Planet, any major celestial body that orbits a star and does not emit visible light of its own but instead shines by reflected light. Smaller bodies that also orbit a star and are not satellites of a planet are called asteroids or planetoids. In the solar system, there are nine planets: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto. Planets that orbit stars other than the Sun are collectively called extrasolar planets. Some extrasolar planets are nearly large enough to become stars themselves. Such borderline planets are called brown dwarfs. See also Planetary Science.
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The distance between the sun and the earth varies because the earth travels in an elliptical rather than circular orbit. The distance is r... -
Galaxy, a massive ensemble of hundreds of millions of stars, all gravitationally interacting, and orbiting about a common center. Astronomer... -
Ecliptic, in astronomy, the apparent great-circle annual path of the sun in the celestial sphere , as seen from the earth . It is so named b...