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  Astronomy is the science of the celestial bodies: the sun, the moon, and the planets; the stars and galaxies; and all other objects in the universe. It is concerned with their positions, motions, distances, and physical conditions and with their origins and evolution. It is divided into fields such as astrophysics, celestial mechanics, and cosmology. Astronomy is perhaps the oldest recorded science; there are observational records from ancient Babylonia, China, Egypt, and Mexico. The first true astronomers were the Greeks, who deduced the earth to be a sphere and attempted to measure its size. A summary of Greek astronomy is provided in Ptolemy of Alexandria's Almagest. The Arabs developed the astrolabe and produced good star catalogs. In 1543 the Polish astronomer Copernicus demonstrated that the sun, not the earth, is the center of our planetary system. The Italian scientist Galileo was the first to use a telescope for astronomical study, in 1609–10. In the 17th and 18th centuries astronomy was mostly concerned with positional measurements. The British astronomer William Herschel's suggestions on the shape of our galaxy were verified in 1923 by the U.S. astronomer Edwin Hubble's telescope at the Mount Wilson Observatory, California. The most remarkable recent extension of the powers of astronomy to explore the universe is in the use of rockets, satellites, space stations, and space probes, while the launching of the Hubble Space Telescope into permanent orbit in 1990 has enabled the detection of celestial phenomena seven times more distant than by any earth-based telescope.  
  The Universe  
  The universe embraces all of space and its contents, the study of which is called cosmology. The universe is thought to be between 10 billion and 20 billion years old, and is mostly empty space, dotted with stars collected into vast aggregations called galaxies for as far as telescopes can see. The most distant detected galaxies and quasars (quasi-stellar objects) lie 10 billion light-years or more from earth, and are moving farther apart as the universe expands. Several theories attempt to explain how the universe came into being and evolved: for example, the Big Bang theory of an expanding universe originating in a single explosive event, and the contradictory steady-state theory.  
  Big Bang  
  This is the hypothetical "explosive" event that marked the origin of the universe as we know it. At the time of the Big Bang, the entire universe was squeezed into a hot, superdense state. The Big Bang explosion threw this compact material outward, producing the expanding universe. The cause of the Big Bang is unknown; observations of the current rate of expansion of the universe suggest that it took place about 10–20 billion years ago. The Big Bang theory began modern cosmology.  
  According to a modified version of the Big Bang, called the inflationary theory, the universe underwent a rapid period of expansion shortly after the Big Bang, which accounts for its current large size and uniform nature. The inflationary theory is supported by recent observations of the cosmic background radiation (see below).  
  Scientists have calculated that one 10–36 second (equivalent to one million-million-million-million-million-millionth of a second) after the Big Bang, the universe was the size of a pea, and the temperature was 10 billion million million million°C/18 billion million million million °F. One second after the Big Bang, the temperature was about 10 billion°C/18 billion°F.  




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  steady-state theory  
  This rival theory to that of the Big Bang claims that the universe has no origin but is expanding because new matter is being created continuously throughout the universe. The theory was proposed in 1948 by Austrianborn British cosmologist Hermann Bondi, Austrian-born U.S. astronomer and physicist Thomas Gold (1920– ), and English astronomer Fred Hoyle, but was dealt a severe blow in 1965 by the discovery of cosmic background radiation and is now largely rejected.  
  Unsolved Mysteries
  Part of a larger site on cosmology provided by PBS Online, this page features seven articles that address the most difficult questions regarding the mysteries of our universe. Some of the articles include "Where does matter come from?," "Is time travel possible?," "Where is the missing matter?," "An inhabited universe?," and ''Is there a theory for everything?" You can follow the link to the main site to explore other aspects of the cosmos.  
  cosmic background radiation This is electromagnetic radiation left over from the original formation of the universe in the Big Bang. It corresponds to an overall background temperature of 3 K (–270°C/–454°F), or 3°C above absolute zero. Cosmic background radiation was first detected in 1965 by U.S. physicists Arno Penzias (1933– ) and Robert Wilson (1936– ). In 1992 the Cosmic Background Explorer satellite, COBE, detected slight "ripples" in the strength of the background radiation that are believed to mark the first stage in the formation of galaxies.  
  Brief History of Cosmology
  Based at St Andrews University, Scotland, a site chronicling the history of cosmology from the time of the Babylonians to the Hubble Space Telescope.  
  The Celestial Sphere and Constellations  
  celestial sphere  
  The celestial sphere is an imaginary sphere surrounding  
  celestial sphere The main features of the celestial sphere. Declination, the
equivalent of latitude on earth, runs from 0° at the celestial equator to 90° at
the celestial poles. Right ascension, the equivalent of longitude, is measured in
hours eastward from the vernal equinox, one hour corresponding to 15° of longitude.




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  the earth, on which the celestial bodies seem to lie. The positions of bodies such as stars, planets, and galaxies are specified by their coordinates on the celestial sphere. The equivalents of latitude and longitude on the celestial sphere are called declination (measured in degress) and right ascension (measured in hours from 0 to 24). The celestial poles lie directly above the earth's poles, and the celestial equator lies over the earth's Equator. The celestial sphere appears to rotate once around the earth each day, actually a result of the rotation of the earth on its axis.  
  A constellation is one of the 88 areas into which the sky is divided for the purposes of identifying and naming celestial objects. The first constellations were simple, arbitrary patterns of stars in which early civilizations visualized gods, sacred beasts, and mythical heroes.  
  The constellations in use today are derived from a list of 48 known to the ancient Greeks, who inherited some from the Babylonians. The current list of 88 constellations was adopted by the International Astronomical Union, astronomy's governing body, in 1930. Within the current system the definitive boundaries are arcs of constant right ascension or declination for the equinox of 1875. Each constellation includes not only the historic star grouping but also all the variable stars that have become associated with it. The genitive, or possessive, form of the name is used when an object is being identified by its constellation letter or number. For example, the star Polaris is Alpha Ursae Minoris, which is usually contracted to alpha UMi.  
  Constellations and Their Stars
  Notes on the constellations (listed alphabetically, by month, and by popularity), plus lists of the 25 brightest stars and the 32 nearest stars, and photographs of the Milky Way.  
  The zodiac is the zone of sky containing the 12 zodiacal constellations (after which the astrological signs of the zodiac are named) through which the paths of the sun, moon, and planets appear to move. The 12 astronomical constellations are uneven in size and do not between them cover the whole zodiac, or even the line of the ecliptic (the path that the sun appears to follow each year as the earth orbits the sun), much of which lies in the constellation of Ophiuchus.  
  The sequence of the astrological signs (which are each 30° wide and do not cover the same areas of sky as the astronomical constellations) is eastwards, following the motions of the sun and moon through the constellations, and is regarded as beginning at the point that marks the position of the sun at the time of the March equinox. This point is sometimes called "The First Point of Aries."  
  The equinoxes occur as the sun enters the signs of Aries and Libra, at which times the sun passes directly above the Equator. The solstices occur as the sun enters the signs of Cancer and Capricorn and passes directly over the Tropic of Cancer and Tropic of Capricorn, circles of latitude 23° 27' north and south of the Equator.  
  Zodiac constellations  
  To remember the constellations of the zodiac:  
  A tense gray cat lay very low, sneaking slowly, contemplating a pounce  
  (Aries, Taurus, Gemini, Cancer, Leo, Virgo, Libra, Scorpio, Sagittarius, Capricorn, Aquarius, Pisces)  


  A star is a luminous globe of gas, mainly hydrogen and helium, which produces its own heat and light by nuclear reactions. Although stars shine for a very long time—many billions of years—they are not eternal, and have been found to change in appearance at different stages in their lives.  
  The smallest mass possible for a star is about 8% that of the sun (80 times that of Jupiter, the largest planet in the solar system), otherwise nuclear reactions cannot occur. Objects with less than this critical mass shine only dimly, and are termed brown dwarfs.  
  Stars are born when nebulae (giant clouds of dust and gas) contract under the influence of gravity. These clouds consist mainly of hydrogen and helium, with traces of other elements and dust grains. A huge volume of interstellar matter gradually separates from the cloud, and the temperature and pressure in its core rises as the star grows smaller and denser. As the star is forming, it is surrounded by evaporating gaseous globules (EGGs), the oldest of which was photographed in the Eta Carina Nebula in 1996 by the Hubble Space Telescope.  
  At first the temperature of the star scarcely rises, as dust grains radiate away much of the heat, but as it grows denser less of the heat generated can escape,  




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A constellation is one of the 88 areas into which the sky is divided for the purposes of identifying and naming celestial objects. The first constellations were simple, arbitrary patterns of stars in which early civilizations visualized gods, sacred beasts, and mythical heroes.
(– = not applicable.)
Constellation Abbreviation Popular name
Andromeda And
Antlia Ant Airpump
Apus Aps Bird of Paradise
Aquarius Aqr Water-bearer
Aquila Aqi Eagle
Ara Ara Altar
Aries Ari Ram
Auriga Aur Charioteer
Boötes Boo Herdsman
Caelum Cae Chisel
Camelopardalis Cam Giraffe
Cancer Cnc Crab
Canes Venatici CVn Hunting Dogs
Canis Major CMa Great Dog
Canis Minor CMi Little Dog
Capricornus Cap Sea-goat
Carina Car Keel
Cassiopeia Cas
Centaurus Cen Centaur
Cepheus Cep
Cetus Cet Whale
Chameleon Cha Chameleon
Circinus Cir Compasses
Columba Col Dove
Coma Berenices Corn Berenice's Hair
Corona Australis CrA Southern Crown
Corona Borealis CrB Northern Crown
Corvus Crv Crow
Crater Crt Cup
Crux Cru Southern Cross
Cygnus Cyn Swan
Delphinus Del Dolphin
Dorado Dor Goldfish
Draco Dra Dragon
Equuleus Equ Foal
Eridanus Eri River
Fornax For Furnace
Gemini Gem Twins
Grus Gru Crane
Hercules Her -
Horologium Hor Clock
Hydra Hya Watersnake
Hydrus Hyi Little Snake
Indus Ind Indian
Lacerta Lac Lizard
Leo Leo Lion
Leo Minor LMi Little Lion
Lepus Lep Hare
Libra Lib Balance
Lupus Lup Wolf
Lynx Lyn
Lyra Lyr Lyre
Mensa Men Table
Microscopium Mic Microscope
Monoceros Mon Unicorn
Musca Mus Southern Fly
Norma Nor Rule
Octans Oct Octant
Ophiuchus Oph Serpent-bearer
Orion Ori
Pavo Pav Peacock
Pegasus Peg Flying Horse
Perseus Per
Phoenix Phe Phoenix
Pictor Pic Painter
Pisces Psc Fishes
Piscis Austrinus PsA Southern Fish
Puppis Pup Poop
Pyxis Pyx Compass
Reticulum Ret Net
Sagitta Sge Arrow
Sagittarius Sgr Archer
Scorpius Sco Scorpion
Sculptor Scl
Scutum Sct Shield
Serpens Ser Serpent
Sextans Sex Sextant
Taurus Tau Bull
Telescopium Tel Telescope
Triangulum Tri Triangle
Triangulum Australe TrA Southern Triangle
Tucana Tuc Toucan
Ursa Major UMa Great Bear
Ursa Minor UMi Little Bear
Vela Vel Sails
Virgo Vir Virgin
Volans Vol Flying Fish
Vulpecula Vul Fox


  and it gradually warms up. At about 10 million°C/18 million°F the temperature is hot enough for a nuclear reaction to begin, and hydrogen nuclei fuse to form helium nuclei; vast amounts of energy are released, contraction stops, and the star begins to shine. Stars at this stage are called main-sequence stars.  




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  types of stars  
  binary star Binary stars are pairs of stars moving in orbit around their common center of mass. Observations show that most stars are binary, or even multiple—for example, the nearest star system to the sun, Alpha Centauri.  
  One of the stars in the pair called Epsilon Aurigae may be the largest star known. Its diameter is 2,800 times that of the sun. If it were in the position of the sun, it would engulf Mercury, Venus, earth, Mars, Jupiter, and Saturn. A spectroscopic binary is a binary in which two stars are so close together that they cannot be seen separately, but their separate light spectra can be distinguished by a spectroscope. Another type is the eclipsing binary (see variable star below).  
  brown dwarf A brown dwarf is an object less massive than a star, but heavier than a planet. Brown dwarfs do not have enough mass to ignite nuclear reactions at their centers, but shine by heat released during their contraction from a gas cloud. Some astronomers believe that vast numbers of brown dwarfs exist throughout the galaxy. Because of the difficulty of detection, none were spotted until 1995, when U.S. astronomers discovered a brown dwarf, GI229B, in the constellation Lepus. It is about 20–40 times as massive as Jupiter but emits only 1% of the radiation of the smallest known star.  
  neutron star A neutron star is a very small, "superdense" star composed mostly of neutrons. Neutron stars are thought to form when massive stars explode as supernovae, during which the protons and electrons of the star's atoms merge, owing to intense gravitational collapse, to make neutrons. A neutron star may have the mass of up to three suns, compressed into a globe only 20 km/12 mi in diameter.  
neutron star
  Neutron stars are so condensed that a fragment the size of a sugar cube would weigh as much as all the people on earth put together.  


  If its mass is any greater, its gravity will be so strong that it will shrink even further to become a black hole. Being so small, neutron stars can spin very quickly. The rapidly flashing radio stars called pulsars are believed to be neutron stars. The flashing is caused by a rotating beam of radio energy similar in behavior to a lighthouse beam of light.  
  Hertzsprung—Russell diagram The Hertzsprung—Russell diagram relates
the brightness (or luminosity) of a star to its temperature. Most stars fall
within a narrow diagonal band called the main sequence. A star moves off
the main sequence when it grows old. The Hertzsprung—Russell diagram
is one of the most important diagrams in astrophysics.




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  nova A nova is a faint star that suddenly increases in brightness by a factor of 10,000 or more, remains bright for a few days, and then fades away and is not seen again for very many years, if at all. Novae are believed to occur in close binary star systems, where gas from one star flows to a companion white dwarf. The gas ignites and is thrown off in an explosion at speeds of 1,500 kps/930 mps or more. Unlike a supernova, the star is not completely disrupted by the outburst. After a few weeks or months it subsides to its previous state, though it may erupt many more times.  
  Two or three such stars are detected in our galaxy each year, but on average, a nova is visible to the naked eye only about once every ten years. Novae very similar to those appearing in our own galaxy have also been observed in other galaxies.  
  pulsar Pulsars are celestial sources that emit pulses of energy at regular intervals, ranging from a few seconds to a few thousandths of a second. They are thought to be rapidly rotating neutron stars, which flash at radio and other wavelengths as they spin. They were discovered in 1967 by British astronomers Jocelyn Bell Burnell and Antony Hewish at the Mullard Radio Astronomy Observatory, Cambridge, England. Over 500 radio pulsars are now known in our galaxy, although a million or so may exist.  
  Pulsars slow down as they get older, and eventually the flashes fade. Of the 500 known radio pulsars, 20 are millisecond pulsars (flashing 1,000 times a second). Such pulsars are thought to be more than a billion years old. Two pulsars, one (estimated to be 1,000 years old) in the Crab nebula and one (estimated to be 11,000 years old) in the constellation Vela, give out flashes of visible light.  
  The closest pulsar to the earth is named PSR J0108–1431 and lies 280 light-years away in the constellation of Cetus; it was discovered in 1994.  
  quasar Quasars (the name is derived from quasi-stellar object, or QSO) are some of the most distant extragalactic objects known, and were discovered in 1963. Quasars appear starlike, but each emits more energy than 100 giant galaxies. They are thought to be at the center of galaxies, their brilliance emanating from the stars and gas falling toward an immense black hole at their nucleus. Most quasars are found in elliptical galaxies.  
  Quasar light shows a large red shift, indicating that they are very distant. Some quasars emit radio waves, which is how they were first identified, but most are radio-quiet. The furthest are over 10 billion light-years away.  
  red dwarf Any star that is cool, faint, and small (about one-tenth the mass and diameter of the sun) is a red dwarf. Red dwarfs burn slowly, and have estimated lifetimes of 100 billion years. They may be the most abundant type of star, but are difficult to see because they are so faint. Two of the closest stars to the sun, Proxima Centauri and Barnard's Star, are red dwarfs.  
  red giant A red giant is any large bright star with a cool surface. It is thought to represent a late stage in the evolution of a star like the sun, as it runs out of hydrogen fuel at its center and begins to burn heavier elements, such as helium, carbon, and silicon. Because of more complex nuclear reactions that then occur in the red giant's interior, it eventually becomes gravitationally unstable and begins to collapse and heat up. The result is either explosion of the star as a supernova, leaving behind a neutron star, or loss of mass by more gradual means to produce a white dwarf.  
  Red giants have diameters between 10 and 100 times that of the sun. They are very bright because they are so large, although their surface temperature is lower than that of the sun, about 2,000–3,000 K (1,700–2,700°C/3,000– 5,000°F).  
  supergiant Supergiants are the largest and most luminous type of star known, with a diameter up to 1,000 times that of the sun and absolute magnitudes of between –5 and –9. Supergiants are likely to become supernovae.  
  supernova A supernova is the explosive death of a star, which temporarily attains a brightness of 100 million suns or more, so that it can shine as brilliantly as a small galaxy for a few days or weeks. Very approximately, it is thought that a supernova explodes in a large galaxy about once every 100 years. Many supernovae—astronomers estimate some 50%—remain undetected because they are obscured by interstellar dust.  
  The name "supernova" was coined by U.S. astronomers Fritz Zwicky and Walter Baade in 1934. Zwicky was also responsible for their classification into types I and II. Type I supernovae are thought to occur in binary star systems, in which gas from one star falls on to a white dwarf, causing it to explode. Type II supernovae occur in stars ten or more times as massive as the sun, which suffer runaway internal nuclear reactions at the ends of their lives, leading to explosions. These are thought to leave behind neutron stars and black holes. Gas ejected by such an explosion causes an expanding radio source, such as the Crab nebula. Supernovae are thought to be the main source of elements heavier than hydrogen and helium.  




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Nearest Stars
Distance (light-years)
  Proxima Centauri  
  Alpha Centauri A  
  Alpha Centauri B  
  Barnard's Star  
  Wolf 359  
  Lalande 21185  
  UV Ceti A  
  UV Ceti B  
  Sirius A  
  Sirius B  
  Ross 154  
  Ross 249  


  variable star A variable star's brightness changes, either regularly or irregularly, over a period ranging from a few hours to months or years. The Cepheid variables regularly expand and contract in size every few days or weeks.  
  The 20 Brightest Stars  
  A star's brightness is referred to as its "magnitude." "Apparent magnitude" is brightness as seen from earth. "Absolute magnitude'' is measured at a standard distance of 32.6 light-years or 10 parsecs from the star.  
  Scientific name Common name
  Distance (light-years)  
1 Alpha Canis Majoris Sirius
2 Alpha Carinae Canopus
3 Alpha Centauri Rigil Kent
4 Alpha Boötis Arcturus
5 Alpha Lyrae Vega
6 Alpha Aurigae Capella
7 Beta Orionis Rigel
8 Alpha Canis Minoris Procyon
9 Alpha Eridani Achernar
10 Alpha Orionis Betelgeuse
11 Beta Centauri Hadar
12 Alpha Aquilae Altair
13 Alpha Tauri Aldebaran
14 Alpha Crucis Acrux
15 Alpha Scorpü Antares
16 Alpha Virginis Spica
17 Beta Geminorum Pollux
18 Alpha Piscis Austrini Fomalhaut
19 Alpha Cygni Deneb
20 Beta Crucis Mimosa


  Stars that change in size and brightness at less precise intervals include long-period variables, such as the red giant Mira in the constellation Cetus (period about 330 days), and irregular variables, such as some red supergiants. Eruptive variables emit sudden outbursts of light. Some suffer flares on their surfaces, while others, such as a nova, result from transfer of gas between a close pair of stars. In an eclipsing binary, the variation is due not to any change in the star itself, but to the periodic eclipse of a star by a close companion. The different types of variability are closely related to different stages of stellar evolution.  
  Brightest star  
  The brightest known star is the Pistol Star, discovered near the center of the Milky Way in 1997 by the Hubble Space Telescope. It emits as much energy in seconds as the sun does in one year, making it 10 million times brighter and 100 times larger.  


  white dwarf A white dwarf is a small, hot star, the last stage in the life of a star such as the sun. White dwarfs make up 10% of the stars in our galaxy; most have a mass 60% of that of the sun, but, with only 1% of the sun's diameter, are similar in size to the earth. Most have surface temperatures of 8,000°C/14,400°F or more, hotter than the sun. Yet, being so small, their overall luminosities may be less than 1% of that of the sun. The Milky Way contains an estimated 50 billion white dwarfs.  
  White dwarfs consist of degenerate matter in which gravity has packed the protons and electrons together as tightly as is physically possible, so that a spoonful of it weighs several tons. White dwarfs are thought to be the shrunken remains of stars that have exhausted their internal energy supplies. They slowly cool and fade over billions of years.  
  Stars and Constellations
  Hugely informative site on stars and constellations. It includes star charts of all major stars and constellations, details of the origins of the various names, photographs of our galaxy, and details on what stars can be seen at any given time.  
  some notable stars  
  Alpha Centauri, or Rigil Kent, is the brightest star in the constellation Centaurus and the third brightest star in the sky. It is actually a triple star (see binary star above); the two brighter stars orbit each other every 80 years, and the third, Proxima Centauri, is the closest star to the sun, 4.2 light-years away, 0.1 light-years closer than the other two.  




