Editing Definition of planet (section)

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| title = The [[International Astronomical Union]]'s<br />definition of a planet in the [[Solar System]]
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Object is in [[orbit]] around the Sun|
Object has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a [[hydrostatic equilibrium]] (nearly round) state.|
Object has [[cleared the neighbourhood]] around its orbit}}

Source: {{cite news|url=http://www.iau.org/static/resolutions/Resolution_GA26-5-6.pdf|title=IAU 2006 General Assembly: Resolutions 5 and 6|date=August 24, 2006|publisher=IAU|access-date=June 23, 2009}}
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The definition of the term ''[[planet]]'' has changed several times since the word was coined by the [[ancient Greeks]]. [[Greek astronomy|Greek astronomers]] employed the term {{lang|grc|ἀστέρες πλανῆται}} ({{Transliteration|grc|asteres planetai}}), 'wandering stars', for star-like objects which apparently moved over the sky. Over the millennia, the term has included a variety of different celestial bodies, from the [[Sun]] and the [[Moon]] to [[natural satellite|satellites]] and [[asteroid]]s.

In modern astronomy, there are two primary conceptions of a ''planet''. A ''planet'' can be an [[astronomical object]] that ''dynamically dominates'' its region (that is, whether it controls the fate of other smaller bodies in its vicinity) or  it is defined to be in ''hydrostatic equilibrium'' (it has become gravitationally rounded and compacted). These may be characterized as [[IAU definition of planet|the dynamical dominance definition]] and [[geophysical definition of planet|the geophysical definition]].

The issue of a clear [[definition]] for ''planet'' came to a head in January 2005 with the discovery of the [[trans-Neptunian object]] [[Eris (dwarf planet)|Eris]], a body more massive than the smallest then-accepted planet, [[Pluto]].<ref name="NYT-20220118">{{cite news |last=Chang |first=Kenneth |title=Quiz - Is Pluto A Planet? - Who doesn't love Pluto? It shares a name with the Roman god of the underworld and a Disney dog. But is it a planet? - Interactive |url=https://www.nytimes.com/interactive/2022/science/is-pluto-a-planet.html  |date=January 18, 2022 |work=[[The New York Times]] |accessdate=January 18, 2022 }}</ref> In its August 2006 response, the [[International Astronomical Union]] (IAU), which is recognised by astronomers as the international governing body responsible for resolving issues of [[nomenclature]], released [[IAU definition of planet|its decision]] on the matter during a meeting in [[Prague]]. This definition, which applies only to the Solar System (though exoplanets had been addressed in 2003), states that a planet is a body that orbits the Sun, is massive enough for its [[hydrostatic equilibrium|own gravity to make it round]], and has "[[Clearing the neighbourhood|cleared its neighbourhood]]" of smaller objects approaching its orbit. Pluto fulfills the first two of these criteria, but not the third and therefore does not qualify as a planet under this formalized definition. The IAU's decision has not resolved all controversies. While many astronomers have accepted it, some planetary scientists have rejected it outright, proposing a geophysical or similar definition instead.