A

English astronomer and mathematician who, at the age of 24, was the first person to predict the position of a planetary mass beyond Uranus. But, unfortunately, Adams did not publish his prediction. Galle confirmed the existence of Neptune based on independent calculations done by Le Verrier.

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Aldrin, Edwin (Buzz)  (1930- )

The American astronaut piloted the lunar module of Apollo 11 and on July 20, 1969, became the second man to walk on the moon. Aldrin was an engineer by training and an elder of the Presbyterian Church. In November 1966, he had made a record 5-hour space walk during the Gemini 12 mission.

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French astronomer and physicist and Director of the Paris Observatory, who discovered the phenomenon of the production of magnetism by rotation.

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Aristarchus of Samos  (about 320-250 BC)

Greek astronomer who, using geometry, measured the distance between the Sun and Moon. He used this to calculate that the sun was 20 times farther away than the moon (it is actually 400 times farther). He also suggested that because the Sun was seven bigger than Earth ( it is actually 109 times bigger), Earth must travel around the Sun. It was 18 centuries before this idea started to become accepted.

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Philosopher in ancient Greece. He developed a great educational outline called “Aristoteles outline” and he is called as the “founder of universal education”. His idea of Universe was that, celestial spheres are rotating around Earth. This is called as the geocentric theory.

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American air force test pilot who, as commander of the Apollo 11 mission, was the first man to walk on the Moon on July 20, 1969. As he stepped onto the Moon he said "That's one small step for man, one giant leap for mankind." He left NASA in 1971 and became a university professor before going into business.

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d'Arrest, Heinrich Louis

Danish astronomer who assisted Galle with the first observations of Neptune. After receiving its predicted position from Le Verier, Galle and d'Arrest began searching. With Galle at the eyepiece and d'Arrest reading the chart, they scanned the sky and checked that each star seen was actually on the chart. Just a few minutes after their search began, d'Arrest cried out, "That star is not on the map!" and earned his place in the history books.

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B

Emigrating to the US from Germany in 1931, Baade worked at Mount Wilson Observatory in California and in 1948 moved to nearby Palomar Observatory. In 1943 he discovered that the universe contains two types of stars: very old ones containing few metals, and newer ones rich in metals. This also applied to the Cepheid variable stars, whose properties can be used to help calculate the size of the universe. The universe was then found to be twice as big as previously thought.

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American astronomer; discovered Jupiter's satellite Amalthea and Barnard's star, the second-nearest star system to the Sun.

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Bessel, Friedrich  (1784-1846)

German astronomer who supervised the construction of a new observatory at Königsberg and became its first director in 1813. He concentrated on measuring the exact positions of stars. In 1838 he observed the slight movement of the star 61 Cygni, movement he knew to be caused by viewing it when Earth is at opposite points on its orbit around the Sun. From this, he calculated that the star was 10.3 light-years away. This was the first star to have its distance measured by parallax, and helped establish a scale for the universe.

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German astronomer, known for the bogus "Bode's Law" which attempts to explain the sizes of the planetary orbits.

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One of the earliest American astronomers of note; rose from poverty and overcame a lack of formal education to become the first director of the Harvard College Observatory where he studied Saturn and (with Lassell) discovered its moon Hyperion.

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Brahe, Tycho (a.k.a. Ottensen, Tyge)  (1546-1601)

Danish astronomer whose accurate astronomical observations formed the basis for Johannes Kepler's laws of planetary motion. At the age of 30, Brahe's astronomical talents were such that King Frederick II of Denmark gave him the Baltic island of Hven on which to build an observatory. Brahe's instruments were well made and accurate, and he measured the position of the sun Sun and planets against the stars for more than 20 years. Between 1572 and 1574, he recorded a new star - a supernova - in the distance to the great comet of 1577 and showed that it was farther away than the Moon, and that it had an elongated orbit that passed the planets. He moved to Prague in 1597 and recruited Johannes Kepler as his assistant. Kepler used Brahe's results to calculate the orbits of the planets.

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British astronomer who, as a research student at Cambridge, discovered pulsars. On August 6, 1967, while observing the rapid variations in signals from radio sources and looking for quasars, she discovered an unusual radio signal consisting of a rapid series of pulses that occurred precisely every 1.337 seconds. This turned out to be a pulsating neutron star (a pulsar), a star slightly more massive than the Sun but only a few kilometers in diameter.

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C

American astronomer who classified the spectra of more than 300,000 stars into a temperature sequence. She joined the staff of Harvard College Observatory in 1896 and stayed there until she retired in 1940. Her work was cornerstone of the Henry Draper Catalog of stellar spectra.

