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Laplace, Pierre Simon, marquis de

(Encyclopedia)Laplace, Pierre Simon, marquis de pyĕr sēmôNˈ märkēˈ də läpläsˈ [key], 1749–1827, French astronomer and mathematician. At 18 he went to Paris, proved his gift for mathematical analysis to...

Tethys , in astronomy

(Encyclopedia)Tethys tēˈthĭs [key], in astronomy, one of the named moons, or natural satellites, of Saturn. Also known as Saturn III (or S3), Tethys is 659 mi (1060 km) in diameter, orbits Saturn at a mean dista...

Djilas, Milovan

(Encyclopedia)Djilas, Milovan mēˈləvän jēˈläs [key], 1911–95, Yugoslav political leader and writer, b. Montenegro. A Communist party member from 1932, he helped Josip Broz Tito organize volunteers to fight...

Brahe, Tycho

(Encyclopedia)Brahe, Tycho tīˈkō brä [key], 1546–1601, Danish astronomer. The most prominent astronomer of the late 16th cent., he paved the way for future discoveries by improving instruments and by his prec...

Musk, Elon

(Encyclopedia)Musk, Elon ēˈlŏn [key], 1971–, American business executive and entrepreneur, b. Pretoria...

Hubble Space Telescope

(Encyclopedia)Hubble Space Telescope (HST), the first large optical orbiting observatory. Built from 1978 to 1990 at a cost of $1.5 billion, the HST (named for astronomer E. P. Hubble) was expected to provide the c...

Iapetus, in astronomy

(Encyclopedia)Iapetus īăpˈĭtəs [key], in astronomy, one of the named moons, or natural satellites, of Saturn. Also known as Saturn VIII (or S8), Iapetus is 907 mi (1460 km) in diameter, orbits Saturn at a mean...

celestial mechanics

(Encyclopedia)celestial mechanics, the study of the motions of astronomical bodies as they move under the influence of their mutual gravitation. Celestial mechanics analyzes the orbital motions of planets, dwarf pl...

satellite, natural

(Encyclopedia)satellite, natural, celestial body orbiting a planet, dwarf planet, asteroid, or star of a larger size. The most familiar natural satellite is the earth's moon; thus, satellites of other planets are o...

day

(Encyclopedia)day, period of time for the earth to rotate once on its axis. The ordinary day, or solar day, is measured relative to the sun, being the time between successive passages of the sun over a stationary o...