Editing Moon

{{Short description|Natural satellite orbiting Earth}}
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{{About|Earth's natural satellite|moons in general|Natural satellite|other uses}}
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{{Use American English|date=March 2024}}
{{Use mdy dates|date=August 2024}}
{{Infobox planet
| name = Moon
| apsis = gee
| symbol = [[File:Moon decrescent symbol (bold).svg|24px|☾|class=skin-invert]] or [[File:Moon crescent symbol (bold).svg|24px|☽|class=skin-invert]]
| image = FullMoon2010.jpg
| image_alt = Full Moon in the darkness of the night sky. It is patterned with a mix of light-tone regions and darker, irregular blotches, and scattered with varied circles surrounded by out-thrown rays of bright ejecta: impact craters.
| caption = [[Near side of the Moon]], [[lunar north pole]] at top
| background = #ddd
| mpc_name = Earth I
| alt_names = {{hlist |[[Luna (goddess)|Luna]] |{{nowrap|[[Selene]] (poetic)}}|{{nowrap|[[wikt:Cynthia|Cynthia]] (poetic)}}}}
| adjectives = {{hlist |[[wikt:lunar|Lunar]] |{{nowrap|[[wikt:selenian|Selenian]] (poetic)}}|{{nowrap|[[wikt:Cynthian|Cynthian]] (poetic)}}|{{nowrap|[[wikt:moonly|Moonly]] (poetic)}}}}
| periapsis = {{gaps |362 |600}}&nbsp;km<br />({{gaps |356 |400}}–{{gaps |370 |400}}&nbsp;km)
| apoapsis = {{gaps |405 |400}}&nbsp;km<br />({{gaps |404 |000}}–{{gaps |406 |700}}&nbsp;km)
| mean_orbit_radius = {{val |384784|u=km}}{{cn|date=March 2025|reason=added by [[User:Imapisces235]]: asked on talk page for source; sofar no answer}}{{nbsp |2}}<br/>({{val |1.28 |u=[[light-second|ls]]}}; 1/384 [[Astronomical unit|AU]]; {{val |1.001|ul=LD}})
| semimajor = {{val |384399 |u=km}}{{nbsp |2}}({{val |1.28 |u=[[light-second|ls]]}}; 1/389 [[Astronomical unit|AU]]; {{val |1 |ul=LD}})<ref name="W06"/>
| eccentricity = {{val |0.0549}}<ref name="W06"/>
| period = {{longitem |{{val |27.321661 |ul=d}}<br />(27&thinsp;d 7&thinsp;h 43&thinsp;min 11.5&thinsp;s<ref name="W06"/>)}}
| synodic_period = {{longitem |{{val |29.530589 |u=d}}<br />(29&thinsp;d 12&thinsp;h 44&thinsp;min 2.9&thinsp;s)}}
| avg_speed = {{val |1.022 |ul=km/s}}
| inclination = 5.145° to the [[ecliptic]]<ref name="Lang2011"/>{{efn|name=inclination|Between 18.29° and 28.58° to Earth's [[equator]]<ref name="W06"/><!--Wieczorek et al. 2006; 18.29° when the longitude of the Moon's ascending node is 180°, 28.58° when it is 0°-->}}
| asc_node = {{longitem |[[Lunar precession#Nodal precession|Regressing]] by one revolution in 18.61&nbsp;years}}
| arg_peri = {{longitem |[[Lunar precession#Apsidal precession|Progressing]] by one<br /> revolution in 8.85&nbsp;years}}
| satellite_of = [[Earth]]{{efn|name=near-Earth asteroids}}<ref name="Morais2002"/>
| flattening = {{val |0.0012}}<ref name="NSSDC"/>
| equatorial_radius = {{val |1738.1 |u=km}}{{nbsp |2}}<br />(0.2725 of Earth's)<ref name="NSSDC"/>
| polar_radius = {{val |1736.0 |u=km}}{{nbsp |2}}<br />(0.2731 of Earth's)<ref name="NSSDC"/>
| mean_radius = {{val |1737.4 |u=km}}{{nbsp |2}}<br />(0.2727 of Earth's)<ref name="W06"/><ref name="NSSDC"/><ref>{{cite journal |last1=Smith |first1=David E. |last2=Zuber |first2=Maria T. |last3=Neumann |first3=Gregory A. |last4=Lemoine |first4=Frank G. |title=Topography of the Moon from the Clementine lidar |journal=[[Journal of Geophysical Research]] |date=January 1, 1997 |volume=102 |issue=E1 |page=1601 |doi=10.1029/96JE02940 |bibcode=1997JGR...102.1591S |hdl=2060/19980018849 |s2cid=17475023 |hdl-access=free |issn=0148-0227}}</ref>
| circumference = {{val |10921 |u=km}}{{nbsp |2}}([[equator]]ial)
| surface_area = {{val |3.793 |e=7 |u=km2}}{{nbsp |2}}<br />(0.074 of Earth's)
| volume = {{val |2.1958 |e=10 |u=km3}}{{nbsp |2}}<br />(0.02 of Earth's)<ref name="NSSDC"/>
| mass = {{val |7.346 |e=22 |u=kg}}{{nbsp |2}}<br />({{val |0.0123}} of Earth's)<ref name="W06"/><ref name="NSSDC"/><ref>{{cite book |title=Top 10 of Everything |first=Paul |last=Terry |publisher=Octopus Publishing Group Ltd |year=2013 |isbn=978-0-600-62887-3 |page=226}}</ref>
| density = {{val |3.344 |ul=g/cm3}}<ref name="W06"/><ref name="NSSDC"/><br />{{val |0.606}} × Earth
| surface_grav = {{cvt|1.622|m/s2|ft/s2}}<ref name="NSSDC"/><br>{{cvt|1.622|m/s2|g0|disp=out|lk=out}}
| moment_of_inertia_factor = {{val |0.3929 |0.0009}}<ref name="Williams1996" />
| escape_velocity = {{convert|2.38|km/s|km/h mph|comma=gaps|abbr=on|disp=x|<br />(|)}}
| rotation = {{longitem |{{val |29.530589 |u=d}}<br />(29&thinsp;d 12&thinsp;h 44&thinsp;min 2.9&thinsp;s; [[synodic day|synodic; solar day]]) ([[tidal locking|spin-orbit locked]])}}
| sidereal_day = {{val |27.321661 |u=d}}{{nbsp |2}}(spin-orbit locked)
<!-- Wieczorek et al. 2006 -->| rot_velocity = {{nowrap |4.627 m/s}}
| axial_tilt = {{ublist |1.5424° to [[ecliptic]]<ref name="SolarViews" /><!--1.533° according to Conn 2007-->|6.687° to [[Orbital plane (astronomy)|orbit plane]]<ref name="Lang2011"/><!--6.4° according to Grego; <ref name="Grego2005">Grego, Peter, [https://books.google.com/books?id=z6Pgt9xEW9gC&pg=PA48 ''The Moon and How to Observe It''], Springer, 2005</ref> 6.6783° according to Conn.<ref name="Conn2007">Conn, David (2007); ''Lednorf's Dilemma'', AuthorHouse, Bloomington (IN)</ref>-->|24° to Earth's equator&thinsp;<ref>{{cite journal |last=Makemson |first=Maud W. |year=1971 |title=Determination of selenographic positions |journal=The Moon |volume=2 |issue=3 |pages=293–308 |doi=10.1007/BF00561882 |bibcode=1971Moon....2..293M |s2cid=119603394}}</ref>}}
| epoch = [[J2000]]
| uncertainty = 0
| right_asc_north_pole = {{plainlist |
* {{RA|17|47|26}}
* 266.86°<ref name="report">{{cite journal |doi=10.1007/s10569-010-9320-4 |title=Report of the IAU Working Group on Cartographic Coordinates and Rotational Elements: 2009 |url=http://astropedia.astrogeology.usgs.gov/alfresco/d/d/workspace/SpacesStore/28fd9e81-1964-44d6-a58b-fbbf61e64e15/WGCCRE2009reprint.pdf |journal=Celestial Mechanics and Dynamical Astronomy |volume=109 |issue=2 |pages=101–135 |year=2010 |last1=Archinal |first1=Brent A. |last2=A'Hearn |first2=Michael F. |last3=Bowell |first3=Edward G. |last4=Conrad |first4=Albert R. |last5=Consolmagno |first5=Guy J. |last6=Courtin |first6=Régis |last7=Fukushima |first7=Toshio |last8=Hestroffer |first8=Daniel |last9=Hilton |first9=James L. |last10=Krasinsky |first10=George A. |last11=Neumann |first11=Gregory A. |last12=Oberst |first12=Jürgen |last13=Seidelmann |first13=P. Kenneth |last14=Stooke |first14=Philip J. |last15=Tholen |first15=David J. |last16=Thomas |first16=Paul C. |last17=Williams |first17=Iwan P. |bibcode=2011CeMDA.109..101A |s2cid=189842666 |access-date=September 24, 2018 |archive-url=https://web.archive.org/web/20160304065344/http://astropedia.astrogeology.usgs.gov/alfresco/d/d/workspace/SpacesStore/28fd9e81-1964-44d6-a58b-fbbf61e64e15/WGCCRE2009reprint.pdf |archive-date=March 4, 2016 |url-status=dead}} also available {{cite web |title=via usgs.gov |url=http://astropedia.astrogeology.usgs.gov/download/Docs/WGCCRE/WGCCRE2009reprint.pdf |access-date=September 26, 2018 |archive-date=April 27, 2019 |archive-url=https://web.archive.org/web/20190427144731/https://astropedia.astrogeology.usgs.gov/download/Docs/WGCCRE/WGCCRE2009reprint.pdf |url-status=live}}</ref>
  }}
| declination = 65.64°<ref name="report" />
| albedo = 0.136<ref name="Saari"/>
| temp_name1 = Equator
| min_temp_1 = 100&nbsp;[[Kelvin|K]]<ref name=Bugby_et_al_2010/>
| mean_temp_1 = 250&nbsp;K
| max_temp_1 = 390&nbsp;K<ref name=Bugby_et_al_2010>{{cite conference |title=Two-Phase Thermal Switching System for a Small, Extended Duration Lunar Surface Science Platform |first1=D. C. |last1=Bugby |first2=J. T. |last2=Farmer |first3=B. F. |last3=O’Connor |first4=M. J. |last4=Wirzburger |first5=E. D. Abel |last5=C. J. Stouffer |series=AIP Conference Proceedings |volume=1208 |pages=76–83 |date=January 2010 |doi=10.1063/1.3326291 |bibcode=2010AIPC.1208...76B |hdl=2060/20100009810 |hdl-access=free}}</ref>
| temp_name2 = 85°N&nbsp;
| min_temp_2 = 
| mean_temp_2 = 150&nbsp;K
| max_temp_2 = 230&nbsp;K<ref name="Vasavada1999"/>
| surface_equivalent_dose_rate = {{convert |1.369 |mSv/d |μSv/h |disp=out}}<br />(during lunar daytime)<ref name="surface-radiation">{{Cite journal |vauthors=Zhang S, Wimmer-Schweingruber RF, Yu J, Wang C, Fu Q, Zou Y, Sun Y, Wang C, Hou D, Böttcher SI, Burmeister S |display-authors=6 |title=First measurements of the radiation dose on the lunar surface |journal=Science Advances |year=2020 |volume=6 |issue=39 |doi=10.1126/sciadv.aaz1334 |pmc=7518862 |pmid=32978156 |bibcode=2020SciA....6.1334Z |quote=We measured an average total absorbed dose rate in silicon of 13.2 ± 1 μGy/hour ... LND measured an average dose equivalent of 1369 μSv/day on the surface of the Moon}}</ref>
| surface_absorbed_dose_rate = 13.2 μGy/h<br />(during lunar [[daytime]])<ref name="surface-radiation"/>
| magnitude = {{ublist |−2.5 to −12.9{{efn |name=maxval}} |−12.74{{nbsp |2}}(mean [[full moon]])<ref name="NSSDC"/>}}
| abs_magnitude = 0.2<ref name="IMCCE">{{cite web |title=Encyclopedia – the brightest bodies |website=IMCCE |url=https://promenade.imcce.fr/en/pages1/101.html |access-date=June 1, 2023 |archive-date=March 21, 2023 |archive-url=https://web.archive.org/web/20230321023334/https://promenade.imcce.fr/en/pages1/101.html |url-status=live}}</ref>
| angular_size = 29.3 to 34.1 [[arcminutes]]<ref name="NSSDC"/>{{efn |name=angular size}}
| atmosphere = trace
| atmosphere_ref = <ref name="L06"/>
| surface_pressure = {{ublist |10{{sup |−7}} [[Pascal (unit)|Pa]] (1 [[picobar]]){{nbsp |2}}(day) |10{{sup |−10}} Pa (1 femtobar) {{nbsp |2}} <br />(night){{efn |name=pressure explanation}}}}
| atmosphere_composition = {{hlist |[[Helium|He]] |[[Argon|Ar]] |[[Neon|Ne]] |[[Sodium|Na]] |[[Potassium|K]] |[[Hydrogen|H]]}}
}}

The '''Moon''' is [[Earth]]'s only [[natural satellite]]. It [[Orbit of the Moon|orbits]] around Earth at [[Lunar distance|an average distance]] of {{val|384399|u=km}} ({{cvt|384399|km|mi|disp=out}}; about 30 times [[Earth diameter|Earth's diameter]]). The Moon [[rotation|rotates]], but keeps facing Earth with the same [[near side of the Moon|near side]]. This [[tidal locking]] results from Earth's [[tidal forces|gravitational pull]] having synchronized the Moon's rotation period ([[lunar day]]) to its orbital period ([[Lunar month#Synodic month|lunar month]]) of 29.5 Earth days. Conversely, the gravitational pull of the Moon on Earth is the main driver of Earth's [[tide]]s.

In [[geophysical definition of planet|geophysical terms]], the Moon is a [[planetary-mass object]] or [[satellite planet]]. Its mass is 1.2% that of the Earth, and its diameter is {{cvt|3474|km|mi}}, roughly one-quarter of Earth's (about as wide as the [[contiguous United States]]). Within the [[Solar System]], it is the [[List of Solar System objects by size|largest and most massive]] satellite in relation to its [[primary body|parent planet]], the fifth-largest and fifth-most massive moon overall, and larger and more massive than all known [[dwarf planet]]s.<ref name="Metzger2021"/> Its [[surface gravity]] is about one-sixth of Earth's, about half that of [[Mars]], and the second-highest among all moons in the Solar System, after [[Jupiter]]'s moon [[Io (moon)|Io]]. The body of the Moon is [[planetary differentiation|differentiated]] and [[Terrestrial planet|terrestrial]], with no significant [[hydrosphere]], [[Atmosphere of the Moon|atmosphere]], or [[Magnetic field of the Moon|magnetic field]]. The [[lunar surface]] is covered in [[lunar dust]] and marked by [[List of mountains on the Moon|mountains]], [[impact crater]]s, [[Ejecta blanket|their ejecta]], [[Ray system|ray-like streaks]], [[rille]]s and, mostly on the near side of the Moon, by dark [[lunar mare|maria]] ('seas'), which are plains of [[Basalt|cooled lava]]. These maria were formed when molten lava flowed into ancient impact basins. The [[Origin of the Moon|Moon formed]] 4.51&nbsp;billion years ago, not long after [[Age of Earth|Earth's formation]], out of the debris from [[giant-impact hypothesis|a giant impact]] between Earth and a hypothesized Mars-sized body called [[Theia (planet)|Theia]].

The Moon is, except when passing through [[Earth's shadow]] during a [[lunar eclipse]], always illuminated by the Sun, but from Earth the visible illumination shifts during its orbit, producing the [[lunar phase]]s. The Moon is the [[List of brightest natural objects in the sky|brightest celestial object]] in Earth's [[night sky]]. This is mainly due to its large [[angular diameter]], while the [[reflectance]] of the lunar surface is comparable to that of [[asphalt concrete|asphalt]]. The apparent size is nearly the same as that of the Sun, allowing it to cover the Sun completely during a total [[solar eclipse]]. From Earth about 59% of the lunar surface is visible due to cyclical shifts in perspective ([[libration]]), making parts of the far side of the Moon visible.

The Moon has been an important source of inspiration and knowledge for humans, having been crucial to [[cosmography]], mythology, [[Lunar deity|religion]], art, [[Lunar calendar|time keeping]], [[natural science]], and [[spaceflight]]. The [[Timeline of Solar System exploration|first human-made objects to fly to an extraterrestrial body]] were sent to the Moon, starting in 1959 with the flyby of the Soviet Union's ''[[Luna 1]]'' and the [[Impactor (spacecraft)|intentional impact]] of ''[[Luna 2]]''. In 1966, the first [[soft landing]] (by ''[[Luna 9]]'') and [[orbital insertion]] (by ''[[Luna 10]]'') followed. On July 20, 1969, humans for the first time stepped on an extraterrestrial body, landing on the Moon at [[Mare Tranquillitatis]] with the lander ''[[Lunar Module Eagle|Eagle]]'' of the United States' [[Apollo 11]] mission. Five more crews were sent between then and 1972, each with two men landing on the surface. The longest stay was 75 hours by the [[Apollo 17]] crew. Since then, [[exploration of the Moon]] has continued robotically, and crewed missions are being [[Artemis program|planned to return]] beginning in the late 2020s.

== Names and etymology ==
{{See also|Moon#Cultural representation}}

The English proper name for Earth's natural satellite is typically written as ''Moon'', with a capital ''M''.<ref>{{cite web |url=http://www.iau.org/public_press/themes/naming/#spelling |title=Naming Astronomical Objects: Spelling of Names |publisher=[[International Astronomical Union]] |access-date=April 6, 2020 |url-status=dead |archive-url=https://web.archive.org/web/20081216024716/http://www.iau.org/public_press/themes/naming/#spelling |archive-date=December 16, 2008}}</ref><ref name="PN-FAQ" /> The noun ''moon'' is derived from [[Old English]] {{lang|ang|mōna}}, which stems from [[Proto-Germanic]] ''*mēnōn'',<ref>{{cite book |first=Vladimir |last=Orel |year=2003 |url=https://archive.org/details/Orel-AHandbookOfGermanicEtymology/mode/2up/search/moon |title=A Handbook of Germanic Etymology |publisher=Brill |access-date=March 5, 2020}}</ref> which in turn comes from [[Proto-Indo-European]] ''*mēnsis'' 'month'<ref>{{cite web |first=Fernando |last=López-Menchero |url=https://indo-european.info/dictionary-translator/word.inc.php/ine/m%c4%93nsis |title=Late Proto-Indo-European Etymological Lexicon |date=May 22, 2020 |access-date=July 30, 2022 |archive-date=May 22, 2020 |archive-url=https://web.archive.org/web/20200522153418/https://indo-european.info/dictionary-translator/word.inc.php/ine/m%c4%93nsis |url-status=live}}</ref> (from earlier ''*mēnōt'', genitive ''*mēneses'') which may be related to the verb 'measure' (of time).<ref name="barnhart1995" />

Occasionally, the name ''Luna'' {{IPAc-en|'|l|uː|n|ə}} is used in scientific writing<ref>For example: {{cite book |first=James A. |last=Hall III |date=2016 |title=Moons of the Solar System |publisher=Springer |isbn=978-3-319-20636-3}}</ref> and especially in science fiction to distinguish the Earth's moon from others, while in poetry "Luna" has been used to denote personification of the Moon.<ref>{{OED|Luna}}</ref> ''Cynthia'' {{IPAc-en|ˈ|s|ɪ|n|θ|i|ə}} is a rare poetic name for the Moon personified as a goddess,<ref>{{OED|Cynthia}}</ref> while ''[[Selene]]'' {{IPAc-en|s|ə|ˈ|l|iː|n|iː}} (literally 'Moon') is the Greek goddess of the Moon.

