two common Cross spiders named Arabella and Anita. At first, the spiders were confused, and wove sloppy webs. But as they got used to weightlessness, they wove an increasingly regular pattern, just as if they were on Earth. One of them, Arabella, became a television star as her efforts were broadcast to Earth. The picture shows Arabella's first web. Notice that it is irregular, especially at the outer edge. Said astronaut Owen Garriott, "It seems she learned very rapidly in zero g [weightlessness] without the benefit of any previous experience." Most animals and plants adapt to zero gravity after a period of adjustment. The minnows were confused at first, swimming in loops. But the fish that were born from the minnow eggs swam normally. ALanding on Water and Land 1961-1980 AD MID-PACIFIC While Soviet spacecraft always came down on land, US spacecraft always came down in the water. Why is that? Technically, there was no reason why the craft couldn't come down in either location, but there were other good reasons why each country chose the course it did. The Soviet Union had a huge empty tract of land called Siberia, where spacecraft could safely come down without endangering people on the ground. Also, the USSR did not have very good access to the ocean. Therefore having spacecraft land on the land made perfect sense. The United States, however, is relatively well populated from ocean to ocean, and landing a spacecraft on land could be dangerous. Also, the United States has easy access to the ocean and has a large navy, which made it preferable to bring its spacecraft down in the sea. ╓The Beep Heard Round the World Oct. 4, 1957 AD EARTH ORBIT It wasn't a very good conversationalist. Its only vocabulary consisted of "beep-beep-beep," but Sputnik 1 woke up the world like nothing else could have and launched the race for outer space. On Oct. 4, 1957, the Soviet Union put the world's first artificial satellite into orbit. Sputnik 1 was an 84 kilogram (184 pound), 58 centimeter (23 inch) wide ball with four radio antennas streaming off to one side. That may not sound too impressive, but at the time the United States was still at the drawing board, planning to get a 1.4 kilogram (three pound) satellite into orbit. Sputnik had two radio transmitters that sent out regular signals as it circled the globe. Even amateur radio operators could pick up the distinctive "beep-beep-beep" as it passed overhead. There were no scientific experiments aboard Sputnik, and what information came from from the satellite was from observing its orbit and the speed at which it decayed. The Soviets followed that triumph the next month by sending up a 500 kilogram (1,100 pound) satellite containing a dog. America -- overconfident that it was the world's leader in technology -- went into a tizzy. The US didn't have anything in space! But as a result of the national debate, the National Aeronautics and Space Administration (NASA) was created by President Dwight Eisenhower and Congress enacted the National Defense Education Act of 1958 to beef up the educational system to make it competitive with the Russian system. gSpy Satellites: The Peacemaker EARTH ORBIT Spy satellites helped to end the Cold War. For decades, it was impossible to sign a nuclear arms reduction treaty because the Soviet Union would not allow inspectors to visit places where the United States suspected nuclear weapons were being built and tested. But orbiting spy satellites were able to solve many of the objections. The satellites fly so far overhead that they are in international territory, unlike spy planes, which would have to enter Soviet airspace. As a result, the US Department of Defense was able to monitor Soviet military activity, and this allowed arms-reduction treaties to be negotiated. These photographs show the kind of information that can be obtained from such spy photography. They were taken by military aircraft, but the quality is similar to what is obtained by a good spy satellite. It shows Soviet military activities in Cuba, not far from Florida. Spy satellites can spot troop movements, missile outposts, ship movements and can observe above-ground nuclear weapons tests. Without spy satellites, it would probably have taken much longer for the Cold War to end. ÑStarbirth 10 Billion BC UNIVERSE According to current theory, following the Big Bang roughly 15 billion years ago, the universe expanded rapidly, but everything was still just simple hydrogen and helium atoms. At first there were no stars, but then gravity got to work. About 10 billion years ago the hydrogen atoms' own gravity pulled them together in dense clouds. Eventually the centers of these clouds became so compacted that nuclear fusion reactions began, squeezing hydrogen atoms into helium. Trillions of stars blinked on all over the universe. This process is still going on. Astronomers recently observed the birth of a new star in the Large Magellanic Cloud, a nearby galaxy. These early stars were very important, scientists believe, because at their centers lighter atoms were fused into heavier ones. Without this, the universe would have almost no carbon or oxygen, and we could not exist. Then, when these first stars died, some of them exploded in supernovas that scattered these atoms across space. Some of this gas later condensed to become our solar system, including the planet Earth. Every star evolves, growing through stages from birth to death. Our own Sun was born about five billion years ago as an average star, neither unusually big nor small. It soon became the yellow star we are familiar with, mostly made of hydrogen. But for five billion years it has been burning up that hydrogen, fusing it into helium. As it gets older, it also gets warmer. Fortunately, it has enough hydrogen to last for another five billion years. Then, it will run out of fuel. It will then expand, becoming a red giant star. It will be so big that its outer atmosphere will reach the Earth. By then, humanity will have to move elsewhere to avoid being vaporized. Finally, the red giant will collapse down into a star the size of the Earth, called a white dwarf. PHOTO CREDIT: Copyright Anglo-Australian Telescope Board. Photography by David Malin. áStarwisp: To Alpha Centauri 2010 AD UNIVERSE What may be the first probe to another star has already been designed. Robert L. Forward, an aerospace scientist, has developed Starwisp, an ingenious design that takes advantage of new technology and could be launched in the foreseeable future. He started with the assumption that there would be a solar-powered satellite in orbit around Earth, converting sunlight into electricity and beaming it to Earth. He proposed taking this energy and briefly pointing it at the back of Starwisp, which would have a large antenna like an umbrella that would pick up this energy and be pushed by it. This is similar to the principle of the solar sail, except that instead of using the pressure of sunlight, it uses the pressure of microwaves. Both light and radio waves are fundamentally similar types of energy, and both can push against an object. With the aid of this microwave pressure, the space probe would be accelerated away from the Sun at a great rate, until it was moving close to the speed of light. The nearest star to the Sun is Alpha Centauri, which is four light years away, around 40 trillion kilometers (30 trillion miles). Even using this design, it would take 21 years to reach the star. Forward also came up with an ingenious idea for transmitting data back from the star to Earth. After traveling for two decades, the spaceship would use its giant antenna to beam information back to Earth. The antenna would have sensors to pick up light from the star and from any planets around it. In the meantime, the solar-powered satellite circling Earth would have sent out a large beam of microwaves aimed at the star. The spacecraft would pick up that energy and use it to power the electronics to run its sensors and to transmit information back to the Earth. That information would travel at the speed of light. So, four years after it flew by the star, pictures from Alpha Centauri would be received by antennas on Earth. No one has yet agreed to provide the money to build this spacecraft, but it shows what may someday be possible. If we can design interstellar space probes using technology that is almost here, then the possibilities of the future are nearly limitless. ╡Stonehenge: An Observatory? 2800 BC SALISBURY PLAIN, ENGLAND Nobody really knows the purpose of the large circle of stone pillars that make up Stonehenge. Scientists have speculated, however, that the monument may have been an astronomical observatory, perhaps designed to calculate eclipses of the Moon. Careful measurements have shown that the stones are oriented carefully with respect to the stars. Science historian Gerald Hawkins believes that Stonehenge was a giant, primitive computer, designed to predict eclipses. Eclipses, disappearances of the Sun and Moon, must have been terrifying to the superstitious ancients, and they probably created religious rituals around these events. But over the years, souvenir hunters and builders looking for construction materials have carried away many of the smaller stones, making it difficult to determine its true purpose. Scientists believe Stonehenge was begun about 2800 BC and modified in about 2100 BC, when the huge 25-ton sandstone monoliths we see today were added. Many other ancient monuments have been found around the world that are oriented with respect to the stars. These include the Great Pyramid of Kheops in Egypt and the medicine wheels of the Native Americans. YMaking the Weather Man Better ATLANTIC OCEAN Along the East Coast of the United States, and in other parts of the world, hurricanes can be devastating. Their fierce winds can level houses, flood towns and kill people. Before weather satellites, meteorologists had to rely on measurements from a few points on the ground, sea and air, and this system was not always complete enough or quick enough to pick up a sudden change of direction that could bring a hurricane smashing into a densely populated area. But weather satellites can see a whole storm at a glance, catch it developing and easily track its progress and give quick warning of any changes of direction. Modern weather satellites also watch crop growth, note changes in the temperature of land and sea, and spot shifting ocean currents. While satellites have been particularly helpful in predicting the weather, they have also been important in communications, navigation, mapping and studying ecology. Recently, they have been crucial in watching the effects of a build-up of carbon dioxide in the atmosphere (the greenhouse effect) and of changes in the ozone layer. Our Atmospheric Shield EARTH'S ATMOSPHERE The Sun is Earth's main source of energy and all life depends on it, directly or indirectly. But the Sun can also be dangerous. Sometimes its vast storms -- bigger than Earth -- throw out X-rays, ultraviolet light, and particles (mainly electrons and protons). All these can hit Earth, though fortunately, our magnetic field and atmosphere shield us from most of them. A solar storm can also disturb the upper part of the atmosphere (the ionosphere, a layer of electrically charged atoms and electrons). Since many radio and television transmitters bounce their signals off the ionosphere, this can cause interference with radio and television reception. Energetic solar particles can also cause the sky to glow like colorful curtains at night near the poles. This is called the aurora (the Northern and Southern Lights). There is some evidence that solar activity can affect our weather and climate, but this is hotly debated. Sunspots (small dark regions on the Sun's surface that usually appear during solar storms) are particularly blamed for influencing Earth's weather and climate. They are often the source of solar flares that spit particles out with great energy. From 1645 to 1715, for example, there was a period (called the Maunder minimum) when there were hardly any sunspots, and Earth's weather was unusually cold. It's still a mystery to what extent the Sun's storms affect our weather and climate, but we