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  Arcturus, or Alpha Boötis, is the brightest star in the constellation Boötes and the fourth brightest star in the sky. It is a red giant about 28 times larger than the sun and 70 times more luminous, 36 light-years away from earth. Arcturus was the first star for which a proper motion was detected. In 1718 the English astronomer Edmond Halley noticed that, relatively to the surrounding stars, it had moved by about one degree from the position recorded by Ptolemy in the Almagest. Its name is derived from the Greek and means "the Guardian of the Bear."  
  Canopus, or Alpha Carinae, is the second brightest star in the night sky (after Sirius), lying in the southern constellation Carina. It is a first-magnitude yellow–white supergiant about 120 light years from earth, and thousands of times more luminous than the sun.  
  It may have been named in honor of the chief pilot of the Greek fleet that sailed against Troy, or the name may be derived from two Coptic words signifying "Golden Earth."  
  Capella, or Alpha Aurigae, is the brightest star in the constellation Auriga and the sixth brightest star in the night sky. It is a visual and spectroscopic binary that consists of a pair of yellow-giant stars 45 light-years from earth, orbiting each other every 104 days. It is a first-magnitude star, whose Latin name means the "the Little Nanny Goat": its kids are the three adjacent stars Epsilon, Eta, and Zeta Aurigae. Deneb, or Alpha Cygni, is the brightest star in the constellation Cygnus, and the 19th brightest star in the night sky. It is one of the greatest supergiant stars known, with a true luminosity about 60,000 times that of the sun. Deneb is about 1,800 light-years from earth. Its name is derived from the Arabic word for "tail."  
  Mira, or Omicron Ceti, is the brightest long-period pulsating variable star, located in the constellation Cetus. Mira was the first star discovered to vary periodically in brightness. It has a periodic variation between third or fourth magnitude and ninth magnitude over an average period of 331 days. It can sometimes reach second magnitude and once almost attained first magnitude in 1779. At times it is easily visible to the naked eye, being the brightest star in that part of the sky, while at others it cannot be seen without a telescope. It was named "Stella Mira," "the wonderful star," by Hevelius, who observed it 1659–82.  
  Polaris, or the Pole Star or North Star, is the bright star closest to the north celestial pole, and the brightest star in the constellation Ursa Minor. Its position is indicated by the "pointers" in Ursa Major. Polaris is a yellow supergiant about 500 light-years away. It is a Cepheid variable, whose magnitude varies between 2.1 and 2.2 over 3.97 days. It is also known as Alpha Ursae Minoris.  
  Polaris currently lies within 1° of the north celestial pole; precession (Earth's axial wobble) will bring it closest to the celestial pole (less than 0.5° away) in about A.D. 2100. Then its distance will start to increase, reaching 1° in 2205 and 47° in 28000.  
  Procyon, or Alpha Canis Minoris, is the brightest star in the constellation Canis Minor and the eighth brightest star in the sky. Procyon is a first-magnitude white star 11.4 light-years from earth, with a mass of 1.7 suns. It has a white dwarf companion that orbits it every 40 years. The name, derived from Greek, means "before the dog," and reflects the fact that in midnorthern latitudes Procyon rises shortly before Sirius, the Dog Star. Procyon and Sirius are sometimes called "the Dog Stars."  
  Rigel, or Beta Orionis, is the brightest star in the constellation Orion. It is a blue—white supergiant, with an estimated diameter 50 times that of the sun. It is 900 light-years from earth, and is intrinsically the brightest of the first-magnitude stars, its luminosity being about 100,000 times that of the sun. It is the seventh brightest star in the sky. Its name is derived from the Arabic for "foot."  
  Sirius, or the Dog Star or Alpha Canis Majoris, is the the brightest star in the night sky, 8.6 light years from earth in the constellation Canis Major. Sirius is a white star with a mass 2.3 times that of the sun, a diameter 1.8 times that of the sun, and a luminosity of 23 suns. It is orbited every 50 years by a white dwarf, Sirius B, also known as the Pup. The name "Sirius" is derived from the Greek word for "sparkling." In ancient Egypt, where its hieroglyph was a dog, its reappearance in the early morning sky heralded the annual rising of the River Nile.  
  Vega, or Alpha Lyrae, is the brightest star in the constellation Lyra and the fifth brightest star in the night sky. It is a blue—white star, 25 light-years from earth, with a luminosity 50 times that of the sun. In 1983 the Infrared Astronomy Satellite (IRAS) discovered a ring of dust around Vega, possibly a disk from which a planetary system is forming. As a result of precession (Earth's axial wobble), Vega will become the north polar star about the year 14000.  
  Each galaxy is a congregation of millions or billions of stars, held together by gravity. Spiral galaxies, such as the Milky Way, are flattened in shape, with a central bulge of old stars surrounded by a disk of younger stars, arranged in spiral arms like a Catherine wheel. Barred spirals are spiral galaxies that have a straight  




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  bar of stars across their center, from the ends of which the spiral arms emerge. The arms of spiral galaxies contain gas and dust from which new stars are still forming. Elliptical galaxies contain old stars and very little gas. They include the most massive galaxies known, containing a trillion stars. At least some elliptical galaxies are thought to be formed by mergers between spiral galaxies. There are also irregular galaxies. Most galaxies occur in clusters, containing anything from a few to thousands of members.  
  Our own galaxy is the Milky Way Galaxy, with the sun lying in one of its spiral arms. Only two galaxies, the Magellanic Clouds, are easily visible to the naked eye. The next brightest, the Andromeda galaxy, is just visible; it is 2.2 million light-years away, in the constellation Andromeda. About 20 galaxies are known to be within 2.5 million light-years away, and several thousand within 50 million light-years. More than 100 million can be photographed with modern telescopes.  
  Milky Way  
  The Milky Way appears as a faint band of light crossing the night sky, consisting of stars in the plane of our galaxy. The name "Milky Way" is also used for the galaxy itself. It is a spiral galaxy, 100,000 light-years in diameter and 2,000 light-years thick, containing at least 100 billion stars. The sun is in one of its spiral arms, about 25,000 light-years from the center, not far from its central plane.  
  The densest parts of the Milky Way, toward the galaxy's center, lie in the constellation Sagittarius. In places, the Milky Way is interrupted by lanes of dark dust that obscure light from the stars beyond, such as the Coalsack nebula in Crux (the Southern Cross). It is because of these that the Milky Way is irregular in width and appears to be divided into two between Centaurus and Cygnus.  
  The Milky Way passes through the constellations of Cassiopeia, Perseus, Auriga, Orion, Canis Major, Puppis, Vela, Carina, Crux, Centaurus, Norma, Scorpius, Sagittarius, Scutum, Aquila, and Cygnus.  
  Magellanic Clouds  
  These are the two galaxies nearest to our own galaxy. They are irregularly shaped, and appear as detached parts of the Milky Way, in the southern constellations Dorado, Tucana, and Mensa. The Large Magellanic Cloud spreads over the constellations of Dorado and Mensa. The Small Magellanic Cloud is in Tucana. The Large Magellanic Cloud is 169,000 light-years from earth, and about a third the diameter of our galaxy; the Small Magellanic Cloud, 180,000 light-years away, is about a fifth the diameter of our galaxy. They are named for the Portuguese navigator Ferdinand Magellan, who first described them. Being the nearest galaxies to ours, the Clouds are especially useful for studying stellar populations and objects such as supergiant stars.  
  radio galaxies  
  All galaxies, including our own, emit some radio waves, but those emitted by radio galaxies are up to a million times more powerful. In many cases the strongest radio emission comes not from the visible galaxy but from two clouds, invisible through an optical telescope, that can extend for millions of light-years either side of the galaxy. This double structure is also shown by some quasars, suggesting a close relationship between the two types of object. In both cases, the source of energy is thought to be a massive black hole at the center. Some radio galaxies are thought to result from two galaxies in collision or recently merged.  
  Other Astronomical Objects  
  black holes  
  A black hole is an object in space whose gravity is so great that nothing can escape from it, not even light. Thought to form when massive stars shrink at the end of their lives, a black hole sucks in more matter, including other stars, from the space around it. Matter that falls into a black hole is squeezed to infinite density at the center of the hole. Black holes can be detected because gas falling toward them becomes so hot that it emits X-rays.  
  Black holes containing the mass of millions of stars are thought to lie at the centers of quasars. Satellites have detected X-rays from a number of objects that may be black holes, but only four likely black holes in our galaxy had been identified by 1994.  
  Microscopic black holes may have been formed in the chaotic conditions of the Big Bang. The English physicist Stephen Hawking has shown that such tiny black holes could "evaporate" and explode in a flash of energy.  
  A nebula is a cloud of gas and dust in space. Nebulae are the birthplaces of stars, but some nebulae (planetary nebulae and supernovae remnants) are produced by gas thrown off from dying stars. Nebulae are classified according to on whether they emit, reflect, or absorb light.  
  An emission nebula, such as the Orion nebula, glows brightly because its gas is energized by the stars that have formed within it. In a reflection nebula, such as the one surrounding the stars of the Pleiades cluster,  




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  starlight reflects off the grains of dust within it. A dark nebula is a dense cloud, composed of molecular hydrogen, which partially or completely absorbs the light behind it. Examples include the Coalsack nebula in Crux and the Horsehead nebula in Orion.  
  Web Nebulae
  Images of nebulae, plus a short account of the different types of nebulae, and a glossary of related terms.  
  Crab nebula  
  The Crab nebula, the most famous supernova remnant (named for its crablike shape), is a cloud of gas 6,000 light-years from earth, in the constellation Taurus. It is the remains of a star that, according to Chinese records, exploded on July 4, 1054 as a brilliant point of light (now known to be a supernova). At its center is a pulsar that flashes 30 times a second.  
  It is a powerful radio and X-ray source. Optically it appears as a diffuse elliptical area on which is superimposed an intricate network of bright filaments. Observations show that it is increasing in size; its present dimensions are of the order of 10 light-years. The light is highly polarized, suggesting the presence of strong magnetic fields. This suggestion is strengthened by the fact that the diffuse portion is emitting radiation throughout the whole electromagnetic spectrum from radio to gamma waves, the energy coming from a pulsar near the center.  
  The Solar System  
  The solar system comprises the sun (a star) and all the bodies orbiting it: the nine planets (Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto), their moons, the asteroids, and the comets. The sun contains 99.86% of the mass of the solar system.  
  Solar System
  Educational tour of the solar system. It contains information and statistics about the sun, earth, planets, moons, asteroids, comets, and meteorites found within the solar system, supported by images.  
  The solar system gives every indication of being a strongly unified system having a common origin and development. It is isolated in space; all the planets go round the sun in orbits that are nearly circular and coplanar, and in the same direction as the sun itself rotates; moreover this same pattern is continued in the regular system of satellites that accompany Jupiter, Saturn, and Uranus. It is thought to have formed by condensation from a cloud of gas and dust about 4.6 billion years ago.  
  the sun  
  The sun is the star at the center of the solar system, and the source of daylight on earth. Its diameter is 1,392,000 km/865,000 mi; its temperature at the surface is about 5,800 K (5,500°C/9,900°F), and at the center 15,000,000 K (about 15,000,000°C/  
  solar system Most of the objects in the solar system lie close to the plane of the ecliptic. The
planets are tiny compared to the sun (not to scale). If the sun were the size of a basketball, the
planet closest to the sun, Mercury, would be the size of a mustard seed 15 m/48 ft from the sun.
The most distant planet, Pluto, would be a pinhead 1.6 km/1 mi away from the sun. The earth,
which is the third planet out from the sun, would be the size of a pea 32 m/100 ft from the sun.




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  sun The structure of the sun. Nuclear reactions at the core releases vast amounts of
energy in the form of light and heat that radiate out to the photosphere and corona.
Surges of glowing gas rise as prominences from the surface of the sun and cooler
areas, known as sunspots appear as dark patches on the giant stars surface.
  27,000,000°F). It is composed of about 70% hydrogen and 30% helium, with other elements making up less than 1%. The sun's energy is generated by nuclear-fusion reactions that turn hydrogen into helium at its center. The gas core is far denser than mercury or lead on earth. The sun is about 4.7 billion years old, with a predicted lifetime of 10 billion years.  
  All you ever wanted to know about our closest star, including cross sections, photographs, a history of exploration, animations of eclipses, and much more. You can also take a multimedia tour of the sun or find out what today's weather is like on the sun.  
  At the end of its life, it will expand to become a red giant the size of Mars's orbit, then shrink to become a white dwarf. The sun spins on its axis every 25 days near its equator, but more slowly towards its poles. Its rotation can be followed by watching the passage of dark sunspots across its disk. Sometimes bright eruptions called flares occur near sunspots. Above the sun's photosphere, or visible surface, lies a layer of thinner gas called the chromosphere, visible only by means of special instruments or at eclipses. Tongues of gas called prominences extend from the chromosphere into the corona, a halo of hot, tenuous gas surrounding the sun. Gas boiling from the corona streams outward through the solar system, forming the solar wind. Activity on the sun, including sunspots, flares, and prominences, waxes and wanes during the solar cycle, which peaks every 11 years or so, and seems to be connected with the solar magnetic field.  
  Stanford Solar Center
  Introduction to the sun and its effect on the earth, designed with schoolchildren in mind. The site contains information about the sun's part in global warming, as well as a quiz, solar art, and various folklore tales about the sun.  
  the moon  
  The moon is earth's closest neighbor and its natural satellite. It is 3,476 km/2,160 mi in diameter, with a mass 0.012 (approximately one-eightieth) that of earth. Its surface gravity is only 0.16 (one-sixth) that of earth. Its average distance from earth is 384,400 km/238,855 mi, and it orbits in a west-to-east direction every 27.32 days (the sidereal month). It spins on its axis with one side permanently turned towards earth. The moon has no atmosphere and was thought to have no water until ice was discovered on its surface in 1998.  
  The moon is illuminated by sunlight, and goes through a cycle of phases of shadow, waxing from new (dark) via first quarter (half moon) to full, and waning back again to new every 29.53 days (the synodic month, also known as a lunation). On its sunlit side, temperatures reach 110°C/230°F, but during  




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  the two-week lunar night the surface temperature drops to –170°C/–274°F  
  The origin of the moon is still open to debate. Scientists suggest the following theories: that it split from the earth; that it was a separate body captured by earth's gravity; that it formed in orbit around earth; or that it was formed from debris thrown off when a body the size of Mars struck earth. Future exploration of the moon may detect water permafrost, which could be located at the permanently shadowed lunar poles.  
  The moon's composition is rocky, with a surface heavily scarred by meteorite impacts that have formed craters up to 240 km/150 mi across. Seismic observations indicate that the moon's surface extends downward for tens of kilometers; below this crust is a solid mantle about 1,100 km/688 mi thick, and below that a silicate core, part of which may be molten. Rocks brought back by astronauts show the moon is 4.6 billion years old, the same age as earth. It is made up of the same chemical elements as earth, but in different proportions, and differs from earth in that most of the moon's surface features were formed within the first billion years of its history when it was hit repeatedly by meteorites.  
  The youngest craters are surrounded by bright rays of ejected rock. The largest scars have been filled by dark lava to produce the lowland plains called seas, or maria (plural of mare). These dark patches form the so-called "man-in-the-moon" pattern. One of the moon's easiest features to observe is the mare Plato, which is about 100 km/62 mi in diameter and 2,700 m/8,860 ft deep, and at times is visible with the naked eye alone.  
  The far side of the moon was first photographed from the Soviet space probe Lunik 3 in October 1959. Much of our information about the moon has been derived from this and other photographs and measurements taken by U.S. and Soviet moon probes, from geological samples brought back by U.S. Apollo astronauts and by Soviet Luna probes, and from experiments set up by the U.S. astronauts in 1969–72. The U.S. probe Lunar Prospector, launched in January 1998, is intended to examine the composition of the lunar crust, record gamma rays, and map the lunar magnetic field.  
  eclipse An eclipse is the passage of an astronomical body through the shadow of another. The term is usually employed for solar and lunar eclipses, which may be either partial or total, but also, for example, for eclipses by Jupiter of its satellites. An eclipse of a star by a body in the solar system is called an occultation.  
  Detailed description of the moon. It includes statistics and information about the surface, eclipses, and phases of the moon, along with details of the Apollo landing missions.  
  A solar eclipse occurs when the moon passes in front of the sun as seen from earth, and can happen only at new moon. During a total eclipse the sun's corona can be seen. A total solar eclipse can last up to 7.5 minutes. When the moon is at its farthest from earth it does not completely cover the face of the sun, leaving a ring of sunlight visible. This is an annular eclipse  
Phases of the Moon 2000
Phases of the moon shown to the nearest hour with timings given in Greenwich Mean Time (GMT).
New moon
First quarter
Full moon
Last quarter
Time Month
Time Month
Time Month
18:14 January
13:34 January
04:40 January
13:03 February
23:21 February
16:27 February
05:17 March
06:59 March
04:44 March
18:12 April
13:30 April
17:41 April
04:12 May
20:00 May
07:34 May
12:14 June
03:29 June
22:27 June
19:20 July
12:53 July
13:55 July
02:25 August
01:02 August
05:13 August
10:19 September
16:27 September
19:37 September
19:53 October
10:59 October
08:53 October
07:58 November
07:27 November
21:15 November
23:11 December
03:55 December
09:03 December





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  Eclipse The two types of eclipse: lunar and solar. A lunar eclipse occurs when
the moon passes through the shadow of the earth. A solar eclipse occurs when
the moon passes between the sun and the earth, blocking out the sun's light.
During a total solar eclipse, when the moon completely covers the sun, the
moon's shadow sweeps across the earth's surface from west to east at a speed
of 3,200kph/2,000mph.
  (from the Latin word annulus "ring"). Between two and five solar eclipses occur each year.  
  A lunar eclipse occurs when the moon passes into the shadow of the earth, becoming dim until emerging from the shadow. Lunar eclipses may be partial or total, and they can happen only at full moon. Total lunar eclipses last for up to 100 minutes; the maximum number each year is three.  
Solar and Lunar Eclipses
  Table does not include partial eclipses of the moon.  
Day Type of eclipse Duration of maximum eclipse Region for observation
21 lunar total 4 hr 44 min the Americas, Europe, Africa, western Asia
5 solar partial 12 hr 50 min Antarctica
1 solar partial 19 hr 34 min southeastern Pacific Ocean
16 lunar total 13 hr 56 min southeastern Asia, Australasia
31 solar partial 2 hr 14 min Arctic regions
25 solar partial 17 hr 36 min United States, eastern Canada, Central America, Caribbean
9 lunar total 20 hr 21 min Africa, Europe, Asia
21 solar total 12 hr 4 min central and southern Africa
  December 2002  
14 solar annular 20 hr 52 min Pacific Ocean
10 solar annular 23 hr 44 min Pacific Ocean
4 solar total 7 hr 31 min Southern Africa, Indian Ocean, Australia
16 lunar total 3 hr 40 min Americas, E. W. Africa
31 solar annular 4 hr 8 min Iceland, Greenland
9 lunar total 1 hr 18 min Americas, Africa, Europe
23 solar total 22 hr 49 min Antarctica





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  A planet is a large celestial body in orbit around a star, composed of rock, metal, or gas. The nine planets in the solar system are: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto. The inner four, called the terrestrial planets, are small and rocky, and include the planet earth. The outer planets, with the exception of Pluto, are called the major planets, and consist of large balls of rock, liquid, and gas; the largest is Jupiter, which contains a mass equivalent to 70% of all the other planets combined. Planets do not produce light, but reflect the light of their parent star.  
  As seen from the earth, all the historic planets—Mercury, Venus, Mars, Jupiter, and Saturn—are conspicuous objects moving in looped paths against the stellar background. The size of these loops, which are caused by the earth's own motion round the sun, are inversely proportional to the planet's distance from the earth.  
  Mercury is the closest planet to the sun. Its mass is 0.056 that of earth. On its sunward side the surface temperature reaches over 400°C/752°F, but on the "night" side it falls to –170°C/–274°F.  
  mean distance from the Sun: 58 million km/36 million mi  
  equatorial diameter: 4,880 km/3,030 mi  
  rotation period: 59 earth days  
  year: 88 earth days  
  atmosphere: Mercury has an atmosphere with minute traces of argon and helium.  
  surface: composed of silicate rock often in the form of lava flows. In 1974 the U.S. space probe Mariner 10 showed that Mercury's surface is cratered by meteorite impacts.  
  satellites: none  
  Detailed description of the planet Mercury. It includes statistics and information about the planet, along with a chronology of its exploration supported by a good selection of images.  
  Its largest known feature is the Caloris Basin, 1,400 km/870 mi wide. There are also cliffs hundreds of miles long and up to 4 km/ 2.5 mi high, thought to have been formed by the cooling of the planet billions of years ago. Inside is an iron core three-quarters of the planet's diameter, which produces a magnetic field 1% the strength of earth's.  
  Venus is the second planet from the sun. It can approach earth to within 38 million km/24 million mi, closer than any other planet. Its mass is 0.82 that of earth. Venus rotates on its axis more slowly than any other planet, from east to west, the opposite direction to the other planets (except Uranus and possibly Pluto).  
  mean distance from the sun: 108.2 million km/67.2 million mi  
  equatorial diameter: 12,100 km/7,500 mi  
  rotation period: 243 earth days  
  year: 225 earth days  
  atmosphere: Venus is shrouded by clouds of sulfuric acid droplets that sweep across the planet from east to west every four days. The atmosphere is almost entirely carbon dioxide, which traps the sun's heat by the greenhouse effect and raises the planet's surface temperature to 480°C/900°F, with an atmospheric pressure 90 times that at the surface of the earth.  
  surface: consists mainly of silicate rock and may have an interior structure similar to that of earth: an iron—nickel core, a mantle composed of mafic rocks (rocks made of one or more dark-colored, ferromagnesian minerals), and a thin siliceous outer crust. The surface is dotted with deep impact craters. Some of Venus's volcanoes may still be active.  
  satellites: no moons  
  The largest highland area is Aphrodite Terra near the equator, half the size of Africa. The highest mountains are on the northern highland region of Ishtar Terra, where the massif of Maxwell Montes rises to 10,600 m/35,000 ft above the average surface level. The highland areas on Venus were formed by volcanoes.  
  Venus has an ion-packed tail, 45 million km/28 million mi in length, that stretches away from the sun and is caused by the bombardment of the ions in Venus's upper atmosphere by the solar wind.  
  The first human-made object to hit another planet was the Soviet probe Venera 3, which crashed on Venus on March 1, 1966. Later Venera probes parachuted down through the atmosphere and landed successfully on its surface, analysing surface material and sending back information and pictures. In December 1978 a U.S. Pioneer Venus probe went into orbit around the planet and mapped most of its surface by radar, which penetrates clouds. In 1992 the U.S. space probe Magellan mapped 99% of the planet's surface to a resolution of 100 m/330 ft.  
  Earth is the third planet from the sun. It is almost spherical, flattened slightly at the poles, and is composed of three concentric layers: the core, the mantle, and the crust. About 70% of the surface (including the north and south polar icecaps) is covered with water. The earth is surrounded by a life-supporting atmosphere and is the only planet on which life is known to exist.  




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Discovery of the Major Planets
  By Tony Jones  
the first five
Other than the earth, there are eight major planets in the solar system. Five of them—Mercury, Venus, Mars, Jupiter, and Saturn—have been known since antiquity. Looking like bright stars, they reveal their true nature by moving slowly form night to night against the background of the constellations. Indeed, the word "planet" comes form the ancient Greek for "wanderer."
Venus is unmistakable. Shining brilliant white, it is by far the brightest object in the sky after the sun and moon and is often visible in daylight. Every few months it is an arresting sight in the evening or morning sky. Jupiter, Mars and Saturn are also prominent, and Mercury may escape attention only because it is close to the sun and never seen in darkness. These five, together with the sun and moon, were familiar sights in the heavens throughout recorded history and have been woven into religious and astrological myth since ancient times.
The world was taken by surprise then, when a humble music teacher discovered a new member of the sun's family of planets in 1781. William Herschel was a committed amateur astronomer anda skilled telescope maker. He had built a series of' superb telescopes at his home in Bath, England. On March 13, while conducting a survey of the night sky, he came across a curious star that appeared as a disk rather than a point of light. A few nights later it had changed position and within months the astronomical world had confirmed that Herschel's object was a new planet far beyond the orbit of Saturn, then the outermost known member of the solar system.
Herschel wanted to call it George's Star, in honor of King George III, but the name Uranus, after the Greek sky god and father of Cronos (Saturn), was eventually accepted. The king was dazzled none the less, and Herschel, the first person ever to discover a new planet, became a favorite at the royal court and soon the most influential astronomer of his day.
Uranus, though faint, is actually visible to the naked eye under good conditions. It was later found that the planet had been recorded on at least 20 occasions, as far back as 1690, and had been mistaken for a star each time. The earlier observers had not had the benefit of Herschel's powerful telescopes, which were able to discern the greenish disk of the planet.
Some years later astronomers were having problems with the orbit of Mercury, the planet closest to the sun. Its movements could not be completely accounted for by Newton's laws of gravity. A French astronomer, Urbain Leverrier, proposed in 1845 that the discrepancy could be explained by the gravitational attraction of an undiscovered planet, which he called Vulcan, orbiting within the orbit of Mercury only 30 million km/18.5 million mi from the sun. All attempts to find Vulcan failed, and the Mercury problem remained unsolved until 1915, when Albert Einstein (1879–1955) showed that the discrepancies in the orbit were a consequence of the general theory of relativity.
Leaving astronomers to search for Vulcan, Leverrier turned his attention to Uranus, which was also deviating from its predicted path. Again, he attributed the perturbation to another planet, this time beyond the orbit of Uranus, and predicted where in the sky it would be found. Johann Galle at the Berlin Observatory pointed a telescope at Leverrier's position on September 23, 1846 and almost at once discovered the new planet only one degree from the predicted location. It became known as Neptune, after the Roman god of the sea.
It turned out that a young Cornish mathematician, John Couch Adams, had predicted the position of Neptune a year earlier but had been unable to persuade the Astronomer Royal, George Airy, to take it seriously. When Airy finally asked James Challis (1803–1882) at Cambridge Observatory to search for the planet, Challis saw it on two occasions more than a month before Galle but failed to recognize it.
Buoyed by this outstanding triumph of Newtonian mechanics, astronomers soon suspected that Neptune in turn was being affected by the pull of a still more distant planet. One of the scientists who attempted to calculate its position was U.S. businessman and astronomer Percival Lowell. He built his own observatory in 1895 at Flagstaff in Arizona but failed to track down the mystery planet. It was not until February 18, 1930, 14 years after Lowell's death, the Clyde Tombaugh, an assistant at the observatory, finally stumbled across the planet. He had ignored the predictions of the mathematicians and had systematically worked his way through the zodiac, the band of sky in which the planets move, comparing pairs of photographs taken on different nights and looking for a "star" that had moved.
The planet, which was named Pluto after the god of the underworld, was much fainter than expected and was later found on several photographs taken during earlier searches.
Though astronomers continue to discover asteroids, comets and other small bodies in the outer solar system, modern search techniques are so thorough that there is little chance of more major planets lying unseen beyond the orbit of Pluto.