The English adjective pertaining to the Moon is ''lunar'', derived from the Latin word for the Moon, {{lang|la|lūna}}. ''Selenian'' {{IPAc-en|s|ə|l|iː|n|i|ə|n}}<ref>{{MW|selenian}}</ref> is an adjective used to describe the Moon as a world, rather than as a celestial object,<ref>{{OED|selenian}}</ref> but its use is rare. It is derived from {{lang|el|σελήνη}} {{tlit|el|selēnē}}, the Greek word for the Moon, and its cognate ''selenic'' was originally a rare synonym<ref>{{OED|selenic}}</ref> but now nearly always refers to the chemical element [[selenium]].<ref>{{MW|selenic}}</ref> The element name ''selenium'' and the prefix ''seleno-'' (as in ''[[selenography]]'', the study of the physical features of the Moon) come from this Greek word.<ref name="oed" /><ref>{{LSJ|selh/nh |σελήνη |ref}}.</ref>

[[Artemis]], the Greek goddess of the wilderness and the hunt, also came to be identified with Selene, and was sometimes called [[Cynthia]] after her birthplace on [[Mount Cynthus]].<ref name="Pannen2010">{{cite book |first=Imke |last=Pannen |title=When the Bad Bleeds: Mantic Elements in English Renaissance Revenge Tragedy |url=https://books.google.com/books?id=37CPbHwqPjwC&pg=PA96 |year=2010 |publisher=V&R |isbn=978-3-89971-640-5 |page=96}}</ref> Her Roman equivalent is [[Diana (mythology)|Diana]]. The names Luna, Cynthia, and Selene are reflected in technical terms for [[lunar orbit]]s such as ''apolune'', ''pericynthion'' and ''selenocentric''.

The [[astronomical symbols]] for the Moon are the crescent [[File:Moon crescent symbol (bold).svg|24px|☽|class=skin-invert]] and decrescent [[File:Moon decrescent symbol (bold).svg|24px|☾|class=skin-invert]], for example in ''M''<sub>☾</sub> 'lunar mass'.

==Natural history==
===Lunar geologic timescale===
{{Main|Lunar geologic timescale}}
{{Timeline Lunar Geological Timescale}}

The lunar geological periods are named after their characteristic features, from most [[impact crater]]s outside the dark [[Lunar mare|mare]], to the mare and later craters, and finally the young, still bright and therefore readily visible craters with [[ray system]]s like [[Copernicus (lunar crater)|Copernicus]] or [[Tycho (lunar crater)|Tycho]].

===Formation===
{{Main|Origin of the Moon |Giant-impact hypothesis|Circumplanetary disk}}
[[File:Far side of the Moon.png|thumb|The [[far side of the Moon]] lacks the near side's characteristic large dark areas of maria. The [[near side of the Moon]] might have looked like this early in the Moon's history.<ref name="The Planetary Society 2022">{{cite web |title=The two-faced Moon |website=The Planetary Society |date=March 14, 2022 |url=https://www.planetary.org/articles/the-two-faced-moon |access-date=April 28, 2023 |archive-date=April 28, 2023 |archive-url=https://web.archive.org/web/20230428213253/https://www.planetary.org/articles/the-two-faced-moon |url-status=live}}</ref><ref name="explanet.info">{{cite web |website=explanet.info |url=https://explanet.info/Chapter04.htm |title=Exploring the Planets: Chapter 4. The Moon |access-date=April 28, 2023 |archive-date=April 28, 2023 |archive-url=https://web.archive.org/web/20230428213755/https://explanet.info/Chapter04.htm |url-status=live}}</ref>]]
[[Isotope dating]] of lunar samples suggests the Moon formed around 50&nbsp;million years after the [[origin of the Solar System]].<ref>{{cite journal |title=Early Moon formation inferred from hafnium-tungsten systematics |last1=Thiemens |first1=Maxwell M. |last2=Sprung |first2=Peter |last3=Fonseca |first3=Raúl O. C. |last4=Leitzke |first4=Felipe P. |last5=Münker |first5=Carsten |journal=Nature Geoscience |volume=12 |issue=9 |pages=696–700 |date=July 2019 |doi=10.1038/s41561-019-0398-3 |pmid=39649009 |bibcode=2019NatGe..12..696T |s2cid=198997377 |pmc=7617097}}</ref><ref name="Age">{{cite news |url=https://www.universetoday.com/143025/the-moon-is-older-than-scientists-thought/ |title=The Moon is older than scientists thought |website=Universe Today |access-date=August 3, 2019 |archive-date=August 3, 2019 |archive-url=https://web.archive.org/web/20190803125139/https://www.universetoday.com/143025/the-moon-is-older-than-scientists-thought/ |url-status=live}}</ref> Historically, several formation mechanisms have been proposed,<ref>{{cite journal |doi=10.1126/sciadv.1602365 |pmid=28097222 |pmc=5226643 |journal=Science Advances |date=2017 |volume=3 |issue=1 |title=Early formation of the Moon 4.51 billion years ago |last=Barboni |first=M. |author2=Boehnke, P. |author3=Keller, C. B. |author4=Kohl, I. E. |author5=Schoene, B. |author6=Young, E. D. |author7=McKeegan, K. D. |page=e1602365 |bibcode=2017SciA....3E2365B}}</ref> but none satisfactorily explains the features of the Earth–Moon system. A fission of the Moon from Earth's crust through [[centrifugal force]]<ref name="Binder" /> would require too great an initial rotation rate of Earth.<ref name="BotM" /> Gravitational capture of a pre-formed Moon<ref name="Mitler" /> depends on an unfeasibly extended [[atmosphere of Earth]] to [[dissipate]] the energy of the passing Moon.<ref name="BotM" /> A co-formation of Earth and the Moon together in the [[Circumplanetary disk|primordial]] [[accretion disk]] does not explain the depletion of metals in the Moon.<ref name="BotM" /> None of these hypotheses can account for the high [[angular momentum]] of the Earth–Moon system.<ref>{{cite journal |last=Stevenson |first=D. J. |title=Origin of the moon–The collision hypothesis |journal=[[Annual Review of Earth and Planetary Sciences]] |date=1987 |volume=15 |issue=1 |pages=271–315 |bibcode=1987AREPS..15..271S |doi=10.1146/annurev.ea.15.050187.001415 |s2cid=53516498}}</ref>

The prevailing theory is that the Earth–Moon system formed after a [[giant impact]] of a [[Mars]]-sized body (named ''[[Theia (planet)|Theia]]'') with the [[proto-Earth]]. The oblique impact blasted material into orbit about the Earth and the material accreted and formed the Moon<ref name="taylor1998" /><ref>{{cite web |url=http://news.nationalgeographic.com/2015/04/150416-asteroids-scars-moon-formation-space/ |title=Asteroids Bear Scars of Moon's Violent Formation |date=April 16, 2015 |url-status=dead |archive-url=https://web.archive.org/web/20161008160812/http://news.nationalgeographic.com/2015/04/150416-asteroids-scars-moon-formation-space/ |archive-date=October 8, 2016}}</ref> just beyond the Earth's [[Roche limit]] of ~{{val|2.56|ul=Earth radius}}.<ref>{{cite journal |title=Scaling in global tidal dissipation of the Earth–Moon system |last=van Putten |first=Maurice H. P. M. |journal=New Astronomy |volume=54 |pages=115–121 |date=July 2017 |doi=10.1016/j.newast.2017.01.012 |arxiv=1609.07474 |bibcode=2017NewA...54..115V |s2cid=119285032}}</ref>

Giant impacts are thought to have been common in the early Solar System. Computer simulations of giant impacts have produced results that are consistent with the mass of the lunar core and the angular momentum of the Earth–Moon system. These simulations show that most of the Moon derived from the impactor, rather than the proto-Earth.<ref>{{cite journal |last=Canup |first=R. |author1-link=Robin Canup |author2=Asphaug, E. |title=Origin of the Moon in a giant impact near the end of Earth's formation |journal=[[Nature (journal)|Nature]] |volume=412 |pages=708–712 |date=2001 |doi=10.1038/35089010 |pmid=11507633 |issue=6848 |bibcode=2001Natur.412..708C |s2cid=4413525}}</ref> However, models from 2007 and later suggest a larger fraction of the Moon derived from the proto-Earth.<ref>{{cite magazine |url=http://news.nationalgeographic.com/news/2007/12/071219-moon-collision.html |title=Earth–Asteroid Collision Formed Moon Later Than Thought |magazine=[[National Geographic]] |date=October 28, 2010 |access-date=May 7, 2012 |url-status=dead |archive-url=https://web.archive.org/web/20090418171528/http://news.nationalgeographic.com/news/2007/12/071219-moon-collision.html |archive-date=April 18, 2009}}</ref><ref>{{cite journal |title=2008 Pellas-Ryder Award for Mathieu Touboul |journal=Meteoritics and Planetary Science |volume=43 |issue=S7 |pages=A11–A12 |date=2008 |url=http://digitalcommons.arizona.edu/objectviewer?o=uadc://azu_maps/Volume43/NumberSupplement/Touboul.pdf |bibcode=2008M&PS...43...11K |last1=Kleine |first1=Thorsten |doi=10.1111/j.1945-5100.2008.tb00709.x |s2cid=128609987 |access-date=April 8, 2020 |archive-url=https://web.archive.org/web/20180727164701/http://digitalcommons.arizona.edu/objectviewer?o=uadc%3A%2F%2Fazu_maps%2FVolume43%2FNumberSupplement%2FTouboul.pdf |archive-date=July 27, 2018 |url-status=dead}}</ref><ref>{{cite journal |doi=10.1038/nature06428 |title=Late formation and prolonged differentiation of the Moon inferred from W isotopes in lunar metals |date=2007 |last1=Touboul |first1=M. |last2=Kleine |first2=T. |last3=Bourdon |first3=B. |last4=Palme |first4=H. |last5=Wieler |first5=R. |journal=[[Nature (journal)|Nature]] |volume=450 |issue=7173 |pages=1206–1209 |pmid=18097403 |bibcode=2007Natur.450.1206T |s2cid=4416259}}</ref><ref>{{cite magazine |url=http://news.nationalgeographic.com/2015/04/150408-moon-form-giant-impact-earth |title=Flying Oceans of Magma Help Demystify the Moon's Creation |magazine=[[National Geographic]] |date=April 8, 2015 |url-status=dead |archive-url=https://web.archive.org/web/20150409220422/http://news.nationalgeographic.com/2015/04/150408-moon-form-giant-impact-earth/ |archive-date=April 9, 2015}}</ref> Other bodies of the inner Solar System such as Mars and [[4 Vesta|Vesta]] have, according to meteorites from them, very different oxygen and tungsten [[isotope|isotopic]] compositions compared to Earth. However, Earth and the Moon have nearly identical isotopic compositions. The isotopic equalization of the Earth–Moon system might be explained by the post-impact mixing of the vaporized material that formed the two,<ref name="Pahlevan2007" /> although this is debated.<ref>{{cite magazine |last=Nield |first=Ted |title=Moonwalk (summary of meeting at Meteoritical Society's 72nd Annual Meeting, Nancy, France) |magazine=[[Geoscientist (magazine)|Geoscientist]] |volume=19 |page=8 |date=2009 |url=http://www.geolsoc.org.uk/gsl/geoscientist/geonews/page6072.html |url-status=dead |archive-url=https://web.archive.org/web/20120927034348/http://www.geolsoc.org.uk/gsl/geoscientist/geonews/page6072.html |archive-date=September 27, 2012}}</ref>

The impact would have released enough energy to liquefy both the ejecta and the Earth's crust, forming a magma ocean. The liquefied ejecta could have then re-accreted into the Earth–Moon system.<ref name="Warren1985" /><ref>{{cite journal |last=Tonks |first=W. Brian |author2=Melosh, H. Jay |date=1993 |title=Magma ocean formation due to giant impacts |journal=[[Journal of Geophysical Research]] |volume=98 |issue=E3 |pages=5319–5333 |bibcode=1993JGR....98.5319T |doi=10.1029/92JE02726}}</ref> The newly formed Moon would have had [[lunar magma ocean|its own magma ocean]]; its depth is estimated from about {{Convert|500|km|4=-2|abbr=in}} to {{Convert|1737|km|4=0|abbr=in}}.<ref name="Warren1985" />

While the giant-impact theory explains many lines of evidence, some questions are still unresolved, most of which involve the Moon's composition.<ref>{{cite journal |journal=[[Science (journal)|Science]] |author=Daniel Clery |title=Impact Theory Gets Whacked |volume=342 |pages=183–185 |date=October 11, 2013 |doi=10.1126/science.342.6155.183 |bibcode=2013Sci...342..183C |issue=6155 |pmid=24115419}}</ref> Models that have the Moon acquiring a significant amount of the proto-earth are more difficult to reconcile with geochemical data for the isotopes of zirconium, oxygen, silicon, and other elements.<ref>{{cite journal |title=Zirconium isotope constraints on the composition of Theia and current Moon-forming theories |first1=W. |last1=Akram |first2=M. |last2=Schönbächler |journal=Earth and Planetary Science Letters |volume=449 |date=September 1, 2016 |pages=302–310 |doi=10.1016/j.epsl.2016.05.022 |bibcode=2016E&PSL.449..302A |doi-access=free |hdl=20.500.11850/117905 |hdl-access=free}}</ref> A study published in 2022, using high-resolution simulations (up to {{val|e=8}} particles), found that giant impacts can immediately place a satellite with similar mass and iron content to the Moon into orbit far outside Earth's [[Roche limit]]. Even satellites that initially pass within the Roche limit can reliably and predictably survive, by being partially stripped and then torqued onto wider, stable orbits.<ref>{{cite journal |last1=Kegerreis |first1=J.A. |last2=Ruiz-Bonilla |first2=S. |last3=Eke |first3=V.R. |last4=Massey |first4=R.J. |last5=Sandnes |first5=T.D. |last6=Teodoro |first6=L.F.A. |display-authors=1 |date=October 4, 2022 |title=Immediate Origin of the Moon as a Post-impact Satellite |journal=The Astrophysical Journal Letters |volume=937 |issue=L40 |pages=L40 |doi=10.3847/2041-8213/ac8d96 |arxiv=2210.01814 |bibcode=2022ApJ...937L..40K |s2cid=249267497 |doi-access=free}}</ref>

On November 1, 2023, scientists reported that, according to computer simulations, remnants of Theia could still be present inside the Earth.<ref name="NYT-20231101">{{cite news |last=Chang |first=Kenneth |title=A 'Big Whack' Formed the Moon and Left Traces Deep in Earth, a Study Suggests – Two enormous blobs deep inside Earth could be remnants of the birth of the moon. |url=https://www.nytimes.com/2023/11/01/science/moon-formation-theia.html |date=November 1, 2023 |work=[[The New York Times]] |url-status=live |archive-url=https://archive.today/20231101232849/https://www.nytimes.com/2023/11/01/science/moon-formation-theia.html |archive-date=November 1, 2023 |access-date=November 2, 2023}}</ref><ref name="NAT-20231101">{{cite journal |author=Yuan, Qian |display-authors=et al. |title=Moon-forming impactor as a source of Earth's basal mantle anomalies |url=https://www.nature.com/articles/s41586-023-06589-1 |date=November 1, 2023 |journal=[[Nature (journal)|Nature]] |volume=623 |issue=7985 |pages=95–99 |doi=10.1038/s41586-023-06589-1 |pmid=37914947 |bibcode=2023Natur.623...95Y |s2cid=264869152 |url-status=live |archive-url=https://archive.today/20231102061800/https://www.nature.com/articles/s41586-023-06589-1 |archive-date=November 2, 2023 |access-date=November 2, 2023}}</ref>

===Natural development===
[[File:Archean.png|thumb|upright=1.5|Artist's depiction of the Moon in Earth's sky as it might have appeared around 4 billion years ago, after the [[Late Heavy Bombardment]]. At that time the Moon orbited the Earth at a third of its current distance, making it appear 2.8 times larger in [[apparent size]] than it does today.<ref name="Lunar and Planetary Institute" />]]

The newly formed Moon settled into a much closer Earth orbit than it has today. Each body therefore appeared much larger in the sky of the other, [[eclipse]]s were more frequent, and [[tidal effect]]s were stronger.<ref name="Lunar and Planetary Institute">{{cite web |title=Earth-Moon Dynamics |website=Lunar and Planetary Institute |url=https://www.lpi.usra.edu/exploration/training/illustrations/earthMoon/ |access-date=September 2, 2022 |archive-date=September 7, 2015 |archive-url=https://web.archive.org/web/20150907215806/https://www.lpi.usra.edu/exploration/training/illustrations/earthMoon/ |url-status=live}}</ref>
Due to [[tidal acceleration]], the Moon's orbit around Earth has become significantly larger, with a longer period.<ref>{{cite journal |title=Early evolution of the Earth-Moon system with a fast-spinning Earth |last1=Wisdom |first1=Jack |last2=Tian |first2=ZhenLiang |journal=Icarus |volume=256 |pages=138–146 |date=August 2015 |doi=10.1016/j.icarus.2015.02.025 |bibcode=2015Icar..256..138W}}</ref>

Following formation, the Moon has cooled and most of [[Atmosphere of the Moon|its atmosphere]] has been stripped.<ref name="John 2017">{{cite magazine |last=John |first=Tara |title=NASA: The Moon Once Had an Atmosphere That Faded Away |magazine=Time |date=October 9, 2017 |url=https://time.com/4974580/nasa-moon-had-atmosphere-volcanoes/ |access-date=May 16, 2023 |archive-date=May 14, 2023 |archive-url=https://web.archive.org/web/20230514100131/https://time.com/4974580/nasa-moon-had-atmosphere-volcanoes/ |url-status=live}}</ref> The [[surface of the Moon|lunar surface]] has since been shaped by large [[impact event]]s and many small ones, forming a landscape featuring [[Lunar crater|craters]] of all ages.

