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astronomy
Science dealing with the origin, evolution, composition, distance, and motion of all bodies and scattered matter in the universe. The most ancient of the sciences, it has existed since the dawn of recorded civilization. Much of the earliest knowledge of celestial bodies is often credited to the Babylonians. The ancient Greeks introduced influential cosmological ideas, incl. theories about the earth in relation to the rest of the universe. Ptolemy's model of an earth-centered universe (2nd cent. AD) influenced astronomical thought for over 1,300 years. In the 16th cent., N. Copernicus assigned the central position to the sun (see Copernican system), ushering in the age of modern astronomy. The 17th cent. saw several momentous developments: J. Kepler's discovery of the principles of planetary motion, Galileo's application of the telescope to astronomical observation, and I. Newton's formulation of the laws of motion and gravitation. In the 19th cent., spectroscopy and photography made it possible to study the physical properties of planets, stars, and nebulae, leading to the development of astrophysics. In 1927 E. Hubble discovered that the universe, hitherto thought static, was expanding. In 1937 the first radio telescope was built. The first man-made satellite, Sputnik, was launched in 1957, and the first deep-space probes (see Pioneer) were launched in the 1960s. See also big bang, cosmology, gamma-ray astronomy, infrared astronomy, radio and radar astronomy, ultraviolet astronomy, X-ray astronomy.
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