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  mean distance from the sun: 149,500,000 km/ 92,860,000 mi  
  equatorial diameter: 12,756 km/7,923 mi  
  circumference: 40,070 km/24,900 mi  
  rotation period: 23 hr 56 min 4.1 sec  
  year: (complete orbit, or sidereal period) 365 days 5 hr 48 min 46 sec. Earth's average speed around the sun is 30 kps/18.5 mps; the plane of its orbit is inclined to its equatorial plane at an angle of 23.5°, the reason for the changing seasons  
  atmosphere: nitrogen 78.09%; oxygen 20.95%; argon 0.93%; carbon dioxide 0.03%; and less than 0.0001% neon, helium, krypton, hydrogen, xenon, ozone, and radon  
  Earth and Moon Viewer
  View a map of the earth showing the day and night regions at this moment, or view the earth from the sun, the moon, or any number of other locations. Alternatively, take a look at the moon from the earth or the sun, or from above various formations on the lunar surface.  
  surface: land surface 150,000,000 sq km/ 57,500,000 sq mi (greatest height above sea level 8,872 m/29,118 ft Mount Everest); water surface 361,000,000 sq km/139,400,000 sq mi (greatest depth 11,034 m/36,201 ft Mariana Trench in the Pacific). The interior is thought to be an inner core about 2,600 km/1,600 mi in diameter, of solid iron and nickel; an outer core about 2,250 km/1,400 mi thick, of molten iron and nickel; and a mantle of mostly solid rock about 2,900 km/1,800 mi thick, separated from the earth's crust by the Mohorovicic discontinuity. The crust and the topmost layer of the mantle form about 12 major moving plates, some of which carry the continents. The plates are in constant, slow motion, called tectonic drift. U.S. geophysicists announced in 1996 that they had detected a difference in the spinning time of the earth's core and the rest of the planet; the core is spinning slightly faster.  
  satellite: the moon  
  age: 4.6 billion years. The earth was formed with the rest of the solar system by consolidation of interstellar dust. Life began 3.5–4 billion years ago.  
  season The cause of the seasons. As the earth orbits the sun, its axis of rotation
always points in the same direction. This means that, during the northern hemi-
sphere summer solstice (June 21), the sun is overhead in the northern hemisphere.
At the northern hemisphere winter solstice (December 22), the sun is overhead
in the southern hemisphere.
  The fourth planet from the sun. It is much smaller than Venus or earth, with a mass 0.11 that of earth. Mars is slightly pear-shaped, with a low, level northern hemisphere, which is comparatively uncratered and geologically "young," and a heavily cratered "ancient" southern hemisphere.  
  mean distance from the sun: 227.9 million km/141.6 million mi  
  equatorial diameter: 6,780 km/4,210 mi  
  rotation period: 24 hr 37 min  
  year: 687 earth days  
  atmosphere: 95% carbon dioxide, 3% nitrogen, 1.5% argon, and 0.15% oxygen. Red atmospheric dust from the surface whipped up by winds of up to 450 kph/280 mph accounts for the light pink sky. The surface pressure is less than 1% of the earth's atmospheric pressure at sea level.  
  surface: The landscape is a dusty, red, eroded lava plain. Mars has white polar caps (water ice and frozen carbon dioxide) that advance and retreat with the seasons.  
  satellites: two small satellites: Phobos and Deimos.  
  There are four enormous volcanoes near the equator, of which the largest is Olympus Mons 24 km/15 mi high, with a base 600 km/375 mi across, and a crater 65 km/40 mi wide. To the east of the four volcanoes lies a high plateau cut by a system of valleys, Valles Marineris, some 4,000 km/2,500 mi long, up to 200 km/120 mi wide and 6 km/4 mi deep; these features  




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  are apparently caused by faulting and wind erosion. Recorded temperatures vary from –100°C/–148°F to 0°C/32°F.  
  Detailed description of the planet Mars, commonly referred to as ''the red planet." It includes statistics and information about the surface, volcanoes, satellites, and clouds of the planet, supported by a good selection of images.  
  Mars may approach earth to within 54.7 million km/34 million mi. The first human-made object to orbit another planet was Mariner 9. Viking 1 and Viking 2, which landed, also provided much information. Studies in 1985 showed that enough water might exist to sustain prolonged missions by space crews.  
  In January 1997 NASA launched the Mars Pathfinder, which made a successful landing on Mars in July 1997 on a flood plain called Ares Vallis. After initial technical problems, its 0.3-m/1-ft rover, "Sojourner," began to explore the Martian landscape and to transmit data back to earth. Photographs from the Mars Pathfinder indicated that the planet is rusting. NASA announced this in July 1997 and said that a supercorrosive force was eroding rocks on the surface due to iron oxide in the soil.  
  In May 1997 American scientists announced that Mars is becoming increasingly colder and cloudier. Images from the Hubble Space Telescope showed that dust storms had covered areas of the planet that had been dark features in the early century, including one section as large as California.  
  The Global Surveyor, which entered Martian orbit in September 1997, revealed that Mars' magnetic field is a mere 800th that of the earth.  
  Welcome to the Mars Missions, Year 2000 and Beyond!
  Well presented NASA site with comprehensive information on current and future missions to Mars. There are fascinating and well written accounts of Pathfinder and Global Surveyor, and large numbers of images of the red planet.  
  Jupiter is the fifth planet from the sun, and the largest in the solar system, with a mass equal to 70% of all the other planets combined, 318 times that of earth. It is largely composed of hydrogen and helium, liquefied by pressure in its interior, and probably with a rocky core larger than earth. Its main feature is the Great Red Spot, a cloud of rising gases, 14,000 km/ 8,500 mi wide and 30,000 km/20,000 mi long, revolving counterclockwise.  
  mean distance from the sun: 778 million km/ 484 million mi  
  equatorial diameter: 142,800 km/88,700 mi  
  rotation period: 9 hr 51 min  
  year: (complete orbit) 11.86 earth years  
  atmosphere: consists of clouds of white ammonia crystals, drawn out into belts by the planet's high speed of rotation (the fastest of any planet). Darker orange and brown clouds at lower levels may contain sulfur, as well as simple organic compounds. Further down still, temperatures are warm, a result of heat left over from Jupiter's formation, and it is this heat that drives the turbulent weather patterns of the planet. In 1995 the Galileo probe revealed Jupiter's atmosphere to consist of 0.2% water, less than previously estimated.  
  surface: although largely composed of hydrogen and helium, Jupiter probably has a rocky core larger than earth.  
  satellites: Jupiter has 16 moons. The four largest moons, Io, Europa (which is the size of our moon), Ganymede, and Callisto, are the Galilean satellites, discovered in 1610 by Galileo (Ganymede, which is about the size of Mercury, is the largest moon in the solar system). Three small moons were discovered in 1979 by the Voyager space probes, as was a faint ring of dust around Jupiter's equator 55,000 km/34,000 mi above the cloud tops.  
  The Great Red Spot was first observed in 1664. Its top is higher than the surrounding clouds; its color is thought to be due to red phosphorus. Jupiter's strong magnetic field gives rise to a large surrounding magnetic "shell," or magnetosphere, from which bursts of radio waves are detected. The Southern Equatorial Belt in which the Great Red Spot occurs is subject to unexplained fluctuation. In 1989 it sustained a dramatic and sudden fading.  
  Full details of the planet and its moons, including a chronology of exploration, various views of the planet and its moons, and links to other planets.  
  Saturn is the second largest planet in the solar system, sixth from the sun, and encircled by bright and easily visible equatorial rings. Viewed through a telescope, it is ocher in color. Its polar diameter is 12,000 km/ 7,450 mi smaller than its equatorial diameter, a result  




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  of its fast rotation and low density, the lowest of any planet. Its mass is 95 times that of earth, and its magnetic field 1,000 times stronger.  
  mean distance from the sun: 1.427 billion km/ 0.886 billion mi  
  equatorial diameter: 120,000 km/75,000 mi  
  rotational period: 10 hr 14 min at equator, 10 hr 40 min at higher latitudes  
  year: 29.46 earth years  
  atmosphere: visible surface consists of swirling clouds, probably made of frozen ammonia at a temperature of –170°C/–274°F, although the markings in the clouds are not as prominent as Jupiter's. The space probes Voyager 1 and 2 found winds reaching 1,800 kph/1,100 mph  
  surface: Saturn is believed to have a small core of rock and iron, encased in ice and topped by a deep layer of liquid hydrogen  
  satellites: 18 known moons, more than for any other planet. The largest moon, Titan, has a dense atmosphere. Other satellites include Epimetheus, Janus, Pandor, and Prometheus. The rings visible from earth begin about 14,000 km/9,000 mi from the planet's cloudtops and extend out to about 76,000 km/ 47,000 mi. Made of small chunks of ice and rock (averaging 1 m/3 ft across), they are 275,000 km/170,000 mi rim to rim, but only 100 m/300 ft thick. The Voyager probes showed that the rings actually consist of thousands of closely spaced ringlets, looking like the grooves in a phonograph record.  
  From earth, Saturn's rings appear to be divided into three main sections. Ring A, the outermost, is separated from ring B, the brightest, by the Cassini division, named for its discoverer Italian astronomer Giovanni Cassini, which is 3,000 km/2,000 mi wide; the inner, transparent ring C is also called the Crepe Ring. Each ringlet of the rings is made of a swarm of icy particles like snowballs, a few centimeters to a few meters in diameter. Outside the A ring is the narrow and faint F ring, which the Voyagers showed to be twisted or braided. The rings of Saturn could be the remains of a shattered moon, or they may always have existed in their present form.  
  How many rings does Saturn have? How many satellites? Find out this and more at this site, which also features a video of a storm in the planet's atmosphere.  
  Uranus is the seventh planet from the sun, discovered by the British astronomer William Herschel in 1781. It is twice as far out as the sixth planet, Saturn. Uranus has a mass 14.5 times that of earth. The spin axis of Uranus is tilted at 98°, so that one pole points towards the sun, giving extreme seasons.  
  Uranian Satellites  
  To remember the Uranian satellites visible from earth:  
  (Miranda, Ariel, Umbriel, Titania, Oberon)  


  mean distance from the sun: 2.9 billion km/1.8 billion mi  
  equatorial diameter: 50,800 km/31,600 mi  
  rotation period: 17.2 hr  
  year: 84 earth years  
  atmosphere: deep atmosphere composed mainly of hydrogen and helium  
  surface: composed primarily of hydrogen and helium but may also contain heavier elements, which might account for Uranus's mean density being higher than Saturn's  
  satellites: 17 moons (two discovered in 1997); 11 thin rings around the planet's equator were discovered in 1977.  
  Uranus has a peculiar magnetic field, whose axis is tilted at 60° to its axis of spin, and is displaced about a third of the way from the planet's center to its surface. Uranus spins from east to west, the opposite of the other planets, with the exception of Venus and possibly Pluto. The rotation rate of the atmosphere varies with latitude, from about 16 hours in mid-southern latitudes to longer than 17 hours at the equator.  
  All Uranus' moons are named for characters from Shakespeare.  


  Uranus's equatorial ring system comprises 11 rings. The ring furthest from the planet center, Epsilon, is 100 km/62 mi at its widest point. In 1995 U.S. astronomers determined that the ring particles contained long-chain hydrocarbons. Looking at the brightest region of Epsilon, they were also able to calculate the precession (axial wobble) of Uranus as 264 days, the fastest known precession in the solar system.  
  The space probe Voyager 2 detected 11 rings, composed of rock and dust, around the planet's  
  Did you know that Uranus is tipped on its side? Find out more about Uranus, its rings, and its moons at this site. Also included are a table of statistics about the planet, photographs, and animations of it rotating.  




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  equator, and found 10 small moons in addition to the 5 visible from earth. Titania, the largest moon, has a diameter of 1,580 km/980 mi. The rings are charcoal black, and may be debris of former "moonlets" that have broken up.  
  Neptune is the eighth planet in average distance from the sun. It is a giant gas planet, with a mass 17.2 times that of earth. It has the highest winds in the solar system.  
  mean distance from the sun: 4.4 billion km/2.794 billion mi  
  equatorial diameter: 48,600 km/30,200 mi  
  rotation period: 16 hr 7 min  
  year: 164.8 earth years  
  atmosphere: methane in its atmosphere absorbs red light and gives the planet a blue coloring. Consists primarily of hydrogen (85%) with helium (13%) and methane (1–2%).  
  surface: hydrogen, helium, and methane. Its interior is believed to have a central rocky core covered by a layer of ice.  
  satellites: of Neptune's eight moons, two (Triton and Nereid) are visible from earth. Six were discovered by the Voyager 2 probe in 1989, of which Proteus (diameter 415 km/260 mi) is larger than Nereid (300 km/200 mi).  
  rings: there are four faint rings: Galle, Le Verrier, Arago, and Adams (in order from Neptune). Galle is the widest at 1,700 km/ 1,060 mi. Leverrier and Arago are divided by a wide diffuse particle band called the plateau.  
  Neptune was located in 1846 by German astronomers Johan Galle and Heinrich d'Arrest (1822–1875) after calculations by English astronomer John Couch Adams and French mathematician Urbain Leverrier had predicted its existence from disturbances in the movement of Uranus. Voyager 2, which passed Neptune in August 1989, revealed various cloud features, notably an earth-sized oval storm cloud, the Great Dark Spot, similar to the Great Red Spot on Jupiter, but images taken by the Hubble Space Telescope in 1994 show that the Great Dark Spot has since disappeared. A smaller dark spot, DS2, has also gone.  
  Detailed description of the planet Neptune. It includes a chronology of the exploration of the planet, along with statistics and information on its rings, moons, and satellites.  
  Pluto is the smallest and, usually, the outermost planet of the solar system. The existence of Pluto was predicted by calculation by the U.S. astronomer Percival Lowell and the planet was located by U.S. astronomer Clyde Tombaugh in 1930. Its highly elliptical orbit occasionally takes it within the orbit of Neptune, as in 1979–99. Pluto has a mass about 0.002 of that of earth.  
  mean distance from the sun: 5.8 billion km/3.6 billion mi  
  equatorial diameter: 2,300 km/1,438 mi  
  rotation period: 6.39 earth days  
  year: 248.5 earth years  
  atmosphere: thin atmosphere with small amounts of methane gas  
  surface: low density, composed of rock and ice, primarily frozen methane; there is an ice cap at Pluto's north pole  
  satellites: one moon, Charon  
  Charon, Pluto's moon, was discovered in 1978 by James Walter Christy (1938– ). It is about 1,200 km/750 mi in diameter, half the size of Pluto, making it the largest moon in relation to its parent planet in the solar system. It orbits about 20,000 km/12,500 mi from the planet's center every 6.39 days—the same time that Pluto takes to spin on its axis. Charon is composed mainly of ice. Some astronomers have suggested that Pluto was a former moon of Neptune that escaped, but it is more likely that it was an independent body that was captured. The Hubble Space Telescope photographed Pluto's surface in 1996.  
  Pluto and Charon
  Site devoted to our most distant planet and its satellite. It contains a table of statistics, photographs, and an animation of their rotation. You can also find out about NASA's planned mission to Pluto and Charon in 2010.  
  An asteroid, or minor planet, is any one of many thousands of small bodies, composed of rock and iron, that orbit the sun. Most lie in a belt between the orbits of Mars and Jupiter, and are thought to be fragments left over from the formation of the solar system. About 100,000 may exist, but their total mass is only a few hundredths the mass of the moon.  
  They include Ceres (the largest asteroid, 940 km/584 mi in diameter), Vesta (which has a light-colored surface, and is the brightest as seen from earth), Eros, and Icarus. Some asteroids are in orbits that bring them close to earth, and some, such as the Apollo asteroids, even cross earth's orbit; at least some of these may be remnants of former comets. One group, the Trojans, moves along the same orbit as Jupiter, 60° ahead and behind the planet. One unusual asteroid, Chiron, orbits beyond Saturn.  




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  The Largest Asteroids  
  An asteroid is a small body, composed of rock and iron, that orbits the sun. Most lie in a belt between the orbits of Mars and Jupiter, and are thought to be fragments left over from the formation of the solar system.  
Name Diameter Average
from sun (Earth = 1)
  Orbital period (yrs)  
    km mi  
Ceres 940 584 2.77
Pallas 588 365 2.77
Vesta 576 358 2.36
Hygeia 430 267 3.13
Interamnia 338 210 3.06
Davida 324 201 3.18


  The first asteroid was discovered by the Italian astronomer Giuseppe Piazzi at the Palermo Observatory, Sicily, on January 1, 1801. The first asteroid moon was observed by the space probe Galileo in 1993, orbiting asteroid Ida.  
  A comet is a small, icy body orbiting the sun, usually on a highly elliptical path. It consists of a central nucleus a few miles across, and has been likened to a dirty snowball because it is mostly made up of ice mixed with dust. As a comet approaches the sun its nucleus heats up, releasing gas and dust, which form a tenuous coma, up to 100,000 km/ 60,000 mi wide, around the nucleus. Gas and dust stream away from the coma to form one or more tails, which may extend for millions of kilometers. U.S. astronomers concluded in 1996 that there are two distinct types of comet: one rich in methanol and one low in methanol. Evidence for this comes in part from observations of the spectrum of Comet Hyakutake.  
  Asteroid Introduction
  What is the difference between an asteroid and a meteorite? Find out at this site, which contains a table of statistics about asteroids, a chronology of asteroid exploration, and images of selected asteroids.  
  Comets are believed to have been formed at the birth of the solar system. Billions of them may reside in a halo (the Oort cloud) beyond the planet Pluto. The gravitational effect of passing stars pushes some toward the sun, when they eventually become visible from earth. Most comets swing around the sun and return to distant space, never to be seen again for  
Major Comets
(– = not applicable.)
  First recorded sighting  
Orbital period (yrs) Interesting facts
Halley's comet
  240 B.C.  
parent of Eta Aquarid and Orionid meteor showers
Comet Tempel-Tuttle A.D. 1366
parent of Leonid meteors
Biela's comet
broke in half in 1846; not seen since 1852
Encke's comet
parent of Taurid meteors
Comet Swift-Tuttle
parent of Perseid meteors; reappeared 1992
Comet Ikeya-Seki
so-called "sun-grazing" comet, passed 500,000 km/300,000 mi above surface of the sun on October 21, 1965
Comet Kohoutek
observed from space by Skylab astronauts
Comet West
nucleus broke into four parts
Comet Bowell
ejected from solar system after close encounter with Jupiter
Comet IRAS-Araki-Alcock
passed only 4.5 million km/2.8 million mi from the earth on May 11, 1983
Comet Austin
passed 32 million km/20 million mi from the earth in 1990
Comet Shoemaker-Levy 9
made up of 21 fragments; crashed into Jupiter in July 1994
Comet Hale-Bopp
spitting out of gas and debris produced a coma, a surrounding hazy cloud of gas and dust, of greater volume than the sun; the bright coma is due to an outgassing of carbon monoxide; clearly visible with the naked eye in March 1997
Comet Hyakutake
passed 15 million km/9,300,000 mi from the earth





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Heaviest Meteorites
(N/A = not available.)        
Name and location Weight (metric tons) Year found Dimensions Composition
Hoba West, Grootfontein, Namibia 60 1920 9 × 9 × 3.5 ft nickel-rich iron
Ahnighito, Greenland 30
Bacuberito, Mexico 27 1863 12 ft long iron
Mbosi, Tanzania 26 1930 13.5 × 4 × 4 ft iron
Agpalik, Greenland 20
Armanty, Mongolia 20 1935 (known in 1917) iron
Chupaderos, Mexico 14 known for centuries; first mentioned in 1852 2 masses iron
Willamette (OR), U.S.A. 14 1902 iron
Campo del Cielo, Argentina 13
Mundrabilla, Western Australia 12
Morito, Mexico 11 known in 1600 iron


  thousands or millions of years, although some, called periodic comets, have their orbits altered by the gravitational pull of the planets so that they reappear every 200 years or less. Periodic comets are thought to come from the Kuiper belt, a zone just beyond the planet Neptune. Of the 800 or so comets whose orbits have been calculated, about 160 are periodic. The one with the shortest known period is Encke's comet, which orbits the sun every 3.3 years. The brightest periodic comet, Hale-Bopp, flew past the earth in March 1997. A dozen or more comets are discovered every year, some by amateur astronomers.  
  Asteroid and Comet-Impact Hazards
  Overview and the latest news on asteroid- and comet-impact hazards from NASA's Ames Space Science Division, with the last Spaceguard Survey Report and a list of future Near Earth Objects (NEOs).  
  A meteor is seen as a flash of light in the sky and is popularly known as a shooting or falling star. It is caused by a particle of dust, a meteoroid, entering the atmosphere at speeds up to 70 kps/45 mps and burning up by friction at a height of around 100 km/60 mi. On any clear night, several sporadic meteors can be seen each hour. Several times each year the earth encounters swarms of dust shed by comets, which give rise to a meteor shower. This appears to radiate from one particular point in the sky, after which the shower is named; the Perseid meteor shower in August appears in the constellation Perseus. A brilliant meteor is termed a fireball. Most meteoroids are smaller than grains of sand. The earth sweeps up an estimated 16,000 tons of meteoric material every year.  
  An ecplosion in Northern Ireland in December 1997 was blamed on terrorists, but was later discovered to be caused by a Meteorite. It left a 1.2-m/4-ft crater.  


  Meteors, Meteorites, and Impacts
  Informative collection of facts about meteorites: how they are formed, classification, and what happens when one hits earth. It includes images of a selection of meteorites.  
  A telescope is traditionally an optical instrument that magnifies images of faint and distant objects; it can also be any of a variety of devices for collecting and focusing light and other forms of electromagnetic radiation—for example, radio telescopes (see below). Telescopes are major research tools in astronomy. An optical telescope with a large aperture, or opening, can distinguish finer detail and fainter objects than one with a small aperture. The refracting telescope uses lenses, and the reflecting telescope uses mirrors. A third type, the catadioptric telescope, is a combination of lenses and mirrors.  
  In a refracting telescope, or refractor, light is collected by a lens called the object glass or objective, which focuses light down a tube, forming an image magnified by an eyepiece. The largest refracting telescope in the world, at Yerkes Observatory, Wisconsin, United States, has an aperture of 102 cm/40 in.  