The Moon was [[volcanism|volcanically active]] until 1.2&nbsp;billion years ago, which laid down the prominent [[lunar maria]]. Most of the [[lunar mare|mare basalts]] erupted during the [[Imbrian|Imbrian period]], 3.3–3.7&nbsp;billion years ago, though some are as young as 1.2&nbsp;billion years<ref name="Hiesinger" /> and some as old as 4.2&nbsp;billion years.<ref name="Papike" /> There are differing explanations for the eruption of mare basalts, particularly their uneven occurrence which mainly appear on the near-side. Causes of the distribution of the [[lunar highlands]] on the [[Far side of the Moon|far side]] are also not well understood. Topological measurements show the near side crust is thinner than the far side. One possible scenario then is that large impacts on the near side may have made it easier for lava to flow onto the surface.<ref name="ESA Science & Technology 2006">{{cite web |title=Lunar Far Side Highlands |website=ESA Science & Technology |date=July 14, 2006 |url=https://sci.esa.int/web/smart-1/-/39791-lunar-far-side-highlands |access-date=September 2, 2022 |archive-date=September 2, 2022 |archive-url=https://web.archive.org/web/20220902221440/https://sci.esa.int/web/smart-1/-/39791-lunar-far-side-highlands |url-status=live}}</ref>

==Physical characteristics==
The Moon is a very slightly scalene [[ellipsoid]] due to tidal stretching, with its long axis displaced 30° from facing the Earth, due to gravitational anomalies from impact basins. Its shape is more elongated than current tidal forces can account for. This 'fossil bulge' indicates that the Moon solidified when it orbited at half its current distance to the Earth,<!--at ≈32 Earth radii, currently at 60.3--> and that it is now too cold for its shape to restore [[hydrostatic equilibrium]] at its current orbital distance.<ref>{{cite journal |last1=Garrick-Bethell |first1=Ian |last2=Perera |first2=Viranga |last3=Nimmo |first3=Francis |last4=Zuber |first4=Maria T. |year=2014 |title=The tidal-rotational shape of the Moon and evidence for polar wander |url=https://escholarship.org/content/qt0012r6g6/qt0012r6g6.pdf?t=npc7m2 |journal=Nature |volume=512 |issue=7513 |pages=181–184 |doi=10.1038/nature13639 |pmid=25079322 |bibcode=2014Natur.512..181G |s2cid=4452886 |access-date=April 12, 2020 |archive-date=August 4, 2020 |archive-url=https://web.archive.org/web/20200804071339/https://escholarship.org/content/qt0012r6g6/qt0012r6g6.pdf?t=npc7m2 |url-status=live}}</ref>

===Size and mass===
{{Further|List of natural satellites}}
[[File:Moons of solar system v7.jpg|thumb|upright=1.5|Size comparison of the main moons of the Solar System with Earth to scale. Nineteen moons are large enough [[Hydrostatic equilibrium|to be round]], several having [[subsurface ocean]]s and one, Titan, having a considerable atmosphere.]]
The Moon is by size and mass the fifth largest natural satellite of the Solar System, categorizable as one of its [[planetary-mass moon]]s, making it a satellite planet under the [[geophysical definition of planet|geophysical definitions of the term]].<ref name="Metzger2021">{{Citation |last1=Metzger |first1=Philip |author-link1=Philip T. Metzger |last2=Grundy |first2=Will |last3=Sykes |first3=Mark |last4=Stern |first4=Alan |last5=Bell |first5=James |last6=Detelich |first6=Charlene |last7=Runyon |first7=Kirby |last8=Summers |first8=Michael |date=2021 |title=Moons are planets: Scientific usefulness versus cultural teleology in the taxonomy of planetary science |journal=[[Icarus (journal)|Icarus]] |volume=374 |page=114768 |doi=10.1016/j.icarus.2021.114768 |arxiv=2110.15285 |bibcode=2022Icar..37414768M |s2cid=240071005}}</ref> It is smaller than [[Mercury (planet)|Mercury]] and considerably larger than the largest [[dwarf planet]] of the Solar System, [[Pluto]]. The Moon is the largest natural satellite in the Solar System relative to its [[Primary (astronomy)|primary]] planet.{{efn |There is no strong correlation between the sizes of planets and the sizes of their satellites. Larger planets tend to have more satellites, both large and small, than smaller planets.}}{{efn|name=Moon vs. Charon}}<ref>{{cite web |url=http://www.planetary.org/explore/topics/pluto/ |title=Space Topics: Pluto and Charon |publisher=[[The Planetary Society]] |access-date=April 6, 2010 |url-status=dead |archive-url=https://web.archive.org/web/20120218223842/http://www.planetary.org/explore/topics/pluto/ |archive-date=February 18, 2012}}</ref>

The Moon's diameter is about 3,500&nbsp;km, more than one-quarter of Earth's, with the face of the Moon comparable to the width of either [[mainland Australia]],<ref name="Australia">{{cite web |url=https://theconversation.com/how-big-is-the-moon-let-me-compare-118840 |date=July 18, 2019 |access-date=November 15, 2020 |title=How big is the Moon? |first=Jonti |last=Horner |archive-date=November 7, 2020 |archive-url=https://web.archive.org/web/20201107223707/http://theconversation.com/how-big-is-the-moon-let-me-compare-118840 |url-status=live}}</ref> Europe or the [[contiguous United States]].<ref name="Dyches 2021 d923">{{cite news |last=Dyches |first=Preston |title=Five Things to Know about the Moon |work=NASA Solar System Exploration |date=July 28, 2021 |url=https://solarsystem.nasa.gov/news/1946/five-things-to-know-about-the-moon/ |access-date=September 24, 2023 |archive-date=July 18, 2023 |archive-url=https://web.archive.org/web/20230718090707/https://solarsystem.nasa.gov/news/1946/five-things-to-know-about-the-moon/ |url-status=live}}</ref> The whole surface area of the Moon is about 38&nbsp;million square kilometers, comparable to that of the [[Americas]].<ref name="y857">{{cite magazine |last=Parks |first=Jake |title=Everything you need to know about the Moon |magazine=Astronomy |date=2023-09-07 |url=https://www.astronomy.com/observing/everything-you-need-to-know-about-the-moon/ |access-date=2024-09-09}}</ref><ref name="f708">{{cite web |title=Global Island Explorer |publisher=United States Geological Survey |url=https://rmgsc.cr.usgs.gov/gie/gie.shtml |access-date=2024-09-09 }}{{Dead link|date=April 2025 |bot=InternetArchiveBot |fix-attempted=yes }}</ref>

The Moon's mass is {{frac|1|81}} of Earth's,<ref name="worldbook" /> being the second densest among the planetary moons, and having the second highest [[surface gravity]], after [[Io (moon)|Io]], at {{val |0.1654 |u=[[G-force|g]]}} and an escape velocity of {{convert|2.38|km/s|km/h mph|comma=gaps|abbr=on}}.

===Structure===
{{Main|Internal structure of the Moon|Geology of the Moon}}
[[File:Return of the moon diagram.svg|thumb|upright=1.5|Moon's internal structure: solid inner core (iron-metallic), molten outer core, hardened mantle and crust. The crust on the Moon's near side permanently facing Earth is thinner, featuring larger areas flooded by material of the once molten mantle forming today's [[lunar mare]].]]
The Moon is a [[planetary differentiation|differentiated]] body that was initially in [[hydrostatic equilibrium]] but has since departed from this condition.<ref>{{cite journal |title=Interpretation of lunar potential fields |first=Stanley Keith |last=Runcorn |date=March 31, 1977 |journal=Philosophical Transactions of the Royal Society of London. Series A, Mathematical and Physical Sciences |doi=10.1098/rsta.1977.0094 |bibcode=1977RSPTA.285..507R |volume=285 |issue=1327 |pages=507–516 |s2cid=124703189}}</ref> It has a [[geochemically]] distinct [[Crust (geology)|crust]], [[Mantle (geology)|mantle]], and [[Planetary core|core]]. The Moon has a solid iron-rich inner core with a radius possibly as small as {{convert|240|km}} and a fluid outer core primarily made of liquid iron with a radius of roughly {{convert|300|km}}. Around the core is a partially molten boundary layer with a radius of about {{convert|500|km}}.<ref>{{cite web |last1=Brown |first1=D. |last2=Anderson |first2=J. |website=NASA |url=http://www.nasa.gov/topics/moonmars/features/lunar_core.html |title=NASA Research Team Reveals Moon Has Earth-Like Core |date=January 6, 2011 |url-status=live |archive-url=https://web.archive.org/web/20120111112210/http://www.nasa.gov/topics/moonmars/features/lunar_core.html |archive-date=January 11, 2012}}</ref><ref name="Weber2011">{{cite journal |last1=Weber |first1=R.C. |last2=Lin |first2=P.-Y. |last3=Garnero |first3=E.J. |last4=Williams |first4=Q. |last5=Lognonne |first5=P. |title=Seismic Detection of the Lunar Core |journal=Science |volume=331 |issue=6015 |date=January 21, 2011 |pages=309–312 |url=http://www.earth.northwestern.edu/people/seth/351/lunarcore.2011.pdf |doi=10.1126/science.1199375 |pmid=21212323 |url-status=dead |archive-url=https://web.archive.org/web/20151015035756/http://www.earth.northwestern.edu/people/seth/351/lunarcore.2011.pdf |archive-date=October 15, 2015 |bibcode=2011Sci...331..309W |s2cid=206530647 |access-date=April 10, 2017}}</ref> This structure is thought to have developed through the [[Fractional crystallization (geology)|fractional crystallization]] of a global magma ocean shortly after the Moon's formation 4.5&nbsp;billion years ago.<ref>{{cite journal |doi=10.1038/ngeo417 |title=Timing of crystallization of the lunar magma ocean constrained by the oldest zircon |date=2009 |last1=Nemchin |first1=A. |last2=Timms |first2=N. |last3=Pidgeon |first3=R. |last4=Geisler |first4=T. |last5=Reddy |first5=S. |last6=Meyer |first6=C. |journal=[[Nature Geoscience]] |volume=2 |issue=2 |pages=133–136 |bibcode=2009NatGe...2..133N |hdl=20.500.11937/44375 |hdl-access=free}}</ref>

Crystallization of this magma ocean would have created a [[mafic]] mantle from the [[Precipitation (chemistry)|precipitation]] and sinking of the minerals [[olivine]], [[clinopyroxene]], and [[orthopyroxene]]; after about three-quarters of the magma ocean had crystallized, lower-density [[plagioclase]] minerals could form and float into a crust atop.<ref name="S06" /> The final liquids to crystallize would have been initially sandwiched between the crust and mantle, with a high abundance of [[Compatibility (geochemistry)|incompatible]] and heat-producing elements.<ref name="W06" /> Consistent with this perspective, geochemical mapping made from orbit suggests a crust of mostly [[anorthosite]].<ref name="L06" /> The [[Moon rock]] samples of the flood lavas that erupted onto the surface from partial melting in the mantle confirm the mafic mantle composition, which is more iron-rich than that of Earth.<ref name="W06" /> The crust is on average about {{convert|50|km}} thick.<ref name="W06" />

The Moon is the second-densest satellite in the Solar System, after [[Io (moon)|Io]].<ref name="Schubert2004" /> However, the inner core of the Moon is small, with a radius of about {{convert|350|km}} or less,<ref name="W06" /> around 20% of the radius of the Moon. Its composition is not well understood but is probably metallic iron alloyed with a small amount of sulfur and nickel. Analyses of the Moon's time-variable rotation suggest that it is at least partly molten.<ref>{{cite journal |last1=Williams |first1=J.G. |last2=Turyshev |first2=S.G. |last3=Boggs |first3=D.H. |last4=Ratcliff |first4=J.T. |title=Lunar laser ranging science: Gravitational physics and lunar interior and geodesy |journal=[[Advances in Space Research]] |date=2006 |volume=37 |issue=1 |pages=67–71 |bibcode=2006AdSpR..37...67W |doi=10.1016/j.asr.2005.05.013 |arxiv=gr-qc/0412049 |s2cid=14801321}}</ref> The pressure at the lunar core is estimated to be {{cvt|5|GPa|atm}}.<ref>{{cite journal |title=The Case Against an Early Lunar Dynamo Powered by Core Convection |last1=Evans |first1=Alexander J. |last2=Tikoo |first2=Sonia M. |first3=Andrews-Hanna |last3=Jeffrey C. |journal=Geophysical Research Letters |date=January 2018 |volume=45 |issue=1 |pages=98–107 |doi=10.1002/2017GL075441 |bibcode=2018GeoRL..45...98E |doi-access=free}}</ref>

=== Gravitational field ===
[[File:Youtubeastronautsonmoonot3.gif|thumb|Astronaut [[John Young (astronaut)|John Young]] jumping on the Moon, illustrating that the [[Gravitational acceleration|gravitational pull]] of the Moon is approximately 1/6 of Earth's. The jumping height is limited by the EVA space suit's weight on the Moon of about {{cvt|13.6|kg|lbs}} and by the suit's pressurization resisting the bending of the suit, as needed for jumping.<ref name="Kluger 2018 z081">{{cite magazine |last=Kluger |first=Jeffrey |title=How Neil Armstrong's Moon Spacesuit Was Preserved for Centuries to Come |magazine=Time |date=October 12, 2018 |url=https://time.com/5422609/armstrong-spacesuit-smithsonian/ |access-date=November 29, 2023 |archive-date=December 3, 2023 |archive-url=https://web.archive.org/web/20231203061321/https://time.com/5422609/armstrong-spacesuit-smithsonian/ |url-status=live}}</ref><ref name="Nast 2013 v237">{{cite magazine |title=How Do You Pick Up Something on the Moon? |magazine=WIRED |date=December 9, 2013 |url=https://www.wired.com/2013/12/how-do-you-pick-up-something-on-the-moon/ |access-date=November 29, 2023 |archive-date=December 3, 2023 |archive-url=https://web.archive.org/web/20231203061321/https://www.wired.com/2013/12/how-do-you-pick-up-something-on-the-moon/ |url-status=live}}</ref>]]

On average the Moon's [[surface gravity]] is {{val|1.62|ul=m/s2}}<ref name="NSSDC" /> ({{val|0.1654|u=[[G-force|g]]}}; {{val|5.318|ul=ft/s2}}), about half of the surface gravity of [[Mars]] and about a sixth of Earth's.

The [[Gravitation of the Moon|Moon's gravitational field]] is not uniform. The details of the gravitational field have been measured through tracking the [[Doppler shift]] of radio signals emitted by orbiting spacecraft. The main lunar gravity features are [[mass concentration (astronomy)|mascons]], large positive gravitational anomalies associated with some of the giant impact basins, partly caused by the dense mare basaltic lava flows that fill those basins.<ref>{{cite journal |last=Muller |first=P. |author2=Sjogren, W. |title=Mascons: lunar mass concentrations |journal=[[Science (journal)|Science]] |volume=161 |pages=680–684 |date=1968 |doi=10.1126/science.161.3842.680 |pmid=17801458 |issue=3842 |bibcode=1968Sci...161..680M |s2cid=40110502}}</ref><ref>{{cite journal |journal=[[Science (journal)|Science]] |author=Richard A. Kerr |title=The Mystery of Our Moon's Gravitational Bumps Solved? |volume=340 |issue=6129 |pages=138–139 |date=April 12, 2013 |doi=10.1126/science.340.6129.138-a |pmid=23580504}}</ref> The anomalies greatly influence the orbit of spacecraft about the Moon. There are some puzzles: lava flows by themselves cannot explain all of the gravitational signature, and some mascons exist that are not linked to mare volcanism.<ref>{{cite journal |last=Konopliv |first=A. |author2=Asmar, S. |author3=Carranza, E. |author4=Sjogren, W. |author5=Yuan, D. |title=Recent gravity models as a result of the Lunar Prospector mission |journal=[[Icarus (journal)|Icarus]] |volume=50 |issue=1 |pages=1–18 |date=2001 |doi=10.1006/icar.2000.6573 |bibcode=2001Icar..150....1K |url=http://techreports.jpl.nasa.gov/2000/00-1301.pdf |url-status=dead |archive-url=https://web.archive.org/web/20041113045200/http://techreports.jpl.nasa.gov/2000/00-1301.pdf |archive-date=November 13, 2004 |citeseerx=10.1.1.18.1930}}</ref>

=== Magnetic field ===
The Moon has [[Magnetic field of the Moon|an external magnetic field]] of less than 0.2 [[Tesla (unit)|nanoteslas]],<ref name="Mighani2020">{{cite journal |last1=Mighani |first1=S. |last2=Wang |first2=H. |last3=Shuster |first3=D.L. |last4=Borlina |first4=C.S. |last5=Nichols |first5=C.I.O. |last6=Weiss |first6=B.P. |title=The end of the lunar dynamo |journal=Science Advances |volume=6 |issue=1 |year=2020 |pages=eaax0883 |doi=10.1126/sciadv.aax0883 |pmid=31911941 |pmc=6938704 |bibcode=2020SciA....6..883M}}</ref> or less than one hundred thousandth [[Earth's magnetic field|that of Earth]]. The Moon does not have a global [[dipolar]] magnetic field and only has crustal magnetization likely acquired early in its history when a dynamo was still operating.<ref name="GB2009" /><ref>{{cite web |url=http://lunar.arc.nasa.gov/results/magelres.htm |publisher=[[Lunar Prospector]] (NASA) |title=Magnetometer / Electron Reflectometer Results |date=2001 |access-date=March 17, 2010 |url-status=dead |archive-url=https://web.archive.org/web/20100527121330/http://lunar.arc.nasa.gov/results/magelres.htm |archive-date=May 27, 2010}}</ref> Early in its history, 4 billion years ago, its magnetic field strength was likely close to that of Earth today.<ref name="Mighani2020" /> This early dynamo field apparently expired by about one billion years ago, after the lunar core had crystallized.<ref name="Mighani2020" /> Theoretically, some of the remnant magnetization may originate from transient magnetic fields generated during large impacts through the expansion of plasma clouds. These clouds are generated during large impacts in an ambient magnetic field. This is supported by the location of the largest crustal magnetizations situated near the [[antipodes]] of the giant impact basins.<ref>{{cite journal |last=Hood |first=L.L. |author2=Huang, Z. |title=Formation of magnetic anomalies antipodal to lunar impact basins: Two-dimensional model calculations |journal=[[Journal of Geophysical Research]] |volume=96 |issue=B6 |pages=9837–9846 |date=1991 |doi=10.1029/91JB00308 |bibcode=1991JGR....96.9837H}}</ref>

=== Atmosphere ===
{{Main|Atmosphere of the Moon}}
[[File:Apollo 17 twilight ray sketch.jpg|thumb|The thin lunar atmosphere is visible on the Moon's surface at [[sunrise]] and [[sunset]] with the [[lunar horizon glow]]<ref name="The Planetary Society 2016">{{cite web |title=Lunar horizon glow from Surveyor 7 |website=The Planetary Society |date=May 6, 2016 |url=https://www.planetary.org/space-images/lunar-horizon-glow-surveyor-7 |access-date=August 8, 2022 |archive-date=August 8, 2022 |archive-url=https://web.archive.org/web/20220808062356/https://www.planetary.org/space-images/lunar-horizon-glow-surveyor-7 |url-status=live}}</ref> and lunar twilight rays, like Earth's [[crepuscular rays]]. This [[Apollo 17]] sketch depicts the glow and rays<ref name="Science Mission Directorate 2013">{{cite web |title=NASA Mission To Study Mysterious Lunar Twilight Rays |website=Science Mission Directorate |date=September 3, 2013 |url=https://science.nasa.gov/science-news/science-at-nasa/2013/03sep_ladee |access-date=August 8, 2022 |archive-date=July 3, 2022 |archive-url=https://web.archive.org/web/20220703030019/https://science.nasa.gov/science-news/science-at-nasa/2013/03sep_ladee/ |url-status=live}}</ref> among the general [[zodiacal light]].<ref name="Colwell Robertson Horányi Wang 2009 pp. 2–9">{{cite journal |last1=Colwell |first1=Joshua E. |last2=Robertson |first2=Scott R. |last3=Horányi |first3=Mihály |last4=Wang |first4=Xu |last5=Poppe |first5=Andrew |last6=Wheeler |first6=Patrick |title=Lunar Dust Levitation |journal=Journal of Aerospace Engineering |volume=22 |issue=1 |date=January 1, 2009 |doi=10.1061/(ASCE)0893-1321(2009)22:1(2) |pages=2–9 |url=https://ascelibrary.org/doi/10.1061/%28ASCE%290893-1321%282009%2922%3A1%282%29 |access-date=August 8, 2022 |archive-date=August 8, 2022 |archive-url=https://web.archive.org/web/20220808202200/https://ascelibrary.org/doi/10.1061/(ASCE)0893-1321(2009)22:1(2) |url-status=live}}</ref><ref name="EarthSky Updates on your cosmos and world 2014">{{cite web |title=The zodiacal light, seen from the moon |website=EarthSky |author=Deborah Byrd |date=April 24, 2014 |url=https://earthsky.org/space/the-zodiacal-light-seen-from-the-moon/ |access-date=August 8, 2022 |archive-date=August 8, 2022 |archive-url=https://web.archive.org/web/20220808062351/https://earthsky.org/space/the-zodiacal-light-seen-from-the-moon/ |url-status=live}}</ref>]]