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Cassini, Giovanni Domenico (a.k.a. Dominique, Jean)  (1625-1712)

Italian-born French astronomer. As professor of astronomy at the University of Bologna, Cassini measured the time it takes Jupiter, Venus, and Mars to spin once on their axes. He also discovered four of Saturn's satellites (Tethys, Dione, Rhea, and Iapetus) and a gap in that planet's rings. Cassini suggested that the rings were not solid but made of individual rocks. In 1669, he moved to France to help build and run the Royal Observatory in Paris. There he measured the distance between Earth and Mars and used this to calculate the Sun-Earth distance. However, he refused to accept that Earth went around the sun or that gravity was universal. Both his son and grandson became directors of the Paris Observatory.

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Indian-born astrophysicist who studied astronomy in Madras and England before moving to the US in 1936. He received the 1983 Nobel Prize for Physics for his work on dying stars. Chandrasekhar realized that a white dwarf star with more than 1.4 times the Sun's mass could stop shrinking: It would become a neutron star or a black hole.

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Discoverer of Pluto's moon Charon.

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Clarke, Arthur C.  (1917- )

In 1945, this British science fiction writer suggested that a satellite in geostationary orbit, 35,800km above Earth, would be useful for communications. One satellite above the Atlantic could be used to transmit TV and telephone signals between Europe and North America. The technology was not available then, but geostationary satellites are now commonplace.

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Polish astronomer who advanced the heliocentric theory that the Earth and other planets revolve around the Sun. This was highly controversial at the time as the Ptolemaic view of the universe, which was the prevailing theory for over 1000 years, was deeply ingrained in the prevailing philosophy and religion. (It should be noted, however, that the heliocentric idea was first put forth by Aristarchus of Samos in the 3rd century BC, a fact known to Copernicus but long ignored.) Copernicus studied mathematics and classics in Poland and law and astronomy in Italy. He returned to Poland in 1506 to become a canon at Frauenberg Cathedral, a post he held until he died. His duties were light and he devoted most of his time to astronomy. By about 1513 he had realized that Earth was not the center of the universe or even of the solar system. Earth, which went around the Sun, was not special as had been thought, but merely one of a collection of planets. He was aware that his idea went against the teachings of the church, and his book De Revolutionibus Orbuim Coelestrium was not published until he was on his deathbed.

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D

American radio astronomer who, in 1960, pioneered the use of radio telescopes to listen for signals from extraterrestrial life. In 1974 this project continued with the use of the Arecibo radio telescope in Puerto Rico. Drake also devised an equation to estimate how many communicating technological civilizations there might be in the Galaxy at any one time.

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E

Eddington, Arthur  (1882-1944)

English Astronomer who showed how the physical characteristics inside a star can be calculated from its surface features. After studying at Cambridge, Eddington worked at the Royal Observatory in Greenwich before returning to Cambridge to become director of its observatory for 31 years. Eddington produced a model of the interior of a star, discovered the relationship between a star's mass and its luminosity, stressed that nuclear fusion produced stellar energy, and measured how much a ray of light is bent by a gravitational field. He also calculated the mass of the universe, arguing that constants, such as the velocity of light, depended on it. A skillful writer, he popularized both astronomy and Einstein's general theory of relativity.

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American physicist born in Germany. He was the first person to succeed in dealing the whole universe theoretically. Einstein received the Nobel Prize for Physics in 1921 for explaining how light is radiated in packets of energy called quanta, but he is best remembered for his theories of relativity. In 1905, he introduced special theory of relativity, and in 1916, introduced general theory of relativity. These showed that nothing could move faster than the velocity of light (c), that is velocity was constant, and that objects became more massive as they moved faster. Einstein found that mass (m) was equivalent to energy (E) according to his now famous equation E = mc². He also realized that gravitational fields can bend light beams and change their wavelengths. Einstein was a life-long pacifist and in 1933 moved to America to avoid Nazi persecution as a Jew. In 1952 he turned down the offer to be president of Israel. Einstein's theory of relativity, together with Quantum theory, forms the base of present cosmology.

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Greek scholar who calculated the size of Earth. Born in north Africa, Eratosthenes was educated in Athens and then became librarian at Alexandria in Egypt and the tutor of the son of King Ptolemy III of Egypt. He was, among other things, a skilled geographer who calculated the curvature of Earth. He did this by measuring the length of shadow cast by the sun at two places 950 km apart. From this he estimated the circumference of Earth to be 46,500km (it is actually 40,075 km at the equator).

