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Mercury, in astronomy

(Encyclopedia)Mercury, in astronomy, nearest planet to the sun, at a mean distance of 36 million mi (58 million km); its period of revolution is 88 days. Mercury passes through phases similar to those of the moon a...

Epimetheus, in astronomy

(Encyclopedia)Epimetheus, in astronomy, one of the named moons, or natural satellites, of Saturn. Also known as Saturn XI (or S11), Epimetheus is an irregularly shaped (nonspherical) body measuring about 89 mi (144...

radar astronomy

(Encyclopedia)radar astronomy, application of radar to the determination of distances and planetary features within the solar system, such as rotation rates. A short burst of radio waves is transmitted in the direc...

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 ...

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...

astronomy

(Encyclopedia)astronomy, branch of science that studies the motions and natures of celestial bodies, such as planets, stars, and galaxies; more generally, the study of matter and energy in the universe at large. ...

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...

Vesta, in astronomy

(Encyclopedia)Vesta vĕsˈtə [key], in astronomy, the fourth asteroid to be discovered. It was found in 1807 by H. Olbers. It is the third largest asteroid in size, with a diameter of c.326 mi (525 km). Its averag...

Hyades, in astronomy

(Encyclopedia)Hyades hīˈədēz [key], in astronomy, open star cluster in the constellation Taurus, located immediately to the right of the bright star Aldebaran. The cluster is about 130 light-years from the eart...