Material that accumulates around a black hole before it is consumed by the gravity of the hole and disappears into it.
Ec[000000]f[16]LBAlbert EinsteinB
A famous scientist and physicist born in Germany in 1879. He is considered to be one of the most brilliant theoretical physicists of all time. His formula E = mc2 (energy equals mass times the speed of light squared) and his theory of relativity formed the basis for the use of atomic energy. Einstein died in 1955.
Ec[000000]f[16]LBAlpha CentauriB
The nearest star to Earth, except for the Sun. It is located in the constellation Centaurus.
Ec[000000]f[16]LBAndromeda GalaxyB
The nearest galaxy to our galaxy, the Milky Way. It is about 2.2 million light-years away but can be seen with a simple telescope on clear nights away from city lights. It is believed to contain about 200 billion stars.
Ec[000000]f[16]LBAquariusB
A large constellation of the zodiac located between Pisces and Capricornus. Aquarius represents the Water Carrier.
Ec[000000]f[16]LBAquilaB
A constellation found north of Sagittarius and Capricornus. It lies partly in the Milky Way and contains the bright star Altair. Aquila represents the Eagle.
Ec[000000]f[16]LBArcturusB
A bright star in the constellation Bootes, the Herdsman. Arcturus is the fourth-brightest star in the sky. Its diameter is about ten times that of our Sun, and it is one hundred times as bright as our Sun.
Ec[000000]f[16]LBAriesB
A constellation in the zodiac located between Pisces and Taurus. Aries represents the Ram.
Ec[000000]f[16]LBAristotleB
A Greek scientist and philosopher who lived in the fourth century B.C. He was one of the first to say that Earth was round like a ball, not flat. He theorized that Earth was the center of the universe, and the Sun and planets revolved around it.
Ec[000000]f[16]LBastrolabeB
An ancient device invented by the Arabs to find the altitude of a star. Sailors once relied on the astrolabe for navigation. It has largely been replaced by the sextant.
Ec[000000]f[16]LBastronautB
A person trained for space flight.
Ec[000000]f[16]LBastronomerB
A scientist who studies astronomy or any of its modern subfields: astrophysics, cosmology, radio astronomy, or any of the other specialties of space science.
Ec[000000]f[16]LBastronomyB
The science of space study. Originally restricted to observing the stars and the planets, it has now branched off into many subfields.
Ec[000000]f[16]LBaxisB
The line around which Earth rotates. All the planets have an axis around which they rotate.
Ec[000000]f[16]LBBabyloniaB
An ancient empire that flourished from about 2800 to 700 B.C. in the lower Euphrates valley of Southwest Asia.
Ec[000000]f[16]LBBermuda TriangleB
An area in the Atlantic Ocean between Florida and the islands of Bermuda and Puerto Rico in which planes and ships have supposedly disappeared for unknown causes. The mysterious "power" of the Bermuda Triangle has never been proven to exist.
Ec[000000]f[16]LBBetelgeuseB
A bright star in the constellation Orion. It is a red supergiant star and is more than 13,000 times as bright as our Sun.
Ec[000000]f[16]LBBig DipperB
Seven stars in the constellation Ursa Major, the Great Bear. If you connect these seven stars with imaginary lines, it looks like a large dipper in the sky. The two stars on the outside edge of the cup form a line that points to Polaris, or the North Star.
Ec[000000]f[16]LBBootesB
A constellation representing the Herdsman. It contains the bright star Arcturus.
Ec[000000]f[16]LBcalendarB
A chart or table that shows the months, weeks, and days of the year.
Ec[000000]f[16]LBCancerB
A constellation of the zodiac located between Leo and Gemini. Cancer represents the Crab.
Ec[000000]f[16]LBCanis MajorB
A southern constellation containing Sirius, or the Dog Star, which is the brightest star in the sky. Sirius is a binary star; that is, it is really two stars close together, revolving around a common center of gravity. The name ICanis MajorI means "great dog."
Ec[000000]f[16]LBCapricornusB
A constellation in the zodiac located between Sagittarius and Aquarius. Capricornus represents the Goat.
Ec[000000]f[16]LBCassiopeiaB
A bright constellation representing the Queen. When connected, five stars in Cassiopeia resemble the letter IWI; some skywatchers refer to this as Cassiopeia's Chair. The constellation is found on the opposite side of the North Star from the Big Dipper.