The Moon has an [[atmosphere]] consisting of only an [[exosphere]],<ref name="l546">{{cite web | last=Barry | first=Caela | title=The Moon's Atmosphere | website=NASA Science | date=2025-01-30 | url=https://science.nasa.gov/moon/lunar-atmosphere/ | access-date=2025-03-07}}</ref> which is so tenuous as to be nearly [[vacuum]], with a total mass of less than {{Convert|10 |t}}.<ref>{{cite book |editor=Richard D. Johnson & Charles Holbrow |last=Globus |first=Ruth |title=Space Settlements: A Design Study |chapter=Chapter 5, Appendix J: Impact Upon Lunar Atmosphere |publisher=NASA |chapter-url=http://settlement.arc.nasa.gov/75SummerStudy/5appendJ.html |date=1977 |access-date=March 17, 2010 |url-status=dead |archive-url=https://web.archive.org/web/20100531205037/http://settlement.arc.nasa.gov/75SummerStudy/5appendJ.html |archive-date=May 31, 2010}}</ref> The surface pressure of this small mass is around 3 × 10<sup>−15</sup>&nbsp;[[Atmosphere (unit)|atm]] (0.3&nbsp;[[nanopascal|nPa]]); it varies with the lunar day. Its sources include [[outgassing]] and [[sputtering]], a product of the bombardment of lunar soil by solar wind ions.<ref name="L06" /><ref>{{cite journal |last=Crotts |first=Arlin P.S. |title=Lunar Outgassing, Transient Phenomena and The Return to The Moon, I: Existing Data |date=2008 |url=http://www.astro.columbia.edu/~arlin/TLP/paper1.pdf |bibcode=2008ApJ...687..692C |volume=687 |issue=1 |pages=692–705 |journal=[[The Astrophysical Journal]] |doi=10.1086/591634 |arxiv=0706.3949 |s2cid=16821394 |url-status=dead |archive-url=https://web.archive.org/web/20090220081142/http://www.astro.columbia.edu/~arlin/TLP/paper1.pdf |archive-date=February 20, 2009 |access-date=September 29, 2009}}</ref> Elements that have been detected include [[sodium]] and [[potassium]], produced by sputtering (also found in the atmospheres of Mercury and [[Io (moon)|Io]]); [[helium-4]] and [[neon]]<ref name="NASA-20150817">{{cite web |last=Steigerwald |first=William |title=NASA's LADEE Spacecraft Finds Neon in Lunar Atmosphere |url=http://www.nasa.gov/content/goddard/ladee-lunar-neon |date=August 17, 2015 |work=NASA |access-date=August 18, 2015 |archive-date=August 19, 2015 |archive-url=https://web.archive.org/web/20150819035151/http://www.nasa.gov/content/goddard/ladee-lunar-neon/ |url-status=live}}</ref> from the solar wind; and [[Argon|argon-40]], [[Radon|radon-222]], and [[polonium-210]], outgassed after their creation by [[radioactive decay]] within the crust and mantle.<ref name="Stern1999" /><ref>{{cite journal |last=Lawson |first=S. |author2=Feldman, W. |author3=Lawrence, D. |author4=Moore, K. |author5=Elphic, R. |author6=Belian, R. |title=Recent outgassing from the lunar surface: the Lunar Prospector alpha particle spectrometer |journal=[[Journal of Geophysical Research]] |volume=110 |issue=E9 |page=1029 |date=2005 |doi=10.1029/2005JE002433 |doi-access=free |bibcode=2005JGRE..110.9009L}}</ref> The absence of such neutral species (atoms or molecules) as [[oxygen]], [[nitrogen]], [[carbon]], [[hydrogen]] and [[magnesium]], which are present in the [[regolith]], is not understood.<ref name="Stern1999" /> Water vapor has been detected by ''[[Chandrayaan-1]]'' and found to vary with latitude, with a maximum at ~60–70&nbsp;degrees; it is possibly generated from the [[sublimation (chemistry)|sublimation]] of water ice in the regolith.<ref name="Sridharan2010" /> These gases either return into the regolith because of the Moon's gravity or are lost to space, either through solar radiation pressure or, if they are ionized, by being swept away by the solar wind's magnetic field.<ref name="Stern1999" />

Studies of Moon magma samples retrieved by the [[Apollo program|Apollo]] missions demonstrate that the Moon had once possessed a relatively thick atmosphere for a period of 70 million years between 3 and 4 billion years ago. This atmosphere, sourced from gases ejected from lunar volcanic eruptions, was twice the thickness of that of present-day [[Mars]]. The ancient lunar atmosphere was eventually stripped away by solar winds and dissipated into space.<ref name="John 2017"/>

A permanent [[Moon dust]] cloud exists around the Moon, generated by small particles from comets. Estimates are 5 tons of comet particles strike the Moon's surface every 24 hours, resulting in the ejection of dust particles. The dust stays above the Moon approximately 10 minutes, taking 5 minutes to rise, and 5 minutes to fall. On average, 120 kilograms of dust are present above the Moon, rising up to 100 kilometers above the surface. Dust counts made by [[LADEE]]'s Lunar Dust EXperiment (LDEX) found particle counts peaked during the [[Geminid]], [[Quadrantid]], [[Taurids|Northern Taurid]], and [[Omicron Centaurids|Omicron Centaurid]] [[meteor shower]]s, when the Earth, and Moon pass through comet debris. The lunar dust cloud is asymmetric, being denser near the boundary between the Moon's dayside and nightside.<ref>{{cite web |title=Lopsided Cloud of Dust Discovered Around the Moon |url=http://news.nationalgeographic.com/2015/06/150617-moon-dust-cloud-comet-space |website=National Geographic News |access-date=June 20, 2015 |first1=Nadia |last1=Drake |author1-link=Nadia Drake |url-status=dead |archive-url=https://web.archive.org/web/20150619052915/http://news.nationalgeographic.com/2015/06/150617-moon-dust-cloud-comet-space/ |archive-date=June 19, 2015 |date=June 17, 2015}}</ref><ref>{{Cite journal |title=A permanent, asymmetric dust cloud around the Moon |journal=[[Nature (journal)|Nature]] |date=June 18, 2015 |pages=324–326 |volume=522 |issue=7556 |doi=10.1038/nature14479 |first1=M. |last1=Horányi |first2=J.R. |last2=Szalay |first3=S. |last3=Kempf |first4=J. |last4=Schmidt |first5=E. |last5=Grün |first6=R. |last6=Srama |first7=Z. |last7=Sternovsky |bibcode=2015Natur.522..324H |pmid=26085272 |s2cid=4453018}}</ref>

===Surface conditions===
[[File:AS17-145-22224.jpg|thumb|[[Gene Cernan]] with [[lunar dust]] stuck on his suit. Lunar dust is highly abrasive and can cause damage to human lungs and nervous and cardiovascular systems.<ref>{{Cite web |last1=James |first1=John |last2=Kahn-Mayberry |first2=Noreen |date=Jan 2009 |title=Risk of Adverse Health Effects from Lunar Dust Exposure |url=https://humanresearchroadmap.nasa.gov/evidence/reports/lunar%20dust.pdf |access-date=December 8, 2022 |archive-date=December 4, 2021 |archive-url=https://web.archive.org/web/20211204004317/https://humanresearchroadmap.nasa.gov/evidence/reports/lunar%20dust.pdf |url-status=live}}</ref>]]
[[Ionizing radiation]] from [[cosmic ray]]s, their resulting [[neutron radiation]],<ref name="Science Mission Directorate 2005">{{cite web|date=September 8, 2005|title=Radioactive Moon|url=https://science.nasa.gov/science-news/science-at-nasa/2005/08sep_radioactivemoon#:~:text=Not%20so.,lunar%20surface%20itself%20is%20radioactive!|url-status=deviated|archive-url=https://web.archive.org/web/20191102123953/https://science.nasa.gov/science-news/science-at-nasa/2005/08sep_radioactivemoon/#:~:text=Not%20so.,lunar%20surface%20itself%20is%20radioactive!|archive-date=November 2, 2019|access-date=July 28, 2022|website=Science Mission Directorate}}</ref> and the Sun results in an average radiation level of 1.369 [[millisievert]]s per day during lunar [[daytime]],<ref name="surface-radiation"/> which is about 2.6 times more than the level on the [[International Space Station]], 5{{endash}}10 times more than the level during a trans-Atlantic flight, and 200 times more than the level on Earth's surface.<ref name="ScienceAlert 2020">{{cite web |date=September 26, 2020 |title=We Finally Know How Much Radiation There Is on The Moon, And It's Not Great News |url=https://www.sciencealert.com/scientists-predict-how-long-humans-can-survive-radiation-on-the-moon |url-status=live |archive-url=https://web.archive.org/web/20220728004319/https://www.sciencealert.com/scientists-predict-how-long-humans-can-survive-radiation-on-the-moon |archive-date=July 28, 2022 |access-date=July 28, 2022 |website=ScienceAlert}}</ref> For further comparison, radiation levels average about 1.84 millisieverts per day on a [[Human mission to Mars|flight to Mars]] and about 0.64 millisieverts per day on Mars itself, with some locations on Mars possibly having levels as low as 0.342 millisieverts per day.<ref name="Paris Davies Tognetti Zahniser 2020">{{cite arXiv |last1=Paris |first1=Antonio |last2=Davies |first2=Evan |last3=Tognetti |first3=Laurence |last4=Zahniser |first4=Carly |title=Prospective Lava Tubes at Hellas Planitia |date=April 27, 2020 |class=astro-ph.EP |eprint=2004.13156v1}}</ref><ref name="Wall 2013">{{cite web |last=Wall |first=Mike |date=December 9, 2013 |title=Radiation on Mars 'Manageable' for Manned Mission, Curiosity Rover Reveals |url=https://www.space.com/23875-mars-radiation-life-manned-mission.html |access-date=August 7, 2022 |website=Space.com |archive-date=December 15, 2020 |archive-url=https://web.archive.org/web/20201215082045/https://www.space.com/23875-mars-radiation-life-manned-mission.html |url-status=live}}</ref>
Solar radiation also [[static electricity|electrically charges]] the highly abrasive [[lunar dust]] and makes it levitate. This effect contributes to the easy spread of the sticky, lung- and gear-damaging lunar dust.<ref name="e657">{{cite web |title=The toxic side of the Moon |website=ESA |url=https://www.esa.int/Science_Exploration/Human_and_Robotic_Exploration/The_toxic_side_of_the_Moon |access-date=2025-01-07}}</ref>

The Moon's [[axial tilt]] with respect to the [[ecliptic]] is only 1.5427°,<ref name="SolarViews" /><ref>{{Cite journal |last1=Rambaux |first1=N. |last2=Williams |first2=J. G. |date=2011 |title=The Moon's physical librations and determination of their free modes |url=https://doi.org/10.1007/s10569-010-9314-2 |url-status=live |journal=Celestial Mechanics and Dynamical Astronomy |volume=109 |issue=1 |pages=85–100 |bibcode=2011CeMDA.109...85R |doi=10.1007/s10569-010-9314-2 |archive-url=https://web.archive.org/web/20220730084921/https://link.springer.com/article/10.1007/s10569-010-9314-2 |archive-date=July 30, 2022 |access-date=July 30, 2022 |s2cid=45209988}}</ref> much less than the 23.44° of Earth. This small axial tilt means that the Moon's solar illumination varies much less with [[season]] than Earth's, and it also allows for the existence of some [[peaks of eternal light]] at the [[Lunar north pole|Moon's north pole]], at the rim of the crater [[Peary (crater)|Peary]].

The lunar surface is exposed to drastic temperature differences ranging from {{val|120|u=°C}} to {{val|−171|u=°C}} depending on the [[solar irradiance]].
Because of the lack of atmosphere, temperatures of different areas vary particularly upon whether they are in sunlight or shadow,<ref>{{cite web |last=Rocheleau |first=Jake |date=May 21, 2012 |title=Temperature on the Moon – Surface Temperature of the Moon |url=http://planetfacts.org/temperature-on-the-moon/ |url-status=live |archive-url=https://web.archive.org/web/20150527194737/http://planetfacts.org/temperature-on-the-moon/ |archive-date=May 27, 2015 |website=PlanetFacts.org}}</ref> making topographical details play a decisive role on local [[Global surface temperature|surface temperature]]s.<ref name="bbc" />
Parts of many craters, particularly the bottoms of many polar craters,<ref name="M03" /> are permanently shadowed. These [[crater of eternal darkness|craters of eternal darkness]] have extremely low temperatures. The ''Lunar Reconnaissance Orbiter'' measured the lowest summer temperatures in craters at the southern pole at {{Convert|35 |K |4=0 |abbr=on}}<ref>{{cite web |date=September 17, 2009 |title=Diviner News |url=http://www.diviner.ucla.edu/blog/?p=123 |url-status=dead |archive-url=https://web.archive.org/web/20100307031354/http://www.diviner.ucla.edu/blog/?p=123 |archive-date=March 7, 2010 |access-date=March 17, 2010 |publisher=[[UCLA]]}}</ref> and just {{Convert |26 |K |4=0 |abbr=on}} close to the winter solstice in the north polar crater [[Hermite (crater)|Hermite]]. This is the coldest temperature in the Solar System ever measured by a spacecraft, colder even than the surface of [[Pluto]].<ref name="bbc" />

Blanketed on top of the Moon's crust is a highly [[Comminution|comminuted]] (broken into ever smaller particles) and [[impact gardening|impact gardened]] mostly gray surface layer called [[regolith]], formed by impact processes. The finer regolith, the [[lunar soil]] of [[silicon dioxide]] glass, has a texture resembling snow and a scent resembling spent [[gunpowder]].<ref>{{cite web |date=January 30, 2006 |title=The Smell of Moondust |url=https://science.nasa.gov/headlines/y2006/30jan_smellofmoondust.htm |url-status=dead |archive-url=https://web.archive.org/web/20100308112332/http://science.nasa.gov/headlines/y2006/30jan_smellofmoondust.htm |archive-date=March 8, 2010 |access-date=March 15, 2010 |publisher=NASA}}</ref> The regolith of older surfaces is generally thicker than for younger surfaces: it varies in thickness from {{convert|10|{{endash}}|15|m|abbr=on}} in the highlands and {{convert|4|{{endash}}|5|m|abbr=on}} in the maria.<ref>{{cite book |last=Heiken |first=G. |url=https://archive.org/details/lunarsourcebooku0000unse/page/286 |title=Lunar Sourcebook, a user's guide to the Moon |date=1991 |publisher=[[Cambridge University Press]] |isbn=978-0-521-33444-0 |editor1-last=Vaniman |editor1-first=D. |location=New York |page=[https://archive.org/details/lunarsourcebooku0000unse/page/286 286] |access-date=December 17, 2019 |editor2-last=French |editor2-first=B. |archive-url=https://web.archive.org/web/20200617181609/https://archive.org/details/lunarsourcebooku0000unse/page/736 |archive-date=June 17, 2020 |url-status=live}}</ref> Beneath the finely comminuted regolith layer is the megaregolith, a layer of highly fractured bedrock many kilometers thick.<ref>{{cite journal |last=Rasmussen |first=K.L. |author2=Warren, P.H. |date=1985 |title=Megaregolith thickness, heat flow, and the bulk composition of the Moon |journal=[[Nature (journal)|Nature]] |volume=313 |issue=5998 |pages=121–124 |bibcode=1985Natur.313..121R |doi=10.1038/313121a0 |s2cid=4245137}}</ref>

These extreme conditions are considered to make it unlikely for spacecraft to harbor bacterial spores at the Moon for longer than just one lunar orbit.<ref>{{cite journal |last1=Schuerger |first1=Andrew C. |last2=Moores |first2=John E. |last3=Smith |first3=David J. |last4=Reitz |first4=Günther |date=June 2019 |title=A Lunar Microbial Survival Model for Predicting the Forward Contamination of the Moon |journal=Astrobiology |volume=19 |issue=6 |pages=730–756 |bibcode=2019AsBio..19..730S |doi=10.1089/ast.2018.1952 |pmid=30810338 |s2cid=73491587 |doi-access=free}}</ref>

===Surface features===
{{Main|Selenography|Lunar terrane|List of lunar features|List of quadrangles on the Moon}}
[[File:Apollo 17 AS17-140-21497.jpg|thumb|[[Apollo 17]] astronaut [[Harrison H. Schmitt]] next to the large Moon boulder nicknamed "[[Tracy's Rock]]"]]
The [[topography of the Moon]] has been measured with [[laser altimetry]] and [[stereoscopy|stereo image analysis]].<ref>{{cite journal |title=Topography of the South Polar Region from Clementine Stereo Imaging |last1=Spudis |first1=Paul D. |last2=Cook |first2=A. |last3=Robinson |first3=M. |last4=Bussey |first4=B. |last5=Fessler |first5=B. |bibcode=1998nvmi.conf...69S |journal=Workshop on New Views of the Moon: Integrated Remotely Sensed, Geophysical, and Sample Datasets |page=69 |date=January 1998}}</ref> Its most extensive [[List of features on the Moon|topographic feature]] is the giant far-side [[South Pole–Aitken basin]], some {{Convert|2240 |km |abbr=on}} in diameter, the largest crater on the Moon and the second-largest confirmed impact [[List of largest craters in the Solar System|crater in the Solar System]].<ref name="Spudis1994" /><ref>{{cite journal |doi=10.1029/97GL01718 |first1=C. M. |last1=Pieters |first2=S. |last2=Tompkins |first3=J. W. |last3=Head |first4=P. C. |last4=Hess |title=Mineralogy of the Mafic Anomaly in the South Pole-Aitken Basin: Implications for excavation of the lunar mantle |journal=[[Geophysical Research Letters]] |volume=24 |issue=15 |pages=1903–1906 |date=1997 |bibcode=1997GeoRL..24.1903P |hdl=2060/19980018038 |s2cid=128767066 |hdl-access=free}}</ref> At {{Convert |13 |km |abbr=on}} deep, its floor is the lowest point on the surface of the Moon,<ref name="Spudis1994" /><ref>{{cite journal |url=http://www.psrd.hawaii.edu/July98/spa.html |title=The Biggest Hole in the Solar System |page=20 |last=Taylor |first=G. J. |date=July 17, 1998 |journal=Planetary Science Research Discoveries |access-date=April 12, 2007 |url-status=live |archive-url=https://web.archive.org/web/20070820042129/http://www.psrd.hawaii.edu/July98/spa.html |archive-date=August 20, 2007 |bibcode=1998psrd.reptE..20T}}</ref> reaching {{convert|-9.178|km}} at {{coord|70.368|S|172.413|W|globe:moon_type:landmark|display=inline}} in a crater within [[Antoniadi (lunar crater)|Antoniadi crater]].<ref name="n402">{{cite journal | last1=Li | first1=ChunLai | last2=Ren | first2=Xin | last3=Liu | first3=JianJun | last4=Zou | first4=XiaoDuan | last5=Mu | first5=LingLi | last6=Wang | first6=JianYu | last7=Shu | first7=Rong | last8=Zou | first8=YongLiao | last9=Zhang | first9=HongBo | last10=Lü | first10=Chang | last11=Liu | first11=JianZhong | last12=Zuo | first12=Wei | last13=Su | first13=Yan | last14=Wen | first14=WeiBin | last15=Bian | first15=Wei | last16=Wang | first16=Min | last17=Xu | first17=Chun | last18=Kong | first18=DeQing | last19=Wang | first19=XiaoQian | last20=Wang | first20=Fang | last21=Geng | first21=Liang | last22=Zhang | first22=ZhouBin | last23=Zheng | first23=Lei | last24=Zhu | first24=XinYing | last25=Li | first25=JunDuo | last26=Ouyang | first26=ZiYuan | title=Laser altimetry data of Chang'E-1 and the global lunar DEM model | journal=Science China Earth Sciences | volume=53 | issue=11 | date=2010 | issn=1674-7313 | doi=10.1007/s11430-010-4020-1 | pages=1582–1593| bibcode=2010ScChD..53.1582L }}</ref> The [[List of tallest mountains in the Solar System|highest elevations]] of the Moon's surface, with the so-called [[Selenean summit]] at {{convert|10.629|km}} , are located directly to the northeast ({{coord|5.441|N|158.656|W|globe:moon_type:landmark|display=inline}}),<ref name="n402"/> which might have been thickened by the oblique formation impact of the South Pole–Aitken basin.<ref>{{cite journal |last=Schultz |first=P.H. |date=March 1997 |page=1259 |volume=28 |title=Forming the south-pole Aitken basin – The extreme games |journal=Conference Paper, 28th Annual Lunar and Planetary Science Conference |bibcode=1997LPI....28.1259S}}</ref> Other large impact basins such as [[Mare Imbrium|Imbrium]], [[Mare Serenitatis|Serenitatis]], [[Mare Crisium|Crisium]], [[Mare Smythii|Smythii]], and [[Mare Orientale|Orientale]] possess regionally low elevations and elevated rims.<ref name="Spudis1994" /> The far side of the lunar surface is on average about {{Convert |1.9 |km |abbr=on}} higher than that of the near side.<ref name="W06" />

The discovery of [[fault scarp]] cliffs suggest that the Moon has shrunk by about 90 metres (300&nbsp;ft) within the past billion years.<ref>{{cite web |publisher=NASA |title=NASA's LRO Reveals 'Incredible Shrinking Moon' |date=August 19, 2010 |url=http://www.nasa.gov/mission_pages/LRO/news/shrinking-moon.html |url-status=live |archive-url=https://web.archive.org/web/20100821124252/http://www.nasa.gov/mission_pages/LRO/news/shrinking-moon.html |archive-date=August 21, 2010}}</ref> Similar shrinkage features exist on [[Geology of Mercury|Mercury]]. Mare Frigoris, a basin near the north pole long assumed to be geologically dead, has cracked and shifted. Since the Moon does not have tectonic plates, its tectonic activity is slow, and cracks develop as it loses heat.<ref>{{Cite journal |last1=Watters |first1=Thomas R. |last2=Weber |first2=Renee C. |last3=Collins |first3=Geoffrey C. |last4=Howley |first4=Ian J. |last5=Schmerr |first5=Nicholas C. |last6=Johnson |first6=Catherine L. |date=June 2019 |title=Shallow seismic activity and young thrust faults on the Moon |journal=Nature Geoscience |publication-date=May 13, 2019 |volume=12 |issue=6 |pages=411–417 |doi=10.1038/s41561-019-0362-2 |bibcode=2019NatGe..12..411W |s2cid=182137223 |issn=1752-0894}}</ref>