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  telescope Three kinds of telescope. The refracting
telescope uses a large objective lens to gather light
and form an image which the smaller eyepiece lens
magnifies. A reflecting telescope uses a mirror to
gather light. The Cassegrain telescope uses a
corrective lens to achieve a wide field of view. It is
one of the most widely used tools of astronomy.
  In a reflecting telescope, or reflector, light is collected and focused by a concave mirror. Large mirrors are cheaper to make and easier to mount than large lenses, so all the largest telescopes are reflectors. The largest reflector with a single mirror, 6 m/236 in, is at Zelenchukskaya, Russia. Telescopes with larger apertures composed of numerous smaller segments have been built, such as the Keck Telescope on Mauna Kea, Hawaü. A multiple-mirror telescope was installed on Mount Hopkins, Arizona, United States, in 1979. It consists of six mirrors of 1.8 m/72 in aperture, which perform like a single 4.5-m/176-in mirror.  
  Schmidt telescopes are used for taking wide-field photographs of the sky. They have a main mirror plus a thin lens at the front of the tube to increase the field of view.  
  The liquid-mirror telescope is a reflecting telescope constructed with a rotating mercury mirror. In 1995 NASA completed a 3-m/9.8-ft liquid mirror telescope at its Orbital Debris Observatory in New Mexico, United States.  
  Large telescopes can now be placed in orbit above the distorting effects of the earth's atmosphere. Telescopes in space have been used to study infrared, ultraviolet, and X-ray radiation that does not penetrate the atmosphere but carries a great deal of information about the births, lives, and deaths of stars and galaxies. The 2.4-m/94-in Hubble Space Telescope, launched in 1990, can see the sky more clearly than can any telescope on earth.  
  In 1996 an X-ray telescope was under development by U.K., U.S., and Australian astronomers, based on the structure of a lobster's eye, which has thousands of square tubes reflecting light onto the retina. The £4 million Lobster Eye telescope will contain millions of tubes 10–20 micrometers across and is intended for use on a satellite.  
  FAQ on Telescope Buying and Usage
  Extensive "plain English" guide to buying a telescope. For anybody interested in astronomy and contemplating buying a telescope or setting up an observatory, this is an indispensable source of noncommercial advice.  
  Hubble Space Telescope  
  The Hubble Space Telescope (HST) is a space-based astronomical observing facility, orbiting the earth at an altitude of 610 km/380 mi. It consists of a 2.4-m/94-in telescope and four complimentary scientific instruments, is roughly cylindrical, 13 m/43 ft long, and 4 m/ 13 ft in diameter, with two large solar panels. The HST produces a wealth of scientific data, and allows astronomers to observe the birth of stars, find planets around neighboring stars, follow the expanding remnants of exploding stars, and search for black holes in the center of galaxies. The HST is a cooperative program between the European Space Agency (ESA) and the U.S. agency NASA, and is the first spacecraft specifically designed to be serviced in orbit as a permanent space-based observatory. It was launched in 1990.  
  Before the HST could reach its full potential, a flaw in the shape of its main mirror, discovered two months after the launch, had to be corrected. In 1993, as part of a planned servicing and instrument upgrade mission, NASA astronauts aboard the space shuttle Endeavour installed a set of corrective lenses to compensate for the error in the mirror figure.  
  Hubble discoveries In December 1995 the Hubble Space Telescope was trained on an "empty" area of sky near the Big Dipper, now termed the Hubble Deep Field. Around 1,500 galaxies, mostly new discoveries, were photographed.  
  In May 1997, three months after astronauts had installed further new equipment, U.S. scientists reported that Hubble had made an extraordinary finding. Within 20 minutes of searching, it discovered  




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Major Ground-Based Telescopes and Observatories
Observatory/ Telescope Location Description Year opened Run by
Algonquin Radio Observatory Ontario, Canada radio telescope, 46 m/150 ft in diameter 1966 National Research Council (NRC) of Canada
Arecibo Observatory Puerto Rico home of the largest radar-radio telescope in the world; a 305-m/1,000-ft diameter spherical reflector with a surface made up of nearly 40,000 perforated aluminum panels. Each panel can be adjusted to maintain a precise spherical shape that varies less than 3 mm/0.12 in over the whole 20-acre surface. inaugurated in 1963; upgraded in 1974, and again in the mid-1990s National Astronomy and Ionosphere Center, which is operated by Cornell University and the National Science Foundation
Australia Telescope National Facility New South Wales, Australia giant radio telescope consisting of six 22-m/72-ft antennae at Culgoora, a similar antenna at Siding Spring Mountain, and the 64-m/210-ft Parkes radio telescope; together they simulate a dish 300 km/186 mi across 1993 Commonwealth Scientific and Industrial Research Organization (CSIRO)
Cerro Tololo Inter-American Observatory Cerro Tololo mountain in the Chilean Andes main instrument is a 4-m/158-in reflector, a twin of that at Kitt Peak, Arizona, U.S.A. 1974 Association of Universities for Research into Astronomy (AURA)
David Dunlap Observatory Richmond Hill, Ontario, Canada 1.88-m/74-in reflector, the largest optical telescope in Canada 1935 University of Toronto
Dominion Astrophysical Observatory near Victoria, British Columbia, Canada 1.85-m/73-in reflector 1918 NRC of Canada
Dominion Radio Astrophysical Observatory Penticton, British Columbia, Canada 26-m/84-ft radio dish and an aperture synthesis radio telescope 1996 NRC of Canada through its Herzborg Institute of Astrophysics
Effelsberg Radio Telescope near Bonn, Germany the world's largest fully steerable radio telescope; 100-m/328-ft radio dish 1971 Max Planck Institute for Radio Astronomy
European Southern Observatory La Silla, Chile telescopes include: 3.6-m/142-in reflector
3.58-m/141-in New Technology Telescope
operated jointly by Belgium, Denmark, France, Germany, Italy, the Netherlands, Sweden, and Switzerland with head-quarters near Munich, Germany
Gemini 8-Meter Telescopes Project   Very Large Telescope (VLT), consisting of four 8-m/315-in reflectors mounted independently but capable of working in combination 1999 international partnership of United States, U.K., Canada, Chile, Argentina, and Brazil
  Mauna Kea (HI), U.S.A.; Cerro two 8-m/26-ft Aperture Optical/Infrared Telescopes 1999; 2001  


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Observatory/ Telescope Location Description Year opened Run by
Green Bank Telescope Green Bank, Pocahontas County (WV), U.S.A. largest fully steerable radio telescope in the world, with a 100 m × 110 m/328 ft × 360 ft surface under construction; expected inauguration in 1999 National Radio Astronomy Observatory (NRAO)
Jodrell Bank Cheshire, U.K. Lovell Telescope, a 76-m/250-ft radio dish

elliptical radio dish 38 m × 25 m/125 ft × 82 ft capable of working at shorter wavelengths
1957, modified 1970

Nuffield Radio Astronomy
Laboratories of the University of Manchester, England
Keck I Mauna Kea (HI), U.S.A. world's largest optical telescope, with a primary mirror 10-m/33-ft in diameter, with 36 hexagonal sections, each controlled by a computer to generate single images of the objects observed first images 1990 jointly owned by the California Institute of Technology and the University of California/Lick Observatory
Keck II Mauna Kea (HI), U.S.A. identical to Keck I: primary mirror 10 m/33 ft in diameter, with 36 hexagonal sections, each controlled by a computer 1996 jointly owned by the California Institute of Technology and the University of California/Lick Observatory
Kitt Peak National Observatory Quinlan Mountains near Tucson (AZ), U.S.A. numerous telescopes including the 4-m/158-in Mayall reflector 1973 AURA in agreement with the National Science Foundation of the U.S.A.
    McMath-Pierce Solar Telescope, the world's largest of its type 1960 National Solar Observatory (NSO)
    3.5-m/138-in reflecting telescope 1994 WIYN consortium comprising the University of Wisconsin, Indiana University, Yale University, and National Optical Astronomy Observatories (NOAO)
La Palma Observatory or the Observatorio del Roque de los Muchachos La Palma, Canary Islands Isaac Newton Group of telescopes, including the 4.2- m/165-in William Herschel Telescope 1987 Royal Greenwich Observatories (RGO)
Las Campanas Observatory Chile 2.5-m/100-in Irénée du Pont telescope 1977 Carnegie Institution of Washington
Lick Observatory or the University of California/Lick Observatory Mount Hamilton (CA), U.S.A. several instruments including: 3.04 m/120 in Shane reflector 1959 University of California
    91-cm/36-in refractor, the second-largest refractor in the world 1888  
Lowell Observatory Flagstaff (AZ), U.S.A. 8 telescopes, including the 61- cm/24-in Alvan Clark refractor 1894 Lowell Observatory staff


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Observatory/ Telescope Location Description Year opened Run by
  Anderson Mesa several telescopes, including the 1.83-m/72-in Perkins reflector   Ohio State and Ohio Wesleyan universities
McDonald Observatory Davis Mountains (TX), U.S.A. 2.72-m/107-in reflector 1969 University of Texas
    2.08-m/82-in reflector 1939  
    9.2-m/30-ft Hobby-Eberly telescope (HET) for spectral analysis 1997 Penn State University, Stanford University, and the Ludwig-Maximilians Universität
Magellan Las Campanas, Chile 6.5-m/21.3-ft honeycomb-back optical mirror 1997 Carnegie Institution of Washington, University of Arizona, and Harvard College Observatory
Mauna Kea Mauna Kea (HI), U.S.A. telescopes include: the 2.24-m/88-in University of Hawaü reflector 1970 University of Hawaü
    3.8-m/150-in United Kingdom Infrared Telescope (UKIRT) (also used for optical observations) 1978 Royal Observatory, Edinburgh
    3-m/120-in NASA Infrared Telescope Facility (IRTF) 1979 NASA
    3.6-m/142-in Canada-France-Hawaü Telescope (CFHT), designed for optical and infrared work 1979 NRC of Canada, University of Hawaü, and Centre National de la Recherche Scientifique of France
    15-m/50-ft diameter UK/Netherlands James Clerk Maxwell Telescope (JCMT), the world's largest telescope specifically designed to observe millimeter wave radiation from nebulae, stars, and galaxies 1987 Joint Astronomy Center in Hilo (HI) for the NRC of Canada, Particle Physics and Astronomy Research Council (PPARC) of the U.K., and Netherlands Organization for Scientific Research (NOSR)
    Keck I and Keck II telescopes 1990 and 1996 California Institute of Technology and the University of California/Lick Observatory
Mount Palomar 80 km/50 mi northeast of San Diego (CA), U.S.A. 5-m/200-in diameter reflector called the Hale; 1.2-m/48-in Schmidt telescope; it was the world's premier observatory during the 1950s 1948 California Institute of Technology and the University of California/Lick Observatory
Mount Wilson Observatory San Gabriel Mountains, near Los Angeles (CA), U.S.A. several telescopes including: 2.5-m/100-in Hooker telescope, with which Edwin Hubble discovered the expansion of the universe 1917 Mount Wilson Institute
    solar telescopes in towers 18.3 m/60 ft and 45.7 m/150 ft tall 1912 operated presently by University of California at Los Angeles (UCLA)


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Observatory/ Telescope Location Description Year opened Run by
Mullard Radio Astronomy Observatory Cambridge, U.K. Ryle Telescope, eight dishes 12.8 m/42 ft wide in a line 5 km/3 mi long 1972 University of Cambridge, U.K.
Multiple Mirror Telescope Mt. Hopkins (AZ), U.S.A. 6.5-m/21.3-ft honeycomb-back optical telescope conversion 1979 University of Arizona and the Smithsonian Institute
    6 mirrors of 1.8-m/72-in aperture, which perform as a single 4.5 m/176 in mirror 1996  
New Technology Telescope La Silla, Chile optical telescope that forms part of the European Southern Observatory; it has a thin, lightweight mirror, 3.38 m/141 in across with active optics, which is kept in shape by computer-adjustable supports 1991 operated jointly by Belgium, Denmark, France, Germany, Italy, the Netherlands, Sweden, and Switzerland with head-quarters near Munich
Royal Greenwich Observatory (RGO) Cambridge, U.K. operates Isaac Newton Group of telescopes, including: founded 1675 (moved to Cambridge in 1990) RGO
  La Palma, Canary Islands 4.2-m/165-in William Herschel Telescope 1987 Anglo-Australian Observatory
Siding Spring Mountain 400 km/250 mi northwest of Sydney, Australia 1.2-m/48-in U.K. Schmidt Telescope 1973  
    3.9-m/154-in Anglo-Australian Telescope 1975  
South African Astronomical Observatory Sutherland, South Africa main telescope is a 1.88-m/74-in reflector founded 1973 Council for Scientific and Industrial Research of South Africa
Subaru ("Pleiades") Mauna Kea (HI), U.S.A. 8-m/26.4-ft optical-infrared telescope 1999 National Astronomical Observatory (NAO) of the University of Tokyo
United Kingdom Infrared Telescope (UKIRT) Mauna Kea (HI), U.S.A. 3.8-m/150-in reflecting telescope for observing at infrared wavelengths 1979 Royal Observatory, Edinburgh
U.S. Naval Observatory Washington DC, U.S.A. several telescopes including: 66-cm/26-in refracting telescope 1873 US Naval Observatory
  Flagstaff (AZ), U.S.A. 1.55-m/61-in reflector for measuring positions of celestial objects 1964  
Very Large Array (VLA) Plains of San Augustine (NM), U.S.A. largest and most complex single-site radio telescope in the world, comprising 27 dish antennae, each 25 m/82 ft in diameter, forming a Y-shaped array 1981 NRAO
Very Large Telescope (VLT) Cerro Paranal, Chile 4 × 8 m/26 ft optical array 1999 European Southern Observatory consisting of eight European countries


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Observatory/ Telescope Location Description Year opened Run by
Very Long Baseline Array (VLBA) St. Croix (VI); Hancock (NH); North Liberty (IA); Fort Davis (TX); Los Alamos (NM); Pie Town (NM); Kitt Peak (AZ); Owens Valley (CA); Brewster (WA); Mauna Kea (HI), U.S.A. system of 10 radio telescopes, each a 25-m/82-ft diameter dish antenna, controlled remotely from the Array Operations Center in Socorro, New Mexico, that work together as the world's largest dedicated, full-time astronomical instrument   NRAO
Yerkes Observatory Wisconsin, U.S.A. houses the world's largest refracting optical telescope, with a lens of diameter 102 cm/40 in observatory founded 1897 University of Chicago Department of Astronomy and Astrophysics
Zelenchukskaya Caucasus Mountains of Russia site of the world's largest single mirror optical telescope, with a mirror of 6 m/236 in diameter 1976 Special Astrophysical Observatory of the Russian Academy of Sciences (RAS) in St. Petersburg
    Radio Astronomy Telescope of the Russian Academy of Sciences (RATAN) 600 radio telescope, consisting of radio reflectors in a circle 600 m/2,000 ft in diameter    


  evidence of a black hole 300 million times the mass of the sun. It is located in the middle of galaxy M84 about 50 million light-years from earth. Further findings in December 1997 concerned different shapes of dying stars. Previously, astronomers had thought that most stars die with a round shell of burning gas expanding into space. The photographs taken by the HST show shapes such as pinwheels and jet exhaust.  
  Space Telescope Electronic Information Service
  Home page of the Hubble Space Telescope, which includes an archive of past observations, a description of the instruments aboard, and a section for educators, students, and the general public–with pictures, audio clips, and press releases.  
  radio telescopes  
  This type of telescope is used in radio astronomy to detect radio waves emitted naturally by objects in space. Radio emission comes from hot gases (thermal radiation); electrons spiraling in magnetic fields (synchrotron radiation); and specific wavelengths (lines) emitted by atoms and molecules in space, such as the 21-cm/8-in line emitted by hydrogen gas. Radio telescopes usually consist of a metal bowl that collects and focuses radio waves the way a concave mirror collects and focuses light waves. Radio telescopes are much larger than optical telescopes, because the wavelengths they are detecting are much longer than the wavelength of light. The largest single dish is 305 m/1,000 ft across, at Arecibo, Puerto Rico.  
  A large dish such as that at Jodrell Bank, England, can see the radio sky less clearly than a small optical telescope sees the visible sky. Interferometry is a technique in which the output from two dishes is combined to give better resolution of detail than with a single dish. Very long baseline interferometry (VBLI) uses radio telescopes spread across the world to resolve minute details of radio sources.  
  In aperture synthesis, several dishes are linked together to simulate the performance of a very large single dish. This technique was pioneered by Martin Ryle at Cambridge, England, site of a radio telescope consisting of eight dishes in a line 5 km/3 mi long. The Very Large Array in New Mexico, United States, consists of 27 dishes arranged in a Y-shape, which simulates the performance of a single dish 27 km/17 mi in diameter. Other radio telescopes are shaped like long troughs, and some consist of simple rod-shaped antennae.  




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  Radio astronomy has greatly improved our understanding of the evolution of stars, the structure of galaxies, and the origin of the universe. Astronomers have mapped the spiral structure of the Milky Way from the radio waves given out by interstellar gas, and they have detected many individual radio sources within our galaxy and beyond. Radio astronomy is also used in the search for extraterrestrial intelligence, which has been ongoing since 1983.  
  The Exploration of Space  
  Rockets are used as the means of propelling satellites into geostationary orbit and spacecraft out of the earth's atmosphere into and through space. To escape from earth's gravity rockets must reach an escape velocity of 11.2 kps/6.9 mps. They are driven by the reaction of gases produced by a fast-burning fuel, such as liquid hydrogen and kerosene. Unlike jet engines, which are also reaction engines, modern rockets carry their own oxygen supply (usually in liquid form) to burn their fuel and do not require any surrounding atmosphere. Being the only form of propulsion available that can function in a vacuum, rockets are essential to exploration in outer space. Multistage rockets have to be used, consisting of a number of rockets joined together.  
  One of the largest rockets ever built, the Saturn V moon rocket, was a three-stage design, standing 111 m/365 ft high, as tall as a 30-story skyscraper. It weighed more than 2,700 metric tons/2,976 U.S. tons on the launch pad, developed a takeoff thrust of some 3.4 million kg/7.5 million lb, and could place almost 140 metric tons/154 U.S. tons into low earth orbit.  
  Artificial satellites, used for scientific purposes, communications, weather forecasting, and military applications, have been rocket-launched into orbit around the earth since the late 1950s. The first, Sputnik 1, was launched by the USSR in 1957. Most satellites are in geostationary orbit, following a circular path 35,900 km/22,300 mi above the earth's Equator and taking 24 hours, moving from west to east, to complete an orbit, thus appearing to hang stationary over one place on the earth's surface. The brightest artificial satellites can be seen by the naked eye.  
  At any time, there are several thousand artificial satellites orbiting the earth, including active satellites, satellites that have ended their working lives, and discarded sections of rockets. Artificial satellites eventually reenter the earth's atmosphere. Usually they burn up by friction, but sometimes debris falls to the earth's surface, as with Skylab and Salyut 7. In 1997 there were 300 active artificial satellites in orbit around earth, the majority used in communications.  
  rocket The three-stage Saturn V rocket used in
the Apollo moonshots of the 1960s and 1970s.
It developed a power equivalent to 50 Boeing 747
jumbo jets.




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  J-Track Satellite Tracker
  Real-time tracking system that displays on a world map the current position and orbit information for the space shuttle, Mir, Hubble Space Telescope, and the UARS and COBE satellites.  
  Space Programs  
  Mercury project U.S. project to put a human in space in the one-seat Mercury spacecraft 1961–63. The first two Mercury flights, on Redstone rockets, were short flights to the edge of space and back. The orbital flights, beginning with the third in the series (made by John Glenn), were launched by Atlas rockets.  
  Project Mercury
  Official NASA archive of the program that led to the first crewed U.S. space flight. There are comprehensive details (technical and of general interest) on all the crewed and uncrewed flights included in the project.  
  Gemini project U.S. space program 1965–66 in which astronauts practiced rendezvous and docking of spacecraft, and working outside their spacecraft, in preparation for the Apollo moon landings. Gemini spacecraft carried two astronauts and were launched by Titan rockets.  
  Project Gemini
  Official NASA archive of the project that paved the way for the first moon landing. There are comprehensive details (technical and of general interest) on all the missions included in the project.  
  Apollo project U.S. space project to land a person on the moon, achieved on July 20, 1969, when Neil Armstrong was the first to set foot there. He was accompanied on the moon's surface by Buzz Aldrin; Michael Collins remained in the orbiting command module.  
  The program was announced in 1961 by President Kennedy. The world's most powerful rocket, Saturn V, was built to launch the Apollo spacecraft, which carried three astronauts. When the spacecraft was in orbit around the moon, two astronauts would descend to the surface in a lunar module to take samples of rock and set up experiments that would send data back to earth. After three other preparatory flights, Apollo 11 made the first lunar landing. Five more crewed landings followed.  
  Apollo 1: during a preliminary check on the ground, the three crew were killed by a fire on January 27, 1967  
  Apollo 4: launched on November 9, 1967 into an orbit around the earth; the first time the Saturn V rocket was used  
  Apollo 7: the first Apollo mission carrying a crew, Apollo 7 was a test flight sent into orbit around the earth on October 11, 1968  
  Apollo 8: launched on December 21, 1968; the first rocket to take a crew round the moon  
  Apollo 9: launched on March 3, 1969; the lunar module was tested in orbit around the earth  
  Apollo 10: launched on May 18, 1969; the lunar module was successfully tested 14.5 km/9 mi above the surface of the moon  
  Apollo 11: launched on July 16, 1969; Armstrong and Aldrin landed the lunar module (named ''Eagle") in an area called the Sea of Tranquility on the moon's surface on July 20, 1969. Armstrong had to land manually because the automatic navigation system was heading for a field of boulders. On landing, Armstrong announced "Tranquility base here. The Eagle has landed." The module remained on the moon for 22 hours during which time they collected rocks, set up experiments, and mounted a U.S. flag. Apart from a slight wobble when rejoining the command module, the return flight went without a hitch. After splashdown the astronauts were quarantined as a precaution against unknown illnesses from the moon  
  Apollo 12: launched on November 14, 1969; in spite of twice being struck by lightning, another successful moon landing was achieved.  
  Apollo 13: intended to be the third moon landing, Apollo 13 was launched on April 11, 1970 with the crew of John Swigert, Fred Haise, and James Lovell. On the third day of the mission Swigert reported to Houston "We seem to have a problem." An electrical fault had caused an explosion in one of the oxygen tanks, cutting off supplies of power and oxygen to the command module. The planned landing was abandoned and the rocket was sent around the moon before heading back to earth. The crew used the lunar module Aquarius as a "lifeboat," though they had to endure near-freezing temperatures to save power, making sleep almost impossible. Attempting reentry in the crippled ship almost led to disaster, but the crew splashed down safely on April 17  
  Apollo 15: launched on July 26, 1971; the first surface vehicle, "Lunar Rover," was used  
  Apollo 17: launched on December 7, 1972, this was the last of the Apollo moon landings. Detailed geological studies were carried out and large amounts of rock and soil were brought back.  




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Notable Crewed Space Flight
Launch date Spacecraft Crew Duration Remarks
April 12, 1961 Vostok 1 Yuri Gagarin 1 hr 58 min first man in space; Gagarin landed separately from the spacecraft after ejecting at 1 hr 48 min, in a procedure followed by all Vostok pilots
May 5, 1961 Freedom 7 Alan Shepard 15 min 28 sec first American in space; suborbital flight ended in planned splashdown
August 6, 1961 Vostok 2 Gherman Titov 1 day 1 hr 18 min at 25, Titov was the youngest person in space; he was spacesick and the first to sleep in space
February 20, 1962 Friendship 7 John Glenn 4 hr 55 min first American to orbit the earth
August 11, 1962 Vostok 3 Andrian Nikolyev 3 days 22 hr 25 min long duration flight
June 14, 1963 Vostok 5 Valeri Bykovsky 4 days 23 hr 7 min solo flight record-holder
June 16, 1963 Vostok 6 Valentina Tereshkova 2 days 22 hr 50 min first woman in space, flew close to Vostok 5
October 12, 1964 Voskhod 1 Vladimir Komarov, Konstantin Feoktistov, Boris Yegerov 1 day 17 min first multicrewed spaceflight without spacesuits or ejection seats, flying in stripped down one-man Vostok
March 18, 1965 Voskhod 2 Pavel Belyayev, Alexei Leonov 1 day 2 hr 2 min Leonov made first walk in space
March 25, 1965 Gemini 3 Gus Grissom, John Young 4 hr 52 min first U.S. two-man flight; Grissom first man to return to space
June 3, 1965 Gemini 4 James McDivitt, Edward White 4 days 1 hr 56 min White makes first American spacewalk
December 4, 1965 Gemini 7 Frank Borman, James Lovell 13 days 18 hr 35 min acted as rendezvous target for Gemini 6; broke endurance record
December 15, 1965 Gemini 6 Wally Schirra, Tom Stafford 1 day 1 hr 51 min first rendezvous in space
September 12, 1966 Gemini 11 Charles Conrad, Richard Gordon 2 days 23 hr 17 min docking on first orbit; spacewalk; reboost to altitude of 1368 km/850 mi; automatic landing
November 11, 1966 Gemini 12 James Lovell, Edwin Aldrin 3 days 22 hr 34 min record spacewalk of over 2 hr by Aldrin
April 23, 1967 Soyuz 1 Vladimir Komarov 1 day 2 hr 47 min Komarov killed when parachute failed after emergency landing; intended to dock with Soyuz 2
October 11, 1968 Apollo 7 Wally Schirra, Donn Eisele, Walt Cunningham 10 days 20 hr 9 min earth orbit maiden flight of Apollo Command/service modules
December 21, 1968 Apollo 8 Frank Borman, James Lovell, William Anders 6 days 3 hr first crewed craft to orbit the moon
January 15, 1969 Soyuz 5 Boris Volynov, Alexei Yeleseyev, Yevgeny Khrunov 3 days 54 min Yeleseyev and Khrunov spacewalk to Soyuz 4 after docking with it
May 18, 1969 Apollo 10 Tom Stafford, John Young, Eugene Cernan 8 days 3 min lunar module tested in lunar orbit and flew to 14.5 km/9 mi from the moon
July 16, 1969 Apollo 11 Neil Armstrong, Michael Collins, Edwin Aldrin 8 days 3 hr 18 min first crewed lunar landing; Armstrong and Aldrin walked on the moon for over 2 hr
November 14, 1969 Apollo 12 Charles Conrad, Richard Gordon, Alan Bean 10 days 4 hr 36 min 25 sec pinpoint landing near uncrewed Surveyor craft on the moon; two moonwalks
April 11, 1970 Apollo 13 James Lovell, Jack Swigert, Fred Haise 5 days 22 hr 54 min service module exploded 55 hr into mission; crew limped home using lunar module as lifeboat
June 6, 1971 Soyuz 11 Georgi Dobrovolsky, Vladislav Volkov, Viktor Patsayev 23 days 18 hr 21 min crew died as craft depressurized before re-entry; they were not wearing spacesuits
July 26, 1971 Apollo 15 David Scott, Alfred Worden, James Irwin 12 days 7 hr 11 min use of first lunar rover
April 16, 1972 Apollo 16 John Young, Ken Mattingly, Charles Duke 11 days 1 hr 51 min Mattingly in lunar orbit makes longest solo U.S. flight; three moonwalks were taken
May 25, 1973 Skylab 2 Charles Conrad, Joe Kerwin, Paul Weitz 28 days 49 min spacewalk to repair severely disabled Skylab 1 space station
November 16, 1973 Skylab 4 Gerry Carr, Edward Gibson, Bill Pogue 84 days 1 hr 15 min longest U.S. crewed spaceflight until 1996
May 24, 1975 Soyuz 18 Pyotr Klimuk, Vitali Sevastyanov 62 days 23 hr 20 min record stay on Salyut 4
July 15, 1975 Soyuz 19 Alexei Leonov, Valeri Kubasov 5 days 22 hr 30 min docked with Apollo 18 in joint Apollo–Saturn Test Project (ASTP) mission
July 5, 1975 Apollo 18 Tom Stafford, Vance Brand, Donald "Deke" Slayton 9 days 1 hr 28 docked with Soyuz 19; first US-Soviet space linkup
December 10, 1977 Soyuz 26 Yuri Romanenko, Georgi Grechko 96 days 10 hr aboard Salyut 6; broke endurance record
April 9, 1980 Soyuz 35 Leonid Popov, Valeri Ryumin 184 days 20 hr 11 min record Salyut 6 mission, with Ryumin achieving 361 days' space experience
April 12, 1981 Columbia STS 1 John Young, Bob Crippen 2 days 6 hr 20 min maiden flight of space shuttle
May 13, 1982 Soyuz T5 Anatoli Berezevoi, 211 days 9 hr 4 min first record-breaking visit to Salyut 7
    Valentin Lebedev    
June 27, 1982 Columbia STS 4 Ken Mattingly, Hank Hartsfield 7 days 1 hr 9 min military flight; final shuttle test flight
November 11, 1982 Columbia STS 5 Vance Brand, Robert Overmyer, Joe Allen, William Lenoir 5 days 2 hr 14 min first commercial mission of Shuttle; deployed two communications satellites; first four-person flight
June 18, 1983 Challenger STS 7 Bob Crippen, Rick Hauck, John Fabian, Sally Ride, Norman Thagard 6 days 2 hr 24 min satellite deployment mission; first with five-person crew and first U.S. woman in space


