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Roche limit

(Encyclopedia)Roche limit, the closest distance that a celestial body held together only by its own gravity can come to a planet without being pulled apart by the planet's tidal (gravitational) force. This distance...

Korolev, Sergei Pavlovich

(Encyclopedia)Korolev, Sergei Pavlovich, 1907–66, Soviet rocket designer. His role as chief designer of the Soviet space program was revealed only after his death. After he successfully launched two intercontinen...

Arecibo Observatory

(Encyclopedia)Arecibo Observatory, radio-astronomy facility located near Arecibo, Puerto Rico, part of the National Astronomy and Ionosphere Center. Conceived by, designed by, and built under the supervision of Wil...

direction finder

(Encyclopedia)direction finder, electronic device used to determine the position of a ship or aircraft. In a simple direction finder a radio receiver is equipped with a revolving directional antenna. The antenna re...

Eris, in astronomy

(Encyclopedia)Eris, in astronomy, the largest known dwarf planet. Eris, whose highly eccentric elliptical orbit ranges from 38 AU to 97 AU and is inclined more than 44°, is the largest known object of the Kuiper b...

Hyperion, in astronomy

(Encyclopedia)Hyperion hīpērˈēən [key], in astronomy, one of the named moons, or natural satellites, of Saturn. Also known as Saturn VII (or S7), Hyperion is the largest highly irregular (nonspherical) body in...

Phoebe, in astronomy

(Encyclopedia)Phoebe fēˈbē [key], in astronomy, one of the named moons, or natural satellites, of Saturn. Also known as Saturn IX (or S9), Phoebe is 137 mi (220 km) in diameter, orbits Saturn at a mean distance ...

Prometheus, in astronomy

(Encyclopedia)Prometheus prōmēˈthēəs [key], in astronomy, one of the named moons, or natural satellites, of Saturn. Also known as Saturn XVI (or S16), Prometheus is an irregularly shaped (nonspherical) body me...

Dione, in astronomy

(Encyclopedia)Dione dīōˈnē [key], in astronomy, one of the named moons, or natural satellites, of Saturn. Also known as Saturn IV (or S4), Dione is 695 mi (1,120 km) in diameter, orbits Saturn at a mean distanc...

Enceladus

(Encyclopedia)Enceladus ĕnsĕlˈədəs [key], in astronomy, one of the named moons, or natural satellites, of Saturn. Also known as Saturn II (or S2), Enceladus is 310 mi (500 km) in diameter, orbits Saturn at a m...