Scientists have confirmed the presence of a cave on the Moon near the [[Sea of Tranquillity]], not far from the 1969 [[Apollo 11]] landing site. The cave, identified as an entry point to a collapsed lava tube, is roughly 45 meters wide and up to 80 m long. This discovery marks the first confirmed entry point to a lunar cave. The analysis was based on photos taken in 2010 by NASA's [[Lunar Reconnaissance Orbiter]]. The cave's stable temperature of around {{val|17|u=°C}} could provide a hospitable environment for future astronauts, protecting them from extreme temperatures, solar radiation, and micrometeorites. However, challenges include accessibility and risks of avalanches and cave-ins. This discovery offers potential for future lunar bases or emergency shelters.<ref>{{Cite web |date=July 18, 2024 |title=Cave on the Moon: What this discovery means for space exploration |url=https://indianexpress.com/article/explained/everyday-explainers/cave-on-the-moon-explained-9459805/ |access-date=July 19, 2024 |website=The Indian Express |language=en}}</ref>

==== Volcanic features ====
{{Main |Volcanism on the Moon}}
[[File:Moon names.svg|thumb|upright=1.35|The names of the main volcanic features, the [[lunar mare|maria]] (blue), and of some [[lunar craters|craters]] (brown) of the near side of the Moon]]
The main features visible from Earth by the naked eye are dark and relatively featureless lunar plains called ''[[lunar mare|maria]]'' (singular ''mare''; [[Latin]] for "seas", as they were once believed to be filled with water)<ref>{{cite book |author=Wlasuk, Peter |title=Observing the Moon |url=https://books.google.com/books?id=TWtLIOlPwS4C |date=2000 |publisher=[[Springer Science+Business Media|Springer]] |isbn=978-1-85233-193-1 |page=19}}</ref> are vast solidified pools of ancient [[basalt]]ic lava. Although similar to terrestrial basalts, lunar basalts have more iron and no minerals altered by water.<ref>{{cite web |url=http://www.psrd.hawaii.edu/April04/lunarAnorthosites.html |title=The Oldest Moon Rocks |last=Norman |first=M. |work=Planetary Science Research Discoveries |publisher=Hawai'i Institute of Geophysics and Planetology |date=April 21, 2004 |access-date=April 12, 2007 |url-status=live |archive-url=https://web.archive.org/web/20070418152325/http://www.psrd.hawaii.edu/April04/lunarAnorthosites.html |archive-date=April 18, 2007}}</ref> The majority of these lava deposits erupted or flowed into the depressions associated with [[impact basins]], though the Moon's largest expanse of basalt flooding, [[Oceanus Procellarum]], does not correspond to an obvious impact basin. Different episodes of lava flow in maria can often be recognized by variations in surface albedo and distinct flow margins.<ref>{{cite journal |last1=Friedman |first1=R.C. |last2=Blewett |first2=D. T. |last3=Taylor |first3=G.J. |last4=Lucey |first4=P. G. |year=1996 |title=FeO and TiO2 Variations in Mare Imbrium |journal=Lunar and Planetary Science |volume=27 |pages=383 |bibcode=1996LPI....27..383F |url=https://adsabs.harvard.edu/full/1996LPI....27..383F}}</ref>

As the maria formed, cooling and contraction of the basaltic lava created [[wrinkle ridge]]s in some areas. These low, sinuous ridges can extend for hundreds of kilometers and often outline buried structures within the mare. Another result of maria formation is the creation of concentric depressions along the edges, known as [[rille|arcuate rilles]]. These features occur as the mare basalts sink inward under their own weight, causing the edges to fracture and separate.

In addition to the visible maria, the Moon has mare deposits covered by ejecta from impacts. Called cryptomares, these hidden mares are likely older than the exposed ones.<ref>{{cite journal |last1=Izquierdo |first1=Kristel |last2=Sori |first2=M. M. |last3=Checketts |first3=B. |last4=Hampton |first4=I. |last5=Johnson |first5=B.C. |last6=Soderblom |first6=J.M. |year=2024 |title=Global Distribution and Volume of Cryptomare and Visible Mare on the Moon From Gravity and Dark Halo Craters |journal=Journal of Geophysical Research: Planets |volume=129 |issue=2 |doi=10.1029/2023JE007867 |bibcode=2024JGRE..12907867I |doi-access=free}}</ref> Conversely, mare lava has obscured many impact melt sheets and pools. Impact melts are formed when intense shock pressures from collisions vaporize and melt zones around the impact site. Where still exposed, impact melt can be distinguished from mare lava by its distribution, albedo, and texture.<ref>{{cite journal |last1=Spudis |first1=Paul |year=2016 |title=Mapping Melts on the Moon |journal=Smithsonian Air and Space Magazine |url=https://www.smithsonianmag.com/air-space-magazine/mapping-melted-moon-180958645/}}</ref>

[[Sinuous rilles]], found in and around maria, are likely extinct [[lava channels]] or collapsed [[lava tubes]]. They typically originate from volcanic [[Volcanism on the Moon|vents]], meandering and sometimes branching as they progress. The largest examples, such as [[Schroter's Valley]] and [[Hadley–Apennine|Rima Hadley]], are significantly longer, wider, and deeper than terrestrial lava channels, sometimes featuring bends and sharp turns that again, are uncommon on Earth.

Mare volcanism has altered impact craters in various ways, including filling them to varying degrees, and raising and fracturing their floors from uplift of mare material beneath their interiors. Examples of such craters include [[Taruntius (crater)|Taruntius]] and [[Gassendi (crater)|Gassendi]]. Some craters, such as [[Hyginus (crater)|Hyginus]], are of wholly volcanic origin, forming as [[caldera]]s or [[pit crater|collapse pits]]. Such craters are relatively rare and tend to be smaller (typically a few kilometers wide), shallower, and more irregularly shaped than impact craters. They also lack the upturned rims characteristic of impact craters.

Several [[geologic province]]s containing [[shield volcano]]es and volcanic [[lunar dome|domes]] are found within the near side maria.<ref>{{cite journal |last1=Wilson |first1=Lionel |last2=Head |first2=James W. |title=Lunar Gruithuisen and Mairan domes: Rheology and mode of emplacement |journal=[[Journal of Geophysical Research]] |date=2003 |volume=108 |url=http://www.agu.org/pubs/crossref/2003/2002JE001909.shtml |access-date=April 12, 2007 |issue=E2 |doi=10.1029/2002JE001909 |page=5012 |bibcode=2003JGRE..108.5012W |citeseerx=10.1.1.654.9619 |s2cid=14917901 |url-status=live |archive-url=https://web.archive.org/web/20070312071105/http://www.agu.org/pubs/crossref/2003/2002JE001909.shtml |archive-date=March 12, 2007}}</ref> There are also some regions of [[pyroclastic rock|pyroclastic deposits]], [[scoria cones]] and [[volcanism on the Moon|non-basaltic domes]] made of particularly high viscosity lava.

Almost all maria are on the near side of the Moon, and cover 31% of the surface of the near side<ref name="worldbook" /> compared with 2% of the far side.<ref>{{cite journal |last1=Gillis |first1=J. J. |last2=Spudis |first2=P. D. |title=The Composition and Geologic Setting of Lunar Far Side Maria |journal=[[Lunar and Planetary Science]] |date=1996 |volume=27 |page=413 |bibcode=1996LPI....27..413G}}</ref> This is likely due to a [[KREEP|concentration of heat-producing elements]] under the crust on the near side, which would have caused the underlying mantle to heat up, partially melt, rise to the surface and erupt.<ref name="S06" /><ref>{{cite journal |title=Global Elemental Maps of the Moon: The Lunar Prospector Gamma-Ray Spectrometer |last1=Lawrence |first1=D. J. |last2=Feldman |first2=W. C. |last3=Barraclough |first3=B. L. |last4=Binder |first4=A. B. |last5=Elphic |first5=R. C. |last6=Maurice |first6=S. |last7=Thomsen |first7=D. R. |journal=[[Science (journal)|Science]] |volume=281 |issue=5382 |pages=1484–1489 |doi=10.1126/science.281.5382.1484 |date=August 11, 1998 |pmid=9727970 |bibcode=1998Sci...281.1484L |doi-access=free}}</ref><ref>{{cite journal |url=http://www.psrd.hawaii.edu/Aug00/newMoon.html |title=A New Moon for the Twenty-First Century |page=41 |last=Taylor |first=G. J. |journal=Planetary Science Research Discoveries |date=August 31, 2000 |access-date=April 12, 2007 |url-status=live |archive-url=https://web.archive.org/web/20120301074958/http://www.psrd.hawaii.edu/Aug00/newMoon.html |archive-date=March 1, 2012 |bibcode=2000psrd.reptE..41T}}</ref> Most of the Moon's [[lunar mare|mare basalts]] erupted during the [[Imbrian|Imbrian period]], 3.3–3.7&nbsp;billion years ago, though some being as young as 1.2&nbsp;billion years<ref name="Hiesinger" /> and as old as 4.2&nbsp;billion years.<ref name="Papike" />

[[File:Lava flows in Mare Imbrium (AS15-M-1558).png|thumb|Old [[basalt|hardened]] lava flows of [[Mare Imbrium]] forming [[wrinkle ridge]]s]]

In 2006, a study of [[Ina (crater)|Ina]], a tiny depression in [[Lacus Felicitatis]], found jagged, relatively dust-free features that, because of the lack of erosion by infalling debris, appeared to be only 2 million years old.<ref name=Berardelli>{{cite journal |url=https://www.science.org/content/article/long-live-moon |title=Long Live the Moon! |journal=[[Science (journal)|Science]] |date=November 9, 2006 |author=Phil Berardelli |url-status=live |archive-url=https://web.archive.org/web/20141018153016/http://news.sciencemag.org/2006/11/long-live-moon |archive-date=October 18, 2014 |access-date=October 14, 2014}}</ref> [[Moonquake]]s and releases of gas indicate continued lunar activity.<ref name="Berardelli"/> Evidence of recent lunar volcanism has been identified at 70 [[irregular mare patch]]es, some less than 50 million years old. This raises the possibility of a much warmer lunar mantle than previously believed, at least on the near side where the deep crust is substantially warmer because of the greater concentration of radioactive elements.<ref>{{cite web |url=http://news.discovery.com/space/imps-reveal-volcanoes-erupted-recently-on-the-moon-141014.htm |title=Volcanoes Erupted 'Recently' on the Moon |publisher=[[Discovery News]] |date=October 14, 2014 |author=Jason Major |url-status=live |archive-url=https://web.archive.org/web/20141016190653/http://news.discovery.com/space/imps-reveal-volcanoes-erupted-recently-on-the-moon-141014.htm |archive-date=October 16, 2014}}</ref><ref>{{cite web |url=http://www.nasa.gov/press/2014/october/nasa-mission-finds-widespread-evidence-of-young-lunar-volcanism/#.VDxNw0t3uxo |title=NASA Mission Finds Widespread Evidence of Young Lunar Volcanism |publisher=NASA |date=October 12, 2014 |url-status=live |archive-url=https://web.archive.org/web/20150103095208/http://www.nasa.gov/press/2014/october/nasa-mission-finds-widespread-evidence-of-young-lunar-volcanism/#.VDxNw0t3uxo |archive-date=January 3, 2015}}</ref><ref>{{cite journal |url=https://www.science.org/content/article/recent-volcanic-eruptions-moon |title=Recent volcanic eruptions on the moon |journal=[[Science (journal)|Science]] |date=October 12, 2014 |author=Eric Hand |url-status=live |archive-url=https://web.archive.org/web/20141014092239/http://news.sciencemag.org/space/2014/10/recent-volcanic-eruptions-moon |archive-date=October 14, 2014}}</ref><ref>{{cite journal |title=Evidence for basaltic volcanism on the Moon within the past 100 million years |journal=[[Nature Geoscience]] |last1=Braden |first1=S.E. |last2=Stopar |first2=J.D. |last3=Robinson |first3=M.S. |last4=Lawrence |first4=S.J. |last5=van der Bogert |first5=C.H. |last6=Hiesinger |first6=H. |volume=7 |issue=11 |pages=787–791 |bibcode=2014NatGe...7..787B |doi=10.1038/ngeo2252 |year=2014}}</ref> Evidence has been found for 2–10 million years old basaltic volcanism within the crater Lowell,<ref>{{cite journal |last1=Srivastava |first1=N. |last2=Gupta |first2=R.P. |year=2013 |title=Young viscous flows in the Lowell crater of Orientale basin, Moon: Impact melts or volcanic eruptions? |journal=[[Planetary and Space Science]] |volume=87 |pages=37–45 |doi=10.1016/j.pss.2013.09.001 |bibcode=2013P&SS...87...37S}}</ref><ref>{{cite journal |last1=Gupta |first1=R.P. |last2=Srivastava |first2=N. |last3=Tiwari |first3=R.K. |year=2014 |title=Evidences of relatively new volcanic flows on the Moon |journal=[[Current Science]] |volume=107 |issue=3 |pages=454–460 |jstor=24103498}}</ref> inside the Orientale basin. Some combination of an initially hotter mantle and local enrichment of heat-producing elements in the mantle could be responsible for prolonged activities on the far side in the Orientale basin.<ref>{{cite journal |last1=Whitten |first1=Jennifer |last2=Head |first2=James W. |last3=Staid |first3=Matthew |last4=Pieters |first4=Carle M. |last5=Mustard |first5=John |last6=Clark |first6=Roger |last7=Nettles |first7=Jeff |last8=Klima |first8=Rachel L. |last9=Taylor |first9=Larry |year=2011 |title=Lunar mare deposits associated with the Orientale impact basin: New insights into mineralogy, history, mode of emplacement, and relation to Orientale Basin evolution from Moon Mineralogy Mapper (M3) data from Chandrayaan-1 |journal=[[Journal of Geophysical Research]] |volume=116 |page=E00G09 |doi=10.1029/2010JE003736 |bibcode=2011JGRE..116.0G09W |s2cid=7234547 |doi-access=free}}</ref><ref>{{cite journal |last1=Cho |first1=Y. |display-authors=etal |year=2012 |title=Young mare volcanism in the Orientale region contemporary with the Procellarum KREEP Terrane (PKT) volcanism peak period 2 b.y. ago |journal=[[Geophysical Research Letters]] |volume=39 |issue=11 |page=L11203 |bibcode=2012GeoRL..3911203C |doi=10.1029/2012GL051838 |s2cid=134074700}}</ref>

The lighter-colored regions of the Moon are called ''terrae'', or more commonly ''highlands'', because they are higher than most maria. They have been radiometrically dated to having formed 4.4&nbsp;billion years ago and may represent [[plagioclase]] [[cumulates]] of the lunar magma ocean.<ref name="Hiesinger" /><ref name="Papike" /> In contrast to Earth, no major lunar mountains are believed to have formed as a result of tectonic events.<ref>{{cite web |last=Munsell |first=K. |publisher=NASA |work=Solar System Exploration |title=Majestic Mountains |url=http://sse.jpl.nasa.gov/educ/themes/display.cfm?Item=mountains |date=December 4, 2006 |access-date=April 12, 2007 |url-status=dead |archive-url=https://web.archive.org/web/20080917055643/http://sse.jpl.nasa.gov/educ/themes/display.cfm?Item=mountains |archive-date=September 17, 2008}}</ref>

The concentration of maria on the near side likely reflects the substantially thicker crust of the highlands of the Far Side, which may have formed in a slow-velocity impact of a second moon of Earth a few tens of millions of years after the Moon's formation.<ref>{{cite journal |author=Richard Lovett |url=http://www.nature.com/news/2011/110803/full/news.2011.456.html#B1 |title=Early Earth may have had two moons : Nature News |journal=Nature |access-date=November 1, 2012 |url-status=live |archive-url=https://web.archive.org/web/20121103145236/http://www.nature.com/news/2011/110803/full/news.2011.456.html#B1 |archive-date=November 3, 2012 |doi=10.1038/news.2011.456 |year=2011 |doi-access=free}}</ref><ref>{{cite web |url=http://theconversation.edu.au/was-our-two-faced-moon-in-a-small-collision-2659 |title=Was our two-faced moon in a small collision? |publisher=Theconversation.edu.au |access-date=November 1, 2012 |url-status=dead |archive-url=https://web.archive.org/web/20130130004522/http://theconversation.edu.au/was-our-two-faced-moon-in-a-small-collision-2659 |archive-date=January 30, 2013}}</ref> Alternatively, it may be a consequence of asymmetrical [[tidal heating]] when the Moon was much closer to the Earth.<ref>{{cite journal |title=Near/far side asymmetry in the tidally heated Moon |last1=Quillen |first1=Alice C. |last2=Martini |first2=Larkin |last3=Nakajima |first3=Miki |journal=Icarus |volume=329 |pages=182–196 |date=September 2019 |doi=10.1016/j.icarus.2019.04.010 |pmid=32934397 |pmc=7489467 |arxiv=1810.10676 |bibcode=2019Icar..329..182Q}}</ref>

====Impact craters====
{{Further |List of craters on the Moon}}
[[File:Daedalus crater AS11-41-6151.jpg|alt=A gray, many-ridged surface from high above. The largest feature is a circular ringed structure with high walled sides and a lower central peak: the entire surface out to the horizon is filled with similar structures that are smaller and overlapping.|thumb|A view of a three-kilometer-deep larger crater [[Daedalus (crater)|Daedalus]] on the [[Far side of the Moon|Moon's far side]]]]
A major geologic process that has affected the Moon's surface is [[impact crater]]ing,<ref>{{cite book |last=Melosh |first=H. J. |title=Impact cratering: A geologic process |date=1989 |publisher=[[Oxford University Press]] |isbn=978-0-19-504284-9}}</ref> with craters formed when asteroids and comets collide with the lunar surface. There are estimated to be roughly 300,000 craters wider than {{Convert |1 |km |4=1 |abbr=on}} on the Moon's near side.<ref>{{cite web |title=Moon Facts |url=http://planck.esa.int/science-e/www/object/index.cfm?fobjectid=31412 |work=SMART-1 |publisher=[[European Space Agency]] |date=2010 |access-date=May 12, 2010 |archive-date=March 17, 2012 |archive-url=https://web.archive.org/web/20120317004513/http://planck.esa.int/science-e/www/object/index.cfm?fobjectid=31412 |url-status=dead}}</ref> Lunar craters exhibit a variety of forms, depending on their size. In order of increasing diameter, the basic types are simple craters with smooth bowl shaped interiors and upturned rims, [[complex crater]]s with flat floors, terraced walls and central peaks, [[peak ring]] basins, and [[multi-ring basin]]s with two or more concentric rings of peaks.<ref>[https://www.lpi.usra.edu/exploration/education/hsResearch/moon_101/ImpactCratering.pdf Impact Cratering Notes (LPI)]</ref> The vast majority of impact craters are circular, but some, like [[Cantor (crater)|Cantor]] and [[Janssen (lunar crater)|Janssen]], have more polygonal outlines, possibly guided by underlying faults and joints. Others, such as the [[Messier (crater)|Messier]] pair, [[Schiller (crater)|Schiller]], and [[Daniell (crater)|Daniell]], are elongated. Such elongation can result from highly oblique impacts, [[binary asteroid]] impacts, fragmentation of impactors before surface strike, or closely spaced [[secondary crater|secondary]] impacts.<ref>{{cite journal |last1=Herrick |first1=R.R. |last2=Forsberg-Taylor |first2=N. K. |year=2003 |title=The shape and appearance of craters formed by oblique impact on the Moon and Venus |journal=Meteoritics & Planetary Science |volume=38 |issue=11 |pages=1551–1578 |doi=10.1111/j.1945-5100.2003.tb00001.x |bibcode=2003M&PS...38.1551H |url=https://onlinelibrary.wiley.com/doi/pdfdirect/10.1111/j.1945-5100.2003.tb00001.x}}</ref>

