plan·et (pl n t)n.1. A nonluminous celestial body larger than an asteroid or comet, illuminated by light from a star, such as the sun, around which it revolves. In the solar system there are nine known planets: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto. 2. One of the seven celestial bodies, Mercury, Venus, the moon, the sun, Mars, Jupiter, and Saturn, visible to the naked eye and thought by ancient astronomers to revolve in the heavens about a fixed Earth and among fixed stars. 3. One of the seven revolving astrological celestial bodies that in conjunction with the stars are believed to influence human affairs and personalities.
[Middle English, from Old French planete, from Late Latin plan ta, from Greek plan t s, variant of plan s, plan t-, from plan sthai, to wander; see pel -2 in Indo-European roots.] Planets of the Solar SystemListed below are the nine planets that have been identified in our solar system and their respective satellites. The sidereal period of a planet is the amount of time required for that planet to make one revolution about the sun with respect to the stars. The rotational period of a planet is the amount of time required for the planet to perform one complete rotation about its own axis. If the planet rotates on its axis in a manner opposite to that of Earth, the rotation is called retrograde and the number is given with a - sign in front of it. PLANETS: PHYSICAL PROPERTIES| PLANET | EQUATORIAL RADIUS: | MASS: x 1024 kilograms | SIDEREAL PERIOD: days | ROTATIONAL PERIOD: days | AVERAGE SURFACE TEMPERATURE: | MEAN DISTANCE FROM SUN: |
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| kilometers | miles | degrees Celsius | degrees Fahrenheit | x 106 kilometers | x 106 miles |
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| Mercury | 2,440 | 1,516 | 0.3302 | 87.97 | 58.6462 | 179 | 354 | 57.909 | 35.983 | | Venus | 6,052 | 3,761 | 4.869 | 224.7 | -243.01 | 453 | 847 | 108.21 | 67.239 | | Earth | 6,378.14 | 3,963 | 5.9742 | 365.2564 | 0.99727 | 7.9 | 46 | 149.5979 | 92.956 | | Mars | 3,397 | 2,111 | 0.64191 | 686.98 | 1.025957 | -63 | -81 | 227.941 | 141.63 | | Jupiter | 71,492 | 44,423 | 1,899.00 | 4,332.71 | 0.41354 | -153 | -244 | 778.332 | 483.63 | | Saturn | 60,268 | 37,449 | 568.8 | 10,759.22 | 0.4375 | -185 | -301 | 1,426.98 | 886.69 | | Uranus | 25,559 | 15,882 | 86.6 | 30,685.40 | -0.65 | -215 | -355 | 2,870.99 | 1,783.95 | | Neptune | 24,764 | 15,388 | 102.78 | 60,189.00 | 0.768 | -225 | -373 | 4,497.072 | 2,794.36 | | Pluto | 1,151 | 715 | 0.013 | 90,780.80 | -6.3872 | -236 | -393 | 5,913.514 | 3,674.5 |
PLANETARY SATELLITES| IN ALPHABETICAL ORDER | BY PLANET, FROM NEAREST SATELLITE TO FURTHEST SATELLITE |
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| Satellite | Planet, Orbital Order | Satellite | Planet, Orbital Order | Planet | Satellite | Planet | Satellite |
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| Adrastea | Jupiter, 2 | Leda | Jupiter, 9 | Earth | Moon | | Rhea | | Amalthea | Jupiter, 3 | Lysithea | Jupiter, 11 | Mars | Phobos | | Titan | | Ananke | Jupiter, 13 | Metis | Jupiter, 1 | | Deimos | | Hyperion | | Ariel | Uranus, 12 | Mimas | Saturn, 6 | Jupiter | Metis | | Iapetus | | Atlas | Saturn, 2 | Miranda | Uranus, 11 | | Adrastea | | Phoebe | | Belinda | Uranus, 9 | Moon | Earth | | Amalthea | Uranus | Cordelia | | Bianca | Uranus, 3 | Naiad | Neptune, 1 | | Thebe | | Ophelia | | Callisto | Jupiter, 8 | Nereid | Neptune, 8 | | Io | | Bianca | | Calypso** | Saturn, 8 | Oberon | Uranus, 15 | | Europa | | Cressida | | Carme | Jupiter, 14 | Ophelia | Uranus, 2 | | Ganymede | | Desdemona | | Charon | Pluto | Pan | Saturn, 1 | | Callisto | | Juliet | | Cordelia | Uranus, 1 | Pandora | Saturn, 4 | | Leda | | Portia | | Cressida | Uranus, 4 | Pasiphae | Jupiter, 15 | | Himalia | | Rosalind | | Deimos | Mars, 2 | Phobos | Mars, 1 | | Lysithea | | Belinda | | Desdemona | Uranus, 5 | Phoebe | Saturn, 14 | | Elara | | Puck | | Despina | Neptune, 3 | Portia | Uranus, 7 | | Ananke | | Miranda | | Dione*** | Saturn, 9 | Prometheus | Saturn, 3 | | Carme | | Ariel | | Elara | Jupiter, 12 | Proteus | Neptune, 6 | | Pasiphae | | Umbriel | | Enceladus | Saturn, 7 | Puck | Uranus, 10 | | Sinope | | Titania | | Epimetheus* | Saturn, 5 | Rhea | Saturn, 10 | Saturn | Pan | | Oberon | | Europa | Jupiter, 6 | Rosalind | Uranus, 8 | | Atlas | (unofficial name) | Caliban | | Galatea | Neptune, 4 | Sinope | Jupiter, 16 | | Prometheus | (unofficial name) | Sycorax | | Ganymede | Jupiter, 7 | Telesto** | Saturn, 8 | | Pandora | Neptune | Naiad | | Helene*** | Saturn, 9 | Tethys** | Saturn, 8 | | Epimetheus* | | Thalassa | | Himalia | Jupiter, 10 | Thalassa | Neptune, 2 | | Janus* | | Despina | | Hyperion | Saturn, 12 | Thebe | Jupiter, 4 | | Mimas | | Galatea | | Iapetus | Saturn, 13 | Titan | Saturn, 11 | | Enceladus | | Larissa | | Io | Jupiter, 5 | Titania | Uranus, 14 | | Tethys** | | Proteus | | Janus* | Saturn, 5 | Triton | Neptune, 7 | (Trojan) | Telesto** | | Triton | | Juliet | Uranus, 6 | Umbriel | Uranus, 13 | (Trojan) | Calypso** | | Nereid | | Larissa | Neptune, 5 | | | | Dione*** | Pluto | Charon | | | | | | (Trojan) | Helene*** | | |
*The satellites Epimetheus and Janus orbit so closely together that gravitational interactions cause them to regularly exchange orbits. **The satellites Tethys, Telesto, and Calypso have been determined to be the same distance from Saturn to within current experimental accuracy. ***The satellites Dione and Helene have been determined to be the same distance from Saturn to within current experimental accuracy. Copyright © 2000 by Houghton Mifflin Company |
planet Noun any of the nine celestial bodies, Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, or Pluto, that revolve around the sun in oval-shaped orbits [Greek planaein to wander] planetary adj
planet (pl n t) A large celestial body, smaller than a star but larger than an asteroid, that does not produce its own light but is illuminated by light from the star around which it revolves. In our solar system there are nine known planets: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto. Because of Pluto's small size  about two-thirds the diameter of Earth's moon  and its unusual orbit, many astronomers believe it should actually be classed as a Kuiper belt object rather than a planet. A planetlike body with more than about ten times the mass of Jupiter would be considered a brown dwarf rather than a planet. See also extrasolar planetinner planetouter planet
planetary adjective |
ThesaurusLegend: Synonyms Related Words Antonyms | Noun | 1. | planet - (astronomy) any of the nine large celestial bodies in the solar system that revolve around the sun and shine by reflected light; Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto in order of their proximity to the sun; viewed from the constellation Hercules, all the planets rotate around the sun in a counterclockwise directionastronomy, uranology - the branch of physics that studies celestial bodies and the universe as a whole biosphere - the regions of the surface and atmosphere of the Earth (or other planet) where living organisms exist inferior planet - any of the planets whose orbit lies inside the earth's orbit gas giant, Jovian planet - any of the four outermost planets in the solar system; much larger than Earth and gaseous in nature (like Jupiter) outer planet - (astronomy) a major planet whose orbit is outside the asteroid belt (Jupiter, Saturn, Uranus, Neptune, Pluto) solar system - the sun with the celestial bodies that revolve around it in its gravitational field superior planet - any of the planets whose orbit lies outside the earth's orbit terrestrial planet - a planet having a compact rocky surface like the Earth's; the four innermost planets in the solar system | | 2. | planet - a person who follows or serves anotherfollower - a person who accepts the leadership of another | | 3. | planet - any celestial body (other than comets or satellites) that revolves around a star |
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