planet
A celestial body moving in an elliptical orbit around a star, large enough to be rounded by its own gravity, and having cleared its orbital path of other debris.
The definition of 'planet' has evolved, notably with Pluto's reclassification. The key is its orbit around a star, its spherical shape due to gravity, and its dominant gravitational influence in its orbital zone.
Word relationships
- world: Often used interchangeably with 'planet,' especially when referring to Earth or a hypothetical inhabited planet.
Commonly confused with
- star: A planet reflects light and orbits a star, while a star generates its own light and heat through nuclear fusion.
- moon: A moon orbits a planet, whereas a planet orbits a star.
Word family
- planetary (adjective): relating to planets.
Collocations
- dwarf planet
- gas giant planet
- terrestrial planet
- habitable planet
- rogue planet
Idioms & expressions
- out of this world (informal, excellent)
Example sentences
- "Earth is the third planet from the Sun and the only known celestial body to harbor life." Basic astronomy.
- "The discovery of a new planet within a habitable zone always sparks excitement among astronomers." Discussing scientific discovery.
Memory hook
A PLANET is a PLANar object that wanders around a star. PLANET = wanderer.
When not to use
Do not use 'planet' for stars, moons, asteroids, or comets, as they do not meet all the criteria (especially clearing their orbit).
Fun facts
- The largest planet in our solar system is Jupiter.
- The International Astronomical Union (IAU) defined 'planet' in 2006, leading to Pluto's reclassification as a dwarf planet.
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