This is another new direction that we are trying. We have published many quizzes in the past, but most of them were "cold;" that is you either knew the material or you didn't. This month we'll try a new approach. This text file is an "astronomy essay" that gives a short course on modern astronomy. The quiz program on this disk ("QUIZ.EXE") and the quiz file ("COSMOS.QZR") ask questions that relate directly to this essay. If you think you know a lot about astronomy, then go ahead and take the quiz now. If you would like a refresher course before taking the quiz, then read this file first. If you are reading this file from the On Disk Monthly shell program, you can activate the "Run" button at the bottom left of this window to take the quiz.
^CDEFINITIONS
Astronomy is defined as "the science of the universe." This sounds pretty all-inclusive, so one of the first questions you might have is "Well, then what is 'astrophysics'?" Strictly speaking, astronomy is a discipline with several branches. Astrophysics, for example, is the study of the physics of the universe and deals with questions like "What makes a star shine?" or "How does a pulsar work?" Another branch of astronomy is "Cosmography," or the study of the structure of the universe. Cosmographers examine the distribution of galaxies in the universe, stars in a galaxy and planets in a solar system. Astronomy, in the general sense, is the study of the sky and the objects we find there.
A fundamental tool in the understanding of our universe is the "Cosmological Principle." This can be paraphrased as "there is nothing special or unique about our vantage point in the universe. The universe would look more or less the same from any random location." Contrast this with the earlier belief that the Earth was the CENTER of the universe, and you can see what a fundamental shift in our attitude about the universe and our place in it has occurred in the last few centuries. Although this Principle may seem like a minor philosophical argument, it is a powerful tool in the actual theorizing of the dynamics of the universe. The Cosmological Principle allows us to say that stars must operate under the same set of physical laws that we experience in a laboratory. It implies that a quasar, too, is subject to the laws of the universe, at least as well as we understand them. And, finally, it suggests that whatever happens "out there" can be made to happen here, if we can puzzle out the proper set of circumstances.
^CBEGINNINGS
Astronomy is sometimes called the "oldest scientific discipline" because of mankind's timeless fascination with the stars. In fact it is difficult to find a culture that has not examined the night sky in detail and developed some system of predicting the paths of the moon and planets. Even cultures which have limited written languages frequently have remarkably sophisticated astronomical observatories and detailed records of astronomical events. A clear understanding of the repetitive nature of the apparent motions of the stars and planets can lead to precise predictions of seasons, solar eclipses (when the moon falls between the earth and the sun) and lunar eclipses (when the earth falls between the moon and the sun), planting and harvesting dates and much more.
Astronomy as a true science can be traced to the observations of Nicholas Copernicus (1473-1543) and his assertion that the earth and the other planets revolve around the sun. Although this was not a unique idea, his detailed observations allowed him to show how the motion of the planets was greatly simplified by placing them, and the Earth, in orbit around the sun. Although his ideas were vigorously attacked by religious authority, his writings strongly influenced the future of astronomy.
The great astronomer Tycho Brahe (1546-1601) was a man obsessed with the observation of the heavens. He devoted his life to the detailed recording of astronomical events. He recorded the variation in the brightness of stars, the appearance of comets and much more. His observations became the basis for the work of his protege, Johannes Kepler.
Johannes Kepler (1571-1630) created the first rigorous mathematical examination of the motions of the heavenly bodies. Using the data collected over half a century by Tycho Brahe, Kepler devised the first mathematical "laws" which could be used to predict the motions of the planets. This was the birth of the first true "dynamics" of astronomy.
Galileo Galilei (1564-1642) completely revolutionized astronomy. Galileo was a brilliant and innovative thinker, and his scientific contributions were not restricted to astronomy. He was a particularly gifted physicist. As a physicist Galileo was intensely interested in the nature of light. He became aware of the ability of a lens to magnify objects and realized that a combination of lenses could be employed to magnify distant objects. Galileo built his first telescope in 1609 and the clarity of detail he observed on the moon's surface was startling. Turning his gaze to the heavens, Galileo quickly discovered that Jupiter was orbited by several moons, and that Venus went through a cycle of phases similar to those of the moon. The use of the telescope transformed astronomy, and had ramifications that shook the very foundations of society.