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Launch date Spacecraft Crew Duration Remarks
November 28, 1983 Columbia STS 9 John Young, Brewster Shaw, Owen Garriott, Robert Parker, Byron Lichtenberg, Ulf Merbold 10 days 7 hr 47 min flight of European Spacelab 1; Merbold from West Germany; first six-person flight
February 3, 1984 Challenger STS 41B Vance Brand, Robert Gibson, Bruce McCandless, Robert Stewart, Ronald McNair 7 days 23 hr 15 min first independent spacewalk using Manned mission Maneuvring Unit (MMU) by McCandless; first space mission to end at launch site (Kennedy/Canaveral);
February 8, 1984 Soyuz T10 Leonid Kizim, Vladimir Solovyov, Oleg Atkov 236 days 22 hr 9 min longest crewed space mission to date; Kizim and Solovyov made record six spacewalks
April 6, 1984 Challenger STS 41C Bob Crippen, Dick Scobee, George Nelson, Terry Hart, James van Hoften 6 days 23 hr 40 min repaired Solar Max; with Soyuz T10 and T11 crews in space; 11 people in space at once
July 17, 1984 Soyuz T12 Vladimir Dhzanibekov, Svetlana Savitskaya, Oleg Volk 11 days 19 hr 14 min Savitskaya became first woman space-walker, outside Salyut 7
September 17, 1985 Soyuz T14 Vladimir Vasyutin, Georgi Grechko, Alexander Volkov 64 days 21 hr 52 min mission cut short after Vasyutin suffered depression and anxiety
January 28, 1986 Challenger STS 51 Dick Scobee, Mike Smith, Judith Resnik, Ronald McNair, Ellison Onizuka, Christa McAuliffe, Gregory Jarvis 73 sec broke apart at 14,325 m/47,000 ft; crew killed; first flight to take off but not to reach space; first American in-flight fatalities
March 13, 1986 Soyuz T15 Leonid Kizim, Vladimir Solovyov 125 days 1 min first mission to new space station Mir 1; also docked with Salyut 7; Kizim achieved over a year in space experience
December 21, 1987 Soyuz TM4 Vladimir Titov, Musa Manarov, Anatoli Levchenko 365 days 22 hr 39 min longest duration mission by Titov and Manarov
November 26, 1988 Soyuz TM7 Alexander Volkov, Sergei Krikalev, Jean-Loup Chretien 151 days 11 hr 10 min visit to Mir, Frenchman Chretien is first non-U.S., non-USSR astronaut to make two space flights, to make spacewalk, and the oldest spacewalker at 50; Chretien returned in TM6 after 25 days
May 4, 1989 Atlantis STS 30 David Walker, Ron Grabe, Norman Thagard, Mary Cleave, Mark Lee 4 days 57 min deployed Magellan for its journey to orbit the planet Venus; first deployment of a planetary spacecraft from a crewed spacecraft
October 18, 1989 Atlantis STS 34 Donald Williams, Michael McCulley, Shannon Lucid, Franklin Chang-Diaz, Ellen Baker 4 days 23 hr 39 min deployed Jupiter orbiter Galileo
April 24, 1990 Discovery STS 31 Loren Shriver, Charles Bolden, Steven Hawley, Bruce McCandless, Kathryn Sullivan 5 days 1 hr 16 min 532 km/319 mi deployed Hubble Space Telescope; reached record Shuttle altitude
May 18, 1991 Soyuz TM12 Anatoli Artsebarski, Sergei 144 days 15 hr 22 min Sharman first non-Soviet, non-U.S. woman and first
    Krikalev, Helen Sharman   Briton in space, returned in TM11 after seven days; Krikalev stayed aboard Mir and returned after 311 days; Artsebarski and Krikalev made a record six spacewalks in 33 days
January 22, 1992 Discovery STS 42 Ronald Grabe, Stephen Oswald, Norman Thagard, David Hilmers, William Readdy, Roberta Bondar, Ulf Merbold 8 days 1 hr 14 min International Microgravity Laboratory mission; Bondar from Canada and Merbold from Germany; Thagard achieves record 25-day Shuttle flight time on fourth mission
May 7, 1992 Endeavour STS 49 Dan Brandenstein, Kevin Chilton, Rick Heib, Bruce Melnick, Pierre Thuot, Kathryn Thornton, Tom Akers 8 days 21 hr 17 min retrieved Intelsat 6 and reboosted it into geostationary orbit; record breaking 8 hr 29 min extra-vehicular activity (EVA) by Thuot, Hieb, and Akers
July 31, 1992 Atlantis STS 46 Loren Shriver, Andrew Allen, Claude Nicollier, Marsha Ivins, Jeff Hoffman, Franklin Chang-Diaz, Franco Malerba 7 days 23 hr 15 min deployed Eureca and tethered satellites; Nicollier first Swiss astronaut and first non-U.S. NASA mission specialist; Malerba first Italian in space; 12 people in space at once, with record five space nations being represented, with Mir mission
December 2, 1993 Endeavour STS 61 Richard Covey, Ken Bowersox, Claude Nicollier, Story Musgrave, Jeff Hoffman, Tom Akers, Kathryn Thornton 10 days 19 hr 58 min Hubble Space Telescope servicing and repair mission; Musgrave, first to fly five Shuttle missions, achieves record 35 days' flight time
January 8, 1994 Soyuz TM18 Viktor Afanasyev, Yuri Usachev, Valeri Poliakov 182 days 27 min new residency aboard Mir 1 space station; Poliakov remained on Mir and landed on March 22, 1995 with a flight time of 437 days
February 3, 1994 Discovery STS 60 Charles Bolden, Kenneth Reightler, Franklin Chang-Diaz, Jan Davis, Ron Sega, Sergei Krikalev 8 days 7 hr 9 min Krikalev first Russian to fly on U.S. rocket
October 3, 1994 Soyuz TM20 Alexander Viktorenko, Yelena Kondakova, Ulf Merbold 169 days 5 hr 21 min new crew to Mir, including Kondakova, the first woman to make a long duration flight, and German European Space Agency (ESA) visitor Merbold, the first non-U.S., non-Soviet spaceperson to make three flights and first Western European to fly both U.S. and Russian rockets; with Shuttle in space, 12 people in orbit at once; Merbold landed in TM19 after 31 days


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Launch date Spacecraft Crew Duration Remarks
February 3, 1995 Discovery STS 63 James Wetherbee, Eileen Collins, Michael Foale, Bernard Harris, Janice Ford, Vladimir Titov 8 days 6 hr 28 min Spacelab science rendezvous mission with Mir space station and spacewalk–first by British-born astronaut, Foale; Collins first female Shuttle pilot; Titov from Russia
March 14, 1995 Soyuz TM21 Vladimir Dezhurov, Gennady Strekalov, Norman Thagard 115 days 8 hr 44 min mission to Mir 1 with first U.S. astronaut to ride a Russian rocket; record 13 people in space at same time on 14–18 March; crew landed in STS 71
June 27, 1995 Atlantis
STS 71
Robert Gibson, Charles Precourt, Ellen Baker, Bonnie Dundar, Gregory Harbaugh, Anatoli Solovyov, Nikolai Budarin 9 days 19 hr 23 min 100th U.S. crewed flight including Thagard's Soyuz to TM21 launch; Shuttle/Mir 1 mission 1; 5 days joined Mir, delivered Solovyov and Budarin and returned with the TM21 crew; first time ten people on board one spacecraft (223 metric tons/246 U.S. tons) in orbit
November 12, 1995 Atlantis
STS 74
Ken Cameron, James Halsall, Jerry Ross, Bill McArthur, Chris Hadfield 8 days 4 hr 30 min Shuttle/Mir mission 2; carried docking module to be left at Mir; Hadfield NASA mission specialist from Canada
February 22, 1996 Columbia STS 75 Andrew Allen, Scott Horowitz, Maurizio Cheli, Claude Nicollier, Jeff Hoffman, Franklin Chang-Diaz, Umberto Guidoni 15 days 17 hr 40 min tethered satellite system reflight, satellite lost when tether broke; 12 people, five nations (two from Italy) in space with TM22 and TM23 crews also orbiting
March 22, 1996 Atlantis
STS 76
Kevin Chilton, Richard Searfoss, Ronald Sega, Ric hr Clifford, Linda Godwin, Shannon Lucid 9 days 5 hr 15 min Shuttle/Mir mission 3, delivered Shannon Lucid for extended stay on Mir; returned 26 September aboard STS 79; after stay of 188 days, a record for a woman; spacewalk
August 17, 1996 Soyuz
Valeri Korzun, Alexander Kaleri, Claudie Andre-Deshays 196 days 16 hr 26 min new crew for Mir 1 with Deshays, the first French woman in space, as commercial crew-person on 15-day flight, landing in TM23; Korzun and Kaleri first back-up crew to fly since Soyuz 11 in 1971 after prime commander Gennady Manakov hospitalized (if one crew member unable to fly, backup crew takes over) with heart attack
January 12, 1997 Atlantis
STS 81
Mike Baker, Brent Jett, John Grunsfield, Jeff Wisoff, Marsha Ivins, Jerry Linenger 10 days 4 hr 55 min Shuttle/Mir mission 5, delivered Jerry Linenger and returned John Blaha from Mir after 128 days; Lineger made first U.S.-Russian spacewalk with Tsiblyev, wearing Russian spacesuit
February 10, 1997 Soyuz
Vasili Tsiblyev, Alexander Lazutkin, Reinhold Ewald 184 days 22 hr 7 min new crew for Mir with German Ewald flying shorter commercial mission; this crew experienced a fire on the space station and a collision with the Progress M34 supply ship
February 11, 1997 Discovery STS 82 Ken Bowersox, Scott Horowitz, Steven Hawley, Mark Lee, Joe Tanner, Greg Harbaugh, Steve Smith 9 days 23 hr 37 min second mission to service the Hubble Space Telescope; featured five spacewalks
August 5, 1997 Soyuz
Anatoli Solovyov, Pavel Vinogradev, 9 days 23 hr 37 min 200th launched crewed spaceflight in history; new crew to Mir to carry out major repair work


  Apollo 11
  This NASA page relives the excitement of the Apollo 11 mission, with recollections from the participating astronauts, images, audio clips, access to key White House documents, and a bibliography.  
  Soyuz project The Soviet Soyuz series of spacecraft, capable of carrying up to three cosmonauts, was launched in 1967. Soyuz spacecraft consist of three parts: a rear section containing engines; the central crew compartment; and a forward compartment that gives additional room for working and living space. They are now used for ferrying crews up to space stations, though they were originally used for independent space flight.  
  Soyuz 1 crashed on its first flight in April 1967, killing the lone pilot, Vladimir Komarov. Soyuz 11 had three deaths on re-entry in 1971. In 1975 the Apollo–Soyuz test project resulted in a successful docking in orbit.  
  space shuttles The first space shuttle, a reusable crewed spacecraft, was launched on April 12, 1981 by the United States. It was developed by NASA to reduce the cost of using space for commercial, scientific, and military purposes.  
  The space-shuttle orbiter, the part that goes into space, is 37.2 m/122 ft long and weighs 68 metric tons. Two to eight crew members occupy the orbiter's nose section, and missions last up to 30 days. In its cargo bay the orbiter can carry up to 29 metric tons/32 U.S. tons of satellites, scientific equipment, Spacelab (see below), or military payloads. After leaving its payload in space, the orbiter can be flown back to earth to land on a runway, and is then available for reuse.  
  Four orbiters were built: Columbia, Challenger, Discovery, and Atlantis. Challenger was destroyed in a midair explosion just over a minute after its tenth launch on January 28, 1986, killing all seven crew members, the result of a failure in one of the solid rocket boosters. Flights resumed with redesigned boosters in September 1988. A replacement orbiter, Endeavour, was built, which had its maiden flight in May 1992.  
  The USSR produced a shuttle of similar size and  




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Notable Uncrewed Space Flights
Date Remarks
October 1957 first artificial earth satellite, Soviet Union's Sputnik 1
November 1957 first living being (dog, Laika) in orbit aboard Sputnik 2
January 1958 first U.S. satellite, first science satellite, Explorer 1
December 1958 first experimental communications satellite, Score 1
April 1959 first military spy satellite, Discoverer 2
September 1959 first craft to reach the moon, by USSR's Luna 2
October 1959 first pictures of lunar far side from Luna 3
April 1960 first weather satellite, Tiros I first navigation satellite, Transit 1B
August 1960 first recovery of craft from orbit, Discoverer 13
  first recovery of living creatures (two dogs) from orbit, Sputnik 5
July 1962 first commercial communications satellite, Telstar 1
December 1962 first fly-by of Venus by U.S. Mariner 2
July 1963 first geostationary orbiting communications satellite, Syncom 2
July 1964 first close-up images of the moon from Ranger 7
July 1965 first successful fly-by of Mars with first images of the planet from Mariner 4
January 1966 first "soft" lunar landing and surface images from Luna 9
April 1966 first lunar orbiter, Luna 10
  first astronomical satellite, OAO 1
December 1966 first French satellite launch, A1
October 1967 first successful exploration of Venus's atmosphere by Venera 4
  first automatic, unmanned docking in orbit, Cosmos 186 and 188
September 1968 first spacecraft to fly around the moon and return to earth, Zond 5
February 1970 first Japanese satellite launch, Ohsumi
April 1970 first Chinese satellite launch, Tungfanghung
September 1970 first return of sample from moon by uncrewed craft, Luna 16
November 1970 first lunar rover, Lunakhod 1
December 1970 first successful Venus landing by Venera 7
October 1971 first British satellite launch, Prospero
November 1971 first Mars orbiter, Mariner 9
July 1972 first earth resources remote-sensing satellite, Landsat 1
December 1973 first craft to explore Jupiter, Pioneer 10
March 1974 first fly-by of Mercury by Mariner 10
October 1975 first craft to orbit Venus and return surface pictures, Venera 9
February 1976 first maritime mobile communications satellite, Marisat 1
July 1976 first soft landing on Mars by Viking I
September 1979 first exploration of Saturn by Pioneer 11
July 1980 first Indian satellite launch, Rohini
June 1981 first European operational satellite launch by Ariane, Meteosat 2
October 1983 first mapping of Venus by radar, Venera 15
April 1984 first satellite to be captured, repaired, and redeployed, SMM 1
May 1984 first fully commercial satellite launch by Arianespace, Spacenet1
November 1985 first satellite capture and return to earth, Palapa and Westar
January 1986 first exploration of Uranus, Voyager 2
February 1986 first privately operated, commercial, remote-sensing craft, Spot 1
March 1986 first encounter with coma of comet (Halley) by Giotto
September 1988 first Israeli satellite launch, Ofeq 1
December 1988 first privately operated, commercial TV satellite, Astra 1A
August 1989 first exploration of Neptune by Voyager 2
April 1990 first optical telescope in orbit, Hubble Space Telescope
October 1991 first fly-by of a comet, Gaspra, by Galileo
December 1995 first craft to enter Jupiter's atmosphere, Galileo probe
  first Jupiter orbiter, Galileo


  appearance to the U.S. one. The first Soviet shuttle, Buran, was launched without a crew by the Energiya rocket on November 15, 1988. In Japan, development of a crewless shuttle began in 1986.  
  Spacelab Spacelab is a small space station built by the European Space Agency, carried in the cargo bay of the U.S. space shuttle, in which it remains throughout each flight, returning to earth with the shuttle.  




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  Galileo Project Information
  Site dedicated to the Galileo Project and the opportunities it has offered scientists and astronomers to enhance our understanding of the universe.  
  Spacelab consists of a pressurized module in which astronauts can work, and a series of pallets, open to the vacuum of space, on which equipment is mounted.  
  Spacelab is used for astronomy, earth observation, and experiments utilizing the conditions of weightlessness and vacuum in orbit. The pressurized module can be flown with or without pallets, or the pallets can be flown on their own, in which case the astronauts remain in the shuttle's crew compartment. All the sections of Spacelab can be reused many times. The first Spacelab mission, consisting of a pressurized module and pallets, lasted ten days November–December 1983.  
  History of Space Exploration
  Who was the first woman astronaut? Find out at this site, which also contains information on the history of rocketry, and chronologies of exploration by the United States, Russia, Japan, and Europe.  
  space probes  
  Space probes are uncrewed, instrumented objects sent beyond earth to collect data from other parts of the solar system and from deep space. The first probe was the Soviet Lunik 1, which flew past the moon in 1959. The first successful planetary probe was the U.S. Mariner 2, which flew past Venus in 1962, using transfer orbit. The first space probe to leave the solar system was Pioneer 10 in 1983. Space probes include Galileo, Giotto, Magellan, Mars Observer, Ulysses, the moon probes, and the Mariner, Pioneer, Viking, and Voyager series.  
  space stations  
  Space stations are large structures designed for human occupation in space for extended periods of time. They are used for carrying out astronomical observations and surveys of earth, as well as for biological studies and the processing of materials in weightlessness. The first space station was Salyut 1, and the United States has launched Skylab.  
  NASA plans to build a larger space station, to be called Alpha in cooperation with other countries, including the European Space Agency, which is building a module called Columbus; Russia and Japan are also building modules.  
  Salyut Salyut was cylindrical in shape, 15 m/50 ft long, and weighed 19 metric tons/20.9 U.S. tons. It housed two or three cosmonauts at a time, for missions lasting up to eight months. Seven Salyut space stations were launched by the USSR 1971–82.  
  Salyut 1 was launched on April 19, 1971. It was occupied for 23 days in June 1971 by a crew of three, who died during their return to earth when their Soyuz ferry craft depressurized. In 1973 Salyut 2 broke up in orbit before occupation. The first fully successful Salyut mission was a 14-day visit to Salyut 3 in July 1974. In 1984–85 a team of three cosmonauts endured a record 237-day flight in Salyut 7. In 1986 the Salyut series was superseded by Mir, an improved design capable of being enlarged by additional modules sent up from earth. Salyut 7 crashed to earth in February 1991, scattering debris in Argentina.  
  Official Web site of the Shuttle–Mir joint operations. There is extensive information ranging from the technical to human interest stories from crew members. The site also includes some low- and high-resolution images of the spacecraft, the crew at work, and the earth.  
  Mir Soviet space station, the core of which was launched on February 20, 1986. It is intended to be a permanently occupied space station. Mir weighs almost 21 metric tons/23 U.S. tons, is approximately 13.5 m/44 ft long, and has a maximum diameter of 4.15 m/13.6 ft. It carries a number of improvements over the earlier Salyut series of space stations, including six docking ports; four of these can have scientific and technical modules attached to them. The first of these was the Kvant (quantum) astrophysics module, launched in 1987. This had two main sections: a main experimental module, and a service module that would be separated in orbit. The experimental module was 5.8 m/19 ft long and had a maximum diameter matching that of Mir. When attached to the Mir core, Kvant added a further 40 cu m/1,413 cu ft of working space to that already there. Among the equipment carried by Kvant were several X-ray telescopes and an ultraviolet telescope. In June 1995 the U.S. space shuttle Atlantis docked with Mir, exchanging crew members. In 1997, Mir suffered a series of problems, culminating in its collision with an crewless cargo ship in June.  
  This U.S. space station, launched on May 14, 1973, was made from the adapted upper stage of a Saturn V rocket. At 75 tonnes/82.6 U.S. tons, it was the heaviest object ever put into space, and was 25.6 m/84 ft long. Skylab contained a workshop for carrying out experiments in weightlessness, an observatory for monitoring the sun, and cameras for photographing the earth's surface.  




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  Project Skylab
  Official NASA archive of the project that launched the U.S.A's first experimental space station. There are comprehensive details (technical and of general interest) on all the experiments included in the project.  
  Damaged during launch, it had to be repaired by the first crew of astronauts. Three crews, each of three astronauts, occupied Skylab for periods of up to 84 days, at that time a record duration for human spaceflight. Skylab finally fell to earth on July 11, 1979, dropping debris on Western Australia.  
  NASA Home Page
  Latest news from NASA, plus the most recent images from the Hubble Space Telescope, answers to questions about NASA resources and the space program, and a gallery of video, audio clips, and still images.  
  Directory of World Space Agencies  
  Argentina Comision Nacional de Investig-aciones Espaciales, Avenida Torrego 4010, Buenos Aires; phone: +54 1 776 2913  
  Australia Australian Space Office, 40 Allara Street, Canberra, ACT 2601; phone: +61 6 276 1000; fax: +61 6 276 1942)  
  Austria Austrian Space Agency, Garnisongasse 7, 1090 Wien; phone: +43 1 40 38 177; fax: +43 1 42 82 28  
  Belgium Science Policy Office, Rue de la Science 8, 1040 Brussels; phone: +32 2 238 3411; fax: +32 2 230 5912  
  Brazil Instituto de Atividades Espaciales, c/o Secretaria de Assuntos Estratégicos, Palácio do Planalto 4 andar, 70150-900 Brasilia-DF; phone: +55 61 211 1410; fax: +55 61 321 2466)  
  Canada Canadian Space Agency, 500 René-Lévesque Boulevard West, Montréal, Quebec H2Z 1Z7; phone: +1 514 496 4000; fax: +1 514 496 4039  
  China Ministry of Aero-Space Industry, 8 Fucheng Road, Haidian District, Beijing 100830; phone: +86 10 683 72 221; fax: +86 10 683 70 849  
  Denmark Danish Space Board, Bredgade 43, 1260 Copenhagen K; phone: +45 33 929 700; fax: +45 33 323 501  
  Europe European Space Agency, 8–10 rue Mario-Nikis, 75015 Paris; phone: +33 1 42 73 76 54; fax: +33 1 42 73 75 60  
  Finland Finnish Space Committee, c/o Technology Development Center, PO Box 69, 00101 Helsinki; phone: +358 0 693 691; fax: +358 0 694 9196  
  France Centre National d'Etudes Spatiales, 2 place Maurice Quentin, 75039 Paris; phone: +33 1 45 08 75 00; fax: +33 1 45 08 76 76  
  Germany Deutsche Argentur für Raumfahrtangelegenheiten, Königswinterer Strasse 522–524, 5300 Bonn 3; phone: +49 228 447 0; fax: +49 228 447 700  
  India Indian Space Research Organization, Antariksh Bhavan, New BEL Road, Bangalore 560094; phone: +91 80 333 4474; fax: +91 80 333 2253  
  Indonesia National Institute for Aeronautics and Space, JL Pemuda Persil 1, Jakarta; phone: +62 21 489 4941; fax: +62 21 489 4815  
  Ireland, Republic of Forbairt Science and Technology Directorate, Glasnevin, Dublin 9; phone: +353 1 808 2000; fax: +353 1 808 2587  
  Israel Israeli Space Agency, Kiryat Hamenshala, 3rd Building PO Box 18195, Jerusalem 91181; phone: +972 2 584 7096; fax: + 972 2 582 5581  
  Italy Agenzia Spaziale Italiana, Via di Villa Patrizi 13, 00161 Rome; phone: +39 6 85 679; fax: +39 6 44 04 212  
  Japan Space Activities Commission, 2-2-1 Kasumigaseki, Chiyoda-ku, Tokyo 100; phone: +81 3 35 81 15 59. National Space Development Agency, World Trade Center Building, 2-4-1 Hamamatau-cho, Minato-ku, Tokyo 105; fax: +81 3 54 02 79 34  
  Korea, South Korea Aerospace Research Institute, c/o Korea Advanced Institute of Science and Technology Head-quarters, 373-1 Kusong-Dong, Yusong-Gu, Taegu; phone: +82 53 869 2114  
  Netherlands The Netherlands Institute for Air and Space Development, Kluyverweg 1, PO Box 35, 2600 AA Delft; phone: +31 15 78 80 25; fax: +31 15 62 30 96  
  Norway Norsk Romesenter, Hoffsveien 65A, PO Box 85, Smestad, 0309 Oslo 3; phone: +47 2 523 800; fax: +47 2 522 397  
  Pakistan Pakistan Space and Upper Atmosphere Research Commission, Sector 28, Gulaz-e-Hujri, Off University Road, PO Box 8402, Karachi 75270; phone: +92 21 472 630; fax: +92 21 466 902  
  Russia Russian Space Agency, Shchepkin Street 42, 129857 Moscow; phone: +7 095 971 9176; fax: +7 095 975 6936  
  Spain Centro para el Desarollo Tecnologico Industrial, Paseo de la Castellana 141, 28046 Madrid; phone: +34 1 581 5500; fax: +34 1 581 5584  
  Sweden Swedish Board for Space Activities, Rymdstyrelsen, Box 4006, 171 04 Solna; phone: +46 8 627 6480; fax: +46 8 627 5014  
  Switzerland Federal Space Affairs Commission, Federal Department of Foreign Affairs, 3003 Berne; phone: +41 31 324 1065; fax: +41 31 324 1073  
  Taiwan National Science Council, No. 106 Ho-Ping East Road, Sector 2, Taipei 10636; phone: +886 2 737 7501; fax: +886 2 737 7668  
  U.K. British National Space Centre, Dean Bradley House, 52 Horseferry Road, London SW1P 2AG; phone: +44 171 276 2688; fax: +44 171 276 2377  
  U.S.A. National Aeronautics and Space Administration, Head-quarters, Washington, D.C. 20546; phone: +1 202 358 0000; fax: +1 202 358 0037  