Ec[000000]f[16]LBCetusB
Cetus, the Whale, is a constellation seen in autumn near Pegasus. It contains a variable star, or a star that grows alternately brighter and dimmer.
Ec[000000]f[16]LBClyde TombaughB
An American astronomer of the twentieth century who is credited with discovering Pluto. Tombaugh worked at the Lowell Observatory, basing his research on the calculations of Percival Lowell, who had suggested the existence of Pluto in the early twentieth century. In 1930, Ec[000000]f[16]LFTombaugh found Pluto where Lowell had predicted it would be.
Ec[000000]f[16]LBcometB
A body in space that consists of a core of frozen rock and a tail of ice-covered particles of dust. Trillions of comets may exist in an area called the Oort Cloud, which astronomers believe surrounds our solar system. Comets have an irregular orbit around the Sun.
Ec[000000]f[16]LBconstellationB
An easily identified group of stars that has been given a name, such as Ursa Major and Orion. There are eighty-eight constellations visible in the sky above Earth.
Ec[000000]f[16]LBCopernican systemB
The plan of the universe devised by Nicolaus Copernicus, a sixteenth-century Polish astronomer. Copernicus suggested that the Sun was the center of our solar system, and all planets and other celestial objects in the solar system revolved around the Sun. Copernicus's theories are the basis of modern astronomy.
Ec[000000]f[16]LBcoronaB
The luminous layer of gases surrounding the surface of the Sun. During a total solar eclipse, when the Moon blocks out the body of the Sun, the corona is still visible around the edges of the Moon. The corona can also be viewed with a coronagraph.
Ec[000000]f[16]LBcoronagraphB
An instrument for observing and photographing activity in the Sun's corona.
Ec[000000]f[16]LBcosmologyB
One of the branches of astronomy or space science. It is the study of the structure and evolution of the universe.
Ec[000000]f[16]LBcosmonautB
The Russian term for a person trained for spaceflight. Americans trained for spaceflight are called astronauts.
Ec[000000]f[16]LBcraterB
A large pit in the surface of Earth or any other planetary body. Large meteorites can create craters when they strike Earth.
Ec[000000]f[16]LBcrescent moonB
The phase of the Moon when only a small, crescent-shaped part of it can be seen on Earth.
Ec[000000]f[16]LBDianaB
The Roman goddess of the Moon. Some cults worshiped her as an earth goddess.
Ec[000000]f[16]LBEinstein ringB
A ring of light that comes from a distant star and curves around another star on its way to Earth. Because the light is visible on Earth as a ring of light, rather than a point of light, it is called an Einstein ring. It is also called a gravitational lens.
Ec[000000]f[16]LBEdmund HalleyB
An English astronomer who lived from 1656 to 1742. He determined that comets have regular orbits around the Sun and predicted that a large comet that had been seen in 1682 would return in 1758. When it did, it was named for him.
Ec[000000]f[16]LBEdwin HubbleB
Twentieth-century astronomer (1889-1953) who formulated the principle of the expanding universe. According to Hubble's law, the universe is constantly growing larger as the distance between galaxies steadily grows. The Hubble Space Telescope is named after him. Ironically, Ec[000000]f[16]LFstudies made with the Hubble Telescope are challenging certain parts of Hubble's theories.
Ec[000000]f[16]LBequatorB
An imaginary line drawn around a planet midway between the two poles of its axis. On Earth's equator, the Sun is always directly overhead at noon.
Ec[000000]f[16]LBEratosthenesB
An ancient Greek astronomer who lived in the third century B.C. Eratosthenes constructed a map of the known world and served as head of the great library at Alexandria, which housed some 700,000 volumes. In about the year 240 B.C., he observed that when the Sun was directly Ec[000000]f[16]LFoverhead in one city, it cast a shadow in another city about 500 miles (800 kilometers) to the north. From these observations, he concluded that Earth was a round sphere about 25,000 miles (40,000 kilometers) around. Ec[000000]f[16]LBEvening StarB
Venus is called the Evening Star because it appears as one of the brightest objects in the sky at dusk. Venus is also called the Morning Star.
Ec[000000]f[16]LBfull moonB
The phase of the Moon when the entire face of the Moon reflects sunlight to Earth.