The [[lunar geologic timescale]] is based on the most prominent impact events, such as multi-ring formations like [[Nectarian|Nectaris]], [[Lower Imbrian|Imbrium]], and [[Mare Orientale|Orientale]] that are between hundreds and thousands of kilometers in diameter and associated with a broad apron of ejecta deposits that form a regional [[stratigraphy|stratigraphic horizon]].<ref name="geologic" /> The lack of an atmosphere, weather, and recent geological processes mean that many of these craters are well-preserved. Although only a few [[multi-ring basins]] have been definitively dated, they are useful for assigning relative ages. Because impact craters accumulate at a nearly constant rate, counting the number of craters per unit area can be used to estimate the age of the surface.<ref name="geologic" />
However care needs to be exercised with the [[crater counting]] technique due to the potential presence of [[secondary crater]]s. Ejecta from impacts can create secondary craters that often appear in clusters or chains but can also occur as isolated formations at a considerable distance from the impact. These can resemble primary craters, and may even dominate small crater populations, so their unidentified presence can distort age estimates.<ref>{{cite journal |last1=Xiao |first1=Z. |last2=Strom |first2=R.G. |year=2012 |title=Problems determining relative and absolute ages using the small crater population |journal=Icarus |volume=220 |issue=1 |pages=254–267 |doi=10.1016/j.icarus.2012.05.012 |bibcode=2012Icar..220..254X |url=https://www.uni-muenster.de/imperia/md/content/planetology/lectures/ss2015/143897-hottopics/xiao_and_strom_2012.pdf}}</ref>

The radiometric ages of impact-melted rocks collected during the [[Apollo missions]] cluster between 3.8 and 4.1&nbsp;billion years old: this has been used to propose a [[Late Heavy Bombardment]] period of increased impacts.<ref>{{cite journal |last1=Hartmann |first1=William K. |last2=Quantin |first2=Cathy |last3=Mangold |first3=Nicolas |date=2007 |volume=186 |issue=1 |pages=11–23 |journal=[[Icarus (journal)|Icarus]] |title=Possible long-term decline in impact rates: 2. Lunar impact-melt data regarding impact history |doi=10.1016/j.icarus.2006.09.009 |bibcode=2007Icar..186...11H}}</ref>

High-resolution images from the Lunar Reconnaissance Orbiter in the 2010s show a contemporary crater-production rate significantly higher than was previously estimated. A secondary cratering process caused by [[distal ejecta]] is thought to churn the top two centimeters of regolith on a timescale of 81,000 years.<ref>{{cite web |url=https://www.newscientist.com/article/2108929-the-moon-has-hundreds-more-craters-than-we-thought/ |title=The moon has hundreds more craters than we thought |first=Rebecca |last=Boyle |url-status=live |archive-url=https://web.archive.org/web/20161013143743/https://www.newscientist.com/article/2108929-the-moon-has-hundreds-more-craters-than-we-thought/ |archive-date=October 13, 2016}}</ref><ref>{{cite journal |title=Quantifying crater production and regolith overturn on the Moon with temporal imaging |first1=Emerson J. |last1=Speyerer |first2=Reinhold Z. |last2=Povilaitis |first3=Mark S. |last3=Robinson |first4=Peter C. |last4=Thomas |first5=Robert V. |last5=Wagner |date=October 13, 2016 |journal=[[Nature (journal)|Nature]] |volume=538 |issue=7624 |pages=215–218 |doi=10.1038/nature19829 |pmid=27734864 |bibcode=2016Natur.538..215S |s2cid=4443574}}</ref> This rate is 100 times faster than the rate computed from models based solely on direct micrometeorite impacts.<ref>{{cite web |title=Earth's Moon Hit by Surprising Number of Meteoroids |date=October 13, 2016 |publisher=NASA |url=https://www.nasa.gov/press-release/goddard/2016/lro-lunar-cratering |access-date=May 21, 2021 |archive-date=July 2, 2022 |archive-url=https://web.archive.org/web/20220702225136/https://www.nasa.gov/press-release/goddard/2016/lro-lunar-cratering/ |url-status=live}}</ref>

====Lunar swirls====
{{Main|Lunar swirls}}
[[File:Reiner-gamma-clem1.jpg|thumb|Wide-angle image of a lunar swirl, the 70-kilometer-long [[Reiner Gamma]]]]
Lunar swirls are enigmatic features found across the Moon's surface. They are characterized by a high albedo, appear optically immature (i.e. the optical characteristics of a relatively young [[regolith]]), and often have a sinuous shape. Their shape is often accentuated by low [[albedo]] regions that wind between the bright swirls. They are located in places with enhanced surface [[magnetic field]]s and many are located at the [[antipodal point]] of major impacts. Well known swirls include the [[Reiner Gamma]] feature and [[Mare Ingenii]]. They are hypothesized to be areas that have been partially shielded from the [[solar wind]], resulting in slower [[space weathering]].<ref>{{cite journal |title=Reflectance spectra of seven lunar swirls examined by statistical methods: A space weathering study |last1=Chrbolková |first1=Kateřina |last2=Kohout |first2=Tomáš |last3=Ďurech |first3=Josef |journal=Icarus |volume=333 |pages=516–527 |date=November 2019 |doi=10.1016/j.icarus.2019.05.024 |bibcode=2019Icar..333..516C |doi-access=free}}</ref>

=== Presence of water ===
{{Main|2 = Lunar water}}
Liquid water cannot persist on the lunar surface. When exposed to solar radiation, water quickly decomposes through a process known as [[photodissociation]] and is lost to space. However, since the 1960s, scientists have hypothesized that water ice may be deposited by impacting [[comets]] or possibly produced by the reaction of oxygen-rich lunar rocks, and hydrogen from [[solar wind]], leaving traces of water which could possibly persist in cold, permanently shadowed craters at either pole on the Moon.<ref name="Margot1999" /><ref>
 {{cite journal |first=William R. |last=Ward |title=Past Orientation of the Lunar Spin Axis |journal=[[Science (journal)|Science]] |date=August 1, 1975 |volume=189 |issue=4200 |pages=377–379 |doi=10.1126/science.189.4200.377 |pmid=17840827 |bibcode=1975Sci...189..377W |s2cid=21185695}}</ref> Computer simulations suggest that up to {{Convert |14000 |km2 |abbr=on}} of the surface may be in permanent shadow.<ref name="M03" /> The presence of usable quantities of water on the Moon is an important factor in rendering [[Colonization of the Moon|lunar habitation]] as a cost-effective plan; the alternative of transporting water from Earth would be prohibitively expensive.<ref name="seedhouse2009" />

In years since, signatures of water have been found to exist on the lunar surface.<ref name="moonwater_18032010" /> In 1994, the [[Clementine mission#Bistatic Radar Experiment|bistatic radar experiment]] located on the ''[[Clementine (spacecraft)|Clementine]]'' spacecraft, indicated the existence of small, frozen pockets of water close to the surface. However, later radar observations by [[Arecibo Telescope|Arecibo]], suggest these findings may rather be rocks ejected from young impact craters.<ref>{{cite web |last=Spudis |first=P. |title=Ice on the Moon |url=http://www.thespacereview.com/article/740/1 |publisher=[[The Space Review]] |date=November 6, 2006 |access-date=April 12, 2007 |url-status=dead |archive-url=https://web.archive.org/web/20070222083000/http://www.thespacereview.com/article/740/1 |archive-date=February 22, 2007}}</ref> In 1998, the [[Lunar Prospector#Neutron Spectrometer (NS)|neutron spectrometer]] on the ''Lunar Prospector'' spacecraft showed that high concentrations of hydrogen are present in the first meter of depth in the regolith near the polar regions.<ref name="Feldman1998" /> Volcanic lava beads, brought back to Earth aboard Apollo 15, showed small amounts of water in their interior.<ref name="Saal2008" />

[[File:Chandrayaan1 Spacecraft Discovery Moon Water.jpg|thumb|In 2008, NASA's Moon Mineralogy Mapper equipment on [[India]]'s ''[[Chandrayaan-1]]'' discovered, for the first time, water-rich minerals (shown in blue around a small crater from which they were ejected).|300x300px]]

The 2008 ''[[Chandrayaan-1]]'' spacecraft has since confirmed the existence of surface water ice, using the on-board [[Moon Mineralogy Mapper]]. The spectrometer observed absorption lines common to [[hydroxyl]], in reflected sunlight, providing evidence of large quantities of water ice, on the lunar surface. The spacecraft showed that concentrations may possibly be as high as 1,000&nbsp;[[parts per million|ppm]].<ref name="Pieters2009" /> Using the mapper's reflectance spectra, indirect lighting of areas in shadow confirmed water ice within 20° latitude of both poles in 2018.<ref>{{cite journal |title=Direct evidence of surface exposed water ice in the lunar polar regions |first1=Shuai |last1=Li |first2=Paul G. |last2=Lucey |first3=Ralph E. |last3=Milliken |first4=Paul O. |last4=Hayne |first5=Elizabeth |last5=Fisher |first6=Jean-Pierre |last6=Williams |first7=Dana M. |last7=Hurley |first8=Richard C. |last8=Elphic |journal=Proceedings of the National Academy of Sciences |volume=115 |issue=36 |pages=8907–8912 |date=August 2018 |doi=10.1073/pnas.1802345115 |pmid=30126996 |pmc=6130389 |bibcode=2018PNAS..115.8907L |doi-access=free}}</ref> In 2009, ''[[LCROSS]]'' sent a {{Convert|2300 |kg |abbr=on}} impactor into a [[Permanently shadowed crater|permanently shadowed]] polar crater, and detected at least {{Convert |100 |kg |abbr=on}} of water in a plume of ejected material.<ref name="Planetary" /><ref name="Colaprete" /> Another examination of the LCROSS data showed the amount of detected water to be closer to {{Convert |155 |± |12 |kg |abbr=on}}.<!--, or 5.6% (±2.9%) by mass.--This seems too technical for this overview--><ref name="Colaprete2010" />

In May 2011, 615–1410 ppm water in [[melt inclusions]] in lunar sample 74220 was reported,<ref name="hauri" /> the famous high-titanium "orange glass soil" of volcanic origin collected during the [[Apollo 17]] mission in 1972. The inclusions were formed during explosive eruptions on the Moon approximately 3.7 billion years ago. This concentration is comparable with that of magma in Earth's [[upper mantle]]. Although of considerable selenological interest, this insight does not mean that water is easily available since the sample originated many kilometers below the surface, and the inclusions are so difficult to access that it took 39 years to find them with a state-of-the-art ion microprobe instrument.

Analysis of the findings of the Moon Mineralogy Mapper (M3) revealed in August 2018 for the first time "definitive evidence" for water-ice on the lunar surface.<ref name=":1">{{Cite news |url=https://www.bbc.co.uk/news/science-environment-45251370 |title=Water ice 'detected on Moon's surface' |last=Rincon |first=Paul |date=August 21, 2018 |work=BBC News |access-date=August 21, 2018 |archive-date=August 21, 2018 |archive-url=https://web.archive.org/web/20180821151638/https://www.bbc.co.uk/news/science-environment-45251370 |url-status=live}}</ref><ref>{{Cite news |url=https://www.scientificamerican.com/article/beyond-the-shadow-of-a-doubt-water-ice-exists-on-the-moon/ |title=Beyond the Shadow of a Doubt, Water Ice Exists on the Moon |last=David |first=Leonard |work=Scientific American |access-date=August 21, 2018 |archive-date=August 21, 2018 |archive-url=https://web.archive.org/web/20180821125629/https://www.scientificamerican.com/article/beyond-the-shadow-of-a-doubt-water-ice-exists-on-the-moon/ |url-status=live}}</ref> The data revealed the distinct reflective signatures of water-ice, as opposed to dust and other reflective substances.<ref name=":2">{{Cite news |url=https://www.space.com/41554-water-ice-moon-surface-confirmed.html |title=Water Ice Confirmed on the Surface of the Moon for the 1st Time! |work=Space.com |access-date=August 21, 2018 |archive-date=August 21, 2018 |archive-url=https://web.archive.org/web/20180821134450/https://www.space.com/41554-water-ice-moon-surface-confirmed.html |url-status=live}}</ref> The ice deposits were found on the North and South poles, although it is more abundant in the South, where water is trapped in permanently shadowed craters and crevices, allowing it to persist as ice on the surface since they are shielded from the sun.<ref name=":1"/><ref name=":2"/>

In October 2020, astronomers reported detecting [[Water|molecular water]] on the sunlit surface of the Moon by several independent spacecraft, including the [[Stratospheric Observatory for Infrared Astronomy]] (SOFIA).<ref name="NA-20201026">{{cite journal |author=Honniball, C.I. |display-authors=et al. |title=Molecular water detected on the sunlit Moon by SOFIA |url=https://www.nature.com/articles/s41550-020-01222-x |date=October 26, 2020 |journal=[[Nature Astronomy]] |volume=5 |issue=2 |pages=121–127 |doi=10.1038/s41550-020-01222-x |bibcode=2021NatAs...5..121H |s2cid=228954129 |access-date=October 26, 2020 |archive-date=October 27, 2020 |archive-url=https://web.archive.org/web/20201027143615/https://www.nature.com/articles/s41550-020-01222-x |url-status=live}}</ref><ref name="NA-20201026poh">{{cite journal |author=Hayne, P.O. |display-authors=et al. |title=Micro cold traps on the Moon |url=https://www.nature.com/articles/s41550-020-1198-9 |date=October 26, 2020 |journal=[[Nature Astronomy]] |volume=5 |issue=2 |pages=169–175 |doi=10.1038/s41550-020-1198-9 |arxiv=2005.05369 |bibcode=2021NatAs...5..169H |s2cid=218595642 |access-date=October 26, 2020 |archive-date=October 27, 2020 |archive-url=https://web.archive.org/web/20201027143618/https://www.nature.com/articles/s41550-020-1198-9 |url-status=live}}</ref><ref name="WP-20201026">{{cite news |last1=Guarino |first1=Ben |last2=Achenbach |first2=Joel |title=Pair of studies confirm there is water on the moon – New research confirms what scientists had theorized for years — the moon is wet. |url=https://www.washingtonpost.com/science/2020/10/26/water-on-the-moon/ |date=October 26, 2020 |newspaper=[[The Washington Post]] |access-date=October 26, 2020 |archive-date=October 26, 2020 |archive-url=https://web.archive.org/web/20201026184808/https://www.washingtonpost.com/science/2020/10/26/water-on-the-moon/ |url-status=live}}</ref><ref name="NYT-20201026">{{cite news |last=Chang |first=Kenneth |title=There's Water and Ice on the Moon, and in More Places Than NASA Once Thought – Future astronauts seeking water on the moon may not need to go into the most treacherous craters in its polar regions to find it. |url=https://www.nytimes.com/2020/10/26/science/moon-ice-water.html |date=October 26, 2020 |work=[[The New York Times]] |access-date=October 26, 2020 |archive-date=October 26, 2020 |archive-url=https://web.archive.org/web/20201026170716/https://www.nytimes.com/2020/10/26/science/moon-ice-water.html |url-status=live}}</ref>

==Earth–Moon system==
{{anchor|Orbit and relationship to Earth|Relationship to Earth}}
{{See also|Satellite system (astronomy)|Claimed moons of Earth|Double planet}}

===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]],<ref>{{cite web |date=February 28, 2004 |title=Is the 'full moon' merely a fallacy? |url=https://www.nbcnews.com/id/wbna4402294 |url-status=live |archive-url=https://web.archive.org/web/20230601085529/https://www.nbcnews.com/id/wbna4402294 |archive-date=June 1, 2023 |access-date=May 30, 2023 |website=[[NBC News]]}}</ref> 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]]

===Tidal effects===
{{Main |Tidal force |Tidal acceleration |Tide |Theory of tides}}
[[File:Tide animation.gif|thumb|Simplified diagram of Earth bulging, being pulled and stretched toward the Moon by its gravity, which is the main driver of the [[tide]]s. The Ocean and Earth are being pulled more where it is closer to the Moon, causing [[tidal force]]s to be weaker at the far-side of Earth creating a second bulge and high-tide. The animation shows the change of the Moon's position on its inclined orbit.]]
The gravitational attraction that Earth and the Moon (as well as the Sun) exert on each other manifests in a slightly greater attraction on the sides closest to each other, resulting in [[tidal forces]]. [[Ocean tides]] are the most widely experienced result of this, but tidal forces also considerably affect other mechanics of Earth, as well as the Moon and their system.

The lunar solid crust experiences tides of around {{Convert |10 |cm |4=0 |abbr=on}} amplitude over 27&nbsp;days, with three components: a fixed one due to Earth, because they are in [[synchronous rotation]], a variable tide due to orbital eccentricity and inclination, and a small varying component from the Sun.<ref name="touma1994" /> The Earth-induced variable component arises from changing distance and [[libration]], a result of the Moon's orbital eccentricity and inclination (if the Moon's orbit were perfectly circular and un-inclined, there would only be solar tides).<ref name="touma1994" /> According to recent research, scientists suggest that the Moon's influence on the Earth may contribute to maintaining [[Earth's magnetic field]].<ref>{{cite web |author=Iain Todd |date=March 31, 2018 |title=Is the Moon maintaining Earth's magnetism? |url=https://www.skyatnightmagazine.com/news/is-the-moon-maintaining-earths-magnetism/ |url-status=live |archive-url=https://web.archive.org/web/20200922194637/https://www.skyatnightmagazine.com/news/is-the-moon-maintaining-earths-magnetism/ |archive-date=September 22, 2020 |access-date=November 16, 2020 |website=[[BBC Sky at Night]] Magazine}}</ref>

The cumulative effects of stress built up by these tidal forces produces [[moonquakes]]. Moonquakes are much less common and weaker than are earthquakes, although moonquakes can last for up to an hour&nbsp;– significantly longer than terrestrial quakes&nbsp;– because of scattering of the seismic vibrations in the dry fragmented upper crust. The existence of moonquakes was an unexpected discovery from [[seismometer]]s placed on the Moon by [[Apollo program|Apollo]] [[astronaut]]s from 1969 through 1972.<ref>{{cite journal |last1=Latham |first1=Gary |date=1972 |last2=Ewing |first2=Maurice |last3=Dorman |first3=James |last4=Lammlein |first4=David |last5=Press |first5=Frank |last6=Toksőz |first6=Naft |last7=Sutton |first7=George |last8=Duennebier |first8=Fred |last9=Nakamura |first9=Yosio |title=Moonquakes and lunar tectonism |journal=[[Earth, Moon, and Planets]] |volume=4 |issue=3–4 |pages=373–382 |doi=10.1007/BF00562004 |bibcode=1972Moon....4..373L |s2cid=120692155}}</ref>

The most commonly known effect of tidal forces is elevated sea levels called ocean tides.<ref name="Lambeck1977" /> While the Moon exerts most of the tidal forces, the Sun also exerts tidal forces and therefore contributes to the tides as much as 40% of the Moon's tidal force; producing in interplay the [[Spring tide|spring and neap tides]].<ref name="Lambeck1977" />

The tides are two bulges in the Earth's oceans, one on the side facing the Moon and the other on the side opposite. As the Earth rotates on its axis, one of the ocean bulges (high tide) is held in place "under" the Moon, while another such tide is opposite. The tide under the Moon is explained by the Moon's gravity being stronger on the water close to it. The tide on the opposite side can be explained either by the centrifugal force as the Earth orbits the [[barycenter]] or by the water's inertia as the Moon's gravity is stronger on the solid Earth close to it and it is pull away from the farther water.<ref>{{cite web |last1=Feynman |first1=Richard |title=Feynman's Lectures on Physics – The Law of Gravitation |url=https://www.youtube.com/watch?v=-UFr1X0prbo&t=1503s |website=YouTube |date=October 24, 2020 |access-date=5 December 2024}}</ref> 

Thus, there are two high tides, and two low tides in about 24 hours.<ref name="Lambeck1977" /> Since the Moon is orbiting the Earth in the same direction of the Earth's rotation, the high tides occur about every 12 hours and 25 minutes; the 25 minutes is due to the Moon's time to orbit the Earth.