can be thankful that our atmosphere and magnetic field insulate us from the worst effects. òSolar Wind: The Comets' Clues 1951 AD SOLAR SYSTEM It may seem impossible, but there is actually a wind in space, caused by the Sun. The first clue was noticed in the 19th century. Astronomers saw that some comet tails were fairly straight, and others were highly curved. Often, the same comet would have two tails at the same time, one straight and one curved. This was a major mystery. With the 20th century, it became possible to measure the speed of the comet tails by studying changes in their light (spectral lines). Astronomers found the tails of two-tailed comets were radically different. The curved tails traveled at close to the speed of the comet and were largely made of atoms and molecules of gas. Clearly they were gases escaping from the comet and just drifting away. But the straight tails traveled about ten times faster than the curved ones. They were made not of ordinary gas but of ions -- gas atoms with electrons stripped from them. That made the straight tails the fastest things in the solar system, apart from light itself. What could possibly make them move so fast? In 1951, German astronomer Ludwig Biermann found the answer and taught us something about our Earth at the same time. In a brilliant piece of reasoning, he concluded that the straight comet tails meant that a wind must be streaming from the Sun. Far faster than a hurricane, this solar wind is a hot gas so thin that if it were on Earth, we would call it a vacuum. But in the vast emptiness of space, the solar wind roars outward past all the planets and strikes any comet that happens by. The wind is a plasma, a gas made mainly of protons and electrons, from the Sun. This wind, along with the Sun's ultraviolet light, rips electrons off comet atoms, causing them to become electrically charged ions. Once the comet atoms are charged, they are easily swept up by the solar wind. Years later, when spacecraft ventured away from Earth, they measured this solar wind directly. They found that it typically moves at 300-400 kilometers per second (200-250 miles per second), about a tenth of a percent of the speed of light. This also answered another longstanding mystery: Why do comet tails always point away from the Sun? Most people, if they think about it at all, assume that a comet's tail follows it around behind, like the smoke from a train. In fact, when the comet first approaches the Sun, the tail is behind it just as you'd expect. But when the comet swings around the Sun and starts to head out, the tail is in front of the comet. The cart is in front of the horse. Around the turn of the century, scientists began to realize that sunlight actually pushes against objects. This force, called radiation pressure, is too feeble to feel on Earth, but in space it is strong enough to push against light objects such as atoms and dust. Indeed, scientists are building solar sails that will travel in space by using this pressure. But solar radiation pressure was not enough to explain the fast ion tails of comets. The solar wind was needed. The train picture actually explains a lot when we throw in the solar wind. If a strong wind is blowing -- one much faster than the train -- the train's smoke will flow in the direction of the wind, not the train. Since the solar wind is much faster than the comet, it blows the tail away from the Sun regardless of which way the comet is going. And here's the answer to the mystery of how there can be a wind in a vacuum. Although the space between the planets is a vacuum by our standards, with almost no gas, there are a few atoms, protons, and electrons. Near the Earth, the solar wind has about five hydrogen atoms per cubic centimeter (80 per cubic inch), mostly split into electrons and protons. In a laboratory, this would be considered a very good vacuum. But in the vastness of space, these particles, moving fast, can push the atoms of comets around. So by studying comets, we unexpectedly learned about the connection between the Sun and Earth. ¢How the Sun Works 1992 AD SUN The Sun is like a vast hydrogen bomb, continuously exploding. Here we see an artist's picture of the Sun, cut away to show its structure. At the very center is the hottest part of the Sun, the place where hydrogen is fused into helium. Just as in the hydrogen bomb, this creates energy. This is what powers the Sun. Next, this heat, in the form of gamma-rays (extremely energetic electromagnetic waves), slowly leaks through the thick layer of the hydrogen gas surrounding the core, passing through layers of boiling gas, until it finally reaches the visible surface: the photosphere. From a temperature of 15 million degrees Celsius (27 million Fahrenheit), it has fallen to a temperature of only 6,000 degrees Celsius (10,000 Fahrenheit) at the visible surface. The struggle to reach the surface has cooled the sunlight and shifted the energy from gamma-rays down to the longer wavelengths of yellow light. Even so, this temperature is hot enough to vaporize any substance we have on Earth. It is also too hot for hydrogen atoms to exist. The atoms are shattered into their protons and electrons. And it's at the surface that we see the solar storms forming, often around sunspots -- slightly cooler, darker areas of the Sun. Then, beyond the visible surface, comes the outer atmosphere of the Sun where electrons and protons stream away from the Sun, forming the solar wind that flows throughout the solar system. The Surface of the Sun SUN Amazingly, what you see in the sky when you look at the Sun is one of the coolest parts of the Sun. The center of the Sun, where hydrogen is fused into helium to generate the Sun's energy, it is like an H-bomb. The temperature is around 15 million degrees Celsius (27 million Fahrenheit). But as the energy works its way toward the surface of the Sun it cools. The Sun's surface, the part we see, is called the photosphere, and is 6,000 degrees Celsius (10,000 Fahrenheit). The Sun is mainly a ball of hydrogen gas, and the outer layers are a kind of atmosphere, although it's so hot that the hydrogen is broken up into its basic parts, electrons and protons. (A gas consisting of ions like that is technically called a plasma.) Only during an eclipse of the Sun can we see the Sun's outermost thin atmosphere, known as the corona, the Latin word for crown. It is about 1.5 million degrees Celsius (2.7 million Fahrenheit). There is weather on the Sun, creating storms and other features, such as solar flares, where the temperature can be even greater -- typically 10 million degrees Celsius (18 million Fahrenheit). The outer atmosphere is so hot that the Sun's tremendous gravitational force cannot keep it from escaping, and it constantly streams away, forming the solar wind. VSunspots: Cooler but Still Hot SUN Sunspots are dark spots on the Sun first seen by Galileo. Some religious authorities of his day could not believe his report of spots on the Sun. They thought the Sun had to be perfect, and that spots would be an insult to God. We now know that sunspots are slightly cooler than the rest of the Sun's surface, even though they are still so hot that they would melt any substance on Earth. Powerful magnetic fields occur in the sunspots and may cause the spots to erupt into a solar flare. There is some evidence that solar activity can affect our weather and climate, but this is hotly debated. Sunspots are particularly blamed for influencing Earth's weather and climate. From 1645 to 1715, for example, there was a period (called the Maunder minimum) when there were hardly any sunspots, and Earth's weather was unusually cold. It was a period known as the Little Ice Age. Will this happen again? One way to learn about the Sun is by studying other stars similar to it. Astronomers at the Mt. Wilson observatory in Southern California have been studying some Sun-like stars for over a decade. They find that many of them have sunspots like our Sun has. They can't see individual sunspots, but they see slight changes in the stars' brightness as they spin slowly. (The Sun spins just like a planet, taking about a month to turn around completely.) By studying these other stars, we may be able to predict when the Sun's pattern of spots will change. Since these spots may affect our temperature, the more we know about them, the better are the odds of being able to predict the future climate of Earth. ªTanzania's Red Spot LAKE NATRON, TANZANIA The great red spot you see here is Lake Natron in northeast Tanzania. If you are surprised by the color, so were the shuttle crew members who first saw it. The color is caused by algae, drying salts, and possibly the thousands of flamingos that eat the algae. Lake Natron is located in the Great Rift Valley, where a vast slice of East Africa is slowly pulling away due to continental drift. ≈Tarter: Top SETI Researcher 1992 AD MOUNTAIN VIEW, CALIFORNIA Jill Tarter is one of the most active researchers in the world in the field of the search for extraterrestrial intelligence (SETI). She was born in 1944 in New York and took mathematics and science courses in high school, despite counselors who advised her, "Don't take so many credits; don't take science courses predominantly; don't expect to go on to the university; you're going to be a housewife, and what do you need all this for?" By doing everything they told her not to, she went on to earn a bachelor's degree in engineering physics from Cornell University and a doctorate in theoretical astrophysics from the University of California at Berkeley. Tarter became a radio astronomer and one of the most active SETI scientists. She has traveled to radiotelescopes in many parts of the world in order to search for radio signals from other civilizations. Today, she is one of the chief scientists on the NASA SETI project at the Ames Research Center in Northern California. ÆTAU: Probing Beyond Pluto 2000 AD UNIVERSE NASA's Jet Propulsion Laboratory (JPL) has designed a space probe that could explore nearby interstellar space. Not quite a true starship, it would nevertheless begin to explore the vast distances beyond our solar system. Like the Voyager and Galileo spacecraft, this vehicle, called TAU, would be powered by radioactive materials. Instead of using rocket fuel, electric power would accelerate electrically charged particles (ions) to provide a gentle thrust for years on end. Because the thrust lasts so long, this ion drive could accelerate the spacecraft to much faster speeds than chemical rockets could do. It's called TAU, for Thousand Astronomical Units. An astronomical unit is the distance of the Earth from the Sun. Tau is designed to travel a thousand astronomical units. Pluto is only 30 astronomical units from the Sun, so TAU would fly more than 30 times the distance of Pluto from the Sun. On the way out of the solar system, TAU could fly by Pluto, which no other spacecraft ever has. TAU could be built tomorrow if the money were available, but so far, NASA has only received enough to do paper studies of this fascinating mission. Tereshkova: First Woman in Orbit June 16, 1963 AD TYURATAM, KAZAKHSTAN, SOVIET UNION On April 12, 1961, when Soviet cosmonaut Yuri Gagarin became the first man in space, Valentina Tereshkova was working in a textile mill. His flight inspired her, however, and just over two years later Tereshkova was orbiting the Earth as the first woman in space. Being a textile worker may not seem very good training for space flight, but Tereshkova was also an accomplished skydiver, with 125 parachute jumps on her record, and it didn't hurt that she was a member of the Communist Party. She was accepted into the cosmonaut program and on June 16, 1963 was blasted into orbit in her Vostok 6 spacecraft. Tereshkova made 48 orbits of the Earth, one every 88 minutes, and spent 70.5 hours in space, more time than all the United States' Mercury astronauts combined. During the flight she passed within three miles of another orbiting cosmonaut, Valery Bykovsky. When she returned she was named a Hero of the Soviet Union, and that same year married Colonel Andrian Nikolayev, pilot of the Vostok 3 flight. Tethys: Saturn Moon 1981 AD SATURN ORBIT Tethys is one of