Perhaps the greatest thinker in the history of science was Sir Isaac Newton (1643-1727). By the time Newton turned his interest to astronomy, the telescope had been around for almost a century. The orbits of the planets had been mapped to a very high degree of accuracy and most of the planets and their moons had been discovered. Newton used these precise observations to develop the basis of a comprehensive theory that would dominate the physical sciences for three hundred years. It was Newton who determined that the stars, planets and the Earth itself moved in accordance with gravitational forces. According to legend, Newton was dozing under an apple tree as he pondered the mysterious bonds that held the planets to their orbits. When he was startled awake by a falling apple, a flash of insight led him to visualize the apple as a moon, planet or star, and the force that caused the apple to fall, he realized, must be the same force that held the moon, the Earth and all heavenly bodies in their orbits.
^CDISCOVERIES
Astronomy deals with the most fundamental questions that humans ask. For this reason, astronomy and religion can, and frequently do, collide. Galileo was viciously attacked by the church when he published his theories on the structure of the universe. But as time went on and the other physical sciences brought forth advancement after advancement, public sympathy for astronomy and astronomers grew. Ultimately, this led to the universal acceptance of Newton's revolutionary ideas. This opened the way for other scientists to make bold predictions. Sir Edmund Halley (1656-1742), an aide to Newton at one time, decided to devote his attention to astronomy. He realized that comets must obey the same laws as the planets and used observations by generations of astronomers to boldly predict the return of a particular comet. When the comet made an appearance just as Halley had predicted, it was named Halley's Comet, although Edmund Halley had died several years earlier.
The nineteenth century was the heyday of astronomical discovery. One of the most famous astronomers of that time, Percival Lowell (1855-1916), used mathematical analysis of orbital anomalies of other planets to predict the existence of a yet undiscovered planet. A planet was later discovered close to where Lowell predicted and named Pluto. It is an interesting historical note that Pluto could not have caused the orbital fluctuations observed by Lowell and it was sheer coincidence that Pluto happened to be close to the predicted location. Perhaps unfortunately for Lowell, he is probably best remembered for his "discovery" of the canals of Mars. To be fair, Lowell was not the only astronomer to report the existence of the mysterious "canals" but he was their most vocal champion. These canals, he insisted, were proof of life on Mars. Edgar Rice Burroughs used this theory to create his "John Carter of Mars" series, and H.G. Wells did likewise with the "War of the Worlds."
It wasn't until the twentieth century that the theories of Isaac Newton received their first real challenge. A young Albert Einstein (1879-1955) turned the world of astronomy (and physics and just about every other scientific discipline) on its ear with his "Theory of Relativity" in 1916. This radical new theory challenged some of man's most basic assumptions regarding time and space and led directly to the harnessing of nuclear power. Einstein's theories relating to gravitation and the space-time continuum are so complicated that it is unlikely that even one-tenth of one percent of the population of the planet understands them. They are far too involved for any discussion here, other than to point out that they do not allow for physical objects to exceed the speed of light, and that gravity plays a pivotal role in the topology of the space-time continuum.
^CHISTORY OF THE UNIVERSE
Although our concept of the universe has undergone radical change over the centuries, and is subject to major change even today, most astronomers now agree on the basic structure of the universe. The following paragraphs give a quick "history" of the universe.
The universe has not always been as we see it today. Current cosmological theory holds that the universe came into existence through some unknown process about ten or eleven billion years ago. At that time the entire universe was an infinitesimal point of unimaginably dense, hot material. In an explosion that is commonly called the "Big Bang" this tiny point began to expand and cool, and continues to expand and cool to this day. As it cooled great clouds of hydrogen formed. Hydrogen is still the most common substance in the universe, making up about 75% of all observed matter. These clouds eventually condensed into smaller, denser clouds, and the smaller clouds ultimately coalesced into the galaxies we see today. This explains why galaxies are moving away from each other at great speed, and also explains why galaxies occur in clusters. If the Big Bang theory is true, then the cooling of the universe should still be going on today, and should be detectable as radiant energy. One of the most important discoveries of the twentieth century was the detection of just such radiant energy, now called "background radiation," which is, in effect, an "echo" of the Big Bang.