Ec[000000]f[16]LBgalaxyB
A large system of stars held together by gravity and isolated from other galaxies by large distances in space. Our galaxy is the Milky Way.
Ec[000000]f[16]LBGalileoB
Galileo Galilei was an Italian physicist and astronomer who lived from 1564 to 1642. He made important improvements in telescopes that allowed more extensive study of the Moon and the planets.
Ec[000000]f[16]LBGeminiB
A constellation of the zodiac located between Taurus and Cancer. Gemini represents the Twins and contains the bright twin stars Castor and Pollux.
Ec[000000]f[16]LBgravitational lensB
A ring of light that is emitted from a distant star and curves around another star on its way to Earth. It is also called an Einstein ring.
Ec[000000]f[16]LBgravitational pullB
The force from a planet, star, or other body in space that pulls other bodies toward it. The gravitational pull of Earth holds our Moon in orbit around us.
Ec[000000]f[16]LBgravityB
The attraction of a mass in space, such as a planet or satellite, that holds bodies on its surface. Earth's gravity causes items to fall to the ground.
Ec[000000]f[16]LBhemisphereB
Any of the halves into which the surface of the Earth can be divided. The equator divides the Earth into the Northern and Southern Hemispheres, and a meridian running through Greenwich, England, divides it from top to bottom into the Eastern and Western Hemispheres.
Ec[000000]f[16]LBhoroscopeB
A prediction of the future based on the positions of the planets in the sky. Those who cast horoscopes are called astrologers, and the "science" of star-based prophecy, astrology. Although many place their faith in astrology, it has never been proven true or reliable.
Ec[000000]f[16]LBHubble Space TelescopeB
An orbiting space telescope launched by the United States in 1990. After it was launched, it was found to have a faulty mirror, which produced slightly distorted images. The images can be corrected by computer, however. Discoveries made possible by the telescope have challenged Ec[000000]f[16]LFmany theories in astronomy and cosmology.
Ec[000000]f[16]LBKeck TelescopeB
A reflecting telescope in Hawaii that uses thirty-six mirrors--each about 6 feet (1.8 meters) wide--to collect light. It is among the world's most powerful reflecting telescopes.
Ec[000000]f[16]LBLeoB
A constellation of the zodiac located between Virgo and Cancer. It represents the Lion and contains the bright variable star Regulus.
Ec[000000]f[16]LBLibraB
A zodiac constellation located between Virgo and Scorpio. It represents the balance, or scales.
Ec[000000]f[16]LBlunar eclipseB
A lunar eclipse occurs when the Earth passes between the Moon and the Sun. It casts a shadow on the Moon and thus obscures our view of the Moon.
Ec[000000]f[16]LBLyraB
A northern constellation representing the lyre of Orpheus. It contains the bright star Vega, one of the three stars of the summer triangle. Lyra reaches its highest point in the evening sky in August.
Ec[000000]f[16]LBMilky WayB
The name of the galaxy in which our solar system resides. It is a spiral galaxy and appears to us on Earth as a milky white band arching across the night sky. There are more than 100 billion stars in the Milky Way, but it is only an average-sized galaxy in our universe.
Ec[000000]f[16]LBMorning StarB
One of the names given to the planet Venus. When visible shortly before sunrise, it is one of the brightest objects in the sky. It is also called the Evening Star.
Ec[000000]f[16]LBMount PalomarB
Location of one of the most powerful reflecting telescopes in the world. For many years, its 200-inch mirror was the largest in the world. Russia has a telescope with a 236-inch mirror in the Caucasus Mountains, but problems with the mirror make the telescope less useful Ec[000000]f[16]LFthan the telescopes on Mount Palomar or in Hawaii.
Ec[000000]f[16]LBmythologyB
The myths and legends of a people, telling of the exploits of gods, goddesses, heroes, demons, and other imaginary characters.
Ec[000000]f[16]LBNeil ArmstrongB
An American astronaut and the first human to walk on the Moon in the famous IApollo 11I mission in July 1969. Armstrong had been a U.S. Navy fighter pilot during the Korean War.
Ec[000000]f[16]LBneutrinoB
A subatomic particle with almost no mass that is given off in great numbers by dying stars.