Saturn's medium-sized moons. It is 295,000 kilometers (183,000 miles) from the planet and is 1,048 kilometers (652 miles) in diameter. It is a mixture of rock and ice. The picture shown here was taken by the Voyager 2 spacecraft. áThrusters: Maneuvering in Space 1980s-1990s AD EARTH ORBIT In space, rockets cannot move wing flaps to maneuver, as an airplane can in the atmosphere, so they use small rockets called "thrusters." Thrusters, like other rockets, work on Newton's reaction principle: the action (flame going one way out the nozzle of the rocket) has an equal and opposite reaction (the movement of the rocket itself in the opposite direction). One of these thruster systems is the space shuttle's Orbital Maneuvering System (OMS, pronounced "ohmz"). It was built in part by McDonnell Douglas during the late 1970s and early 1980s. It allows the spacecraft to change orbits, rendezvous, and dock in space. The system has two 2,700 kilogram (6,000 pound) thrust engines in the OMS pods located above the three main engines, just below the tail. They swivel eight degrees and are used to make powerful "burns" to change orbits. Each of these OMS pods also contains 12 small primary reaction control (RCS) jets and two tiny vernier (fine-tuning) jets. The primary jets have 400 kilograms (870 pounds) of thrust, and the verniers 11 kilograms (25 pounds) of thrust. In the shuttle's nose, there are 14 more RCS thrusters and two verniers. Together these thrusters allow for precision orbit adjustments. With computer control the shuttle can maintain a pointing accuracy to a half degree. The RCS and vernier thrusters have their own fuel tanks, but can also access the two larger OMS fuel tanks. BThe Moon with an Atmosphere 1979 AD SATURN ORBIT Titan is the largest moon of Saturn, larger than our Moon. What's most remarkable is that it's the only moon in the solar system with a thick atmosphere. Its atmosphere is mostly nitrogen, with methane and other gases. Titan has a pressure about 50 percent higher than Earth's air. Analyzing this unusually thick atmosphere shows evidence that there are probably oceans of liquid organic (carbon-containing) chemicals on its surface. These chemicals may be similar to those on the early Earth, from which life formed. Titan is so cold that it's unlikely to have life on it. The surface temperature is about 180 degrees below zero Celsius (292 below zero Fahrenheit), far colder than any place on Earth. But studying its oceans could reveal some of the secrets of that mystery-shrouded day on which life arose on Earth. If you were floating on Titan's sea, you would see an orange sky lit by the distant Sun. It would be about as bright as a night on Earth during a full Moon. In the late 1990s, the European/NASA spacecraft Cassini will be launched toward Saturn. Like the Galileo spacecraft on its way to Jupiter right now, Cassini will send a satellite to permanently orbit Saturn, and a probe to enter Titan's atmosphere. Exploring this strange moon should be one of the most exciting adventures in the solar system. 9Titania: Uranus Moon 1986 AD URANUS ORBIT Titania is a medium-sized moon of Uranus. It is 436,000 kilometers (271,000 miles) from the planet and 1,600 kilometers (994 miles) in diameter. This dark moon is a mixture of rock and ice. The picture was taken by the Voyager 2 spacecraft from a distance of 500,000 kilometers (300,000 miles). ╗Watching the Weather 1992 AD EARTH ORBIT About 10,000 years ago, the world was in an Ice Age. Much of Europe and Asia was covered with glaciers. Suddenly, the climate warmed up, making it possible for humans to travel farther north. Not long after this, our ancestors discovered how to grow crops. We changed from hunter-gatherers into farmers. That in turn allowed the invention of villages, which grew into cities. This gave birth to modern civilization. What caused this dramatic climate change 10,000 years ago? Scientists believe that there was a sudden shift in ocean currents. Warm water from the equator swept up toward the North Pole, warming Europe. Such a sudden switch could happen again, perhaps creating a new Ice Age. A satellite was launched in 1992 to study these currents. It's is a joint French/NASA spacecraft designed to explore the oceans from space. Called Poseidon by the French after the Greek sea god, Americans call it TOPEX (Topographic Explorer). It is a part of NASA's Mission to Planet Earth, in which our world is being studied as a whole planet, to understand what makes our environment tick. TOPEX radar will measure the height of the oceans very accurately. It will make maps to show how the ocean circulates on a the scale of the whole planet. TOPEX radar will scan the waves, detecting weather patterns and sea currents. It will study how wind energy is converted into waves and currents. We are only now beginning to realize the importance of winds in transferring energy from the atmosphere to the oceans, and the effect that waves have, dragging on the winds. Earth's weather and climate are strongly affected by the oceans. These vast bodies of water are not only sources of water for forming clouds, but they absorb a great deal of the Sun's energy. As the ocean currents circulate, they bring warm water to cool places. Without the Gulf Stream, for example, northern Europe would not be warmed by Caribbean waters. Europe would be much colder, and farming would be much more limited. If there is a change in these ocean currents, either due to nature or to pollution, the ocean currents could be catastrophically changed. TOPEX will help us learn whether there are such disasters lurking in the future. hTrifid the Gas Cloud MILKY WAY GALAXY The Trifid Nebula is a great glowing cloud of gas in our galaxy, 6,000 light years from Earth, near the constellation Sagittarius. Clouds of dust create dark streaks that divide the nebula into three parts, giving it the name Trifid ("cleft into three" in Latin). The pink color is hydrogen gas, shining in the light of the star. This nebula is huge, about 25 light years across. (For comparison, the nearest star to the Sun, Alpha Centauri, is only four light years away.) Trifid contains more than 100 times the matter that is in our Sun. Trifid is an example of an emission nebula, which has a hot, bright star inside it emitting light and causing the gas to glow. The opposite of an emission nebula is a reflection nebula, which reflects the light of stars outside of it. A third type is called a planetary nebula, a roughly spherical ball of gas surrounding an old, dying star (but which has nothing to do with planets). Other types include the cometary nebula, called that because it looks like a comet (but has nothing to do with comets), and the bipolar nebula (which looks like a bow tie). ôTriton's Cold Volcanoes 1989 AD NEPTUNE ORBIT The largest moon of Neptune is one of the rare moons in the solar system where clouds are found. When the Voyager 2 spacecraft flew past this moon, Triton, it found puffs of cloud coming off the surface. Geologists studied the pictures of Triton and were forced, to their surprise, to conclude that there were volcanoes on this very cold world. What could be liquid at these temperatures? Certainly not rock, which is the liquid in Earth's volcanoes. There could not be enough heat inside Triton to melt rocks. Triton turned out to be the coldest place in the solar system, with a surface temperature of 235 degrees below zero Celsius (390 degrees below zero Fahrenheit). (Pluto will get even colder as it moves farther out in the solar system.) Even nitrogen gas, which had been expected, would freeze out on the super-cold surface. But it would be slightly warmer inside of Triton, due to heat from radioactivity, the same thing that heats the Earth's insides. The geologists calculated that nitrogen could be a liquid inside this moon. So this is the picture that emerged: There are pools of liquid nitrogen inside Triton. The liquid is still incredibly cold by our standards, around 210 degrees Celsius below zero (350 degrees Fahrenheit below zero). On Earth, we call it liquid air, since air is mostly nitrogen. It looks like liquid water, but will freeze anything it touches for very long. Occasionally the nitrogen gets "hot" enough to boil. It explodes through the ice. It becomes a volcano of incredibly cold liquid nitrogen, spraying the gas into space, forming clouds. Triton has the coldest volcanoes of any known place in the solar system. ╪Triton: Moon of Icy Volcanoes 1989 AD NEPTUNE ORBIT Triton is the largest moon of Neptune. It's larger than our own Moon and made of ice. When it passed by, the Voyager 2 spacecraft found Triton had a strange surface with a greater variety of features than almost any moon yet seen: mountains, smooth areas, craters, "cantaloupe" terrain and -- the biggest surprise -- active volcanoes. Triton is one of the most remarkable moons of the solar system. Located 354,000 kilometers (220 miles) from Neptune, it is the only large moon around that planet. It is 2,700 kilometers (1,678 miles) in diameter, a bit smaller than our own Moon. Triton's surface is a strange mixture of radically different features. There are smooth areas and rough ones, and there are places where there appear to be volcanoes erupting. Part of its surface is known as cantaloupe terrain, because of its resemblance to the fruit. Geologists aren't sure what causes it, but it may be related to what's going on inside the moon to cause volcanoes to erupt. The Voyager spacecraft saw signs of volcanic eruptions on Triton. The moon is very cold, and what is probably erupting is not liquid rock, as on Earth, but nitrogen. Triton is so far from the Sun that nitrogen can exist as a liquid under the surface. These volcanoes create a very thin atmosphere, 1/70,000th the pressure of Earth's atmosphere -- a virtual vacuum. Triton is also unusual in that it revolves clockwise around Neptune. Most objects in the solar system, including moons, move counterclockwise as viewed from the North Pole, and all of the planets move in this way around the Sun. Why does Triton orbit "backwards"? Astronomers suspect that it formed as an independent planet and was then captured by the gravitational force of Neptune. éTsiolkovsky: Rocket Theorist 1898 AD MOSCOW, RUSSIA It was 1898, five years before the Wright Brothers would get their first simple airplane off the ground, and a provincial Russian schoolteacher had already worked out many of the principles of space travel. Konstantin Tsiolkovsky was inspired in part by Jules Verne's science-fiction novel about a trip around the Moon. But while Verne imagined using a giant gun to launch his spacecraft (which would turn the ship's poor occupants into jelly), Tsiolkovsky suggested using rockets. He was the first to seriously propose this method of propulsion for space travel, and was later recognized by the Soviet Union as the "father of cosmonautics." When Tsiolkovsky became interested in space travel, he read everything he could find on physics, math and astronomy. Though he developed his basic theory of rocket propulsion in 1898, his article on the theory, called, "The Investigation of Outer Space by Means of Reaction Apparatus," was not published until 1903, having been overlooked for several years by the magazine "Science Survey." Initially he -- like many others -- regarded rockets as curious toys, but when he was converted, he was thoroughly converted, and devoted the rest of his life to rockets and space travel. He designed piloted spacecraft, lunar vehicles, space colonies and other space-travel related equipment. He was long the inspiration for the Soviet space program. êThe Very Different Tubeworm PACIFIC OCEAN One of the most amazing events in recent years was the discovery of strange life forms near hot-water vents on the bottom of the ocean. Life -- it turns out -- has an astonishing power to adapt to extreme conditions where its survival would seem very unlikely. The inside of the Earth is very hot, which causes volcanoes to erupt and geysers such as Yellowstone's Old Faithful to spout at regular intervals. Scientists exploring the Pacific Ocean floor found geysers called hydrothermal (hot-water) vents at depths of several kilometers (thousands of