Inside of each galaxy, further condensation of the gas clouds created great nebulae where hydrogen was concentrated in a dense fog. Many of these nebulae still exist in our galaxy today. Within this dense fog, swirling masses of hydrogen eventually condensed into stars. The intense weight and friction of the hydrogen in the stars led to the process of nuclear fusion, where hydrogen was changed into helium and other elements, releasing enormous amounts of energy. This process heated the surface of the stars until they glowed brightly. The largest stars burned their hydrogen rapidly, eventually reaching a point where the nuclear furnace could no longer support their great weight, and they became supernovas, sending great gouts of heavier elements back into space, to be absorbed by the vortices of newly forming stars. This process of "cooking" hydrogen into heavier elements eventually created nebulae which were rich in heaver elements. Our own star was formed in such a nebula, which marks the sun as a second or third generation star. It is from this ash of supernovas that all of our oxygen, iron, silicon and every element up to and including uranium originated.
^COUR SOLAR SYSTEM
Our sun is a fairly boring (to astronomers) "main sequence" star. This means that it should be stable and should follow a predictable life-span, eventually forming a red giant star before finally burning itself into a cinder, becoming a white dwarf star. This should not happen for several billion years yet, so don't worry. Of course there are no guarantees, so if the sun goes out tomorrow, don't sue me. Although we call it "the sun," our star is named "Sol."
A "solar system" is a collection of planets, asteroids, comets, gasses and other debris surrounding a star. Our particular solar system consists of nine known planets, a wide belt of rocky debris known as the "asteroid belt," the various moons of the planets, the comets and a remote halo of icy debris at the "heliopause" or the edge of the solar system. This halo of icy debris is called the Oort cloud and is thought to be the source of the comets. The planets, in order of distance from the sun are:
Mercury is a crater-pocked airless ball of rock somewhat resembling our own moon. Mercury also played a pivotal role in the acceptance of the General Theory of Relativity when Einstein's theory correctly predicted an orbital anomaly that Newton's theory had never explained.
Venus has an atmosphere that is a dense caustic soup of toxic chemicals and acids. It is so caustic that probes are destroyed in a very short time, making it difficult to explore the planet. Because Venus is close to the Earth in size and in orbit, it was once called the Earth's "Sister Planet."
Earth is the only planet with liquid water and an oxygen based atmosphere. It is also, as far as we know, the only planet with plate tectonics, civilization, space travel and professional wrestling.
Mars was once thought to have canals, and there is evidence of running water on the surface of the planet, but it now appears to be a lifeless ball of dust and dry ice. Mars has two moons, Phobos and Deimos.
The origin of the asteroid belt is a source of constant debate among astronomers. Some speculate that the belt is the remains of planets that collided and broke apart, although this theory has few remaining adherents. Some think the gravitational fields of Jupiter and Mars interfered with the normal formation of a planet in that orbit, leaving a mass of half-formed objects that eventually spread out in a huge disk. Asteroids are fairly common throughout the entire Solar System, but the majority of them are concentrated in this belt.
Jupiter is the largest planet and has a "braided ring" that is not as impressive as Saturn's rings but are of intense interest to scientists anyway. Jupiter has several moons, the largest of which is Ganymede. Jupiter's most visible distinction, besides its size, is its "Great Red Spot," The "Great Red Spot" has been discovered to be a massive cyclonic disturbance, similar to a hurricane on Earth, but which has lasted for centuries and shows no signs of abating.
Saturn is frequently called the "crown jewel" of the solar system because of its extensive system of planetary rings. Saturn also has several moons, Titan being the largest and the only moon known to have an atmosphere.
Uranus has the greatest axial tilt of all the planets. It is actually tilted on its side with respect to the "ecliptic," or the plane in which all of the planets except Pluto orbit. Uranus also has rings, although not nearly so extensive as Saturn's.
Neptune is very similar in composition and size to Uranus, although it appears to be more active. A "Great Dark Spot" similar to Jupiter's Great Red Spot has been discovered on its surface.
Pluto may be an escaped moon of Jupiter, Saturn, Neptune or Uranus. It may even be a rock captured from interstellar space. Although Pluto can dip inside the orbit of Neptune, it's average distance is beyond Neptune's average distance. Pluto's orbit is the most eccentric of any planet, and is tilted with respect to the plane in which all other planets orbit.
