Editing Natural satellite (section)

==Terminology==
The first known natural satellite was the [[Moon]], but it was considered a "planet" until [[Nicolaus Copernicus|Copernicus]]' introduction of ''[[De revolutionibus orbium coelestium]]'' in 1543. Until the discovery of the [[Galilean moons|Galilean satellites]] in 1610 there was no opportunity for referring to such objects as a class. [[Galileo Galilei|Galileo]] chose to refer to his discoveries as ''Planetæ'' ("planets"), but later discoverers chose other terms to distinguish them from the objects they orbited.{{citation needed|date=November 2016}}

The first to use the term ''satellite'' to describe orbiting bodies was the German astronomer [[Johannes Kepler]] in his pamphlet ''Narratio de Observatis a se quatuor Iouis satellitibus erronibus'' ("Narration About Four Satellites of Jupiter Observed") in 1610. He derived the term from the [[Latin]] word ''satelles'', meaning "guard", "attendant", or "companion", because the ''satellites'' accompanied their primary planet in their journey through the heavens.<ref name="NASA-firstsatellites"/>

The term ''satellite'' thus became the normal one for referring to an object orbiting a planet, as it avoided the ambiguity of "moon". In 1957, however, the launching of the artificial object [[Sputnik]] created a need for new terminology.<ref name="NASA-firstsatellites"/> The terms ''man-made satellite'' and ''artificial moon'' were very quickly abandoned in favor of the simpler ''satellite''. As a consequence, the term has become linked with artificial objects flown in space.

Because of this shift in meaning, the term ''moon'', which had continued to be used in a generic sense in works of popular science and fiction, has regained respectability and is now used interchangeably with ''natural satellite'', even in scientific articles. When it is necessary to avoid both the ambiguity of confusion with Earth's natural satellite the Moon and the natural satellites of the other planets on the one hand, and artificial satellites on the other, the term ''natural satellite'' (using "natural" in a sense opposed to "artificial") is used. To further avoid ambiguity, the convention is to capitalize the word Moon when referring to Earth's natural satellite (a [[proper noun]]), but not when referring to other natural satellites ([[common noun]]s).

Many authors define "satellite" or "natural satellite" as orbiting some planet or minor planet, synonymous with "moon"&nbsp;– by such a definition all natural satellites are moons, but Earth and other planets are not satellites.<ref>Kenneth R. Lang.
[https://books.google.com/books?id=S4xDhVCxAQIC "The Cambridge Guide to the Solar System"] {{Webarchive|url=https://web.archive.org/web/20230104160756/https://books.google.com/books?id=S4xDhVCxAQIC |date=4 January 2023}}.
2011.
p. 15.
quote: "Any object that orbits a planet is now called a satellite, and a natural satellite is also now called a moon."</ref><ref>
[[Thérèse Encrenaz]], et al.
[https://books.google.com/books?id=Je61Y7UbqWgC "The Solar System"].
2004.
p. 30.
</ref><ref>Tilman Spohn, Doris Breuer, Torrence Johnson.
[https://books.google.com/books?id=0bEMAwAAQBAJ "Encyclopedia of the Solar System"] {{Webarchive|url=https://web.archive.org/web/20230104160757/https://books.google.com/books?id=0bEMAwAAQBAJ |date=4 January 2023 }}.
2014.
p. 18.</ref>
A few recent authors define "moon" as "a satellite of a planet or minor planet", and "planet" as "a satellite of a star"&nbsp;– such authors consider Earth as a "natural satellite of the Sun".<ref>
David Andrew Weintraub.
[https://books.google.com/books?id=ELd-ve_35R8C "Is Pluto a Planet?: A Historical Journey Through the Solar System"].
p. 65
quote: "... the general concept of a "moon" as a satellite of a planet and "planet" as a satellite of a star."
</ref><ref>
{{cite web|title=Satellite
|url=http://www.merriam-webster.com/dictionary/satellite
|website=www.merriam-webster.com|publisher=Merriam Webster|access-date=16 November 2015}}
</ref><ref name="NASA-what-is-a-satellite"/>

=== Definition of a moon ===
[[File:Moon, Earth size comparison.jpg|thumb|Size comparison of [[Earth]] and the [[Moon]]]]

There is no established lower limit on what is considered a "moon". Every natural celestial body with an identified orbit around a planet of the [[Solar System]], some as small as a kilometer across, has been considered a moon, though objects a tenth that size within Saturn's rings, which have not been directly observed, have been called ''[[moonlet]]s''. Small [[Minor-planet moon|asteroid moons]] (natural satellites of asteroids), such as [[Dactyl (moon)|Dactyl]], have also been called moonlets.<ref name="Marchis05">{{cite journal|author=F. Marchis|title=Discovery of the triple asteroidal system 87 Sylvia|journal=Nature|volume=436|pages=822–824|date=2005|bibcode=2005Natur.436..822M|doi=10.1038/nature04018|pmid=16094362|issue=7052|name-list-style=vanc|display-authors=1|last2=Descamps|first2=Pascal|last3=Hestroffer|first3=Daniel|last4=Berthier|first4=Jérome|s2cid=4412813|url=https://escholarship.org/uc/item/7nb376hk}}</ref>

The upper limit is also vague. Two orbiting bodies are sometimes described as a [[double planet]] rather than a primary and satellite. [[Asteroid]]s such as [[90 Antiope]] are considered double asteroids, but they have not forced a clear definition of what constitutes a moon. Some authors consider the Pluto–Charon system to be a double (dwarf) planet. The most common{{citation needed|date=January 2012}} dividing line on what is considered a moon rests upon whether the [[barycentre]] is below the surface of the larger body, though this is somewhat arbitrary because it depends on distance as well as relative mass.