If the Earth were a water world (one with no continents) it would produce a tide of only one meter, and that tide would be very predictable, but the ocean tides are greatly modified by other effects:
* the frictional coupling of water to Earth's rotation through the ocean floors
* the [[inertia]] of water's movement
* ocean basins that grow shallower near land
* the sloshing of water between different ocean basins<ref>{{cite journal |last=Le Provost |first=C. |author2=Bennett, A.F. |author3=Cartwright, D.E. |date=1995 |title=Ocean Tides for and from TOPEX/POSEIDON |pages=639–642 |journal=[[Science (journal)|Science]] |pmid=17745840 |volume=267 |issue=5198 |bibcode=1995Sci...267..639L |doi=10.1126/science.267.5198.639 |s2cid=13584636}}</ref>
As a result, the timing of the tides at most points on the Earth is a product of observations that are explained, incidentally, by theory.

====System evolution====
Delays in the tidal peaks of both ocean and solid-body tides cause [[torque]] in opposition to the Earth's rotation. This "drains" [[angular momentum]] and rotational [[kinetic energy]] from Earth's rotation, slowing the Earth's rotation.<ref name="Lambeck1977" /><ref name="touma1994" /> That angular momentum, lost from the Earth, is transferred to the Moon in a process known as [[tidal acceleration]], which lifts the Moon into a higher orbit while lowering orbital speed around the Earth.

Thus the distance between Earth and Moon is increasing, and the Earth's rotation is slowing in reaction.<ref name="touma1994" /> Measurements from laser reflectors left during the Apollo missions ([[lunar Laser Ranging experiments|lunar ranging experiments]]) have found that the Moon's distance increases by {{Convert |38 |mm |abbr=on}} per year (roughly the rate at which human fingernails grow).<ref>{{cite journal |last=Chapront |first=J. |author2=Chapront-Touzé, M. |author3=Francou, G. |date=2002 |title=A new determination of lunar orbital parameters, precession constant and tidal acceleration from LLR measurements |journal=[[Astronomy and Astrophysics]] |volume=387 |issue=2 |pages=700–709 |bibcode=2002A&A...387..700C |doi=10.1051/0004-6361:20020420 |doi-access=free |s2cid=55131241}}</ref><ref>{{cite news |url=https://www.bbc.co.uk/news/science-environment-12311119 |title=Why the Moon is getting further away from Earth |newspaper=BBC News |date=February 1, 2011 |access-date=September 18, 2015 |url-status=live |archive-url=https://web.archive.org/web/20150925185706/http://www.bbc.co.uk/news/science-environment-12311119 |archive-date=September 25, 2015}}</ref><ref>{{Cite journal |last1=Williams |first1=James G. |last2=Boggs |first2=Dale H. |date=2016 |title=Secular tidal changes in lunar orbit and Earth rotation |url=https://doi.org/10.1007/s10569-016-9702-3 |journal=Celestial Mechanics and Dynamical Astronomy |language=en |volume=126 |issue=1 |pages=89–129 |doi=10.1007/s10569-016-9702-3 |bibcode=2016CeMDA.126...89W |s2cid=124256137 |issn=1572-9478 |access-date=July 30, 2022 |archive-date=July 30, 2022 |archive-url=https://web.archive.org/web/20220730084922/https://link.springer.com/article/10.1007/s10569-016-9702-3 |url-status=live}}</ref>
[[Atomic clock]]s show that Earth's Day lengthens by about 17&nbsp;[[microsecond]]s every year,<ref>{{cite web |last=Ray |first=R. |date=May 15, 2001 |url=http://bowie.gsfc.nasa.gov/ggfc/tides/intro.html |title=Ocean Tides and the Earth's Rotation |publisher=IERS Special Bureau for Tides |access-date=March 17, 2010 |url-status=dead |archive-url=https://web.archive.org/web/20100327084125/http://bowie.gsfc.nasa.gov/ggfc/tides/intro.html |archive-date=March 27, 2010}}</ref><ref>{{Cite journal |last1=Stephenson |first1=F. R. |last2=Morrison |first2=L. V. |last3=Hohenkerk |first3=C. Y. |date=2016 |title=Measurement of the Earth's rotation: 720 BC to AD 2015 |journal=Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences |volume=472 |issue=2196 |pages=20160404 |doi=10.1098/rspa.2016.0404 |pmc=5247521 |pmid=28119545 |bibcode=2016RSPSA.47260404S}}</ref><ref>{{Cite journal |last1=Morrison |first1=L. V. |last2=Stephenson |first2=F. R. |last3=Hohenkerk |first3=C. Y. |last4=Zawilski |first4=M. |date=2021 |title=Addendum 2020 to 'Measurement of the Earth's rotation: 720 BC to AD 2015' |journal=Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences |volume=477 |issue=2246 |pages=20200776 |doi=10.1098/rspa.2020.0776 |bibcode=2021RSPSA.47700776M |s2cid=231938488 |doi-access=free}}</ref> slowly increasing the rate at which [[UTC]] is adjusted by [[leap second]]s.

This tidal drag makes the rotation of the Earth, and the orbital period of the Moon very slowly match. This matching first results in [[tidal locking|tidally locking]] the lighter body of the orbital system, as is already the case with the Moon. Theoretically, in 50 billion years,<ref name="Universe Today 2016">{{cite web |title=When Will Earth Lock to the Moon? |website=Universe Today |date=April 12, 2016 |url=https://www.universetoday.com/128350/will-earth-lock-moon/ |access-date=January 5, 2022 |archive-date=May 28, 2022 |archive-url=https://web.archive.org/web/20220528015905/https://www.universetoday.com/128350/will-earth-lock-moon/ |url-status=live}}</ref> the Earth's rotation will have slowed to the point of matching the Moon's orbital period, causing the Earth to always present the same side to the Moon. However, the Sun will become a [[red giant#The Sun as a red giant|red giant]], most likely engulfing the Earth–Moon system long before then.<ref>{{cite book |last1=Murray |first1=C.D. |last2=Dermott |first2=Stanley F. |title=Solar System Dynamics |date=1999 |publisher=[[Cambridge University Press]] |isbn=978-0-521-57295-8 |page=184}}</ref><ref>{{cite book |last=Dickinson |first=Terence |author-link=Terence Dickinson |title=From the Big Bang to Planet X |date=1993 |publisher=[[Camden House]] |location=Camden East, Ontario |isbn=978-0-921820-71-0 |pages=79–81}}</ref>

If the Earth–Moon system isn't engulfed by the enlarged Sun, the drag from the solar atmosphere can cause the orbit of the Moon to decay. Once the orbit of the Moon closes to a distance of {{convert|18470|km|mi|abbr=on}}, it will cross Earth's [[Roche limit]], meaning that tidal interaction with Earth would break apart the Moon, turning it into a [[ring system]]. Most of the orbiting rings will begin to decay, and the debris will impact Earth. Hence, even if the Sun does not swallow up Earth, the planet may be left moonless.<ref name=space070122>{{citation |first=David |last=Powell |date=January 22, 2007 |title=Earth's Moon Destined to Disintegrate |work=Space.com |publisher=Tech Media Network |url=http://www.space.com/scienceastronomy/070122_temporary_moon.html |access-date=June 1, 2010 |archive-date=September 6, 2008 |archive-url=https://archive.today/20080906222127/http://www.space.com/scienceastronomy/070122_temporary_moon.html |url-status=live}}</ref>

==Position and appearance==
{{anchor|Observation|Appearance from Earth}}
{{See also|Lunar observation}}
[[File:Lunar libration with phase Oct 2007 HD.gif|alt=Over one lunar month more than half of the Moon's surface can be seen from Earth's surface.|thumb|[[Libration]], the slight variation in the Moon's [[apparent size]] and viewing angle over a single lunar month as viewed from somewhere on the Earth's northern hemisphere.]]
The Moon's highest [[altitude (astronomy)|altitude]] at [[culmination]] varies by its [[lunar phase]], or more correctly its orbital position, and time of the year, or more correctly the position of the Earth's axis. The full moon is highest in the sky during winter and lowest during summer (for each hemisphere respectively), with its altitude changing towards dark moon to the opposite.

At the [[North Pole|North]] and [[South Pole]]s the Moon is 24 hours above the horizon for two weeks every [[tropical month]] (about 27.3 days), comparable to the [[polar day]] of the [[tropical year]]. [[Zooplankton]] in the [[Arctic]] use [[moonlight]] when the Sun is [[polar night|below the horizon]] for months on end.<ref>{{cite web |date=January 16, 2016 |title=Moonlight helps plankton escape predators during Arctic winters |url=https://www.newscientist.com/article/dn28738-moonlight-helps-plankton-escape-predators-during-arctic-winters/ |url-status=live |archive-url=https://web.archive.org/web/20160130112225/https://www.newscientist.com/article/mg22930562-500-moonlight-helps-plankton-escape-predators-during-arctic-winters/ |archive-date=January 30, 2016 |work=[[New Scientist]]}}</ref>

The apparent orientation of the Moon depends on its position in the sky and the hemisphere of the Earth from which it is being viewed. In the [[northern hemisphere]] it appears upside down compared to the view from the [[southern hemisphere]].<ref>{{cite web |last=Howells |first=Kate |date=September 25, 2020 |title=Can the Moon be upside down? |url=https://www.planetary.org/articles/can-the-moon-be-upside-down |url-status=live |archive-url=https://web.archive.org/web/20220102132012/https://www.planetary.org/articles/can-the-moon-be-upside-down |archive-date=January 2, 2022 |access-date=January 2, 2022 |publisher=The Planetary Society}}</ref> Sometimes the "horns" of a crescent moon appear to be pointing more upwards than sideways. This phenomenon is called a [[wet moon]] and occurs more frequently in the [[tropics]].<ref>{{cite web |last=Spekkens |first=K. |author1-link=Kristine Spekkens |date=October 18, 2002 |title=Is the Moon seen as a crescent (and not a "boat") all over the world? |url=http://curious.astro.cornell.edu/our-solar-system/46-our-solar-system/the-moon/observing-the-moon/124-is-the-moon-seen-as-a-crescent-and-not-a-boat-all-over-the-world-is-the-same-phase-of-the-moon-visible-from-the-northern-and-southern-hemispheres-advanced |url-status=live |archive-url=https://web.archive.org/web/20151016011356/http://curious.astro.cornell.edu/our-solar-system/46-our-solar-system/the-moon/observing-the-moon/124-is-the-moon-seen-as-a-crescent-and-not-a-boat-all-over-the-world-is-the-same-phase-of-the-moon-visible-from-the-northern-and-southern-hemispheres-advanced |archive-date=October 16, 2015 |access-date=September 28, 2015 |publisher=Curious About Astronomy}}</ref>

The [[Lunar distance|distance between the Moon and Earth]] varies from around {{convert|356,400|km|mi|abbr=on}} ([[perigee]]) to {{convert|406,700|km|mi|abbr=on}} (apogee), making the Moon's distance and apparent size fluctuate up to 14%.<ref name="size1"/><ref name="size2"/> On average the Moon's [[angular diameter]] is about 0.52°, roughly the same apparent size as the Sun (see {{section link||Eclipses}}). In addition, a purely psychological effect, known as the [[Moon illusion]], makes the Moon appear larger when close to the horizon.<ref>{{cite book |last=Hershenson |first=Maurice |title=The Moon illusion |date=1989 |publisher=[[Routledge]] |isbn=978-0-8058-0121-7 |page=5}}</ref>

===Rotation===
[[File:Tidal locking of the Moon with the Earth.gif|thumb|Comparison between the Moon on the left, rotating tidally locked (correct), and with the Moon on the right, without rotation (incorrect)]]
The [[synchronous rotation|tidally locked synchronous rotation]] of the Moon as it orbits the Earth results in it always keeping nearly the same face turned towards the planet. The side of the Moon that faces Earth is called the [[near side]], and the opposite the [[far side of the Moon|far side]]. The far side is often inaccurately called the "dark side", but it is in fact illuminated as often as the near side: once every 29.5 Earth days. During [[dark moon]] to [[new moon]], the near side is dark.<ref>{{cite web |title=Dark Side of the Moon |author=Phil Plait |publisher=[[Bad Astronomy]]: Misconceptions |url=http://www.badastronomy.com/bad/misc/dark_side.html |access-date=February 15, 2010 |url-status=live |archive-url=https://web.archive.org/web/20100412192834/http://www.badastronomy.com/bad/misc/dark_side.html |archive-date=April 12, 2010 |author-link=Phil Plait}}</ref>

The Moon originally rotated at a faster rate, but early in its history its rotation slowed and became [[tidally locked]] in this orientation as a result of [[friction]]al effects associated with [[tidal force|tidal]] deformations caused by Earth.<ref>{{cite journal |last=Alexander |first=M.E. |title=The Weak Friction Approximation and Tidal Evolution in Close Binary Systems |journal=[[Astrophysics and Space Science]] |date=1973 |volume=23 |issue=2 |pages=459–508 |bibcode=1973Ap&SS..23..459A |doi=10.1007/BF00645172 |s2cid=122918899}}</ref> With time, the energy of rotation of the Moon on its axis was dissipated as heat, until there was no rotation of the Moon relative to Earth. In 2016, planetary scientists using data collected on the 1998–99 NASA ''[[Lunar Prospector]]'' mission found two hydrogen-rich areas (most likely former water ice) on opposite sides of the Moon. It is speculated that these patches were the poles of the Moon billions of years ago before it was tidally locked to Earth.<ref>{{cite news |title=Moon used to spin 'on different axis' |url=https://www.bbc.com/news/science-environment-35883576 |access-date=March 23, 2016 |url-status=live |archive-url=https://web.archive.org/web/20160323203442/http://www.bbc.com/news/science-environment-35883576 |archive-date=March 23, 2016 |work=BBC News |date=March 23, 2016}}</ref>

===Illumination and phases===
{{See also|Lunar phase|Moonlight|Halo (optical phenomenon)}}
[[File:Moon phases en.jpg|center|thumb|550x550px|The monthly changes in the angle between the direction of sunlight and view from Earth, and the [[Lunar phase|phases of the Moon]] that result, as viewed from the [[Northern Hemisphere]]. The [[Earth–Moon distance]] is not to scale.]]

The Moon rotates, as it orbits Earth, changing orientation toward the Sun, experiencing a [[lunar day]]. A lunar day is equal to one [[lunar month]] (one synodic orbit around Earth) due to it being [[tidal locking|tidally locked]] to Earth. Since the Moon is not tidally locked to the Sun, lunar daylight and night times both occur around the Moon. The changing position of the illumination of the Moon by the Sun during a lunar day is observable from Earth as the changing [[lunar phase]]s, waxing crescent being the sunrise and the waning crescent the sunset phase of a day observed from afar.<ref name="r040">{{cite web | title=Phases of the Moon explained | website=BBC Sky at Night Magazine | date=January 21, 2025 | url=https://www.skyatnightmagazine.com/space-science/why-does-the-moons-appearance-change | access-date=April 29, 2025}}</ref>

Lunar night is the darkest on the far side and during lunar eclipses on the near side (and darker than a moonless night on Earth). The near side is during its night illuminated by [[Earthlight (astronomy)|Earthlight]], making the near side illuminated enough by the Earthlight to see lunar surface features from Earth where it is dark during its night phase due to Earthlight being reflected back to Earth. Earthshine makes the night on the near side about 43 times brighter, and sometimes even 55 times brighter than a night on Earth illuminated by the light of the full moon.<ref name="u988">{{cite web | last=Siegel | first=Ethan | title=Ask Ethan: How Bright Is The Earth As Seen From The Moon? | website=Forbes | date=March 18, 2017 | url=https://www.forbes.com/sites/startswithabang/2017/03/18/ask-ethan-how-bright-is-the-earth-as-seen-from-the-moon/ | access-date=April 29, 2025}}</ref>

In Earth's sky brightness and apparent size of the Moon changes also due to its elliptic [[Orbit of the Moon|orbit around Earth]]. At [[perigee]] (closest), since the Moon is up to 14% closer to Earth than at [[apogee]] (most distant), it subtends a [[solid angle]] which is up to 30% larger. Consequently, given the same phase, the Moon's brightness also varies by up to 30% between apogee and perigee.<ref>{{cite web |url=http://www.space.com/34515-supermoon-guide.html |title=Supermoon November 2016 |date=November 13, 2016 |access-date=November 14, 2016 |publisher=Space.com |url-status=live |archive-url=https://web.archive.org/web/20161114220725/http://www.space.com/34515-supermoon-guide.html |archive-date=November 14, 2016}}</ref> A full (or new) moon at such a position is called a [[supermoon]].<ref name="size1">{{cite web |title=Super Full Moon |date=March 16, 2011 |author=Tony Phillips |publisher=NASA |access-date=March 19, 2011 |url=https://science.nasa.gov/science-news/science-at-nasa/2011/16mar_supermoon/ |url-status=dead |archive-url=https://web.archive.org/web/20120507035348/https://science.nasa.gov/science-news/science-at-nasa/2011/16mar_supermoon/ |archive-date=May 7, 2012}}</ref><ref name="size2">{{cite news |title=Full moon tonight is as close as it gets |date=March 18, 2011 |author=Richard K. De Atley |newspaper=[[The Press-Enterprise]] |access-date=March 19, 2011 |url=http://www.pe.com/localnews/stories/PE_News_Local_D_moon19.23a6364.html |url-status=dead |archive-url=https://web.archive.org/web/20110322161600/http://www.pe.com/localnews/stories/PE_News_Local_D_moon19.23a6364.html |archive-date=March 22, 2011}}</ref><ref>{{cite news |url=https://www.theguardian.com/science/2011/mar/19/super-moon-closest-point-years |title='Super moon' to reach closest point for almost 20 years |newspaper=The Guardian |date=March 19, 2011 |access-date=March 19, 2011 |url-status=live |archive-url=https://web.archive.org/web/20131225175506/http://www.theguardian.com/science/2011/mar/19/super-moon-closest-point-years |archive-date=December 25, 2013}}</ref>

====Observational phenomena====
There has been historical controversy over whether observed features on the Moon's surface change over time. Today, many of these claims are thought to be illusory, resulting from observation under different lighting conditions, poor [[astronomical seeing]], or inadequate drawings. However, [[outgassing]] does occasionally occur and could be responsible for a minor percentage of the reported [[lunar transient phenomena]]. Recently, it has been suggested that a roughly {{convert|3|km|abbr=on}} diameter region of the lunar surface was modified by a gas release event about a million years ago.<ref>{{cite journal |last=Taylor |first=G. J. |date=November 8, 2006 |title=Recent Gas Escape from the Moon |url=http://www.psrd.hawaii.edu/Nov06/MoonGas.html |url-status=dead |journal=Planetary Science Research Discoveries |page=110 |bibcode=2006psrd.reptE.110T |archive-url=https://web.archive.org/web/20070304055515/http://www.psrd.hawaii.edu/Nov06/MoonGas.html |archive-date=March 4, 2007 |access-date=April 4, 2007}}</ref><ref>{{cite journal |last1=Schultz |first1=P. H. |last2=Staid |first2=M. I. |last3=Pieters |first3=C. M. |date=2006 |title=Lunar activity from recent gas release |journal=[[Nature (journal)|Nature]] |volume=444 |issue=7116 |pages=184–186 |bibcode=2006Natur.444..184S |doi=10.1038/nature05303 |pmid=17093445 |s2cid=7679109}}</ref>

===Albedo and color===
[[File:Two Lunar Phases.jpg|thumb|right|upright=1.35|The changing apparent color of the Moon, filtered by Earth's atmosphere]]
The Moon has an exceptionally low [[albedo]], giving it a [[diffuse reflection|reflectance]] that is slightly brighter than that of worn [[Asphalt concrete|asphalt]]. Despite this, it is the [[List of brightest natural objects in the sky|brightest object in the sky]] after the [[Sun]].<ref name="worldbook" />{{efn|name=brightness}} This is due partly to the brightness enhancement of the [[opposition surge]]; the Moon at quarter phase is only one-tenth as bright, rather than half as bright, as at [[full moon]].<ref name="Moon" /> Additionally, [[color constancy]] in the [[visual system]] recalibrates the relations between the colors of an object and its surroundings, and because the surrounding sky is comparatively dark, the sunlit Moon is perceived as a bright object. The edges of the full moon seem as bright as the center, without [[limb darkening]], because of the [[Lambert's cosine law#Lambertian scatterers and radiators|reflective properties]] of [[lunar soil]], which [[retroreflector|retroreflects]] light more towards the Sun than in other directions. The Moon's color depends on the light the Moon reflects, which in turn depends on the Moon's surface and its features, having for example large darker regions. In general, the lunar surface reflects a brown-tinged gray light.<ref name="Science Mission Directorate 2020">{{cite web |date=November 11, 2020 |title=Colors of the Moon |url=https://science.nasa.gov/colors-moon |url-status=live |archive-url=https://web.archive.org/web/20220409212600/https://science.nasa.gov/colors-moon |archive-date=April 9, 2022 |access-date=April 9, 2022 |website=Science Mission Directorate}}</ref>

At times, the Moon can appear red or blue.
It may appear red during a [[lunar eclipse]], because of the red spectrum of the Sun's light being [[refracted]] onto the Moon by Earth's atmosphere. Because of this red color, lunar eclipses are also sometimes called [[Blood Moon (eclipse)|blood moons]]. The Moon can also seem red when it appears at low angles and through a thick atmosphere.