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  Astronomy Chronology  
Astronomy Chronology
c. 1300 B.C. The Egyptians have identified 43 constellations and are familiar with those planets visible to the naked eye: Mercury, Venus, Mars, Jupiter, and Saturn.
c. 366 B.C. Greek mathematician and astronomer Eudoxus of Cnidus builds and observatory and constructs a model of 27 nested spheres to give the first systematic explanation of the motion of the sun, moon, and planets around the earth.
c. 350 B.C. Aristotle defends the doctrine that the earth is a sphere, in De caelo/Concerning the Heavens, and estimates its circumference to be about 400,000 stadia (one stadium varied from 154 m/505 ft to 215 m/705 ft). It is the first scientific attempt to estimate the circumference of the earth.
c. 280 B.C. Greek astronomer Aristarchus of Samos writes On the Size and Distances of the Sun and the Moon. He is the first to maintain that the earth rotates and revolves around the sun.
c. 200 B.C. The Greeks invent the astrolabe—the first scientific instrument. It is used for observing the positions and altitudes of stars.
129 B.C. Greek scientist Hipparchus of Bithynia completes the first known star catalog. It gives the latitude and longitude and brightness of nearly 850 stars and is later used Ptolemy.
150 Greek astronomer Ptolemy publishes the work known as the Almagest, a highly influential astronomical textbook that outlines a theory of a geocentric (earth-centered) universe based on years of observations.
772 Muslim astronomer Al-Fazari translates the Indian astronomical compendium Mahasiddhanta/Treatise on Astronomy, and begins the establishment of a uniquely Arabic astronomy.
c. 970 The Muslim astronomer Abu al-Wafa' invents the wall quadrant for the accurate measurement of the declination of stars in the sky.
1150 The Hebrew scholar Solomon Jarchus produces the first almanac, a table for the calculation of celestial movements, and a calendar.
1424 Mongolian ruler and astronomer Ulugh Beg, Prince of Samarkand, builds a great observatory, including a 40 m/132 ft sextant, which enables extremely accurate measurements to be made, cataloging over 1,000 stars.
1543 Copernicus publishes De revolutionibus orbium coelestium/On the Revolutions of the Celestial Sphere, detailing his theory that the earth and other planets orbit the sun on circular paths.
1609 Italian astronomer Galileo Galilei, having obtained a Dutch telescope, makes his own instruments, including one that magnifies objects 32 times. They are the first telescopes that can be used for astronomical observation.
1613 Convinced by his telescopic observations of the solar system, Galileo promotes the heliocentric system devised by Polish astronomer Copernicus.
1647 German astronomer Johannes Hevelius first charts the lunar surface accurately in his Selenographia/moon Map.
1668 English physicist and mathematician Isaac Newton constructs the first refelecting telescope, using a series of mirrors instead of lenses to bring light to a focus, and ceating a clearer, brighter image.
Aug 1675 The Royal Greenwich Observatory is established by British king Charles II on the outskirts of London, England. English astronomer John Flamsteed is appointed Astronomical Observator (later Astronomer Royal).
1705 English astronomer Edmund Halley conjectures that a comet seen in 1682 was identical with comets observed in 1607, 1531, and earlier; he correctly predicts its return in 1758.
March 13, 1781 German-born English astronomer William Herschel discovers the planet Uranus.
1798 French astronomer Pierre-Simon Laplace predicts the existence of black holes.
Jan 1, 1801 The Italian astronomer Giuseppe Piazzi discovers the first asteroid, Ceres.
1819 German astronomer Johann Encke discovers the short-period comet (Encke's comet), which returns every 3.29 years.
Oct 11, 1838 Using the method of parallax, German astronomer Friedrich Bessel calculates the star 61 Cygni to be 10.3 light-years away from earth. It is the first determination of the distance of a star other than the sun.
1840 Harvard College professor William Cranch Bond erects the first astronomical observatory in the United States.
1840 U.S. astronomer John William Draper takes the first photograph of the moon.
1842 Bessel accurately explains that the wavy course of Sirius is due to the existence of a companion star—the first binary star to be discovered.
Sept 23, 1846 German astronomer Johann Gotfried Galle discovers the planet Neptune on the basis of French astronomer Urbain Leverrier's calculations of its position.
1865 Maria Mitchell of Massachusetts becomes the first woman professor of astronomy when she receives an appointment of Vassar College in Poughkeepsie, New York.
1905–1907 Danish astronomer Ejnar Hertzsprung discovers that there is a relationship between the color and absolute brightness of stars and classifies them according to this relationship. The relationship is used to determine the distances of stars and forms the basis of theories of stellar evolution.





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1914 British astronomer John Franklin publishes the Franklin—Adams Charts, the first photographic star charts of the entire sky.
1917 Dutch astronomer Willem de Sitter shows that Einstein's theory of general relativity implies that the universe must be expanding.
1917 The 2.5-m/100-in Hooker reflecting telescope is installed at Mount Wilson Observatory, California. It is the world's largest reflecting telescope to date.
1919 The International Astronomical Union (IAU) is founded to promote international cooperation in astronomy.
1923 German mathematician Hermann Oberth is the first to provide the mathematics of how to achieve escape velocity.
1924 U.S. astronomer Edwin Hubble demonstrates that certain Cepheid variable stars are several hundred thousand light-years away and thus outside the Milky Way Galaxy. The nebulae they are found in are the first galaxies to be discovered that are proved to be independent of the Milky Way.
1927 Belgian astronomer Georges Lemaître proposes that the universe was created by an explosion of energy and matter from a "primaeval atom"—the beginning of the Big Bang theory.
c. 1928 English mathematician and physicist James Hopwood Jeans proposes the steady-state hypothesis, which states that the universe is constantly expanding and maintaining a constant average density through the continuous creation of new matter.
1929 Edwin Hubble publishes Hubble's Law, which states that the ratio of the speed of a galaxy to its distance from earth is a constant (now known as Hubble's constant).
Feb 18, 1930 U.S. astronomer Clyde Tombaugh, at the Lowell Observatory, Arizona, discovers the ninth planet, Pluto.
1931 U.S. engineer Karl Jansky discovers that the interference in telephone communications is caused by radio emissions from the Milky Way. He thus begins the development of radio astronomy.
1937 U.S. astronomer Grote Reber builds the first radio telescope. It has a parabolic reflector 9.4 m/31 ft in diameter and begins service in Wheaton, Illinois.
1942 Reber makes the first radio maps of the sky, locating individual radio sources.
1946 Cygnus A, the first radio galaxy, and the most powerful cosmic source of radio waves, is discovered.
1947 The first recorded sighting of an unidentified flying object (UFO) is made in the sky over Kansas, U.S.A., by Kenneth Arnold.
June 3, 1948 The 5-m/200-in Hale reflector telescope is installed at Mount Palomar Observatory, California; it remains the world's largest and most powerful telescope until 1974.
1948 Austrian-born British mathematician Hermann Bondi and Austrian astronomer Thomas Gold publish The Steady State Theory of the Expanding Universe in which they argue that the universe is constantly expanding, but maintaining a constant density through the continual creation of new stars and galaxies at a rate equal to the rate at which old ones become unobservable because of their increasing distance.
1950 Cape Canaveral, Florida, is established as a rocket assembly and launching facility.
1951 U.S. astronomer Gerard Kuiper proposes the existence of a ring of small, icy bodies orbiting the sun beyond Pluto, thought to be the source of comets. It is discovered in the 1990s and named the Kuiper belt.
1953–1956 The British Royal Observatory is moved from Greenwich, London, to Herstmonceux, Sussex
1955 English radio astronomer Martin Ryle builds the first radio interferometer. Consisting of three antennae spaced 1.6 km/1 mi apart, it increases the resolution of radio telescopes, permitting the diameter of a radio source to be determined, or two closely spaced sources to be separated.
Aug 19, 1957 U.S. astronomers, using a 33 cm/12 in telescope on board the uncrewed ballon-telescope STRATOSCOPE I, take the first clear photographs of the sun from 24,384 m/80,000 ft.
Oct 4, 1957 The USSR launches the first artificial satellite, Sputnik 1, to study the cosmosphere. It weighs 84 kg/184 lb and circles the earth in 95 minutes, inaugurating the space age.
Nov 3, 1957–April 13, 1958 The Soviet spacecraft Sputnik 2 is placed in orbit carrying a dog, Laika. It is the first vehicle to carry a living organism into orbit. Laika dies in space.
1957 The Jodrell Bank observatory, located near Manchester, England, begins operating. The first large radio telescope, it has a 76-m/250-ft diameter reflector, which can be rotated horizontally at 20° per minute and vertically at 24° per minute.
Jan 31, 1958 The U.S. Army launches the first U.S. satellite, Explorer 1, into earth orbit. It is used to study cosmic rays.
May 15, 1958 The USSR places Sputnik 3 in orbit. It contains the first multipurpose space laboratory and transmits data about cosmic rays, the composition of the earth's atmosphere, and ion concentrations.
May 1958 Using data from the Explorer rockets, U.S. physicist James Van Allen discovers a belt of radiation around the earth. Now known as the Van Allen belts (additional belts were discovered later), they consist of charged particles from the sun trapped by the earth's magnetic field.
July 29, 1958 The U.S. National Aeronautics and Space Administration (NASA) is created for the research and development of vehicles and activities involved in space exploration.





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Nov 1958 The United States launches Atlas, from Cape Canaveral, Florida. It is a one-half-stage rocket and has a range of 14,400 km/9,000 mi. It was originally designed as an intercontinental ballistic missile (ICBM).
Dec 18, 1958 The United States launches PROJECT SCORE (Signal Communications by Orbiting Relay Equipment), the first U.S. communications satellite. It functions for 13 days relaying messages stored on magnetic tape.
Jan 2, 1959 The USSR launches Lunik 1. The first spacecraft to escape earth's gravity, it passes within 6,400 km/4,000 mi of the moon.
Feb 28, 1959 The U.S. Air force launches Discover 1 into a low polar orbit where it photographs the entire surface of the earth every 24 hours.
Feb 1959 The U.S. Navy launches Vanguard 2, the first weather satellite.
Sept 14, 1959 The Soviet spacecraft Luna 2 (launched on September 12) becomes the first spacecraft to strike the moon.
March 11, 1960 The United States launches Pioneer 5, which relays the first measurements of deep space.
April 12, 1961 Soviet cosmonaut Yury Gagarin, in Vostok 1, is the first person to enter space. His flight lasts 108 minutes.
May 5, 1961 U.S. astronaut Alan Shepard in the Mercury capsule Freedom 7 makes a 14.8-minute single suborbital flight. He is the first U.S. astronaut into space.
May 21, 1961 U.S. president John F. Kennedy commits the country to "landing a man on the moon and returning him safely to earth before this decade is out."
April 26, 1962 The U.S.A. and U.K. launch the earth satellite Ariel. Designed to study the ionosphere, it is the first international cooperative launch.
June 14, 1962 The European Space Research Organization is established in Paris, France.
July 10, 1962 The U.S. telecommunications company AT&T launches Telstar, the first communications satellite, and begins experimental trans-Atlantic transmissions.
Aug 26, 1962 U.S. space probe Mariner 2 is launched. It makes a flyby of Venus (14 December) passing within 34,000 km/21,600 mi of the planet's surface and takes measurements of temperature and atmospheric density.
Dec 5, 1962 The United States and the USSR sign an agreement on cooperation for the peaceful use of outer space.
1962 The USA launches the Orbiting Solar Observatory (OSO). The first of a series of solar observatories, it collects and transmits data on the sun's electromagnetic radiation.
June 16, 1963 Soviet cosmonaut Valentina Tereshkova, the first woman in space, is launched into a three-day orbital flight aboard Vostok 6, to study the problem of weightlessness.
1963 Dutch-born U.S. astronomer Maarten Schmidt discovers the first quasar (3C 273), an extraordinarily distant object brighter than the largest known galaxy yet with a starlike image.
1963 The Arecibo radio telescope in Puerto Rico begins operation; its 300-m/1,000-ft reflector is built into a naturally occurring parabola and is the largest single-reflector telescope in the world.
Jan 1964 In the first U.S.–Soviet joint space venture, the satellite Echo 2 takes off from California's Vandenberg Air Force Base. It will transmit messages around the world.
Nov 28, 1964 The United States launches Mariner 4 to Mars. Passing within 1,865 km/6,118 mi of the planet's surface (July 14, 1965), it relays the first close-up photographs of the planet's surface as well as information on the Martian atmosphere.
March 18, 1965 Soviet cosmonaut Alexey Leonov leaves spacecraft Voskhod 2 and floats in space for 20 minutes—the first spacewalk.
June 1965 The National Aeronautics and Space Administration (NASA) launches Gemini 4, whose four-day mission sees the first U.S. space walk by astronaut Edward White.
1965 The first Soviet Molniya communications satellite is launched.
1965 U.S. astronomers Arno Penzias and Robert Wilson detect microwave background radiation in the universe and suggest that it is the residual radiation from the Big Bang.
Feb 3, 1966 Soviet spacecraft Luna 9 (launched January 31) makes the first soft landing on the moon and transmits photographs and soil data for three days.
March 1, 1966 Soviet probe Venera 3 (launched November 16, 1965) crash-lands on Venus, the first artificial object to land on another planet.
March 16, 1966 U.S. astronauts Neil Armstrong and David Scott, aboard Gemini 8, achieve the first link-up of a crewed spacecraft with another object, an Agena rocket.
Nov 11, 1966 Gemini 12, the last of the Gemini two-person space missions, is launched. It makes the first fully automatically controlled reentry.
Jan 27, 1967 A treaty banning nuclear weapons from outer space is signed by 60 countries, including the United States and USSR. It will be effective from October 10.
Jan 27, 1967 Three U.S. astronauts, Virgil ("Gus") I. Grissom, Edward H White, II, and Roger B Chaffee, die in a fire during a countdown rehearsal on the Apollo 1 spacecraft at Cape Kennedy, Florida. They are the first human casualties of the U.S. space program.
April 24, 1967 Soviet cosmonaut Vladimir Komarov dies





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  during the descent of his Soyuz 1 spacecraft when his parachute fails to open properly. He is the fist fatality of the Soviet space program.
July 7, 1967 British astronomer Jocelyn Bell and English astronomer Anthony Hewish discover the first pulsar (announced in 1968). A new class of stars, they are later shown to be collapsed neutron stars emitting bursts of radio energy.
Oct 18, 1967 The Soviet spacecraft Venera 4 (launched June 12) lands on Venus. The first soft landing on another planet, its instrument-laden capsule transmits information about Venus' atmosphere.
Oct 22, 1967–
Oct 29, 1967
The U.S. spacecraft Cosmos 186 and Cosmos 188 complete the first automatic docking.
Nov 7, 1967 U.S. spacecraft Surveyor 6 photographs one area of the moon then lifts off, repositions itself 2.4 m/8 ft away and resumes photographing. It is the first liftoff from an extraterrestrial body.
1967 The Outer Space Treaty that bans military activities in space is ratified by 63 members of the United Nations.
Sept 14, 1968– Sept 21, 1968 The Soviet spacecraft Zond 5 flies around the moon and returns to earth—the first spacecraft to do so.
Oct 11, 1968– Oct 22, 1968 Apollo 7, the first U.S. Apollo space mission with a crew, tests the Command module used on subsequent flights to the moon, during 163 orbits of the earth. The crew make the first live transmission from space on October 13.
1968 U.S. astronauts Frank Borman, James Lovell, and William Anders become the first astronauts to orbit the moon during the Apollo 8 space mission. They complete 10 orbits.
Jan 16, 1969 Two cosmonauts aboard Soviet spacecraft Soyuz 5 (launched January 15) dock and transfer to Soyuz 4 (launched January 14). Locked together for four hours they form the first experimental space station.
July 20, 1969 U.S. astronaut Neil Armstrong, onboard Apollo 11 (launched July 16), is the first person to walk on the moon, famously saying ''That's one small step for man, one giant leap for mankind." He and astronaut Buzz Aldrin also install and operate the first moon seismograph at Tranquillity base, spending a total of 21 hours 37 minutes on the moon's surface.
April 13–17, 1970 NASA narrowly diverts a disaster aboard the moon-bound spaceship Apollo 13, after a canister of liquid oxygen explodes in the command module. The crew of James Lovell, John Swigert, and Fred Haise enter the lunar module, which they use as a "lifeboat" to return safely to earth.
1970 The Effelsberg radio telescope near Bonn, Germany, begins operating; its 100-m/328-ft moveable dish is the largest fully steerable dish in the world.
July 26,–Aug 7, 1971 Apollo 15 astronauts use a Lunar Roving Vehicle (LRV) to explore the moon's surface.
Nov 12, 1971 The U.S. space probe Mariner 9 (launched in May) becomes the first artificial object to orbit another planet (Mars); it transmits 7,329 photographs of the planet and its two moons, Deimos and Phobos.
1971 The binary X-ray system Cygnus X-1 is discovered; the center is believed to contain a black hole.
July 23, 1972 The United States launches Landsat 1, the first of a series of satellites for surveying the earth's resources from space.
May 14, 1973–Feb 8, 1974 The United States launches the first Skylab space station. It contains a workshop for carrying out experiments in weightlessness. It is visited by three three-person crews and astronauts make observations of the sun, manufacture superconductors, and conduct other scientific and medical experiments. The third mission lasts a record 84 days and gathers data about long space flights.
July 1975 The launch of the Soviet spaceship Soyuz 19 signals the stars of a joint U.S.–Soviet space mission. U.S. and Soviet astronauts meet in space on July 17 when Soyuz 19 docks with its NASA counterpart, Apollo 18.
Aug 1, 1975 The European Space Agency is founded in Paris, France, to undertake research and develop technologies for use in space.
Oct 22–25, 1975 The Soviet spacecraft Venera 9 and 10 land on Venus and transmit the first pictures from the surface of another planet.
1976 The 6-m/19.7-ft UTR-Z telescope is completed at Zelenchukskaya, USSR; it is the largest reflecting telescope in the world.
1976 The Bol'shoi Teleskop Azimutal'nyi on Mount Pastukhov, USSR, begins operating; its 6-m/19.7-ft reflector makes it the largest optical telescope in the world.
1976 The U.S. spacecraft Viking 1 and Viking 2 (launched in 1975) soft-land on Mars (July 20, September 3). They make meteorological readings of the Martian atmosphere and search for traces of bacterial life which prove inconclusive.
Dec 4, 1979 The European Space Agency's first Ariane rocket is launched from the Guiana Space Center in Kourou, French Guiana; it is designed to deploy satellites into orbit.
1979 The 3-m/9.8-ft NASA Infrared Telescope Facility (IRTF) telescope and the 3.8-m/12.5-ft UK Infrared Telescope both begin operation on Mauna Kea, Hawaü.
1979 The Multiple Mirror Telescope begins operation on Mount Hopkins, Arizona; it focuses the light form six 180-cm/70-in





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  telescopes to form one image, giving the light-gathering power of a single 4.5-m/125.7-ft telescope; it becomes the prototype for larger optical telescopes.
1980 A thin layer of iridium-rich clay, about 65 million years old, is found around the world. U.S. physicist Luis Alvarez suggests that it was caused by the impact of a large asteroid or comet which threw enough dust into the sky to obscure the sun and cause the extinction of the dinosaurs.
1980 Alan Guth proposes the theory of the inflationary universe—that the universe expanded very rapidly for a short time after the Big Bang.
1980 The Multi-Element Radio-Linked Interferometer Network (MERLIN) radio telescope begins operation in the UK. It has five dishes measuring 25 m/82 ft, one measuring 32 m/105 ft, and one measuring 76 m/249 ft, making it the largest radio telescope in the world.
1980 The Very Large Array (VLA) radio telescope at Socorro, New Mexico, enters service; its 27 25-m/81-ft dishes are steerable and moveable on railway tracks and are equivalent to one dish 27 km/17 mi in diameter; together they provide high-resolution radio images.
April 12–14, 1981 The U.S. reusable space shuttle, using the orbiter Columbia, makes its first flight (second shuttle flight November 12–14). It achieves the first U.S. spacecraft landing on land (instead of water).
1982 The U.S. rocket Conestoga 1 makes a suborbital flight; it is the first private space craft.
June 13, 1983 The U.S. space probe Pioneer 10 becomes the first artificial object to leave the solar system.
June 18, 1983 Astronauts on board the space shuttle Challenger first use the Remote Manipulating Structure ("arm") to deploy and retrieve a satellite.
1983 The Search for Extraterrestrial Intelligence (SETI) program is established.
Feb 19, 1986 The Soviet space station Mir 1 is launched; it is intended to be permanently occupied.
1986 Scientists at Arizona State University conduct computer simulations that strongly suggest that a Mars-sized object struck the earth a glancing blow about 4.6 billion years ago and was then captured by the earth; by the end of the year the impact theory is the leading hypothesis about the moon's origin.
1986 The California Submillimeter Observatory telescope begins operation on Mauna Kea, Hawaü; its 10.4-m/34-ft disk makes it the largest submillimeter telescope in the world.
Feb 24, 1987 The first supernova (explosion of a star) visible to the naked eye since 1604 is seen.
1987 Radio waves are observed from 3C325—believed to be a galaxy in the process of formation.
1987 The James Clerk Maxwell Telescope, operated by the Royal Observatory, based in Edinburgh, Scotland, begins operation on Mauna Kea, Hawaü; its 15-m/49-ft dish makes it the largest submillimetre telescope in the world.
Aug 25, 1989 The U.S. space probe Voyager 2 reaches Neptune and transmits pictures; it discovers a great dark spot on the planet and six new moons.
1989 The U.S. Cosmic Background Explorer (COBE) satellite is launched to study microwave background radiation, thought to be a vestige of the Big Bang.
1989 The U.S. Delta Star "Star Wars" satellite is launched; it successfully detects and tracks test missiles shortly after they are launched.
Feb 1990 The U.S. space probe Voyager 1, now near the edge of the solar system, turns and takes the first photograph of the entire solar system from space.
April 24, 1990 The space shuttle Discovery places the Hubble Space Telescope in earth orbit; the main mirror proves to be defective.
Aug 10, 1990 The U.S. Magellan radar mapper arrives in orbit around Venus; it transmits the most detailed pictures of the planet's surface yet produced.
Nov 1990 The Keck 1 Telescope on Mauna Kea volcano, Hawaü, is erected; its 10-m/32.8-ft





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  reflector, composed of 36 segments, makes it the largest optical telescope in the world.
Dec 2–12, 1990 The Soviet spacecraft Soyuz TM-11 is launched, marking the first paying-passenger space flight.
1990 The British Royal Observatory is transferred from Herstmonceaux, Sussex, to Cambridge.
May 18–26, 1991 English chemist Helen Sharman becomes the first Briton to go into space, as a participant in a Soviet space mission launched in Soyuz TM-12. She spends six days with Soviet cosmonauts aboard the Mir space station.
Oct 29, 1991 The U.S. space probe Galileo takes the closest ever picture of an asteroi—Gaspra—at a distance of 26,071 km/16,200 mi.
Feb 8, 1992 The gravity of Jupiter is used to swing the U.S. space probe Ulysses towards the sun.
1992 The Cosmic Background Explorer (COBE) satellite detects ripples in the microwave background radiation, thought to originate from the formation of galaxies.
1992 The U.S. space probe Magellan maps 99% of the surface of Venus to a resolution of 100 m/330 ft.
Dec 7, 1993 The Hubble Space Telescope is repaired and reboosted into a nearly circular orbit by five U.S. astronauts operating from the U.S. space shuttle Endeavour.
Dec 6, 1994 Pictures taken by the Hubble Space Telescope of galaxies in their infancy are published.
Dec 1994 The Apollo asteroid (an asteroid with an orbit that crosses that of earth) 1994 XM1 passes within 100,000 km/60,000 mi of earth, the closest observed approach of any asteroid.
Dec 7, 1995 The U.S. spacecraft Galileo's probe enters Jupiter's atmosphere while its parent continues to orbit the planet. The probe radios information back about the chemical composition of the atmosphere to the orbiter for 57 minutes before being destroyed by atmospheric pressure.
1995 The largest liquid-mirror telescope (a reflecting telescope constructed with a rotating mercury mirror) is completed for NASA's Orbital Debris Observatory in New Mexico. It is 3 m/9.8 ft across.
1995 U.S. astronomers discover the first brown dwarf, an object larger than a planet but not massive enough to ignite into a star, in the constellation Lepus. It is about 20–40 times as massive as Jupiter. Four other brown dwarfs are discovered in 1996.
1995 U.S. astronomers discover water in the sun—in the form of superheated steam—in two sunspots where the temperature is only 3,000°C/5,400°F.
March 24, 1996 Comet Hyakutake makes its closest approach, passing within 15.4 million km/9.5 million mi of earth. It is the brightest comet for decades, with a tail extending over 12 degrees of the sky.
Dec 4, 1996 NASA launches the Mars Pathfinder. Its main goal is to demonstrate the feasibility of low-cost landings on, and exploration of, Mars. The spacecraft carries a roving machine to explore the surface.
Dec 6, 1996 Cosmonauts aboard the space station Mir successfully harvest a small wheat crop, the first plants to be successfully cultivated from seed in space.
March 23, 1997 The comet Hale–Bopp comes to within 196 million km/122 million mi of earth, becoming the closest comet since 2000 B.C.. NASA launches rockets to study the comet. Its icy nucleus is estimated to be 40 km/25 mi wide, making it at least ten times larger than that of Comet Hyakutake and twice the size of Comet Halley.
July 4, 1997 The U.S. spacecraft Mars Pathfinder lands on Mars. Two days later the probe's rover Sojourner, a six-wheeled vehicle controlled by an earth-based operator, begins to explore the area around the spacecraft.
Sept 12, 1997 The U.S. spacecraft Mars Global Surveyor goes into orbit around Mars to conduct a detailed photographic survey of the planet, commencing in March 1998.
Jan 1998 The U.S. spaceprobe Lunar Prospector is launched to examine the composition of the lunar crust, record gamma rays, and map the lunar magnetic field.
1998 The European Southern Observatory's Very Large Telescope on Mount Paranal, Chile, transmits its first images.