feet). These vents are sometimes called "smokers" because of the black, dirty water that shoots into the cleaner ocean. Nearby, scientists in deep-sea research submarines found strange, never-before seen creatures, such as giant tubeworms, shown here, which grow up to a meter (about a yard) in length. They also found other new creatures, including giant clams, living around the vents. These life forms have a chemistry based on sulfur, which is quite different from anything else on Earth. Their chemistry was so different from any other known life that some scientists at first suspected they might not even be related to other life. If so, this would have been the first discovery of a totally new form of life. After studying the creatures, however, they found that they have the same basic DNA molecule as all other life on Earth. Since DNA contains the blueprints for all other life that we know of, these creatures are related to the rest of us. But if life can adapt to such bizarre conditions on Earth, perhaps organisms can exist on planets where we would think life is impossible. âScience Fiction's Contribution 1968 AD JUPITER With man's landing on the Moon still a year away, along came a dramatic motion picture that leaped far ahead of the Moon landing and gave a psychological boost to the cause of planetary exploration. The $10.5 million Metro-Goldwyn-Mayer movie, "2001: A Space Odyssey," plunged into the future. Director Stanley Kubrick and science fiction writer Arthur C. Clarke presented lunar travel as a routine affair. The film was unusually accurate scientifically, incorporating many ideas from scientists and engineers. It showed us the adventure of solar system space travel in the year 2001. The heroes have to battle a computer named HAL that's gone crazy, and only one man survives. He passes through a gateway to the galaxy left long ago by an alien civilization. Many people were puzzled by the hero's cosmic trip, full of bizarre, unexplained images. But Clarke explains that "any sufficiently advanced technology looks like magic," just as our televisions and computers would seem like magic to the people of the 19th century. The strange, incomprehensible images in the climax of "2001" are perhaps the closest we will get to glimpsing what a really advanced civilization would be like, unless the scientific search for extraterrestrial intelligence (SETI) is successful. Since "2001," producers have reached even farther into space. The 1966 television program "Star Trek" began each episode with the words: "Space: the final frontier. These are the voyages of the starship Enterprise. Her five-year mission: to explore strange new worlds, to seek out new life and new civilizations, to boldly go where no man has gone before." The United States was ready for the series, because just a year before, in 1965, the US spacecraft Mariner 4 traveled past Mars and the Soviet craft Venera 3 went to Venus, snapping pictures people hoped would answer the question: Is there life on other planets? The answers from the spacecraft were not encouraging, but extraterrestrials had caught the imagination of Hollywood and the public. "Star Trek" was initially short-lived. It was canceled after two seasons but brought back for one more season after a massive letter-writing campaign. But because of millions of loyal fans, it lives on through reruns, movies and an updated version of the show called "Star Trek: The Next Generation." "Star Trek" has been influential in making the public aware of the possibility of life elsewhere in the universe. NASA even used the name of the starship, Enterprise, as the name of the first experimental space shuttle. Another influential science fiction film was the 1977 blockbuster "Star Wars." It had always been easiest for Hollywood to dress an actor up in a rubber suit and say: "Ta Da! An alien." But would an alien really look much like a human being? Possibly, but it seems reasonable that if there are aliens out there, they would fit the environment of their home planet, which would probably differ from Earth. For example, if the gravity there was strong, they might be short and walk on four feet. This is the "Star Wars" approach. Aliens came in all shapes and sizes. "Star Wars" has a classic scene in an alien cantina (bar), where Luke Skywalker (Mark Hamill) and Han Solo (Harrison Ford) meet a wild collection of sleazy nonhumanoid aliens. While "Star Wars" had created alien life forms that looked appropriately alien, the 1982 movie, "E.T.: The Extraterrestrial," took a deeper look, suggesting that underneath, aliens might have something in common with us. Like the aliens in "Star Wars," E.T. looked distinctly non-human, but there was more to him than that. Drew Barrymore, a star in the movie, said: "When I first met E.T. I was scared because he was icky. But after a while I thought he was real and I fell in love with him." E.T. was designed to look "icky." Director Steven Spielberg had pasted Albert Einstein's eyes and forehead on a picture of a newborn baby to get E.T.'s face, and made him short and sweaty and lumpy. His idea was to make E.T. earn the audience's affection. And E.T. did. The movie earned more money than any previous movie. PICTURE CREDIT: Copyright 1968 Turner Entertainment Co. All rights reserved. Comets: Beyond the Atmosphere 1572 AD HVEN ISLAND, DENMARK Just how far away are comets? The Greek philosopher Aristotle said they were disturbances in the atmosphere, but the great Danish astronomer Tycho (pronounced "TY-koh") Brahe proved him wrong. Copernicus had recently begun the revolution that would let us understand the universe, by showing that the Earth was not the center of the solar system. Tycho was to continue that exploration. What probably triggered Tycho's thinking was something extraordinary that happened in 1572: A bright, brand-new star appeared in the sky -- what we now call a supernova. Supernovas are very rare. None has been seen for 400 years in our galaxy. It is fortunate that this one was seen by a world-class astronomer. We now know that a supernova is a large star that dies suddenly. When it runs out of fuel, it explodes so spectacularly that, for a few days, it may be as bright as all of the other hundreds of billions of stars in the Milky Way put together. This was an awesome event for astronomy. Since Aristotle, people had thought the heavens were unchanging. (The occasional meteor was dismissed as an atmospheric phenomenon, which is why meteorology is called what it is, even though it has nothing to do with meteors.) Suddenly, the sky had changed! Could the "star" be just something in the air? That's what Aristotle would have said. But Tycho was a true scientist. He did not just speculate, he experimented. Tycho measured the position of the star and compared it with the position measured in England. If the star were in the atmosphere, it should move against the background stars, just as the position of a building changes against the background mountains if you walk some distance. The star's position did not change. This proved that it was a heavenly body. Aristotle was wrong. The pyramid of philosophical speculations the Greeks had constructed started to crumble. Thus, when the Great Comet of 1577 arrived, Tycho was mentally ready to consider that Aristotle might also have been wrong to think that comets are just atmospheric events. He measured the position of the comet at different times. As the Earth rotated at night, the comet's place among the stars would have changed if it were in our atmosphere. But he found no change. The comet had to be beyond the Moon. Aristotle was wrong again. The groundwork was now laid for understanding the universe. Soon, the German Johannes Kepler would build on Tycho's discoveries, and then the Englishman Isaac Newton would build on Kepler's. The universe would never be the same. Ubar: City Under The Sand 1992 AD UBAR, OMAN Satellites have found a lost city of the Arabian Nights. There once was a city called Ubar, in Arabia. In the time of the Bible it was the center of the frankincense trade. It was described in the Arabian Nights and in the Islamic holy book, the Koran, as the City of Towers. But it had disappeared and no one knew where it was. Like many ancient cities it had been wiped out by some unknown cause and was covered by the desert sands. Expeditions had tried to find it, without success. Then a filmmaker named Nicholas Clapp found clues to its existence in a library, and contacted a scientist, Charles Elachi, at NASA's Jet Propulsion Laboratories (JPL). Elachi was an expert in using the synthetic aperture radar that had flown on the space shuttle. This type of radar, similar to that on SEASAT and on the Magellan Venus spacecraft, lets a small orbiting antenna act like a huge one. Combining the data from the radar with pictures from the NASA LANDSAT and the French SPOT satellites, they traced desert tracks to a water hole in a region of the desert of Oman in the Middle East. In 1992, an expedition to this remote part of Arabia discovered the remains of a castle four thousand years old. The city of Ubar was no longer lost. Indiana Jones had met the space age. PUlysses: A Solar-Polar View 1994 AD SUN The Ulysses spacecraft is on its way to study the Sun. Named after the Greek adventurer (also called Odysseus), Ulysses is a European Space Agency (ESA) probe launched with NASA's help. First, it flew by Jupiter to get a boost from the giant planet's gravity, and now it's on its way to fly over the poles of the Sun. Nobody has ever been able to look down on the solar poles before, and this should give us important clues about how the Sun works. It's very important to understand how the Sun works, since our life depends on it. Ulysses will start its solar-polar flyby in 1994. ┴Umbriel: Uranus Moon 1986 AD URANUS ORBIT Umbriel is a medium-sized moon of Uranus. It is 266,000 kilometers (165,000 miles) from the planet and is 1,190 kilometers (740 miles) in diameter. Its very dark surface is a mixture of ice and rock. It has so many craters that its surface probably hasn't changed much from the earliest days of the solar system, when meteorites were much more common. This picture was taken by the Voyager 2 spacecraft during its flyby of Uranus. ▄ UNIVAC: A Big Pocket Calculator 1951 AD PHILADELPHIA, PENNSYLVANIA The computer was as important to the success of the space program as the rocket. In 1951, UNIVAC was the first commercial, mass-produced computer. Without this computer and the later generations of more sophisticated ones, we never would have been able to calculate the path to the Moon and other planets. When a rocket takes off, devices on board measure its acceleration, temperature and other conditions. These pieces of information are radioed back to Earth, giving what engineers call telemetry, from Greek the roots "tele" (distance), and "meter" (measure). At each instant the computer figures out how fast the rocket is accelerating, and in which direction it is traveling. If necessary, it makes corrections and radios commands back to the rocket to change the direction of thrust. No human could do these calculations fast enough, so computers are essential. The trouble with computers of UNIVAC's era was that they were extremely big and often unreliable. They used vacuum tubes, similar to light bulbs, as their basic electronic switch, and like light bulbs, they tended to burn out. It wasn't until the invention of a transistor, some years later, that computers could be truly miniaturized. Today, a pocket calculator has approximately the same calculating power as that early UNIVAC computer that filled a large room. Transistors are usually made of silicon, an ingredient in common sand. Transistors can be made so small that you need a microscope to see them. A big reason for miniaturization was to put complicated electronics into rockets for the military, so the space program encouraged companies to develop smaller and smaller transistors. As a result, computers could be put into the rockets themselves. Satellites and space probes nowadays usually have at least one -- and sometimes more -- microcomputers on board to control the spacecraft and automatically test conditions. These on-board computers automatically switch to back-up (spare) systems if the main one breaks down. In this way, even if one part of the electronics fails, the spacecraft usually can recover and continue to operate. This miniaturization was perhaps the biggest commercial spinoff of the space program. It revolutionized the consumer electronics industry. The circuit chips developed for the space program eventually found their way into pocket calculators, watches, television sets, video cassette recorders, and practically every other electronic gadget we have today. 