- The definition of a planet is a large mass that revolves around a star, such as one of the celestial bodies moving around the sun.
The Earth is an example of a planet.
- Obsolete any of the celestial objects with apparent motion (as distinguished from the apparently still stars), including the sun, moon, Mercury, Venus, Mars, Jupiter, or Saturn
- now, a large, opaque, nonluminous mass, usually with its own moons, that revolves about a star; esp., one of the sun's nine major planets: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto
- Astrol. any celestial body thought of as influencing human lives
Origin: Middle English planete from Old French from Late Latin planeta from Glassical Greek planētēs, wanderer from planan, to lead astray, wander from Indo-European base an unverified form plā-, flat, spread out from source plain
Used by arrangement with John Wiley & Sons, Inc.
- a. In the traditional model of solar systems, a celestial body larger than an asteroid or comet, illuminated by light from a star, such as the sun, around which it revolves.b. A celestial body that orbits the sun, has sufficient mass to assume nearly a round shape, clears out dust and debris from the neighborhood around its orbit, and is not a satellite of another planet.
- 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.
- One of the seven revolving astrological celestial bodies that in conjunction with the stars are believed to influence human affairs and personalities.
Origin: Middle English, from Old French planete, from Late Latin planēta, from Greek planētēs, variant of planēs, planēt-, from planāsthai, to wander; see pelə-2 in Indo-European roots.Usage Note: Clyde Tombaugh's discovery of Pluto in 1930 added a ninth planet to our solar system, and thereafter students of astronomy were taught the familiar list of nine planets: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto. But in 2006, the International Astronomical Union (IAU) voted to change the definition of planet, requiring that a clestial body must have enough mass to assume a round shape and “clear the neighborhood around its orbit” in order to qualify as a planet. This means that a planet cannot have other objects in or crossing its orbit except smaller objects that have been captured by its gravity, such as those that revolve around it as moons. Because Neptune's large mass has captured Pluto so that the two planets remain in orbits that cross, Pluto has not cleared its own orbit and was therefore demoted from planet status to that of a newly created category, dwarf planet. Like a planet, a dwarf planet orbits the sun, is large enough to assume a nearly round shape, and does not orbit a planet (as our Moon does). But a dwarf planet does not clear the neighborhood around its orbit and may cross the paths of other objects orbiting the sun. Other dwarf planets include Ceres, whose orbit is in the asteroid belt betwen Mars and Jupiter, and Eris, an object in the Kuiper belt beyond Pluto. At the same meeting the IAU created a third category of objects known as small solar system bodies, which includes asteroids (sometimes referred to as “minor planets,” compounding the difficulty of the term planet,) comets, objects beyond Netpune's orbit, and other nonspherical bodies. Although officially approved, this new scheme of the solar system remains controversial among astronomers and may well be revised.
planet - Cultural Definition
An object in orbit around a star. A planet does not give off its own light; rather, it shines by reflecting sunlight. Planets close to the sun are rocky. Those farther out consist mostly of gases and liquids.
planet - Science Definition
- In the traditional model of solar systems, a celestial body larger than an asteroid or comet, illuminated by light from a star, such as the Sun, around which it revolves.
- A celestial body that orbits the Sun, has sufficient mass to assume nearly a round shape, clears out dust and debris from the neighborhood around its orbit, and is not a satellite of another planet. The eight planets are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. Pluto was considered to be a planet until its reclassification in 2006 as a dwarf 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 planet, inner planet, outer planet.
- planetary planetary adjective
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