Ec[000000]f[16]LBneutron starB
A star that has collapsed after using up its supply of fuel. Neutron stars are extremely dense and consist mainly of neutrons. If they become dense enough, they can become black holes. Rapidly spinning neutron stars can send out pulses of radio energy and are then known as pulsars.
Ec[000000]f[16]LBnew moonB
The name given to the first phase of the Moon's twenty-eight-day cycle. The face of the new moon appears totally dark on Earth.
Ec[000000]f[16]LBNicolaus CopernicusB
A sixteenth-century Polish astronomer who formulated a system describing the nature of the solar system. Prior to his work, most thinkers had believed that Earth was the center of the universe and the point around which the Sun and planets and stars revolved.
Ec[000000]f[16]LBNorth PoleB
The point on the surface of the Earth that marks the top of the rotational axis. It is known as true north and differs from magnetic north, the point to which compass needles point.
Ec[000000]f[16]LBNorth StarB
Another name for Polaris, or the Pole Star. It is fixed in the sky directly above the North Pole and remains stationary throughout the night as the other stars spin about the heavens. The Pole Star has guided navigators for centuries.
Ec[000000]f[16]LBOort CloudB
A band of trillions of comets that orbits our Sun far beyond the planet Pluto. It was named for its discoverer, Dutch astronomer Jan Oort. Scientists have never seen the Oort Cloud, but they believe it exists.
Ec[000000]f[16]LBoptical telescopeB
The most common type of telescope. It consists of a series of lenses that focus light on an eyepiece, giving the user an enlarged view of whatever is being observed.
Ec[000000]f[16]LBOrionB
A bright constellation in the winter sky. It represents the Hunter and contains the bright star Betelgeuse, a red giant.
Ec[000000]f[16]LBPegasusB
A constellation seen high up in the autumn sky. It contains four bright stars that form the square of Pegasus.
Ec[000000]f[16]LBPercival LowellB
An American astronomer (1855-1916). Lowell correctly predicted the position of the planet Pluto, although its existence was not proven until fourteen years after his death. The name Pluto was chosen to honor Lowell, with the first two letters in the name representing Lowell's initials. Ec[000000]f[16]LFLowell also suggested that the lines on the surface of Mars were canals dug by intelligent creatures. Studies from space probes have shown that the "canals" are merely unconnected features on the planet's surface.
Ec[000000]f[16]LBphases of the MoonB
Name given to the successive shapes of the Moon that are visible on Earth during each month. The new moon is completely dark, then becomes a waxing crescent, which fills out to a full moon. It then gets smaller (waning crescent) until it once again becomes new moon.
Ec[000000]f[16]LBPiscesB
A constellation of the zodiac located between Aries and Aquarius. It is seen south of Andromeda and represents the Fishes.
Ec[000000]f[16]LBplanetB
Any of the large celestial bodies that revolve around the Sun in our solar system.
Ec[000000]f[16]LBplanetary ringsB
Rings of material surrounding the gas giants in our solar system. Saturn has the most brilliant rings, but Jupiter, Uranus, and Neptune also have very thin rings that are barely visible from Earth.
Ec[000000]f[16]LBpointersB
Two stars on the outside edge of the Big Dipper. A line drawn through the two stars points directly to Polaris, the North Star.
Ec[000000]f[16]LBPolarisB
The North Star. The star appears to be fixed in the sky directly over the North Pole. Its almost stationary position has made it a guide for navigators for centuries. It is located at the end of the handle of the Little Dipper.
Ec[000000]f[16]LBPtolemaic systemB
The plan of the solar system devised by Ptolemy in the second century A.D. Ptolemy's system was a series of spheres inside each other, with Earth at the center and the Sun and other known planets revolving around it. The sky and stars were in the outermost sphere. This Ec[000000]f[16]LFsystem was the accepted plan of the solar system for more than a thousand years.
Ec[000000]f[16]LBPtolemyB
A Greco-Egyptian mathematician and astronomer of the second century A.D. He developed what is now known as the Ptolemaic system, a plan describing the solar system as a group of concentric spheres with Earth at the center and the planets and Sun revolving around it. His Ec[000000]f[16]LFsystem formed the basis of astronomy until the work of Copernicus in the sixteenth century.
Ec[000000]f[16]LBpulsarB
A neutron star that sends out radio waves at regular intervals.