7A Small Giant 1986 AD URANUS No spacecraft had ever visited the distant planet Uranus. Then, in 1986, NASA's Voyager 2 spacecraft, which had flown by Jupiter and Saturn, arrived at the planet. Uranus is one of the four giant planets (the others being Jupiter, Saturn and Neptune), all of which lie outside the orbit of Mars. It's one of the smallest of the four, being 50,800 kilometers (32,000 miles) in diameter. It's one-third the size of Jupiter and just three percent larger than Neptune. Uranus is unusual in that it's tilted on its side, with its south pole currently pointing toward the Sun and its equator lying perpendicular to the solar system. Uranus has five medium-sized moons that orbit it in the plane of its equator. Starting closest to the planet, these are Miranda, Ariel, Umbriel, Titania and Oberon. At Jupiter and Saturn, the spacecraft approached with the moons' orbits essentially edge-on, so it took a week or so to fly through the system. But because Uranus and its moons are tilted perpendicular to the rest of the solar system, they looked like a bull's eye to Voyager. The spacecraft shot like an arrow through the Uranus system in just a couple of days. This made it much harder to make corrections if the camera were pointed wrong, but by careful measurements and planning, they got good pictures of all of them. ¡ Uranus: Lying on its Side 1986 AD URANUS Uranus was the first planet to be discovered since ancient times. In 1781, the German amateur astronomer William Herschel discovered a planet beyond Saturn which became known as Uranus. It was not until 1986 that a spacecraft, Voyager 2, flew by this planet, giving us our first close-up pictures of it. Uranus is a giant planet, similar to Neptune in many ways. Like Neptune, it's substantially smaller than Jupiter or Saturn. It is 50,800 kilometers (32,000 miles) in diameter with a mass about 15 times that of Earth. Its atmosphere is mainly methane (CH4) and hydrogen (H2) gas. The effect of the planet's gravity on the spacecraft allowed scientists to get an idea of what Uranus is made of deep inside. The best bet is that it is largely made of water, with some hydrogen, helium, methane and rock thrown in. Uranus takes 18 hours to spin around its axis, so its day is a bit shorter than on Earth. One of the most remarkable facts about Uranus is that it's tilted on its side. Most planets have their spins roughly perpendicular to their orbits, like the Earth, but Uranus is tilted so much that its spin axis is roughly in the plane of its orbit. In fact, its spin axis is tilted 98 degrees, slightly more than the 90 degrees that would put it precisely in its orbital plane. Technically, this means that Uranus is spinning backwards, clockwise as viewed from the North Star. Astronomers call this a retrograde, meaning the reverse of normal. Most of the other planets, including Earth, spin counterclockwise. It takes Uranus 84 years to orbit the Sun. Currently, its south pole is pointing nearly straight at the Sun, and this is the position the Voyager spacecraft found it in. In around 40 years, its north pole will be pointing toward the Sun. It's the only planet that goes through such seasonal extremes. Why is Uranus so tilted? The early solar system was a messy place, with huge rocks and planets forming all over the place. The gravity of big planets like Jupiter tended to fling some of them out in random directions. Probably sometime in Uranus' history, a planet-sized object crashed into it, knocking it over. Like the other giant planets, Uranus has a strong magnetic field. Its field is very complicated, being tilted so that it isn't even nicely lined up with the spin axis of the planet the way Earth's is. Your pocket compass wouldn't be worth much on Uranus. Uranus has rings similar to Saturn's, but they are much darker and thinner, making them very hard to see. It has five medium-sized moons, substantially smaller than our own, plus a handful of tiny ones. The five main moons are -- starting from the planet and moving out -- Miranda, Ariel, Umbriel, Titania, and Oberon. |V-1: Early Guided Missile June 13, 1944 AD LONDON, ENGLAND On June 13, 1944, during the Second World War, residents of London, England, heard a strange buzzing roar in the air above them. Then the buzz abruptly stopped, and was followed in a few seconds by a terrific explosion. Nazi Germany had introduced a frightful new weapon, called the V-1, for Vengeance 1, or "Vergeltungswaffe 1" in German. It was an all-metal, jet-powered, flying bomb with stubby wings and a nose packed with 850 kilograms (1,870 pounds) of explosives. The unmanned V-1 flew at about 580 kilometers per hour (360 miles per hour) and was directed by a simple gyroscopic guidance mechanism. It wasn't very accurate, but you didn't need to be too accurate to hit a city the size of London. A little propeller in its nose turned in the wind to track the distance the V-1 had traveled, and when the meter said it was over its target, the engine cut off and it dived to the ground, where it exploded. The V-1 was also called the buzz bomb or doodle bug from the noise of its pulse-jet engine. The pulse jet was essentially a long tube with flaps on the front. Air and fuel were mixed in the tube, then ignited. The explosion slammed the flaps shut in front and forced the explosion out the back, pushing the V-1 forward. Then the wind opened the flaps again and air flowed into the tube where it mixed with fuel and was again ignited, pushing the V-1 forward again. There were about 47 of these explosions per second, causing the distinctive buzz. Initially the V-1 was very destructive, but the British got better and better at shooting them down. One trick the Royal Air Force (RAF) discovered was to fly an airplane alongside a buzz bomb. A gutsy pilot could touch the plane's wing to the bomb's wing and tip the V-1 sideways. This caused the bomb's gyroscope to go crazy, and the bomb would crash. By August 1944 almost none of them got through. But still, over the course of their short career, about 2,400 buzz bombs landed in London, and about the same number in Antwerp, Belgium. Like their descendent, today's cruise missile, some V-1s were designed to be launched from bombers, though none were actually used this way. åWhite Sands: Where Old V-2s Went 1950 AD WHITE SANDS, NEW MEXICO One of the most feared weapons of World War II was in many ways the ancestor of the rockets that took us to the Moon. In the late 19th century, a Russian, Konstantin Tsiolkovsky, worked out many of the principles of space travel. Then, between the world wars, an American, Robert Goddard, flew liquid-fueled rockets high into the atmosphere. He was generally ignored by his fellow Americans, but members of the German Society for Space Travel followed his work with great interest. The society's members, including Wernher von Braun, built on Goddard's discoveries, and added to them those of German rocket pioneer Hermann Oberth. When World War II came, the Germans created by far the most powerful rocket ever flown, the V-2. It was 13 meters (46 feet) long and weighed 14 tons. In 1942, it flew to the then-incredible height of 80 kilometers (50 miles). It could be fired as far as 300 kilometers (200 miles), far enough to cross the English Channel from German-occupied France. Soon, it was launched against Holland and England. It was not very accurate, but it was terrifying. It flew faster than sound, so there was no warning when it landed and exploded. At the end of the war, most German rocket engineers and scientists surrendered to the Americans. They were taken to an Army base at White Sands, New Mexico, where captured V-2 rockets were studied and test fired. Wernher von Braun was one of those scientists. He eventually spearheaded one branch of the American rocket program, the one that built missiles for the US Army and the rockets that took Apollo astronauts to the Moon. These were the descendants of the V-2. /Vanguard: Off to a Slow Start March 17, 1958 AD CAPE CANAVERAL, FLORIDA The United States' space program started slowly after World War II. At first Army scientists used captured German V-2 rockets. Then the US went on to develop its own rockets. This first home-development program was the Navy's Vanguard program. Scientists planned to use rockets developed during Vanguard to launch a 1.4 kilogram (three pound) satellite into orbit. But with the Vanguard rockets still on the drawing board, the United States was shocked on October 4, 1957 when the Soviet Union launched the world's first artificial satellite, Sputnik 1. And then came Sputnik 2 -- complete with a dog. America was suddenly under pressure to catch up. So, on December 6, 1957, Vanguard rocket TV-3 sat on its pad, ready for liftoff. As planned, the rocket engine ignited and TV-3 slowly began to rise. But then, only about one meter (one yard) off the pad, it stopped, settled back down to the ground and exploded. Its little satellite broke off and lay at the edge of the blaze, beeping pitifully. There has long been rivalry between the Army and Navy, and with this failure the Army was called in. Led by Wernher von Braun, the Army team succeeded in launching the first American satellite, Explorer 1, into orbit on February 1, 1958. Then the Navy launched its Vanguard TV-3 backup rocket. It did better, but failed about a minute after launch. Finally, on March 17, 1958, Vanguard TV-4 placed a satellite in orbit, a 16 centimeter (six inch) ball weighing 1.5 kilograms (3.25 pounds). The Vanguard program made eleven attempts to put satellites into orbit, three of which were successful. The Vanguard 2 satellite measured Earth's reflectivity and the 24 kilogram (53 pound) Vanguard 3, the last of the series, was sent up on September 18, 1959 to measure X-rays and Earth's magnetic field. VEGA Gets a Boost From Venus 1986 AD VENUS The Russians wanted to go to Venus, and they figured out a way to drop by Halley's Comet at the same time. Several years before the 1986 return of Halley's Comet, the Russians planned to send two spacecraft to Venus. It would drop balloons, designed by the French, into the atmosphere to make measurements. A scientist, Louis Friedman, of The Planetary Society, was discussing this mission with Jacques Blamont, one of the leading French scientists involved with the Soviet Venus mission. Friedman said that if he were standing on Venus, Halley's Comet would be spectacular in 1986. It would be a much better place to see the comet than Earth, because the comet would pass much closer to Venus on its trip around the Sun. Friedman's joke about "how great would be the view of Halley's Comet by the Venusians" got him wondering: Would be possible for a spacecraft to fly by Venus, getting a gravity boost from the planet that would take it on to Halley's Comet? NASA's Jet Propulsion Laboratory (JPL) made the calculation and the answer was: Yes! And the next time Blamont came to JPL, he announced that the Russians had had the same idea and had decided to convert their Venus spacecraft into a Venus/Halley mission. So the Russians redesigned the probes, which they now called VEGA, which stands for Venus/Halley. (In the Russian alphabet, Halley is spelled "Galley.") Two VEGA probes were launched. They flew by Venus in 1985 and dropped off balloons. The balloons floated in the atmosphere and measured winds, temperatures and pressures. Meanwhile, the main VEGA probes continued on to a rendezvous with the comet. In 1986, they flew by Halley's Comet and took pictures. This was probably the most complex Soviet planetary spacecraft ever to succeed completely. lVela and the Gamma-Ray Burster 1973 AD EARTH ORBIT Spy satellites have sometimes