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Eudoxus of Cnidus  (about 408-355 BC)

A Greek astronomer and mathematician who constructed a model of the solar system with Earth at it's center and the planets carried around Earth, supported on a series of transparent spheres. The spheres were nested inside each other, with the axis of each sphere attached to the inside of the surrounding sphere. His model was able to explain the motion of planets as viewed from Earth, but it did not account for everyday changes that occur in the distances between Earth and individual planets. It was replaced after a few centuries.

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F

As England's first Astronomer Royal, Flamsteed was in charge of the new Roayl Observatory at Greenwich near London, which opened in 1676. He used a mural arc and a sextant with telescopic sights in conjunction with the new, accurate clocks that ran for a year to produce a new catalog of 3,000 stars. This was published after he died, in 1725, and the accuracy of the star positions was 15 times better than previous catalogs. Flamsteed also made detailed studies of the shape of the orbits of both the Moon and Earth.

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A Bavarian glass and lens maker, Fraunhofer tried to make a lens that did not disperse light into its rainbow of colors. In 1814, while testing this lens, he noticed that the Sun's spectrum was crossed by numerous fine dark lines. He measured the wavelengths of 324 of the 54 lines that he could see: They are now known as Fraunhofer lines. In the 1820s he found that light could be split into colors by passing it through a grating of fine slits, and that the splitting increased as the slits were moved closer together. Gratings are now used extensively in spectroscopy.

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G

Gagarin, Yuri  (1934-1968)

On April 12, 1961, the Russian cosmonaut Gagarin became the first person to fly in space. The first lasted one orbit of Earth; the Vostok 1 spaceship reached a height of 344km. Gagarin was airborne for 108 minutes before the retrorockets slowed him down and he parachuted the last 7km to the ground. He died in a plane crash while training to return to space.

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Astronomer and physicist from Italy. He is called as the father of modern science. By studying dynamics he approved, law of inertia, constant acceleration of falling object, and the route of a projectile are always describes a parabola. IN 1609, he invented Galilei telescope, and he was the first man to observe universe through a telescope. He found satellites of Jupiter, craters on the Moon, Blackspots on the Sun, etc. He is famous for emphasizing heliocentric theory. He became confident of his idea when he observed the motion of 4 biggest satellites of Jupiter. As professor of mathematics at the universities of Pisa and Padua, Galileo did much to disprove ancient Greek theories of physics. On learning of the invention of the telescope, he built one in 1609 and discovered that the Sun spun around every 25 days, the Moon was mountainous, Jupiter had four satellites, and Venus showed Moonlike phases. The Venus observations helped prove that the Sun and not Earth was at the center of the solar system. These revolutionary ideas, coupled with his belligerent nature and love of publicity, got him into trouble with the church, and late in life he was tried by the Inquisition in Rome and placed under house arrest.

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German astronomer who, with Heinrich Louis d'Arrest, made the first observation of Neptune based on calculations by Le Verrier. Though Galle was the first to observe Neptune, its discovery is usually credited to Adams (who made an earlier calculation) and Le Verrier.

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Gamow, George  (1904-1968)

Ukrainian physicist who in 1933 defected to the US. In 1948, with Ralph Alpher (1921- ) and Hans Bethe (1906- ), he showed how helium could be produced during the Big Bang from protons and neutrons, and how helium could combine with other nuclei to create elements. Gamow also predicted that the universe would be filled with radiation remaining from the intense temperatures that existed during the Big Bang.

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In 1962, Glenn was the first American to orbit Earth; he made three orbits during a 5-hour flight. After retiring from the space program in 1964 he took up politics, and in 1974 was elected senator in Ohio. In 1998, he became the world's oldest astronaut when he flew on a space shuttle mission.

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Goddard was a rocket pioneer whose work was mainly ignored by his own country. From an early age he was fascinated by the idea of space travel, and he carried out experiments at Clark University in Massachusetts, where he was a research student and, for 30 years, a lecturer in physics. In 1919, he published his theories of Konstantin Tsiolkocsky two decades earlier. In the 1930s he launched his first stabilized rocket. This had a liquid-fuel motor that pumped oil and liquid oxygen into a combustion chamber. Its success attracted funding and Goddard went on to produce rockets with gyroscopic control and jet vanes.

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Guth, Alan  (1947- )

American particle physicist who turned to cosmology. He devised the theory of inflation in 1979, in which he proposed that just after the Big Bang the universe expanded from the size of a proton to the size of a grapefruit in a tiny fraction of a second. This both smoothed out space-time and made a universe that looks the same in all directions.

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