Ec[000000]f[16]LBquasarB
An object at the far edges of the universe that looks like an ordinary star through an optical telescope. It has the energy emission of an entire galaxy. The name was taken from "quasistellar" object.
Ec[000000]f[16]LBradio telescopeB
A highly sensitive radio receiver that can detect radio waves from outer space. The radio signals can be analyzed, yielding much information about distant stars and galaxies.
Ec[000000]f[16]LBred giantB
A dying star that has run low on hydrogen fuel and squeezes its helium, raising its central temperature until the outer layers of the star expand. As the star grows larger and larger, the outer layers cool and glow red hot.
Ec[000000]f[16]LBreflecting telescopeB
A telescope that uses a large mirror to collect light from the universe and focus it so that it can be studied by astronomers. The larger the mirror, the better the picture of the sky that will be received.
Ec[000000]f[16]LBrefracting telescopeB
A telescope that uses a series of lenses to magnify images of celestial objects and focus them into an eyepiece where they can be viewed by scientists.
Ec[000000]f[16]LBSagittariusB
A constellation of the zodiac located between Scorpius and Capricornus. Sagittarius represents the Archer.
Ec[000000]f[16]LBScorpiusB
A constellation of the zodiac located partly in the Milky Way between Libra and Sagittarius. Scorpius represents the Scorpion.
Ec[000000]f[16]LBsolar eclipseB
A solar eclipse occurs when the Moon passes between the Sun and Earth, blocking out the light of the Sun. A total solar eclipse lowers surface temperatures on Earth and brings on a dusklike darkness.
Ec[000000]f[16]LBSouth PoleB
The point where the southern end of Earth's axis intersects with Earth's surface.
Ec[000000]f[16]LBSouthern CrossB
A group of four stars visible almost year-round in the Southern Hemisphere. The Southern Cross is part of the Crux, a small, bright constellation, and appears in the sky as a cross that points directly at the South Pole.
Ec[000000]f[16]LBstarB
A celestial object made up primarily of hydrogen. The gas is compacted tightly in the center, causing continuous nuclear reactions that create tremendous heat and make the star glow brightly. Our Sun is the nearest star to Earth.
Ec[000000]f[16]LBtailB
The luminous extension behind a comet that can spread for millions of miles across the sky. It consists of dust particles that become illuminated when the comet is near the Sun. The tail always points away from the Sun.
Ec[000000]f[16]LBtelescopeB
An optical device invented in the seventeenth century and improved by Galileo. It allows us to study distant objects. Galileo discovered the four largest moons of the planet Jupiter in 1610 by using his telescope.
Ec[000000]f[16]LBStonehengeB
A circle of large stones in England that dates back to prehistoric times. The purpose of the structure has been a mystery for centuries, but many have suggested it had a religious use. Some twentieth-century astronomers believe that Stonehenge was designed as a large Ec[000000]f[16]LFastronomical observatory to trace the movement of the Sun and the stars and to predict events such as eclipses.
Ec[000000]f[16]LBsupernovaB
An exploding star that sends out as much as a hundred million times more light and energy than the Sun.
Ec[000000]f[16]LBTaurusB
A constellation of the zodiac located between Gemini and Aries. It represents the Bull and contains the bright star Aldeberan.
Ec[000000]f[16]LBTycho BraheB
A Danish astronomer who lived in the sixteenth century. His observations and research placed the planets and stars in their proper positions and led to the discovery of the orbits of comets.
Ec[000000]f[16]LBuniverseB
Every celestial body that exists, including our own Sun and solar system, the stars, asteroids, quasars, and other galaxies. The universe is vast and stretches far beyond even the imagination of humans.
Ec[000000]f[16]LBVirgoB
A constellation of the zodiac located between Leo and Libra. It represents the Virgin and contains the bright star Spica.
Ec[000000]f[16]LBVLAB
An abbreviation that stands for Very Large Array. The VLA radio telescope is located in Socorro, New Mexico, and consists of twenty-seven radio antennas in a Y-shaped formation. Each arm of the Y is 13 miles (21 kilometers) long.
Ec[000000]f[16]LBzodiacB
A circle of twelve constellations in the sky through which the Sun, Moon, and planets pass. The zodiac constellations are Aries, Taurus, Gemini, Cancer, Leo, Virgo, Libra, Scorpius, Sagittarius, Capricornus, Aquarius, and Pisces.