proven to be of help not only to James Bond but also to astronomers. In the 1960s, the United States launched a series of secret military satellites known as Vela. They carried sensitive instruments similar to Geiger counters to detect X-rays and gamma rays given off by nuclear explosions. (X-rays and gamma rays are both electromagnetic waves like light waves, but of much shorter wavelength.) Some of the gamma-rays detected by the Vela satellites came from space. This led to the detection of one of the most mysterious objects in astronomy, the gamma-ray burster. Unfortunately, the information was kept secret from astronomers until it was finally declassified in 1973. Now we know that there are many gamma-ray bursters in the sky, although no one knows what they are. In 1991, NASA launched the Gamma-Ray Observatory (GRO), a very successful satellite that has been making careful measurements of many of these strange objects. They may be connected with neutron stars, the remainders of exploded supernovas that often become pulsars. Only future observations will tell. ╖Computerized Venus VENUS This amazing picture of the surface of Venus taken by the Magellan spacecraft makes it appear that the spacecraft is flying close to the surface of the planet. In fact, this is a trick of computer processing. As Magellan orbited the planet, its powerful radar made pictures of the surface using techniques similar to those used by the SEASAT radar satellite to map Earth. A photograph shows a two-dimensional picture, a flat image. Radar not only shows two dimensions, but also provides the height. Radar measures how long it takes for a radio signal to travel from the spacecraft to the surface and back again. By measuring that time, it can tell how far away the surface is. Scientists put all this radar information into a three-dimensional database in a computer. There, they can calculate how the surface would look from any angle. This image shows what Venus would look like if you could see with radar eyes very close to the surface. It also exaggerates the height of the mountains, making them look bigger than they really are. It multiplies the height 27 times, so modest hills look like mountains. Geologists use this technique to make it easier to see variations on the surface. ïMagellan Maps Venus With Radar 1992 AD VENUS The Magellan spacecraft has mapped 99 percent of the entire surface of Venus with its radar. Because Venus is forever covered with thick clouds and radio waves pass right through them, radar gives us an image of the surface of Venus that we cannot get any other way. The radar couldn't tell us what the color the surface of Venus is, but Soviet Venera 13 and 14 spacecraft landed on the surface and took color photos. That information was used to color this radar image. This shows the entire surface of one side of Venus. Venus is heavily cratered, much like the Moon, although with lava flows as well as meteorite hits, whereas the Moon shows mostly meteorite craters. Geologists are fascinated by the amazing variety of features on Venus. Volcanoes, past lava flows, meteorite craters, mountains, valleys, and all kinds of strange structures are giving them clues to the history of Venus. ·Venus: Hell in the Sky 1992 AD VENUS Venus has been called "Earth's twin," but it is more like Hell than Earth. Venus is the second closest planet to the Sun, after Mercury. It is covered with a thick atmosphere. The clouds, largely made of sulfuric acid, keep us from seeing the surface with ordinary telescopes. This picture was taken with ultraviolet light from a spacecraft. Venus takes 225 days to orbit the Sun. It's 108 million kilometers (67 million miles) from the Sun, 28 percent closer than the Earth. It is 12,000 kilometers (7,500 miles) in diameter, just slightly smaller than Earth, which is why it has sometimes been called "Earth's twin." On the surface, the atmosphere is about 90 times the pressure of Earth's, and is mostly carbon dioxide (CO2). That would seem to make it very different from Earth, yet scientists now believe that in the early days, Earth may have had a similar atmosphere. The reason is that the carbon dioxide on Earth is mainly locked in rocks. If you could remove the carbon dioxide from the rocks, our atmosphere would be about 100 times denser, similar to Venus's atmosphere. On Earth, water allowed life to exist, and the life, especially shellfish, converted carbon dioxide into limestone and other rocks. Venus has no water, so it is a desert. It also has no moon and spins very slowly, taking 243 days to spin around once (as measured against the stars), longer than its year. Furthermore, it spins backwards compared to most of the planets. While Venus spins clockwise, Earth and most of the other planets spin counterclockwise as viewed from the North Star. It took radar to discover this spin, because the surface cannot be seen by light. In 1992 the Magellan spacecraft used radar to cut through Venus's clouds and map almost all of its surface. From the Earth to the Moon 1865 AD PARIS, FRANCE Jules Verne was the French science-fiction writer who took real scientific ideas and imagined how they might be used in the future. In 1865, just as the American Civil War was ending, he described a trip to the Moon in his classic novel, "From the Earth to the Moon." Not only was this a popular book all over the world, but it turned out to be surprisingly accurate in some of its predictions. Verne made his astronauts American, as would be the case a century later when the Apollo program landed men on the Moon. Amazingly, he even had his astronauts take off from Florida, not far from Cape Canaveral, just as was to happen a century later. His main mistake was in using a kind of giant cannon to shoot the crew into space. Such a launch would create such a huge acceleration that it would kill any humans. Verne's science-fiction was remarkably far-seeing. He not only predicted the flight to the Moon, he also described submarines, 'round the world flights, and other inventions that have come to pass. VMars: No Life Up Top July 20, 1976 AD MARS In 1976, the Viking 1 space probe fulfilled a century-old dream. It became the first spacecraft to successfully land on Mars. Ever since the 19th century astronomers Giovanni Schiaparelli and Percival Lowell had studied the "canals" of Mars, the public had been fascinated by the possibility of Martian life. Because Mars is only 52 percent farther from the Sun than Earth, it is not too far from the Sun for life to be possible. And it has ice caps, which mean that at least one of the ingredients of life, water, is there. So scientists and engineers designed two identical NASA spacecraft, Viking 1 and 2, to look for life. One part of each Viking, the two-ton orbiter, would orbit Mars while the other part, the one-ton lander, would parachute through the thin carbon-dioxide atmosphere and fire rockets, landing softly. So there were two orbiters and two landers. Viking 1 landed on the seventh anniversary of the Apollo 11 moonwalk in an area of Mars called Chryse Planitia. The first thing it did was to look around. It had two television cameras, like two eyes, that could see the ground. As it slowly scanned the landscape, scientists eagerly watched the first pictures ever sent back from the surface of Mars. They saw a landscape of rocks. They searched for signs of plants or animals. Instead, they found a barren, desert-like scene, complete with sand dunes. But the lander had a laboratory on board to test for life. There was a sample arm stored like a carpenter's tape. It unreeled and reached out its scoop until it picked up a handful of Martian soil. It dumped the soil into the laboratory hopper that distributed it to three experiments. Each one tested for life in different ways. One tested for photosynthesis, the technique used by plants to use sunlight for energy. It used carbon dioxide (CO2) made with radioactive carbon, to see if any Martian plants breathed in the CO2 like Earth plants. The radioactivity made it easy to test the movement of carbon atoms with a kind of Geiger counter. Another experiment tested to see if any organism used nutrients (the chemicals of food). Again, radioactive carbon was used to test whether any gas was given off by digestion of the nutrients. The third experiment tested for changes in the Martian air that would have happened if there were any organisms in the soil. At first, two of the experiments seemed to detect life. Were there bacteria? But after analyzing the experiments carefully, scientists concluded that it was a false alarm. Because of the thin atmosphere, about one percent of Earth's, harsh ultraviolet from the Sun passes right through and blasts the surface. Martian sand experiences a kind of sunburn, which forms molecules that are unusual on Earth. When water was added to the sand, the molecules experienced chemical reactions that triggered false alarms. Another experiment measured the chemicals in the soil, and found no organic (carbon) compounds. Sadly, the Viking did not find any sign of life, not even microscopic Martians. Viking 1 continued to measure the temperature and pressure of the Martian atmosphere, and to monitor the surface until 1982. There's still a slim possibility that life might exist somewhere else on Mars. The places where the two Vikings landed were chosen to be as smooth as possible, to avoid the danger of the landers being toppled over by rocks or craters. These were desert-like places where underground water was not likely to exist. There are other places on Mars where frozen water probably exists underground. And there are the ice caps. Perhaps something like moss or bacteria grows on Mars today, using this water. Finding any kind of life would be tremendously important to science, because we don't yet have any example of life on any planet but Earth. Until we prove that life exists somewhere else, we won't know how rare life is in the universe. ·Viking 2 Finds Fluffy Rocks September 3, 1976 AD MARS In 1976, the Viking 2 spacecraft followed Viking 1 to land on Mars. It came down in an area called Utopia Planitia. Viking 2, a duplicate of Viking 1, landed in a rougher spot than the first lander. The area was covered with rocks full of bubbles, like lava. At both places, the sky and soil were pink. In fact, at first this fooled the scientists. When the first color photos of the Martian sky were prepared, the scientists adjusted the colors to make the sky blue, because that's what they expected. These pictures were released to the press. The scientists figured that the Martian sky would be blue for the same reason Earth's is: Air molecules scatter blue light much more strongly than red. So blue light is filtered out of the Sun's rays and bounces all over the sky. Then they carefully tested the Viking cameras, looking at a colored card on board the landers. When they adjusted the television colors to match the correct colors of the card, they found that the sky was really pink. The fine dust that makes Mars red even to the naked eye on Earth is blown around by winds. Some of the dust floats in the sky, making it pink. There were magnets on the Vikings, and the camera found that dust stuck to it. The dust is an iron oxide similar to rust. You might say that Mars is red because it's rusty. Viking 2 tested for life in the soil, but found none. Both Vikings had seismometers to test for earthquakes (really marsquakes). But the one on Viking 1 jammed and wouldn't work. So it was up to Viking 2 to do the job. It found occasional slight vibrations, mostly due to wind. There were a few "earth" tremors (vibrations of the Martian surface), but there weren't the frequent tiny earthquakes that occur on our planet. It appears that Mars is a quiet planet. It doesn't have continents drifting on a molten interior that we have on Earth. It's this drift that causes our continental plates to crash into one another, creating earthquakes and volcanos. Viking 2 continued to monitor Mars through 1978. Viking Orbiters: Circling Mars 1976 AD MARS The two Viking landers that arrived at Mars in 1976 were carried there by spacecraft called orbiters. While the landers landed, the orbiters circled the planet, taking thousands