Editing Moon (section)

===Orbit===
{{Main|Orbit of the Moon|Lunar theory|Lunar orbit|Cislunar space}}
[[File:Dscovrepicmoontransitfull.gif|thumb |A view of the rotating Earth and the [[far side of the Moon]] as the Moon passes on its orbit in between the observing [[DSCOVR satellite]] and Earth]]

The Earth and the Moon form the Earth–Moon [[Satellite system (astronomy)|satellite system]] with a shared center of mass, or [[barycenter]]. This barycenter is {{Convert|1700 |km |abbr=on}} (about a quarter of Earth's radius) beneath the Earth's surface.

The Moon's orbit is slightly elliptical, with an [[orbital eccentricity]] of 0.055.<ref name="W06"/>
The [[semi-major axis]] of the geocentric lunar orbit, called the [[lunar distance]], is approximately 400,000&nbsp;km (250,000 miles or 1.28 light-seconds), comparable to going [[circumference of Earth|around Earth]] 9.5 times.<ref name="The Aerospace Corporation 2023 j509">{{cite web |author=The Aerospace Corporation |title=It's International Moon Day! Let's talk about Cislunar Space. |website=Medium |date=July 20, 2023 |url=https://medium.com/the-aerospace-corporation/its-international-moon-day-let-s-talk-about-cislunar-space-9d108f1a1b0b |access-date=November 7, 2023 |archive-date=November 8, 2023 |archive-url=https://web.archive.org/web/20231108000242/https://medium.com/the-aerospace-corporation/its-international-moon-day-let-s-talk-about-cislunar-space-9d108f1a1b0b |url-status=live}}</ref>

The Moon makes a complete orbit around Earth with respect to the fixed stars, its [[sidereal period]], about once every 27.3&nbsp;days.{{efn |name=orbpd}} However, because the Earth–Moon system moves at the same time in its orbit around the Sun, it takes slightly longer, 29.5&nbsp;days,{{Efn |name=synpd}}<ref name="worldbook"/> to return to the same [[lunar phase]], completing a full cycle, as seen from Earth. This [[synodic period]] or synodic month is commonly known as the [[lunar month]] and is equal to the length of the [[solar day]] on the Moon.<ref name="Day">{{cite news |url=https://www.universetoday.com/20524/how-long-is-a-day-on-the-moon-1/ |date=July 10, 2017 |author=Matt Williams |title=How Long is a Day on the Moon? |newspaper=Universe Today |access-date=December 5, 2020 |archive-date=November 29, 2020 |archive-url=https://web.archive.org/web/20201129020253/https://www.universetoday.com/20524/how-long-is-a-day-on-the-moon-1/ |url-status=live}}</ref>

Due to [[tidal locking]], the Moon has a 1:1 [[orbital resonance|spin–orbit resonance]]. This [[rotation]]–[[orbit]] ratio makes the Moon's orbital periods around Earth equal to its corresponding [[rotation period]]s. This is the reason for only one side of the Moon, its so-called [[near side]], being visible from Earth. That said, while the movement of the Moon is in resonance, it still is not without nuances such as [[libration]], resulting in slightly changing perspectives, making over time and location on Earth about 59% of the Moon's surface visible from Earth.<ref name="Liberation">{{cite web |last=Stern |first=David |date=March 30, 2014 |title=Libration of the Moon |url=https://www-istp.gsfc.nasa.gov/stargaze/Smoon4.htm |url-status=live |archive-url=https://web.archive.org/web/20200522153419/https://www-istp.gsfc.nasa.gov/stargaze/Smoon4.htm |archive-date=May 22, 2020 |access-date=February 11, 2020 |website=NASA}}</ref>

Unlike most satellites of other planets, the Moon's orbital plane is closer to the [[ecliptic plane]] than to the planet's [[equatorial plane]]. The Moon's orbit is subtly [[perturbation (astronomy)|perturbed]] by the Sun and Earth in many small, complex and interacting ways. For example, the plane of the Moon's orbit [[lunar standstill|gradually rotates]] once every 18.61{{nbsp}}years,<ref>{{cite journal |author1=Haigh, I. D. |author2=Eliot, M. |author3=Pattiaratchi, C. |year=2011 |title=Global influences of the 18.61 year nodal cycle and 8.85 year cycle of lunar perigee on high tidal levels |journal=J. Geophys. Res. |volume=116 |issue=C6 |pages=C06025 |doi=10.1029/2010JC006645 |bibcode=2011JGRC..116.6025H |url=https://api.research-repository.uwa.edu.au/files/3380567/A0059.pdf |access-date=September 24, 2019 |archive-date=December 12, 2019 |archive-url=https://web.archive.org/web/20191212170314/https://api.research-repository.uwa.edu.au/files/3380567/A0059.pdf |url-status=live |doi-access=free}}</ref> which affects other aspects of lunar motion. These follow-on effects are mathematically described by [[Cassini's laws]].<ref name="Beletskii2" />

[[File:Moon distance range to scale.svg|center|thumb|upright=3|Minimum, mean and maximum distances of the Moon from Earth with its angular diameter as seen from Earth's surface to scale]]