| planet | an outer gear that revolves about a central sun gear of an epicyclic train |
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| planet | (astrology) one of 12 equal areas into which the zodiac is divided |
| planet | a nebula that was once thought to be a star with its planets but is now thought to be a very hot star surrounded by an expanding envelope of ionized gases that emit a fluorescent glow because of intense radiation from the star |
| planet | one of many small solid celestial bodies thought to have existed at an early stage in the development of the solar system |
| planet | the theory that the solar system was formed by the gravitational accumulation of planetesimals |
| planet | any of numerous small celestial bodies composed of rock and metal that move around the sun (mainly between the orbits of Mars and Jupiter) |