of photographs. They found much evidence for ancient riverbeds and seas, as well as signs of permafrost under the surface, much like that found in the Arctic regions of Earth. They also sent back pictures of huge volcanoes, vast fields of craters, strange layered ice caps, and changing markings caused by wind-blown dust. Making a Super Antenna 1981 AD SOCORRO, NEW MEXICO The Very Large Array (VLA) is a set of 27 large dish antennas on railroad tracks in the desert of New Mexico. Each one is a radiotelescope 25 meters (82 feet) in diameter. (Viewers of the movie "2010," the sequel to "2001: A Space Odyssey," can see it early in the film.) The VLA searches for radio signals from galaxies, quasars, the center of our galaxy, and other objects. By using the antennas in various combinations, scientists can make them act as if they were an antenna 27 kilometers (17 miles) in diameter. Usually, radiotelescopes produce images of nature's signals that look like geologist's contour maps of mountains. But this powerful set of radiotelescopes is able to see exceptionally fine detail, so that it can make pictures that look like photographs. σSunsets and Sulfur Dioxide June 15, 1991 AD MT. PINATUBO, PHILIPPINES In 1991, Mt. Pinatubo volcano in the Philippines exploded. It was the most powerful eruption in this century. The sulfur dioxide (SO2) gas that it shot into the atmosphere formed sulfuric acid (H2SO4) droplets. These made dramatic reddish sunsets all over the world. But that wasn't all the volcano did. Sulfur compounds (sulfates) formed particles that floated into the upper atmosphere (the stratosphere). These hot particles warmed the air and caused the amount of ozone gas to fall about 10 percent. (Ozone is the oxygen molecule that absorbs the Sun's ultraviolet light, serving as a shield to protect us from this cancer-causing light.) Pinatubo's particles have now spread all over Earth's lower stratosphere. The effects of volcano eruptions usually last from three to five years. Scientists are now looking to see if Pinatubo reduces the ozone layer during this period. This picture of Pinatubo's sulfur dioxide was made using NASA's Upper-Atmosphere Research Satellite (UARS). UARS was launched in 1991 by the Space Shuttle Discovery. It is making the most thorough study ever done of our upper atmosphere's chemistry and energy flow, particularly to understand the thinning of the ozone layer. UARS is the first major satellite in a series known as Mission to Planet Earth, and is run by NASA's Goddard Space Flight Center in Greenbelt, Maryland. Mission to Planet Earth will try to understand how our planet operates as a complete unit over a period of years. eFour Planets at Half Price 1977 AD SOLAR SYSTEM Scientists once thought it would take decades to send a spacecraft to the outer planets. But as they studied the problem, they found an ingenious technique that greatly accelerated the exploration of the outer solar system. They discovered there is a way to use the gravity of the planets themselves to speed up a spacecraft. The planet could become, in effect, a slingshot, giving the spacecraft a boost as it flew by. The trick is to take advantage of the planets' movement. The effect is a lot like a ping-pong ball and paddle. If a ball bounces off a paddle that is standing still, the ball has the same speed after the bounce as it had before. It neither gains energy or loses energy, except for a tiny amount lost in the friction of the encounter. But in playing the game, you swing at the ball as it comes in. Some of the energy from your swing goes into the ping-pong ball, making it move faster after it bounces off the paddle. In this case, the energy comes from your arm, and is transferred to the ball. In the same way, if a spacecraft flew by a planet that was just sitting still, it would simply be deflected by the planet's gravity. It would curve past the planet and leave with the same energy it had coming in. However, real planets are moving. They're orbiting the Sun. If the spacecraft is aimed right, it will not only be deflected as it passes the planet, but it will also pick up energy from the planet's motion. When NASA scientists began thinking how they could use this, they realized that there was an unusual arrangement of the outer planets, Jupiter, Saturn, Uranus, Neptune and Pluto. This arrangement meant that if a spacecraft flew by the first planet, it would get a boost that would take it on to the second one, where it would get a boost that would take it on to the next, and so forth. The combined effect of these boosts would be to reduce by decades the time that it took to get to all the outer planets. They proposed this "Grand Tour," but unfortunately Congress only approved money for a trip to Jupiter and Saturn. So NASA designed two smaller spacecraft, Voyagers 1 and 2, to go to Jupiter and then use the gravitational slingshot to reduce the time to get to Saturn. But during the mission, scientists realized that Voyager 2 could still use the gravitational slingshot to complete most of the original Grand Tour mission. Delays in getting the money let Pluto slip out of range, but Uranus and Neptune were still available. So Voyager 2 could get there. Since the spacecraft was a scaled-down version of the original design, it was not, at first, thought possible to get much data back from beyond Saturn. However, the scientists came up with ingenious ways of making the spacecraft operate more efficiently. While it flew on its mission, they reprogrammed its computer. They made its data storage more efficient. By eliminating the duplication of information in a typical picture, they greatly increased the rate at which the data could be sent back. Back on Earth, they increased the sensitivity of their radio receivers and the size of the antennas. All of this compensated for the very weak signals that the spacecraft sent back from the fringes of the solar system. As a result, many more pictures could be sent back from Uranus and Neptune. Ingenuity triumphed and NASA got almost the entire Grand Tour mission, but for a cut-rate price. ┴Wells: Science Fiction Pioneer 1898 AD LONDON, ENGLAND But for a broken leg, the world might have been deprived of some of the finest science fiction ever written. The education of H.G. (Herbert George) Wells really began with a broken leg. As he was recovering from the injury, Wells read and read and read -- everything he could get his hands on. This habit of reading stayed with him for the rest of his life and much of his writing reflects his exploration of current scientific thought. As a young man Wells worked as an assistant to a draper, and later as a teacher. His science fiction career really began with his 1895 novel, "The Time Machine." From then he wrote such novels as "The Island of Dr. Moreau" (1896), "The Invisible Man," (1897) and one of the classics of science fiction, "The War of the Worlds" (1898). All of these have been made into movies. "The War of the Worlds," the story of an invasion of Earth by Martians, was adapted for radio in 1938 by Orson Welles (no relation). Because Welles presented the story as a series of news flashes, many people were terrified, thinking Martians had actually landed. Despite several announcements that the story was fiction, panic-stricken people drove away from the supposed Martian landing site; others claimed to have seen the Martians. H.G. Wells was one of the most influential of all science-fiction writers, inspiring generations of later writers with his inventiveness and his concern for the effects of technology on society. ╝The First US-Only Satellite April 13, 1974 AD EARTH ORBIT The problem with using satellites for communications is that they have to be overhead. The signal has to travel from your city, bounce off the satellite, and travel to the destination city. It doesn't do any good if the satellite is on the other side of the world when you want to place a call. Fortunately, there is a way to keep a satellite in the same place relative to the Earth all the time. British scientist and science-fiction writer Arthur C. Clarke came up with the solution. (This is the same Arthur C. Clarke who wrote the book and movie, "2001: A Space Odyssey.") In 1945, long before the Space Age had begun, he published an idea in the British magazine "Wireless World." He calculated that a satellite placed in an orbit 35,000 kilometers (22,000 miles) above the equator would take 24 hours to orbit the Earth, exactly one day. As a result, it would never seem to move in the sky. As the Earth rotated around its axis, the satellite would circle the planet and always seem to hover above the same point on the ground. He proposed using such a stationary satellite for communication. If, say, you put the satellite above the middle of the Atlantic ocean, you could bounce radio signals from England to America and vice versa. And the satellite would always be there whenever you wanted it. This is called a geosynchronous or geostationary orbit (from the Greek "ge," meaning Earth, as in geography). Clarke has sometimes regretted not patenting the idea, because it is now the basis for the multi-billion-dollar communication satellite industry. So he never received any money for it. But even if he had patented it, the patent would have expired by the time rockets were able to make his dream come true. Westar 1, launched April 13, 1974, was the first of several geosynchronous satellites designed just for communications within the US. It was built by Hughes Aircraft for Western Union. The 306 kilogram (674 pound) satellite looks like a barrel with a fan (an antenna) at one end. It covers all forty-eight contiguous states, plus Puerto Rico. Westar 6's rocket failed to take it up to geosynchronous orbit, so it was retrieved by the space shuttle and brought back to Earth for repair. 4No Gravity: Pleasures and Problems EARTH ORBIT Probably the greatest advantage and problem for humans in space is weightlessness. On the one hand, weightlessness is a joy for many astronauts who have experienced it. At first astronauts often experience spacesickness, similar to seasickness. Some feel as if they have a cold, since weightlessness affects the sense of balance that is found in our ears, which colds often disturb. However, most adapt to weightlessness after a day or two, and become quite comfortable. The real problem with weightlessness comes on long missions. Astronauts who spend weeks in space often come back weakened. Russian cosmonauts have spent the most time in space -- up to a year. When they return home, they are sometimes so weak that they need help emerging from their space capsule. Much of the problem seems to be that weightlessness is so easy for the body. It's very much like extended bed rest. People who have to stay in bed for long periods because of illness often experience similar problems. The muscles become weak and bones lose some of the calcium which gives them their strength. The main technique for reducing this weakening and calcium loss is exercise. Astronauts and cosmonauts have found that with hours of vigorous exercise every day they can remain in reasonably good shape. Scientists are still searching for a medicine that will make it easier for people to retain their normal strength without having to spend great amounts of time doing exercise. One possible solution for long-term missions would be rotating spaceships. Centrifugal force would create artificial gravity, so the body would act just as it would on Earth. The problem is that rotation complicates spacecraft design and makes it harder for people to leave the spacecraft and work in space. It also makes it harder for two spacecraft to dock. ûThe Vast Canyon of Mars 1976 AD MARS In this Viking Orbiter picture, we can see the countless craters, long-dead volcanoes, and huge canyons of the mysterious planet of Mars. The scar across the middle of the planet is Valles Marineris, one of the largest geological features in the solar system. It is 4,500 kilometers (2,800 miles) long. It's so large that the Earth's entire Grand Canyon could fit into one of its minor branches. ≥Wow! Let's Hear it Again 1977 AD COLUMBUS, OHIO In 1977, scientists at Ohio State University recorded one of