^COUR GALAXY
We live in a galaxy, the "Milky Way," along with about 100,000,000,000 (one hundred billion) other stars. The Milky Way is about 100,000 light-years in diameter. A light year is the distance that light can travel in a year. Since light travels at 186,000 miles per second (about 298,000,000 meters per second), a light year is 5,860,000,000,000 (or almost six trillion) miles. In general, the Milky Way is shaped like a spiral pinwheel and is therefore known as a "spiral galaxy." The closest star, other than the sun, is the trinary system known as "Alpha Centauri." This system is about 4.5 light years from earth.
The light-year is not the only measurement that is useful for measuring interstellar distances. In fact, it was only recently adopted. Originally astronomers used a unit of measure known as the "parsec" for "parallax second." The parsec is based on the distance you would calculate for a line which makes up one side of a right triangle using the radius of the Earth's orbit (93,000,000 miles) as a base, with one second of arc less than 90 degrees on the odd angle from the base. This would give a distance of (93,000,000 miles) x 1 / (cos 1 sec) which is equal to about 19,100,000,000,000 (or a little more than 19 trillion) miles, or 3.26 light years. The nearest star is about 1.4 parsecs from earth.
Although we cannot see all of the stars in our galaxy, we can easily see several thousand stars with the naked eye. Many of those stars have distinguishing features that we should note. Polaris, for example, is a star that is slightly off of a line drawn from the south pole through the north pole and extending into space. That means that it is visible for all of the year to all of the northern hemisphere. It also means that if you can locate Polaris, then you know which direction is north. The brightest star in the northern hemisphere is Sirius, sometimes called the "dog star." Venus is frequently mistaken for a star, and is even called the "morning star" or the "evening star." Because of it's cloud cover and its close proximity to the sun, Venus can be very bright, frequently outshining Sirius. Also, because of its proximity to the sun, Venus rises just before the sun, or sets just after the sun on most days. This makes it the last "star" or the first "star" of the morning or evening respectively.
Although the stars are in apparently random locations, people have played "connect the dots" with the stars for centuries. When a pattern is inferred and is communicated to others, that group of stars is known as a "constellation." Constellations play a major role in the field of "astrology." In general there are no physical connections between stars in a constellation.
Within our galaxy there are a number of "clusters" of stars, where several hundred or several thousand stars are grouped together. Because these groups tend to occur in a spherical shape, they are called "globular clusters." As you get closer to the center of the galaxy these clusters get more frequent, eventually blurring into a mass of stars that are virtually rubbing shoulders at the very center. Because of this tight collection of stars, many astronomers speculate that there may be a huge black hole at the center of our galaxy, busily devouring stars at a frightening rate.
^COUR UNIVERSE
Our best estimates, based on years of data collected from every corner of the night sky, indicate there to be about 100,000,000,000 (one hundred billion) galaxies in the observable universe. This number is far more than the grains of sand on a beach, and indicate a universe that is unimaginably vast.
These galaxies are generally found in huge galactic clusters. Recent maps of the distribution of galaxies shows a remarkable structure to the universe and appears to show that galaxies are distributed along the edges of enormous bubbles in space.
By examining the spectrum of light emitted from a galaxy, we can determine it's relative speed compared to us. This is possible because of the "Doppler effect," a change in the frequency of a wave due to velocity. If an object is moving away from us, then its spectrum will be "shifted" toward the red end of the spectrum. This is called a "red shift." Except for those galaxies in our own local cluster, all other galaxies seem to be receding from us. Furthermore the speed of the receding galaxies increases as they get farther away. This, too, is consistent with the Big Bang theory.
^CAPPLIED ASTRONOMY
We have learned to use space to our advantage, although we have just begun our first toddling steps into that frontier. A typical example of our use of space is our ability to communicate with any person on the planet through satellite transmissions. Most of the satellites used for communications are in "geosynchronous orbit," or placed into orbit in such a way that they "hover" over one spot on the Earth. This makes it very easy to beam a signal to the satellite, which then can beam it back over the horizon. Several of these can send a signal around the world in an instant.
Because the atmosphere of the earth creates a "haze" on even the clearest days, astronomers in the 1980s convinced Congress to fund a special telescope that would be launched into orbit by the Space Shuttle. Dubbed the "Hubble Space Telescope," this new tool for exploring the universe was seen as the greatest advancement in astronomy since Galileo pieced together his first telescope. Unfortunately the Hubble Telescope, although an improvement over ground-based telescopes, did not live up to expectations. The computer which ground the lens for the Hubble telescope was programmed improperly and the result was a lens that was slightly blurry, reducing its resolution considerably. The error was not discovered until the telescope was launched into orbit. There are plans to repair the Hubble telescope on an upcoming Shuttle mission. Cross your fingers.