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  Adams, John Couch (1819–1892) English astronomer. He mathematically deduced the existence of the planet Neptune in 1845 from the effects of its gravitational pull on the motion of Uranus, although it was not found until 1846 by J. G. Galle. Adams also studied the moon's motion, the Leonid meteors, and terrestrial magnetism. He was Lowndean professor of astronomy and geometry at Cambridge 1859–92 and director of Cambridge observatory 1861–92.  
  Airy, George Biddell (1801–1892) English astronomer. He became the seventh Astronomer Royal in 1835. He installed a transit telescope at the Royal Observatory at Greenwich, England, and accurately measured Greenwich Mean Time by the stars as they crossed the meridian. Greenwich Mean Time was adopted as legal time in Britain in 1880. Airy's Mathematical Tracts on Physical Astronomy (1826) became a standard work.  
  Anaximander (c. 610–c. 546 B.C.) Greek astronomer and philosopher. He claimed that the earth was a cylinder three times wider than it is deep, motionless at the center of the universe, and that the celestial bodies were fire seen through holes in the hollow rims of wheels encircling the earth. He is thought to have been the first to determine solstices and equinoxes, by means of a sundial, and he is credited with drawing the first geographical map of the whole known world.  
  Aristarchus of Samos (c. 320–c. 250 B.C.) Greek astronomer. The first to argue that the earth moves around the sun, he was ridiculed for his beliefs. He was also the first astronomer to estimate (quite inaccurately) the sizes of the sun and moon and their distances from the earth. His model of the universe described the sun and the fixed stars as stationary in the cosmos, and the planets—including the earth—as traveling in circular orbits around the sun. His only surviving work is Magnitudes and Distances of the Sun and Moon.  
  Baade, (Wilhelm Heinrich) Walter (1893–1960) German-born U.S. astronomer who made observations that doubled the distance, scale, and age of the universe. He discovered that stars are in two distinct populations according to their age, known as Population I (the younger, bluish in color) and Population II (the older, reddish). Later, he found that Cepheid variable stars of Population I are brighter than had been supposed and that distances calculated from them were wrong.  
  Bell Burnell, (Susan) Jocelyn (1943– ) British astronomer. In 1967, while a research student at Cambridge, she discovered the first pulsar (rapidly flashing star) with Antony Hewish and colleagues at Cambridge University, England.  
  Bessel, Friedrich Wilhelm (1784–1846) German astronomer and mathematician. He was the first person to find the approximate distance to a star by direct methods when he measured the parallax (annual displacement) of the star 61 Cygni in 1838. Bessel's work laid the foundations for a more accurate calculation of the scale of the universe and the sizes of stars, galaxies, and clusters of galaxies. He was a pioneer of very precise observation and reduction in astronomy, and published a catalog of 3,222 star positions under the title Fundamenta Astronomiae (1818).  
  Bode, Johann Elert (1747–1826) German astronomer and mathematician. He contributed greatly to the popularization of astronomy. He published the first atlas of all stars visible to the naked eye, Uranographia (1801), and devised Bode's law, a numerical sequence that gives the approximate distances in astronomical units, of the planets from the sun by adding 4 to each term of the series 0, 3, 6, 12, 24, . . . and then adding 10.  
  Bondi, Hermann (1919– ) Austrian-born British cosmologist. In 1948 he joined Fred Hoyle and Thomas Gold in developing the steady-state theory of cosmology, which suggested that matter is continuously created in the universe. Bondi also described the likely characteristics and physical properties of gravitational waves, and demonstrated that such waves are compatible with and are indeed a necessary consequence of the general theory of relativity.  
  Bradley, James (1693–1762) English astronomer. In 1728 he discovered the aberration of starlight. From the amount of aberration in star positions, he was able to calculate the speed of light. In 1748 he announced the discovery of nutation (variation in the earth's axial tilt). He became the third Astronomer Royal in 1742.  
  Brahe, Tycho (1546–1601) Danish astronomer. His accurate observations of the planets enabled German astronomer and mathematician Johannes Kepler to prove that planets orbit the sun in ellipses. Brahe's discovery and report of the 1572 supernova brought him recognition, and his observations of the comet of 1577 proved that it moved in an orbit among the planets, thus disproving Aristotle's view that comets were in the earth's atmosphere.  
  Cannon, Annie Jump (1863–1941) U.S. astronomer. She carried out revolutionary work on the classification of stars by examining their spectra. Her system, still used today, has spectra arranged according to temperature into categories labeled O, B, A, F, G, K, M, R, N, and S. O-type stars are the hottest, with surface temperatures of over 25,000K. She discovered 300 new variable stars and classified the spectra of over 300,000 stars.  
  Cassini, Giovanni Domenico (1625–1712) Italian-born French astronomer. During 1664–67 he determined the rotation periods of Mars, Jupiter, and Venus. He discovered four moons of Saturn and the gap in the rings of Saturn now called the Cassini division.  
  Chandrasekhar, Subrahmanyan (1910–1995) Indian-born U.S. astrophysicist who made pioneering studies of the structure and evolution of stars. The Chandrasekhar limit is the maximum mass of a white dwarf before it turns into a neutron star. He also investigated the transfer of energy in stellar atmospheres by radiation and convection, and the polarization of light emitted from particular stars. He was awarded the Nobel Prize for Physics in 1983.  
  Copernicus, Nicolaus (1473–1543) Polish astronomer who believed that the sun, not the earth, is at the center of the solar system, thus defying the Christian church doctrine of the time. For 30 years, he worked on the hypothesis that the  




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  rotation and the orbital motion of the earth are responsible for the apparent movement of the heavenly bodies. His great work De revolutionibus orbium coelestium/On the Revolutions of the Heavenly Spheres was the important first step to the more accurate picture of the solar system built up by Tycho Brahe, Kepler, Galileo, and later astronomers.  
  Eddington, Arthur Stanley (1882–1944) British astrophysicist. He studied the motions, equilibrium, luminosity, and atomic structure of the stars. In 1919 his observation of stars during a solar eclipse confirmed Albert Einstein's prediction that light is bent when passing near the sun, in accordance with the general theory of relativity. In The Expanding Universe (1933) he expressed the theory that in the spherical universe the outer galaxies or spiral nebulae are receding from one another.  
  Eudoxus of Cnidus (c. 400–c. 347 B.C.) Greek mathematician and astronomer. He devised the first system to account for the motions of celestial bodies, believing them to be carried around the earth on sets of spheres. Work attributed to Eudoxus includes methods to calculate the area of a circle and to derive the volume of a pyramid or a cone. Eudoxus is said to have been the one who first fixed the length of the year as 365.25 days, and to have invented the sundial.  
  Evershed, John (1864–1956) English astronomer who made solar observations. In 1909 he discovered the radial movements of gases in sunspots (the Evershed effect). He also gave his name to a spectroheliograph, the Evershed spectroscope.  
  Flamsteed, John (1646–1719) English astronomer. He began systematic observations of the positions of the stars, moon, and planets at the Royal Observatory he founded at Greenwich, London, in 1676. His observations were published in Historia Coelestis Britannica (1725).  
  As the first Astronomer Royal of England, Flamsteed determined the latitude of Greenwich, the slant of the ecliptic, and the position of the equinox. He also worked out a method of observing the absolute right ascension (a coordinate of the position of a heavenly body) that removed all errors of parallax, refraction, and latitude. Having obtained the positions of 40 reference stars, he then computed positions for the rest of the 3,000 stars in his catalog.  
  Galileo Galilei (1564–1642) Italian mathematician, astronomer, and physicist. He developed the astronomical telescope and was the first to see sunspots, the four main satellites of Jupiter, and the appearance of Venus going through phases, thus proving it was orbiting the sun. Galileo discovered that freely falling bodies, heavy or light, have the same, constant acceleration and that this acceleration is due to gravity. He also determined that a body moving on a perfectly smooth horizontal surface would neither speed up nor slow down. He invented a thermometer, a hydrostatic balance, and a compass, and discovered that the path of a projectile is a parabola. Galileo's work founded the modern scientific method of deducing laws to explain the results of observation and experiment.  
  Galle, Johann Gottfried (1812–1910) German astronomer. He located the planet Neptune in 1846, close to the position predicted by French mathematician Urbain Leverrier and the English astronomer J. C. Adams. He also suggested a method of measuring the scale of the solar system by observing the parallax of asteroids, first applying his method to the asteroid Flora in 1873. The method was employed with great success after Galle's death.  
  Gamow, George (Georgi Antonovich) (1904–1968) Russianborn U.S. cosmologist, nuclear physicist, and popularizer of science. His work in astrophysics included a study of the structure and evolution of stars and the creation of the elements. He explained how the collision of nuclei in the solar interior could produce the nuclear reactions that power the sun. With the "hot Big Bang" theory, he indicated the origin of the universe.  
  Hale, George Ellery (1868–1938) U.S. astronomer. He made pioneer studies of the sun and founded three major observatories. In 1889 he invented the spectroheliograph, a device for photographing the sun at particular wavelengths. In 1917 he established on Mount Wilson, California, a 2.5-m/100-in reflector, the world's largest telescope until superseded in 1948 by the 5-m/200-in reflector on Mount Palomar, which Hale had planned just before he died.  
  He, more than any other, was responsible for the development of observational astrophysics in the United States. He also founded the Yerkes Observatory in Wisconsin 1897, with the largest refractor, 102 cm/40 in, ever built at that time.  
  Halley, Edmond (1656–1742) English astronomer. He identified Halley's Comet, compiled a star catalog, detected the proper motion of stars, using historical records, and began a line of research that, after his death, resulted in a reasonably accurate calculation of the astronomical unit.  
  Halley calculated that the comet sightings reported in 1456, 1531, 1607, and 1682 all represented reappearances of the same comet. He reasoned that the comet would follow a parabolic path and announced in 1705 in his Synopsis Astronomia Cometicae that it would reappear in 1758. When it did, public acclaim for the astronomer was such that his name was irrevocably attached to it. He was Astronomer Royal from 1720.  
  Herschel, Caroline (Lucretia) (1750–1848) German-born English astronomer, sister of William Herschel, and from 1772 his assistant. She discovered eight comets and worked on her brother's catalog of star clusters and nebulas.  
  Herschel, John Frederick William (1792–1871) English scientist, astronomer, and photographer who discovered thousands of close double stars, clusters, and nebulae. Together with James South, he systematically remeasured, from 1821 to 1823, the double stars discovered by his father and, in 1824, published a catalog of double stars. Herschel went on to revise his father's survey of the northern heavens, and mapped the southern skies from the Cape of Good Hope Observatory in South Africa 1834–38.  
  Herschel, (Frederick) William (1738–1822) German-born English astronomer. He was a skilled telescopemaker, and pioneered the study of binary stars and nebulas. He discovered the planet Uranus in 1781 and infrared solar rays in 1801. He cataloged over 800 double stars, and found over 2,500 nebulae, cataloged by his sister Caroline Herschel; this  




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  work was continued by his son John Herschel. By studying the distribution of stars, William established the basic form of our galaxy, the Milky Way.  
  Hewish, Antony (1924– ) English radio astronomer who was awarded, with Martin Ryle, the Nobel Prize for Physics in 1974 for his work on pulsars, rapidly rotating neutron stars that emit pulses of energy.  
  The discovery by Jocelyn Bell Burnell of a regularly fluctuating signal, which turned out to be the first pulsar, began a period of intensive research. Hewish discovered another three straight away, and more than 170 pulsars have been found since 1967.  
  Hipparchus (c. 190–c. 120 B.C.) Greek astronomer and mathematician. He calculated the lengths of the solar year and the lunar month, discovered the precession of the equinoxes, made a catalog of 850 fixed stars, and advanced Eratosthenes' method of determining the situation of places on the earth's surface by lines of latitude and longitude.  
  In 134 B.C. he noticed a new star in the constellation Scorpio, which inspired him to put together his star catalog—the first of its kind. He entered his observations of stellar positions using a system of celestial latitude and longitude, and taking the precaution wherever possible to state the alignments of other stars as a check on present position. He classified the stars by magnitude (brightness). His finished work, completed in 129 B.C., was used by Edmond Halley some 1,800 years later.  
  Hoyle, Fred(erick) (1915– ) English astronomer, cosmologist, and writer. His astronomical research has dealt mainly with the internal structure and evolution of the stars. In 1948 he developed with Hermann Bondi and Thomas Gold the steadystate theory of the universe. In 1957, with William Fowler, he showed that chemical elements heavier than hydrogen and helium may be built up by nuclear reactions inside stars.  
  Hubble, Edwin (Powell) (1889–1953) U.S. astronomer. He discovered the existence of galaxies outside our own, and classified them according to their shape. His theory that the universe is expanding is now generally accepted. It has been said that Hubble opened up the observable region of the universe in the same way that Galileo opened up the solar system and the Herschels the Milky Way.  
  His data on the speed at which galaxies were receding (based on their red shifts) were used to determine the portion of the universe that we can ever come to know, the radius of which is called the Hubble radius. Beyond this limit, any matter will be traveling at the speed of light, so communication with it will never be possible. The ratio of the velocity of galactic recession to distance has been named the Hubble constant.  
  Hubble discovered Cepheid variable stars in the Andromeda galaxy in 1923, proving it to lie far beyond our own Galaxy. In 1925 he introduced the classification of galaxies as spirals, barred spirals, and ellipticals. In 1929 he announced Hubble's law, stating that the galaxies are moving apart at a rate that increases with their distance.  
  Huygens, Christiaan (1629–1695) Dutch mathematical physicist and astronomer. He proposed the wave theory of light, developed the pendulum clock in 1657, discovered polarization, and observed Saturn's rings. His work in astronomy was an impressive defense of the Copernican view of the solar system.  
  Jansky, Karl Guthe (1905–1950) U.S. radio engineer who in 1932 discovered that the Milky Way galaxy emanates radio waves; he did not follow up his discovery, but it marked the birth of radioastronomy.  
  Kepler, Johannes (1571–1630) German mathematician and astronomer. He formulated what are now called Kepler's laws of planetary motion: (1) the orbit of each planet is an ellipse with the sun at one of the foci; (2) the radius vector of each planet sweeps out equal areas in equal times; (3) the squares of the periods of the planets are proportional to the cubes of their mean distances from the sun. Kepler's laws are the basis of our understanding of the solar system, and such scientists as Isaac Newton built on his ideas.  
  His Rudolphine Tables (1627) were based on Tycho Brahe's observations, whose assistant he became in 1600. These were the first modern astronomical tables, enabling astronomers to calculate the positions of the planets at any time in the past, present or future.  
  Korolev, Sergei Pavlovich (1906–1966) Russian designer of the first Soviet intercontinental missile, used to launch the first Sputnik satellite in 1957 and the Vostok spacecraft, also designed by Korolev, in which Yuri Gagarin made the world's first space flight in 1961.  
  Korolev and his research team built the first Soviet liquidfuel rocket, launched in 1933. His innovations in rocket and space technology include ballistic missiles, rockets for geophysical research, launch vehicles, and crewed spacecraft. Korolev was also responsible for the Voskhod spaceship, from which the first spacewalks were made.  
  Kuiper, Gerard Peter (1905–1973) Dutch-born U.S. astronomer who made extensive studies of the solar system. His discoveries included the atmosphere of the planet Mars and that of Titan, the largest moon of the planet Saturn. His spectroscopic studies of Uranus and Neptune led to the discovery of features subsequently named Kuiper bands, which indicate the presence of methane. He was an adviser to many NASA exploratory missions, and pioneered the use of telescopes on high-flying aircraft.  
  Laplace, Pierre Simon, Marquis de Laplace (1749–1827) French astronomer and mathematician. In 1796 he theorized that the solar system originated from a cloud of gas (the nebular hypothesis). He studied the motion of the moon and planets, and published a five-volume survey of celestial mechanics, Traité de méchanique céleste (1799–1825). This work contained the law of universal attraction—the law of gravity as applied to the earth—and explanations of such phenomena as the ebb and flow of tides and the precession of the equinoxes.  
  Leavitt, Henrietta Swan (1868–1921) U.S. astronomer who in 1912 discovered the period–luminosity law, which links the brightness of a Cepheid variable star to its period of variation. This law allows astronomers to use Cepheid variables as "standard candles" for measuring distances in space. She discovered a total of 2,400 new variable stars and four novae.  
  Lemaître, Georges Edouard (1894–1966) Belgian cosmologist.  




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  He proposed the Big Bang theory of the origin of the universe in 1933. The U.S. astronomer Edwin Hubble had shown that the universe was expanding, but it was Lemaître who suggested that the expansion had been started by an initial explosion, the Big Bang, a theory that is now generally accepted.  
  Leverrier, Urbain Jean Joseph (1811–1877) French astronomer. He predicted the existence and position of the planet Neptune from its influence on the orbit of the planet Uranus. It was discovered in 1846.  
  The possibility that another planet might exist beyond Uranus, influencing its orbit, had already been suggested. Leverrier calculated the orbit and apparent diameter of the hypothetical planet, and wrote to a number of observatories, asking them to test his prediction of its position. Johann Galle at the Berlin Observatory found it immediately, within 1° of Leverrier's coordinates.  
  Lovell, (Alfred Charles) Bernard (1913– ) English radio astronomer, director 1951–81 of Jodrell Bank Experimental Station (now Nuffield Radio Astronomy Laboratories). He showed that radar could be a useful tool in astronomy, and lobbied for the setting-up of a radio-astronomy station. Jodrell Bank was built near Manchester 1951–57. Although its high cost was criticized, its public success after tracking the Soviet satellite Sputnik I in 1957 assured its future.  
  Lowell, Percival (1855–1916) U.S. astronomer who predicted the existence of a planet beyond Neptune, starting the search that led to the discovery of Pluto in 1930. In 1894 he founded the Lowell Observatory in Flagstaff, Arizona, where he reported seeing "canals" (now known to be optical effects and natural formations) on the surface of Mars. He led an expedition to the Chilean Andes in 1907, which produced the first high-quality photographs of the planet.  
  Maskelyne, Nevil (1732–1811) English astronomer. He made observations to investigate the reliability of the lunar distance method for determining longitude at sea. In 1774 he estimated the mass of the earth by noting the deflection of a plumb line near Mount Schiehallion in Perthshire, Scotland. He was Astronomer Royal 1765–1811.  
  Messier, Charles (1730–1817) French astronomer. He discovered 15 comets and in 1784 published a list of 103 star clusters and nebulae. Objects on this list are given M (for Messier) numbers, which astronomers still use today, such as M1 (the Crab nebula) and M31 (the Andromeda galaxy).  
  Messier's search was continually hampered by rather obscure forms which he came to recognize as nebulae. During the period 1760–84, therefore, he compiled a list of these nebulae and star clusters, so that he and other astronomers would not confuse them with possible new comets.  
  Oort, Jan Hendrik (1900–1992) Dutch astronomer. In 1927 he calculated the mass and size of our galaxy, the Milky Way, and the sun's distance from its center, from the observed movements of stars around the galaxy's center. In 1950 Oort proposed that comets exist in a vast swarm, now called the Oort cloud, at the edge of the solar system. He established radio observatories at Dwingeloo and Westerbork, which put the Netherlands in the forefront of radio astronomy.  
  Ptolemy (Claudius Ptolemaeus) (c. A.D. 100–c. A.D. 170) Greek astronomer and geographer. His Almagest developed the theory that earth is the center of the universe, with the sun, moon, and stars revolving around it. The Almagest contains all his works on astronomical themes, the only authoritative works until the time of Copernicus. Ptolemy began with the premise that the earth was a perfect sphere. All planetry orbits were circular, but those of Mercury and Venus, and possibly Mars (Ptolemy was not sure), were epicyclic (the planets orbited a point that itself was orbiting the earth). The sphere of the stars formed a dome with points of light attached or pricked through. In 1543 the Polish astronomer Copernicus proposed an alternative to the Ptolemaic system.  
  Ryle, Martin (1918–1984) English radio astronomer. At the Mullard Radio Astronomy Observatory, Cambridge, he developed the technique of sky-mapping using "aperture synthesis," combining smaller dish aerials to give the characteristics of one large one. His work on the distribution of radio sources in the universe brought confirmation of the Big Bang theory. He was Astronomer Royal 1972–82, and, with his co-worker Antony Hewish, won the Nobel Prize for Physics in 1974.  
  Schiaparelli, Giovanni Virginio (1835–1910) Italian astronomer. He drew attention to linear markings on Mars, which gave rise to the popular belief that they were canals. The markings were soon shown by French astronomer Eugène Antoniadi to be optical effects and not real lines. Schiaparelli also gave observational evidence for the theory that all meteor showers are fragments of disintegrating comets.  
  Shapley, Harlow (1885–1972) U.S. astronomer. He established that our galaxy was much larger than previously thought. His work on the distribution of globular clusters showed that the sun was not at the center of the galaxy as then assumed, but two-thirds of the way out to the rim; globular clusters were arranged in a halo around the Galaxy. His surveys recorded tens of thousands of galaxies in both hemispheres.  
  Tombaugh, Clyde William (1906–1997) U.S. astronomer who discovered the planet Pluto in 1930. As an assistant at the Lowell Observatory in Flagstaff, Arizona, from 1929, he photographed the sky in search of the predicted remote planet, discovering it on February 18, 1930. His failure to find any other planets placed strict limits on the possible existence of planets beyond Pluto.  
  Van Allen, James Alfred (1914– ) U.S. physicist whose instruments aboard the first U.S. satellite Explorer 1 in 1958 led to the discovery of the Van Allen belts, two zones of intense radiation around the earth. He pioneered high-altitude research with rockets after World War II and was responsible for the instrumentation of the first U.S. satellites.  
  Whipple, Fred Lawrence (1906– ) U.S. astronomer whose hypothesis in 1949 that the nucleus of a comet is like a dirty snowball was confirmed in 1986 by space-probe studies of Halley's comet. He discovered six new comets and worked on ascertaining cometary orbits and defining the relationship between comets and meteors.  
  Whipple proposed that the nucleus of a comet consisted of a frozen mass of water, ammonia, methane, and other hydrogen compounds together with silicates, dust, and other materials. As the comet's orbit brought it nearer to the sun, solar radiation would cause the frozen material to evaporate, thus producing a large amount of silicate dust which would form the comet's tail.  