the strangest signals ever seen in the search for extraterrestrial intelligence (SETI). They were using a radiotelescope to look for signals that might be sent by alien civilizations. Suddenly, this strong signal came in, much louder than the noise of space. The operator wrote "WOW!" on the record, and since then, it's been called the Wow signal. It looked just like the kind of signal that might be sent by another civilization, but it has never repeated. Until the signal repeats, it can't be analyzed -- you need to have more than one observation to prove that it really came from space. Similar signals have occasionally been picked up by other SETI projects around the world. These, too, have never repeated. They are tantalizing and frustrating. But we live in a civilization that produces all kinds of radio noise. Unless a signal repeats, we have to assume that it was just some unusual noise from our own planet. s Breaking the Sound Barrier Oct. 14, 1947 AD MOJAVE DESERT, CALIFORNIA No one had ever flown a plane faster than the speed of sound. Some thought it would be impossible. Data for supersonic flight was not available. You couldn't be sure of what you got from wind-tunnel experiments because at near-supersonic speeds shock waves bounced all over, off the sides of the tunnel, making a mess of the data. To find out what really happened to a plane at such high speeds, you had to actually build a plane that would go that fast. And judging from the disastrous experiences of some fighter planes that had gone into high speed dives, many believed there was a barrier that would destroy a plane trying to fly faster than sound. In any case, it would be a dangerous undertaking. So it was without much solid information that Bell Aircraft Corp. of Buffalo, New York, went about designing a plane to break the "sound barrier." Bell had been commissioned by NACA (National Advisory Committee for Aeronautics, the forerunner of NASA) to build a plane that would go 1,300 kilometers per hour (800 miles per hour) at a height of 11 kilometers (35,000 feet). Designer Robert Woods came up with a 9.4 meter (31 foot) long rocket-powered airplane with a stubby 8.2 meter (27 foot) wingspan. It looked a lot like a .50 caliber bullet, which is exactly what it was modeled after. It was initially called the XS-1, for Experimental Sonic 1, but the name was soon shortened to X-1. In 1946 the X-1 began test flights at Muroc Army Air Field in the Mojave Desert of California (now Edwards Air Force Base). The plane, painted bright orange for visibility, was carried aloft in a B-29 Superfortress and dropped out of the bomb bay. Slowly, Air Force Captain Charles "Chuck" Yeager, a World War II fighter ace, pushed the plane to greater and greater speeds, past Mach .85, beyond which statistics were unavailable. (Mach 1 is the speed of sound, so Mach .85 is 85 percent of the speed of sound.) Then, on the morning of October 14, 1947 a one-armed Yeager climbed into the X-1. He had fallen off a horse and cracked his ribs. He couldn't use his right arm because of the pain. A friend slipped him a length of broomstick so he could close the safety latch. At six kilometers (20,000) feet, the bomber dropped him and Yeager started the rocket engine. The little X-1 shot up to 13 kilometers (42,000 feet), where Yeager slowed down to make a final check. Then he fired three of the plane's four rocket engines. On the desert floor below, the ground crew heard the crack of a sonic boom. Chuck Yeager had broken the sound barrier for the first time. One of the barriers to getting humans into space had been overcome. Quasars: The Oldest Galaxies? 1963 AD PASADENA, CALIFORNIA Quasars are the fastest astronomical objects that we know of anywhere in the universe. The big breakthrough in understanding quasars occurred in 1963. Astronomer Maarten Schmidt knew there were a number of strange, star-like objects in the sky. They looked like stars, but the spectrum of each "star" was weird. Normal stars produce a rainbow of light -- a spectrum -- which has bright and dark lines across it. The lines are caused by atoms in the atmosphere of the star that absorb and emit particular colors. Each atom has its own pattern of lines. Carbon has one set of lines; nitrogen has another set; hydrogen another, and so on. A spectrum is like a fingerprint that identifies a particular atom. But the fingerprints of the stars Schmidt was examining didn't fit any known atoms. Yet we think we know all the atoms that can exist in the universe; there are only about 100 of them. Schmidt had a brilliant inspiration. He knew that when an object moves, its light is "Doppler shifted." If it moves away from you, the Doppler shift makes the light redder. If it moves toward you, the light is shifted toward blue. Ordinarily, this shift is very tiny. It's only if an object is moving close to the speed of light that the Doppler shift becomes large. The lines in the spectrum can be measured to tell the exact value of the shift, which allows its speed to be calculated. This is how Edwin Hubble had discovered that the universe is expanding. He measured the Doppler shifts in the spectrum of galaxies. No astronomer had ever seen any object moving near the speed of light, so no one had given much thought to the possibility of a huge red or blue shift in a spectrum. But Schmidt wondered if these these "stars" might be moving very, very fast. So he calculated what the spectrum of an atom would look like if it was emitted by an object moving close to the speed of light. He discovered that, in fact, the strange "stars" had standard spectral fingerprints! Suddenly, the mysterious lines were those of familiar atoms like hydrogen. Once astronomers understood that there really were star-like things moving incredibly fast, they found many more of them. They called them quasi-stellar objects, or "quasars," for short. Today, thousands of quasars have been detected. Some of them move as fast as 90 percent of the speed of light. Quasars are very strange things. They emit enormous amounts of light and, in many cases, radio waves. There is a growing suspicion that quasars are actually a special kind of galaxy. But what causes the enormous amounts of energy to be emitted? It may be that there are enormous explosions in the centers of quasars. There may even be giant black holes there. Certainly, something with tremendous energy is occurring in the centers of these quasars. In the theory of the expanding universe, the faster a galaxy moves, the farther away it is. Most astronomers think the same rule applies to quasars. If so, quasars are the most distant objects we can see in the entire universe. Furthermore, the farther away an object is, the longer its light or radio waves take to reach us. So that makes quasars the oldest objects that we can see in the universe. The light from the most distant quasars started shortly after the universe formed in the Big Bang. Bigger Crystals in Space EARTH ORBIT For some scientists, the most valuable advantage of an orbiting spacecraft is weightlessness. For example, in zero gravity, you can grow crystals that are much more regular than is possible on Earth. This may be of great importance in the future. Crystals are an extremely regular pattern of atoms, arranged like oranges piled up neatly for display in a store. Slight impurities can destroy the regular pattern, like a melon mixed in with the oranges. Most metals, such as steel, are made of tiny crystals that form when the molten metal cools. One of the most valuable resources to our civilization is a crystal made from the element silicon, found in most computer chips. Other crystals are used in medicine. Scientists make crystals out of the chemicals in our bodies. By using X-rays, they can figure out how the molecules are shaped. This technique is essential to medical research, and it's how the double-helix shape of the DNA molecule of life was found. One of the troubles with making crystals on Earth is that gravity creates an "up" and a "down." This makes hot air rise and cold air fall, a process called convection. This effect also works inside of liquids, and causes warmer parts of the liquid to rise and colder parts to fall. This can move impurities around and make it harder for the crystal to form. In weightlessness, there's no "up" or "down." Liquids float as spherical blobs. When the liquid cools or evaporates, it can form crystals. Without gravity it's much easier for single crystals to grow large. On Spacelab 1, scientists grew crystals of various proteins. They were able to grow them several times larger than on Earth, making it possible to study their structure. Also, zero gravity makes it possible to create metal alloys that cannot be made on Earth, because some metals do not mix when molten. Some zero-gravity alloys have even turned out to be superconductors, which have absolutely no electrical resistance when cooled to very low temperatures. And superconductors may be an important commercial technology in the future. Studying materials in zero gravity promises to help medical research, and may also result in commercially valuable products for medicine and industry. One day, zero gravity may be viewed as one of the greatest of our natural resources. VYoung: Astronaut's Astronaut March 1965 AD ORLANDO, FLORIDA John Young, who grew up in Orlando, Florida, is an astronaut's astronaut, having flown a record six times in three different space programs. In March 1965, he flew Gemini 3, the first two-man Gemini mission. In July 1966, he and Michael Collins flew Gemini 10 into the highest orbit for a Gemini craft. In May 1969, he flew around the Moon in Apollo 10 to practice separating and redocking the Lunar Module and the Command Service Module. Then in April 1972 he did the big one: He commanded the Apollo 16 mission to the Moon. He walked on the Moon, becoming one of only twelve human beings to have done this. He and astronaut Charles Duke stayed a record 71 hours and two minutes on the Moon's surface, using a lunar rover to make three expeditions to various craters and mountains. Apollo 16 brought back 94 kilograms (206 pounds) of samples from the trip. In April 1981, he commanded the first space shuttle mission into space, flying the Columbia on its shakedown voyage. And in November and December 1983, he flew the first Spacelab into orbit in the payload bay of the Columbia. $Early Earth: Not Very Pleasant 4.6 Billion BC EARTH In its early days, Earth suffered a horrendous bombardment from space. When the solar system formed almost five billion years ago, it was filled with dust, gas and pieces of rock. These tended to cluster together, attracted by gravity. The small clumps became larger ones, which formed moons and planets. Gradually, the planets swept up most of the orbiting debris. Their gravitational fields attracted lumps of rock that flew past them, many of them smashing into the planets. We can see on the surface of the Moon what a typical planet must have looked like after it had formed, with craters almost everywhere. During this period there was a steady rain of meteorites and comets. Each one could contain energy equal to many hydrogen bombs, and when the object hit, it vaporized in a spectacular explosion. Furthermore, the heat of this process of assembling the planet out of rocks kept the interior of the Earth molten. Volcanoes erupted frequently through the cooling crust of the planet. The combination of volcanoes and incoming comets and meteorites must have made the early history of Earth like something out of Hell. It may have taken hundreds of millions of years for the planet to cool enough for water to condense and form lakes and oceans. And it was not until then that life began. Some scientists even suspect that life may have been wiped out by a late storm of meteorites or comets. Perhaps life got several starts, until the solar system became clean enough for it to exist without being obliterated. Collisions with objects from space continued but became less frequent. Then, objects from space large enough to endanger wide areas of the planet would only hit every few tens of millions of years. It was probably such a comet storm that wiped out the dinosaurs 65 million years ago.