Virtually all of our knowledge of the universe comes from the radiant energy that falls on our planet. This "electromagnetic" radiation comes in a wide variety of forms, from radio waves to visible light and beyond. All of this energy is carried to the Earth as "photons," or light particles. It was the study of photons and their tendency to act as waves in some circumstances and particles in others that led to Einstein's brilliant career in physics. Many scientists want to expand our horizons by learning how to detect "gravitational radiation" and view the universe through gravity waves. If we could detect gravity waves, we would gain a crystal clear view of the universe. Electromagnetic waves can be obstructed by dust, gasses, and solid objects, or they can simply be jammed or swamped by static. Gravitational waves are not obstructed by any object. We cannot see the center of our own galaxy because of the mass of dust, gasses, stars and nebulae that obscure the central plane of the galaxy. A gravitational "telescope" could pierce that veil and show us if a black hole is, in fact, at the center of our galaxy.
Not all of our information comes from passive observance of the universe. We have sent probes to most of the planets in our system now, and our first interstellar emissary, the Voyager I probe, will soon leave the solar system, but these are limited attempts to "feel" the universe around us. Eventually we will have to send manned ships beyond our own solar system if we truly wish to explore the universe.
^CBIZARRE NATURAL OBJECTS
Although astronomers may seem to know everything, there are still many great mysteries in the universe. For example, it should be possible, according to theory, for a star to collapse so fast that it can become a "black hole." A black hole is an object that is so dense that light itself cannot escape. If a black hole exists, then it should act in specific ways. For example, a black hole in orbit around a normal sun should draw in matter from that sun, and the friction of the material falling into the black hole should generate powerful X-rays. Scientists have been scanning the sky for objects which emit X-rays with that particular signature, and they think they have found one in the binary star system Cygnus X-1, indicating that a black hole is probably present in that system.
For decades astronomers have scanned the heavens looking for evidence of life beyond our own planet. A few decades ago they thought they found proof. Unknown sources emitted brief bursts of intense radiation at remarkably precise intervals. In most of these cases the signals were emitted several times a second. It wasn't long before a natural explanation was offered and it seems very plausible. That explanation follows:
When a star that is larger than our own sun grows old, it should begin to burn the last of its hydrogen fuel. It will then begin to fuse helium into heavier elements. The increased energy released from fusing helium will cause the star to swell to enormous size. This "red giant" star will then burn helium until the helium is burned away. This process continues with progressively heavier elements until the star is producing iron. At that point the mass of the star is too great for the fusion reaction to "inflate" it. This leads to a massive implosion until the star is compressed into a very tight ball. Consider an ice-skater pulling in his/her arms and increasing the speed of his/her spin. This is the "conservation of angular momentum" and it holds for stars. As a star shrinks, its spin rate increases. A collapsed star can easily spin several times per second. Stars also have magnetic fields, and a rapidly spinning star acts as a dynamo. The combination of the spinning star and the magnetic field can generate a "beam" of energy that sweeps across the galaxy like the beam of a lighthouse. This type of star is called a "pulsar," and it is assumed that a space-faring civilization could use them as interstellar navigational beacons, pinpointing their position in space with ease.
Then there are the "quasi-stellar objects," commonly called "quasars." These are objects that appear to be very small, yet generate intense energy. Some astronomers theorize that a quasar is actually an exploding galaxy. Others speculate that a quasar is an entire galaxy which is disappearing into an enormous black hole. And still others feel that quasars are simply remnants of the original Big Bang, frozen in time by the effects of general relativity, fragments of the original ball of intense energy hurled into nothingness at speeds unimaginably close to the speed of light.
There are other dark secrets of the universe that astronomers and physicists are just beginning to examine. Dark matter, cosmic strings, naked singularities, anti-matter, white holes, worm holes and many other mysteries await our ever-expanding understanding of the universe.
I hope you enjoyed this little essay, and if you like this approach to our quiz programs, we'll do it for future quizzes. If you didn't like it, you probably didn't get this far, but you'll probably let me know that too. Just remember, we aim to please!