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  Zwicky, Fritz (1898–1974) Swiss astronomer. He predicted the existence of neutron stars in 1934. He discovered 18 supernovae and determined that cosmic rays originate in them. Beginning in 1936, he compiled a catalog of galaxies and galaxy clusters in which he listed 10,000 clusters.  
  aberration of starlight
apparent displacement of a star from its true position, due to the combined effects of the speed of light and the speed of the earth in orbit around the sun (about 30 kps/18.5 mps).
zodiacal constellation a little south of the celestial equator near Pegasus. Aquarius is represented as a man pouring water from a jar. The sun passes through Aquarius from late February to early March.
  arc minute, arc second
units for measuring small angles, used in astronomy. An arc minute (symbol ') is one-sixtieth of a degree, and an arc second (symbol ") is one-sixtieth of an arc minute. Small distances in the sky, as between two close stars or the apparent width of a planet's dis'k, are expressed in minutes and seconds of arc.
zodiacal constellation in the northern hemisphere between Pisces and Taurus, near Auriga, represented as the legendary ram whose golden fleece was sought by Jason and the Argonauts. Its most distinctive feature is a curve of three stars of decreasing brightness. The brightest of these is Hamal or Alpha Arietis, 65 light-years from earth.
ancient navigational instrument, forerunner of the sextant. Astrolabes usually consisted of a flat disk with a sighting rod that could be pivoted to point at the sun or bright stars. From the altitude of the sun or star above the horizon, the local time could be estimated.
  astronomical unit
unit (symbol AU) equal to the mean distance of the earth from the sun: 149,597,870 km/92,955,800 mi. It is used to describe planetary distances. Light travels this distance in approximately 8.3 minutes.
use of photography in astronomical research. The first successful photograph of a celestial object was the daguerreotype plate of the moon taken by John W Draper (1811–1882) of the United States in March 1840. The first photograph of a star, Vega, was taken by U.S. astronomer William C. Bond (1789–1859) in 1850. Modern-day astrophotography uses techniques such as charge-coupled devices (CCDs).
study of the physical nature of stars, galaxies, and the universe. It began with the development of spectroscopy in the 19th century, which allowed astronomers to analyze the composition of stars from their light. Astrophysicists view the universe as a vast natural laboratory in which they can study matter under conditions of temperature, pressure, and density that are unattainable on earth.
constellation of the northern hemisphere, represented as a charioteer. Its brightest star is the first-magnitude Capella, about 45 light-years from earth; Epsilon Aurigae is an eclipsing binary star with a period of 27 years, the longest of its kind (last eclipse 1983).
colored light in the night sky near the earth's magnetic poles, called aurora borealis ("northern lights") in the northern hemisphere and aurora australis in the southern hemisphere. Although aurorae are usually restricted to the polar skies, fluctuations in the solar wind occasionally cause them to be visible at lower latitudes. Auroras are caused at heights of over 100 km/60 mi by a fast stream of charged particles from solar flares and low-density "holes" in the sun's corona.
  Bear, Great and Little
common names (and translations of the Latin) for the constellations Ursa Major and Ursa Minor respectively.
  Betelgeuse, or Alpha Orionis
red supergiant star in the constellation of Orion. It is the tenth brightest star in the night sky, although its brightness varies. It is 1,100 million km/700 million mi across, about 800 times larger than the sun, roughly the same size as the orbit of Mars. It is over 10,000 times as luminous as the sun, and lies 650 light-years from earth. Light takes 60 minutes to travel across the giant star.
  blue shift
a manifestation of the Doppler effect in which an object appears bluer when it is moving towards the observer or the observer is moving towards it (blue light is of a higher frequency than other colors in the spectrum). The blue shift is the opposite of the red shift.
constellation of the northern hemisphere represented by a herdsman driving a bear (Ursa Major) around the pole. Its brightest star is Arcturus (or Alpha Boötis), which is about 37 light-years from earth. The herdsman is assisted by the neighboring Canes Venatici, "the Hunting Dogs."
faintest of the zodiacal constellations (its brightest stars are fourth magnitude). It lies in the northern hemisphere between Leo and Gemini, and is represented as a crab. The sun passes through the constellation during late July and early August.
  Cape Canaveral
promontory on the Atlantic coast of Florida, U.S.A., 367 km/228 mi north of Miami, used as a rocket launch site by NASA.
zodiacal constellation in the southern hemisphere next to Sagittarius. It is represented as a fish-tailed goat, and its brightest stars are third magnitude. The sun passes through it late January to mid-February.
prominent constellation of the northern hemisphere, named for the mother of Andromeda. It has a distinctive W-shape, and contains one of the most powerful radio sources in the sky, Cassiopeia A. This is the remains of a supernova (star explosion) that occurred c.
A.D. 1702, too far away to be seen from earth.
  celestial mechanics
the branch of astronomy that deals with the calculation of the orbits of celestial bodies, their gravita-




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  tional attractions (such as those that produce the earth's tides), and also the orbits of artificial satellites and space probes. It is based on the laws of motion and gravity laid down by Isaac Newton.  
  Cepheid variable
yellow supergiant star that varies regularly in brightness every few days or weeks as a result of pulsations. The time that a Cepheid variable takes to pulsate isdirectly related to its average brightness; the longer the period, the brighter the star.
  charge-coupled device
(CCD) device for forming images electronically, using a layer of silicon that releases electrons when struck by incoming light. The electrons are stored in pixels and read off into a computer at the end of the exposure. CCDs have now almost entirely replaced photographic film for applications such as astrophotography where extreme sensitivity to light is paramount.
layer of mostly hydrogen gas about 10,000 km/6,000 mi deep above the visible surface of the sun (the photosphere). It appears pinkish red during eclipses of the sun.
  Comet Hale-Bopp
(C/1995 01) large and exceptionally active comet, which in March 1997 made its closest approach to earth since 2000
B.C., coming within 190 million km/118 million mi. It has a diameter of approximately 40 km/25 mi and an extensive gas coma (when close to the sun, Hale-Bopp released 10 metric tons/11 U.S. tons of gas every second). Unusually, Hale-Bopp has three tails: one consisting of dust particles, one of charged particles, and a third of sodium particles. Comet Hale-Bopp was discovered independently in July 1995 by two amateur U.S. astronomers, Alan Hale and Thomas Bopp.
  communications satellite
relay station in space for sending telephone, television, telex, and other messages around the world. Messages are sent to and from the satellites via ground stations. Most communications satellites are in geostationary orbit, appearing to hang fixed over one point on the earth's surface.
the alignment of two celestial bodies as seen from earth. A superior planet (or other object) is in conjunction when it lies behind the sun. An inferior planet (or other object) comes to inferior conjunction when it passes between the earth and the sun; it is at superior conjunction when it passes behind the sun. Planetary conjunction takes place when a planet is closely aligned with another celestial object, such as the moon, a star, or another planet.
faint halo of hot (about 2,000,000°C/ 3,600,000°F) and tenuous gas around the sun, which boils from the surface. It is visible at solar eclipses or through a coronagraph, an instrument that blocks light from the sun's brilliant disk. Gas flows away from the corona to form the solar wind.
  cosmic radiation
streams of high-energy particles from outer space, consisting of protons, alpha particles, and light nuclei, which collide with atomic nuclei in the earth's atmosphere, and produce secondary nuclear particles (chiefly mesons, such as pions and muons) that shower the earth.
path, against the background of stars, that the sun appears to follow each year as it is orbited by the earth. It can be thought of as the plane of the earth's orbit projected on to the celestial sphere (imaginary sphere around the earth). The ecliptic is tilted at about 23.5° with respect to the celestial equator, a result of the tilt of the earth's axis relative to the plane of its orbit around the sun.
the points in spring and autumn at which the sun's path, the ecliptic, crosses the celestial equator, so that the day and night are of approximately equal length. The vernal equinox occurs about March 21 and the autumnal equinox, September 23.
the sixth largest constellation, which meanders from the celestial equator deep into the southern hemisphere of the sky. Eridanus is represented as a river. Its brightest star is Achernar, a corruption of the Arabic for "the end of the river."
abbreviation for European Space Agency.
  escape velocity
minimum velocity with which an object must be projected for it to escape from the gravitational pull of a planetary body. In the case of the earth, the escape velocity is 11.2 kps/6.9 mps; the moon, 2.4 kps/1.5 mps; Mars, 5 kps/3.1 mps; and Jupiter, 59.6 kps/37 mps.
  European Space Agency
(ESA) organization of European countries (Austria, Belgium, Denmark, Finland, France, Germany, Ireland, Italy, the Netherlands, Norway, Spain, Sweden, Switzerland, and the U.K.) that engages in space research and technology. It was founded in 1975, with head-quarters in Paris.
  falling star
popular name for a meteor.
prominent zodiacal constellation in the northern hemisphere represented as the twins Castor and Pollux. Its brightest star is Pollux; Castor is a system of six stars. The sun passes through Gemini from late June to late July. Each December, the Geminid meteors radiate from Gemini.
  Great Bear
popular name for the constellation Ursa Major.
  Hale-Bopp, Comet
see Comet Hale-Bopp.
  Halley's comet
comet that orbits the sun about every 76 years, named for Edmond Halley, who calculated its orbit. It is the brightest and most conspicuous of the periodic comets. Recorded sightings go back over 2,000 years. It travels around the sun in the opposite direction to the planets. Its orbit is inclined at almost 20° to the main plane of the solar system and ranges between the orbits of Venus and Neptune. It will next reappear in 2061.
  Jodrell Bank
site in Cheshire, England, of the Nuffield Radio Astronomy Laboratories of the University of Manchester. Its largest instrument is the 76-m/250-ft radio dish (the Lovell Telescope), completed in 1957 and modified in 1970. An elliptical radio dish, measuring 38 × 25 m/125 × 82 ft and capable of working at shorter wave lengths, was introduced in 1964.
  Kennedy Space Center
NASA launch site on Merritt Island, near Cape Canaveral, Florida, used for Apollo and spaceshuttle launches. The first flight to land on the moon (1969) and Skylab, the first orbiting laboratory (1973), were launched here.
zodiacal constellation in the northern hemisphere, represented as a lion. The sun passes through Leo from mid-August




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  to mid-September. Its brightest star is first-magnitude Regulus at the base of a pattern of stars called the Sickle.  
faint zodiacal constellation on the celestial equator adjoining Scorpius, and represented as the scales of justice. The sun passes through Libra during November. The constellation was once considered to be a part of Scorpius, seen as the scorpion's claws.
the distance traveled by a beam of light in a vacuum in one year, approximately 9.46 trillion (million million) km/5.88 trillion miles.
  Local Group
a cluster of about 30 galaxies that includes our own, the Milky Way. Like other groups of galaxies, the Local Group is held together by the gravitational attraction among its members, and does not expand with the expanding universe. Its two largest galaxies are the Milky Way and the Andromeda galaxy; most of the others are small and faint.
volume of space, surrounding a planet, controlled by the planet's magnetic field, and acting as a magnetic "shell." The earth's magnetosphere extends 64,000 km/40,000 mi toward the sun, but many times this distance on the side away from the sun.
measure of the brightness of a star or other celestial object. The larger the number denoting the magnitude, the fainter the object. Zero or first magnitude indicates some of the brightest stars. Still brighter are those of negative magnitude, such as Sirius, whose magnitude is –1.46. Apparent magnitude is the brightness of an object as seen from earth; absolute magnitude is the brightness at a standard distance of 10 parsecs (32.6 light-years).
piece of rock or metal from space that reaches the surface of the earth, moon, or other body. Most meteorites are thought to be fragments from asteroids, although some may be pieces from the heads of comets. Most are stony, although some are made of iron and a few have a mixed rock-iron composition.
any natural satellite that orbits a planet. Mercury and Venus are the only planets in the solar system that do not have moons.
(acronym for National Aeronautics and Space Administration) U.S. government agency for space flight and aeronautical research, founded in 1958 by the National Aeronautics and Space Act. Its head-quarters are in Washington, D.C., and its main installation is at the Kennedy Space Center in Florida. NASA's early planetary and lunar programs included Pioneer spacecraft from 1958, which gathered data for the later crewed missions, the most famous of which took the first people to the moon in Apollo 11 on July 16–24, 1969.
a slight "nodding" of the earth in space, caused by the varying gravitational pulls of the sun and moon. Nutation changes the angle of the earth's axial tilt (average 23.5°) by about 9 seconds of arc to either side of its mean position, a complete cycle taking just over 18.5 years.
site or facility for observing astronomical or meteorological phenomena. The earliest recorded observatory was in Alexandria, north Africa, built by Ptolemy Soter in about 300
B.C.. The modern observatory dates from the invention of the telescope. Observatories may be groundbased, carried on aircraft, or sent into orbit as satellites, in space stations, and on the space shuttle.
the moment at which a body in the solar system lies opposite the sun in the sky as seen from the earth and crosses the meridian at about midnight.
path of one body in space around another, such as the orbit of earth around the sun, or the moon around earth. When the two bodies are similar in mass, as in a binary star, both bodies move around their common center of mass. The movement of objects in orbit follows Johann Kepler's laws, which apply to artificial satellites as well as to natural bodies.
very prominent constellation in the equatorial region of the sky, identified with the hunter of Greek mythology.
the change in the apparent position of an object against its background when viewed from two different positions. In astronomy, nearby stars show a shift owing to parallax when viewed from different positions on the earth's orbit around the sun. A star's parallax is used to deduce its distance from the earth. Nearer bodies such as the moon, sun, and planets also show a parallax caused by the motion of the earth. Diurnal parallax is caused by the earth's rotation.
a unit (symbol pc) used for distances to stars and galaxies. One parsec is equal to 3.2616 light-years, 2.063 × 10
5 astronomical units, and 3.086 × 1013 km.
visible surface of the sun, which emits light and heat. About 300 km/200 mi deep, it consists of incandescent gas at a temperature of 5,800K (5,530°C/9,980°F). Rising cells of hot gas produce a mottling of the photosphere known as granulation, each granule being about 1,000 km/620 mi in diameter. The photosphere is often marked by large, dark patches called sunspots.
inconspicuous zodiac constellation, mainly in the northern hemisphere between Aries and Aquarius, near Pegasus. It is represented as two fish tied together by their tails. The Circlet, a delicate ring of stars, marks the head of the western fish in Pisces. The constellation contains the vernal equinox, the point at which the sun's path around the sky (the ecliptic) crosses the celestial equator. The sun reaches this point around March 21 each year as it passes through Pisces from mid-March to late April.
  planetary nebula
shell of gas thrown off by a star at the end of its life. Planetary nebulae have nothing to do with planets. They were named by William Herschel, who thought their rounded shape resembled the disk of a planet. After a star such as the sun has expanded to become a red giant, its outer layers are ejected into space to form a planetary nebula, leaving the core as a white dwarf at the center.
an open star cluster about 400 light-years away in the constellation Taurus, represented as the Seven Sisters of Greek mythology. Its brightest stars (highly luminous, bluewhite giants only a few million years old) are visible to the naked eye, but there are many fainter ones.
slow wobble of the earth on its axis, like that of a spinning top. The gravitational pulls of the sun and moon




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  on the earth's equatorial bulge cause the earth's axis to trace out a circle on the sky every 25,800 years. The position of the celestial poles is constantly changing owing to precession, as are the positions of the equinoxes (the points at which the celestial equator intersects the sun's path around the sky). The precession of the equinoxes means that there is a gradual westward drift in the ecliptic—the path that the sun appears to follow—and in the coordinates of objects on the celestial sphere.  
  radar astronomy
bouncing of radio waves off objects in the solar system, with reception and analysis of the ''echoes." Radar contact with the moon was first made in 1945 and with Venus in 1961. The travel time for radio reflections allows the distances of objects to be determined accurately. Analysis of the reflected beam reveals the rotation period and allows the object's surface to be mapped. The rotation periods of Venus and Mercury were first determined by radar. Radar maps of Venus were obtained first by earth-based radar and subsequently by orbiting space probes.
  red shift
the lengthening of the wavelengths of light from an object as a result of the object's motion away from us. It is an example of the Doppler effect. The red shift in light from galaxies is evidence that the universe is expanding.
  Royal Greenwich Observatory
the national astronomical observatory of the UK, founded in 1675 at Greenwich, SE London, England, to provide navigational information for sailors. After World War II it was moved to Herstmonceux Castle, Sussex; in 1990 it was transferred to Cambridge. It also operates telescopes on La Palma in the Canary Islands, including the 4.2-m/165-in William Herschel Telescope, commissioned in 1987.
bright zodiac constellation in the southern hemisphere, represented as a centaur aiming a bow and arrow at neighbouring Scorpius. The sun passes through Sagittarius from mid-December to mid-January, including the winter solstice, when it is farthest south of the equator. The constellation contains many nebulae and globular clusters, and open star clusters. Kaus Australis and Nunki are its brightest stars. The center of our galaxy, the Milky Way, is marked by the radio source Sagittarius A.
any small body that orbits a larger one, either natural or artificial. Natural satellites that orbit planets are called moons.
bright zodiacal constellation in the southern hemisphere between Libra and Sagittarius, represented as a scorpion. The sun passes briefly through Scorpius in the last week of November. The heart of the scorpion is marked by the bright red supergiant star Antares. Scorpius contains rich Milky Way star fields, plus the strongest X-ray source in the sky, Scorpius X-1. The whole area is rich in clusters and nebulae.
navigational instrument for determining latitude by measuring the angle between some heavenly body and the horizon. It was invented in 1730 by John Hadley (1682–1744) and can be used only in clear weather.
  shooting star
popular name for a meteor.
in astrophysics, the point in space–time at which the known laws of physics break down. Singularity is predicted to exist at the center of a black hole, where infinite gravitational forces compress the infalling mass of a collapsing star to infinite density. It is also thought, according to the Big Bang model of the origin of the universe, to be the point from which the expansion of the universe began.
  solar wind
stream of atomic particles, mostly protons and electrons, from the sun's corona, flowing outwards at speeds of between 300 kps/200 mps and 1,000 kps/600 mps.
either of the days on which the sun is farthest north or south of the celestial equator each year. The summer solstice, when the sun is farthest north, occurs around June 21; the winter solstice around December 22.
  space, or outer space
the void that exists beyond earth's atmosphere. Above 120 km/75 mi, very little atmosphere remains, so objects can continue to move quickly without extra energy. The space between the planets is not entirely empty, but filled with the tenuous gas of the solar wind as well as dust specks.
dark patch on the surface of the sun, actually an area of cooler gas, thought to be caused by strong magnetic fields that block the outward flow of heat to the sun's surface. sunspots consist of a dark central umbra, about 4,000K (3,700°C/6,700°F), and a lighter surrounding penumbra, about 5,500K (5,200°C/9,400°F). They last from several days to over a month, ranging in size from 2,000 km/1,250 mi to groups stretching for over 100,000 km/62,000 mi.
conspicuous zodiacal constellation in the northern hemisphere near Orion, represented as a bull. The sun passes through Taurus from mid-May to late June.
small, rounded glassy stone, found in certain regions of the earth, such as Australasia. Tektites are probably the scattered drops of molten rock thrown out by the impact of a large meteorite.
largest moon of the planet Saturn, with a diameter of 5,150 km/3,200 mi and a mean distance from Saturn of 1,222,000 km/759,000 mi. It was discovered in 1655 by Dutch mathematician and astronomer Christiaan Huygens, and is the second largest moon in the solar system (Ganymede, of Jupiter, is larger).
abbreviation for unidentified flying object.
  unidentified flying object, or UFO
any light or object seen in the sky whose immediate identity is not apparent. Despite unsubstantiated claims, there is no evidence that UFOs are alien spacecraft. On investigation, the vast majority of sightings turn out to have been of natural or identifiable objects, notably bright stars and planets, meteors, aircraft, and satellites, or to have been perpetrated by pranksters. The term flying saucer was coined in 1947.
  Ursa Major
(Latin "Great Bear") the third largest constellation in the sky, in the north polar region. Its seven brightest stars make up the familiar shape, or asterism, of the Big Dipper0. The second star of the handle of the dipper, called Mizar, has a companion star, Alcor. Two stars forming the far side of the bowl act as pointers to the north star, Polaris. Dubhe, one of them, is the constellation's brightest star.




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  Ursa Minor
(Latin "Little Bear") or Little Dipper small constellation of the northern hemisphere. It is shaped like a dipper, with the bright north pole star Polaris at the end of the handle.
  Van Allen radiation belts
two zones of charged particles around the earth's magnetosphere, discovered in 1958 by U.S. physicist James Van Allen. The atomic particles come from the earth's upper atmosphere and the solar wind, and are trapped by the earth's magnetic field. The inner belt lies 1,000–5,000 km/620–3,100 mi above the equator, and contains protons and electrons. The outer belt lies 15,000–25,000 km/9,300–15,500 mi above the equator, but is lower around the magnetic poles. It contains mostly electrons from the solar wind.
zodiacal constellation of the northern hemisphere, the second largest in the sky. It is represented as a maiden holding an ear of wheat, marked by first-magnitude Spica, Virgo's brightest star. The sun passes through Virgo from late September to the end of October.
uppermost point of the celestial horizon, immediately above the observer; the nadir is below, diametrically opposite.
  Further Reading  
  Chown, Marcus Afterglow of Creation (1993)  
  Clark, Stuart Universe in Focus (1997)  
  Gleiser, Marcelo The Dancing Universe: From Creation Myths to the Big Bang (1998)  
  Gribbin, John In Search of the Big Bang (1986), In the Beginning (1993), In Search of the Edge of Time (1992), Companion to the Cosmos (1996), Time and Space (with Mary Gribbin, 1994)  
  Gribbin, John, and Rees, Martin The Stuff of the Universe (1990)  
  Harrington, Philip Eclipse (1997)  
  Hogan, Craig The Little Book of the Big Bang: a Cosmic Primer (1998)  
  Illingworth, Valerie Macmillan Dictionary of Astronomy (1988)  
  King, Henry History of the Telescope (1955)  
  Lewis, H. A. Times Atlas of the Moon (1969)  
  Lovell, Bernard The Story of Jodrell Bank (1968)  
  Mather, John C. The Very First Light: The True Inside Story of the Scientific Journey Back to the Dawn of the Universe (1996)  
  Mitton, Jacqueline Concise Dictionary of Astronomy (1991), Penguin Dictionary of Astronomy (1993)  
  Moore, Patrick Atlas of the Universe (1970), The Amateur Astronomer (1970), Guide to the Planets (1976), Guide to Comets (1977), Exploring the Night Sky with Binoculars (1986), The Guinness Book of Astronomy (1992)  
  Muirden, James Astronomy with a Small Telescope (1985)  
  Nahin, Paul Time Machines (1993)  
  Nicolson, Iain Heavenly Bodies: Beginner's Guide to Astronomy (1995 )  
  North, John Astronomy and Cosmology (1994)  
  Norton, Arthur Philip Norton's 2000 (1989)  
  Overbye, Dennis Lonely Hearts of the Cosmos (1991)  
  Phillips, Kenneth Guide to the sun (1992)  
  Plant, Malcolm Dictionary of Space (1986)  
  Ronan, C. A. The Natural History of the Universe (1994 )  
  Rycroft, Michael (ed.) The Cambridge Encyclopedia of Space (1990)  
  Schweighauser, Charles A. Astronomy from A to Z: A Dictionary of Celestial Objects and Ideas (1991)  
  Sheehan, William The Planet Mars: A History of Observation and Discovery (1996)  
  Smith, Robert The Expanding Universe 1900–31 (1982)  
  Sullivan, Walter We Are Not Alone (1970)  
  Tayler, Roger The Hidden Universe (1991)  
  Whipple, Fred Orbiting the sun: Planets and Satellites of the Solar System (1981)  
  Will, Clifford Was Einstein Right? (1986)