The Moon may appear blue depending on the presence of certain particles in the air,<ref name="Science Mission Directorate 2020" /> such as volcanic particles,<ref>{{cite web |last=Gibbs |first=Philip |date=May 1997 |title=Why is the sky blue? |url=http://math.ucr.edu/home/baez/physics/General/BlueSky/blue_sky.html |url-status=live |archive-url=https://web.archive.org/web/20151102085211/http://math.ucr.edu/home/baez/physics/General/BlueSky/blue_sky.html |archive-date=November 2, 2015 |access-date=November 4, 2015 |website=math.ucr.edu |quote=... may cause the moon to have a blue tinge since the red light has been scattered out.}}</ref> in which case it can be called a [[Blue moon#Whole blue moon|blue moon]].

Because the words "red moon" and "blue moon" can also be used to refer to specific [[full moon]]s of the year, they do not always refer to the presence of red or blue [[moonlight]].

=== Eclipses ===
{{Main |Solar eclipse |Lunar eclipse |Solar eclipses on the Moon|Eclipse cycle}}
{{multiple image
| total_width       = 330
| image1            = Solar_eclipse_1999_4_NR.jpg
| image2            = Full Eclipse of the Moon as seen in from Irvine, CA, USA (52075715442) (cropped).jpg
| caption1          = A [[solar eclipse]] causes the Sun to be covered, revealing the white [[Stellar corona|corona]].
| caption2          = The Moon, tinted reddish, during a [[lunar eclipse]]
}}

Eclipses only occur when the Sun, Earth, and Moon are all in a straight line (termed "[[Syzygy (astronomy)|syzygy]]"). [[Solar eclipse]]s occur at [[new moon]], when the Moon is between the Sun and Earth. In contrast, [[lunar eclipse]]s occur at full moon, when Earth is between the Sun and Moon. The apparent size of the Moon is roughly the same as that of the Sun, with both being viewed at close to one-half a degree wide. The Sun is much larger than the Moon, but it is the vastly greater distance that gives it the same apparent size as the much closer and much smaller Moon from the perspective of Earth. The variations in apparent size, due to the non-circular orbits, are nearly the same as well, though occurring in different cycles. This makes possible both [[total eclipse|total]] (with the Moon appearing larger than the Sun) and [[annular eclipse|annular]] (with the Moon appearing smaller than the Sun) solar eclipses.<ref>{{cite web |first=F. |last=Espenak |date=2000 |url=http://www.mreclipse.com/Special/SEprimer.html |title=Solar Eclipses for Beginners |publisher=MrEclip |access-date=March 17, 2010 |archive-date=May 24, 2015 |archive-url=https://web.archive.org/web/20150524172606/http://www.mreclipse.com/Special/SEprimer.html |url-status=dead}}</ref> In a total eclipse, the Moon completely covers the disc of the Sun and the [[solar corona]] becomes visible to the [[naked eye]].

Because the distance between the Moon and Earth is very slowly increasing over time,<ref name="Lambeck1977" /> the angular diameter of the Moon is decreasing. As it evolves toward becoming a [[red giant]], the size of the Sun, and its apparent diameter in the sky, are slowly increasing.{{efn|name=size changes}} The combination of these two changes means that hundreds of millions of years ago, the Moon would always completely cover the Sun on solar eclipses, and no annular eclipses were possible. Likewise, hundreds of millions of years in the future, the Moon will no longer cover the Sun completely, and total solar eclipses will not occur.<ref name=fourmilab>{{cite web |last=Walker |first=John |url=http://www.fourmilab.ch/images/peri_apo/ |title=Moon near Perigee, Earth near Aphelion |publisher=[[Fourmilab]] |date=July 10, 2004 |access-date=December 25, 2013 |url-status=live |archive-url=https://web.archive.org/web/20131208153430/http://www.fourmilab.ch/images/peri_apo/ |archive-date=December 8, 2013}}</ref>

As the Moon's orbit around Earth is inclined by about 5.145° (5° 9') to the [[ecliptic|orbit of Earth around the Sun]], eclipses do not occur at every full and new moon. For an eclipse to occur, the Moon must be near the intersection of the two orbital planes.<ref name="eclipse" /> The periodicity and recurrence of eclipses of the Sun by the Moon, and of the Moon by Earth, is described by the [[Saros (astronomy)|saros]], which has a period of approximately 18&nbsp;years.<ref>{{cite web |url=http://sunearth.gsfc.nasa.gov/eclipse/SEsaros/SEsaros.html |last=Espenak |first=F. |title=Saros Cycle |publisher=NASA |access-date=March 17, 2010 |url-status=dead |archive-url=https://web.archive.org/web/20071030225501/http://sunearth.gsfc.nasa.gov/eclipse/SEsaros/SEsaros.html |archive-date=October 30, 2007}}</ref>

Because the Moon continuously blocks the view of a half-degree-wide circular area of the sky,{{Efn |name=area}}<ref>{{cite magazine |title=The Square Degree as a Unit of Celestial Area |author=Guthrie, D.V. |date=1947 |magazine=[[Popular Astronomy (US magazine)|Popular Astronomy]] |volume=55 |pages=200–203 |bibcode=1947PA.....55..200G}}</ref> the related phenomenon of [[occultation]] occurs when a bright star or planet passes behind the Moon and is occulted: hidden from view. In this way, a solar eclipse is an occultation of the Sun. Because the Moon is comparatively close to Earth, occultations of individual stars are not visible everywhere on the planet, nor at the same time. Because of the [[precession]] of the lunar orbit, each year different stars are occulted.<ref>{{cite web |url=http://occsec.wellington.net.nz/total/totoccs.htm |title=Total Lunar Occultations |publisher=[[Royal Astronomical Society of New Zealand]] |access-date=March 17, 2010 |url-status=dead |archive-url=https://web.archive.org/web/20100223022627/http://occsec.wellington.net.nz/total/totoccs.htm |archive-date=February 23, 2010}}</ref>

==History of exploration and human presence==
{{anchor |Exploration}}

{{Main|Exploration of the Moon|List of spacecraft that orbited the Moon|List of missions to the Moon|List of lunar probes}}

===Pre-telescopic observation (before 1609)===
It is believed by some that the oldest [[cave painting]]s from up to 40,000 [[Before present|BP]] of bulls and geometric shapes,<ref name="e093">{{cite web |last=Boyle |first=Rebecca |title=Ancient humans used the moon as a calendar in the sky |website=Science News |date=July 9, 2019 |url=https://www.sciencenews.org/article/moon-time-calendar-ancient-human-art |access-date=May 26, 2024 |archive-date=November 4, 2021 |archive-url=https://web.archive.org/web/20211104145754/https://www.sciencenews.org/article/moon-time-calendar-ancient-human-art |url-status=live}}</ref> or 20–30,000 year old [[tally stick]]s were used to observe the phases of the Moon, keeping time using the waxing and waning of [[Lunar phases|the Moon's phases]].<ref name=Burton2011/>
Aspects of the Moon were identified and aggregated in [[lunar deities]] from [[prehistoric times]] and were eventually documented and put into symbols from the very first instances of [[writing]] in the [[4th millennium BC]]. One of the earliest-discovered possible depictions of the Moon is a 3,000 BCE rock carving ''Orthostat 47'' at [[Knowth]], Ireland.<ref name="Knowth">{{cite web |url=https://www.knowth.com/lunar-maps.htm |title=Lunar maps |access-date=September 18, 2019 |archive-date=June 1, 2019 |archive-url=https://web.archive.org/web/20190601184833/https://www.knowth.com/lunar-maps.htm |url-status=live}}</ref><ref name="spacetoday">{{cite web |url=http://www.spacetoday.org/SolSys/Earth/OldStarCharts.html |title=Carved and Drawn Prehistoric Maps of the Cosmos |publisher=Space Today |date=2006 |access-date=April 12, 2007 |url-status=dead |archive-url=https://web.archive.org/web/20120305162253/http://www.spacetoday.org/SolSys/Earth/OldStarCharts.html |archive-date=March 5, 2012}}</ref> The [[#Crescent|crescent]] depicting the Moon as with the lunar deity [[Sin (mythology)|Nanna/Sin]] have been found from the 3rd millennium BCE.<ref name=BlackGreen1992/>

The oldest named astronomer and poet [[Enheduanna]], [[Akkadian Empire|Akkadian]] high priestess to the lunar deity Nanna/Sin and pricess, daughter of [[Sargon the Great]] ({{circa|2334}} &ndash; {{circa|2279}} BCE), had the Moon tracked in her chambers.<ref name="c099">{{cite magazine | last=Winkler | first=Elizabeth | title=The Struggle to Unearth the World's First Author | magazine=The New Yorker | date=2022-11-19 | url=https://www.newyorker.com/books/page-turner/the-struggle-to-unearth-the-worlds-first-author | access-date=2025-02-10}}</ref> The oldest found and identified depiction of the Moon in an astronomical relation to other astronomical features is the [[Nebra sky disc]] from {{circa|1800–1600 BCE}}, depicting features like the [[Pleiades]] next to the Moon.<ref name="g361">{{cite web |title=Nebra Sky Disc |website=State Museum of Prehistory |url=https://www.landesmuseum-vorgeschichte.de/en/nebra-sky-disc |access-date=27 September 2024}}</ref><ref name="k874">{{cite web |last=Simonova |first=Michaela |title=Under the Moonlight: Depictions of the Moon in Art |website=TheCollector |date=January 2, 2022 |url=https://www.thecollector.com/depictions-of-the-moon-in-art/ |access-date=May 26, 2024}}</ref>

[[File:Nebra solstice 2.jpg|thumb|The [[Nebra sky disc]] ({{circa|1800–1600 BCE}}), found near a possibly [[astronomical complex]], most likely depicting the Sun or full Moon, the Moon as a crescent, the [[Pleiades]] and the summer and winter solstices as strips of gold on the side of the disc,<ref name="Meller 2021">{{cite book |url=https://www.academia.edu/80363367 |title=Time is power. Who makes time?: 13th Archaeological Conference of Central Germany |chapter=The Nebra Sky Disc – astronomy and time determination as a source of power |last=Meller |first=Harald |date=2021 |publisher=Landesmuseum für Vorgeschichte Halle (Saale). |isbn=978-3-948618-22-3}}</ref><ref>{{cite AV media |url=https://www.youtube.com/watch?v=0dlijsmVJ9c&t=760s |title=Concepts of cosmos in the world of Stonehenge |website=British Museum |date=2022}}</ref> with the top representing the [[horizon]]<ref name=":03">{{Cite book |last1=Bohan |first1=Elise |url=https://www.worldcat.org/oclc/940282526 |title=Big History |last2=Dinwiddie |first2=Robert |last3=Challoner |first3=Jack |last4=Stuart |first4=Colin |last5=Harvey |first5=Derek |last6=Wragg-Sykes |first6=Rebecca |last7=Chrisp |first7=Peter |last8=Hubbard |first8=Ben |last9=Parker |first9=Phillip |collaboration=Writers |date=February 2016 |publisher=[[DK (publisher)|DK]] |others=Foreword by [[David Christian (historian)|David Christian]] |isbn=978-1-4654-5443-0 |edition=1st American |location=[[New York City|New York]] |page=20 |oclc=940282526}}</ref> and [[north]].]]

The [[ancient Greece|ancient Greek]] philosopher [[Anaxagoras]] ({{died-in|428 BC}}) reasoned that the Sun and Moon were both giant spherical rocks, and that the latter reflected the light of the former.<ref>{{cite web |last=O'Connor |first=J.J. |author2=Robertson, E.F. |date=February 1999 |url=http://www-history.mcs.st-andrews.ac.uk/Biographies/Anaxagoras.html |title=Anaxagoras of Clazomenae |publisher=[[University of St Andrews]] |access-date=April 12, 2007 |url-status=live |archive-url=https://web.archive.org/web/20120112072236/http://www-history.mcs.st-andrews.ac.uk/Biographies/Anaxagoras.html |archive-date=January 12, 2012}}</ref><ref name=Needham1986/>{{rp|page=227}} Elsewhere in the {{nowrap|5th century BC}} to {{nowrap|4th century BC}}, [[Babylonian astronomers]] had recorded the 18-year [[Saros cycle]] of [[lunar eclipse]]s,<ref>{{cite journal |doi=10.2307/1006543 |title=Saros Cycle Dates and Related Babylonian Astronomical Texts |first1=A. |last1=Aaboe |first2=J.P. |last2=Britton |first3=J.A. |last3=Henderson |first4=Otto |last4=Neugebauer |author-link4=Otto Neugebauer |first5=A.J. |last5=Sachs |journal=[[Transactions of the American Philosophical Society]] |volume=81 |issue=6 |pages=1–75 |date=1991 |quote=One comprises what we have called "Saros Cycle Texts", which give the months of eclipse possibilities arranged in consistent cycles of 223&nbsp;months (or 18&nbsp;years). |jstor=1006543}}</ref> <!--The texts discussed in that article are more recent than 490 BC and, as mentioned in the paper, the observations can have occurred no earlier than that. The earliest reference for the Metonic cycle in Neugubauer's (1957) ''The Exact Sciences in Antiquity'' is 380 BC (p. 140).--> and [[Indian astronomy|Indian astronomers]] had described the Moon's monthly elongation.<ref name="Sarma-Ast-Ind" /> The [[Chinese astronomer]] [[Shi Shen]] {{nowrap|([[fl.]] 4th century BC)}} gave instructions for predicting solar and lunar eclipses.<ref name=Needham1986/>{{rp|page=411}}

In [[Aristotle]]'s (384–322&nbsp;BC) [[On the Heavens|description of the universe]], the Moon marked the boundary between the spheres of the mutable elements (earth, water, air and fire), and the imperishable stars of [[aether (classical element)|aether]], an [[Aristotelian physics|influential philosophy]] that would dominate for centuries.<ref>{{cite book |last=Lewis |first=C.S. |author-link=C. S. Lewis |title=The Discarded Image |url=https://archive.org/details/discardedimagein0000lewi |url-access=registration |date=1964 |publisher=[[Cambridge University Press]] |location=Cambridge |isbn=978-0-521-47735-2 |page=[https://archive.org/details/discardedimagein0000lewi/page/108 108] |access-date=November 11, 2019 |archive-date=June 17, 2020 |archive-url=https://web.archive.org/web/20200617181455/https://archive.org/details/discardedimagein0000lewi |url-status=live}}</ref> [[Archimedes]] (287–212 BC) designed a planetarium that could calculate the motions of the Moon and other objects in the Solar System.<ref>{{cite news |url=https://www.nytimes.com/2008/07/31/science/31computer.html?hp |work=The New York Times |title=Discovering How Greeks Computed in 100 B.C. |date=July 31, 2008 |access-date=March 9, 2014 |url-status=live |archive-url=https://web.archive.org/web/20131204053238/http://www.nytimes.com/2008/07/31/science/31computer.html?hp |archive-date=December 4, 2013}}</ref> In the {{nowrap |2nd century BC}}, [[Seleucus of Seleucia]] correctly thought that [[tide]]s were due to the attraction of the Moon, and that their height depends on the Moon's position relative to the [[Sun]].<ref>{{cite journal |first=Bartel Leendert |last=van der Waerden |author-link=Bartel Leendert van der Waerden |date=1987 |title=The Heliocentric System in Greek, Persian and Hindu Astronomy |journal=[[Annals of the New York Academy of Sciences]] |volume=500 |issue=1 |pages=1–569 |pmid=3296915 |bibcode=1987NYASA.500....1A |doi=10.1111/j.1749-6632.1987.tb37193.x |s2cid=84491987}}</ref> In the same century, [[On the Sizes and Distances (Aristarchus)|Aristarchus]] computed the size and distance of the Moon from Earth, obtaining a value of about twenty times the [[radius of Earth]] for the distance.

The Chinese of the [[Han dynasty]] believed the Moon to be energy equated to ''[[qi]]'' and their 'radiating influence' theory recognized that the light of the Moon was merely a reflection of the Sun; [[Jing Fang]] (78–37&nbsp;BC) noted the sphericity of the Moon.<ref name=Needham1986/>{{rp|pages=413–414}} [[Ptolemy]] (90–168&nbsp;AD) greatly improved on the numbers of Aristarchus, calculating a mean distance of 59&nbsp;times Earth's radius and a diameter of 0.292&nbsp;Earth diameters, close to the correct values of about 60 and 0.273 respectively.<ref>{{cite book |last=Evans |first=James |title=The History and Practice of Ancient Astronomy |date=1998 |publisher=[[Oxford University Press]] |location=Oxford & New York |isbn=978-0-19-509539-5 |pages=71, 386}}</ref> In the 2nd century AD, [[Lucian]] wrote the novel ''[[A True Story]]'', in which the heroes travel to the Moon and meet its inhabitants. In 510&nbsp;AD, the Indian astronomer [[Aryabhata]] mentioned in his ''[[Aryabhatiya]]'' that reflected sunlight is the cause of the shining of the Moon.<ref name=Hayashi08Aryabhata>Hayashi (2008), "Aryabhata I", ''Encyclopædia Britannica''.</ref><ref>''Gola'', 5; p. 64 in [https://archive.org/stream/The_Aryabhatiya_of_Aryabhata_Clark_1930#page/n93/mode/2up ''The Aryabhatiya of Aryabhata: An Ancient Indian Work on Mathematics and Astronomy''], translated by [[Walter Eugene Clark]] (University of Chicago Press, 1930; reprinted by Kessinger Publishing, 2006). "Half of the spheres of the Earth, the planets, and the asterisms is darkened by their shadows, and half, being turned toward the Sun, is light (being small or large) according to their size."</ref> The astronomer and physicist [[Ibn al-Haytham]] (965–1039) found that [[sunlight]] was not reflected from the Moon like a mirror, but that light was emitted from every part of the Moon's sunlit surface in all directions.<ref>{{cite book |location=Detroit |date=2008 |publisher=[[Charles Scribner's Sons]] |title=Dictionary of Scientific Biography |chapter=Ibn Al-Haytham, Abū ʿAlī Al-Ḥasan Ibn Al-Ḥasan |author=A.I. Sabra |pages=189–210, at 195}}</ref> [[Shen Kuo]] (1031–1095) of the [[Song dynasty]] created an allegory equating the waxing and waning of the Moon to a round ball of reflective silver that, when doused with white powder and viewed from the side, would appear to be a crescent.<ref name=Needham1986/>{{rp|pages=415–416}} During the [[Middle Ages]], before the invention of the telescope, the Moon was increasingly recognized as a sphere, though many believed that it was "perfectly smooth".<ref>{{cite web |last=Van Helden |first=A. |date=1995 |url=http://galileo.rice.edu/sci/observations/moon.html |title=The Moon |publisher=Galileo Project |access-date=April 12, 2007 |url-status=dead |archive-url=https://web.archive.org/web/20040623085326/http://galileo.rice.edu/sci/observations/Moon.html |archive-date=June 23, 2004}}</ref>

=== Telescopic exploration (1609–1959) ===
[[File:Galileo's sketches of the moon.png|thumb |upright |[[Galileo]]'s sketches of the Moon from the ground-breaking ''[[Sidereus Nuncius]]'' (1610), publishing among other findings the first descriptions of the Moon's topography]]

The [[telescope]] was developed and reported on in 1608. The first record of telescopic astronomy and rough mapping of the Moon's features is from early summer 1609 by [[Thomas Harriot]], but which he did not publish. At the same time [[Galileo Galilei]] too started to use telescopes to observe the sky and the Moon, recording later that year more detailed observations and crucial conclusions, such as that the Moon was not smooth, featuring mountains and craters, which he published in 1610 in his ground-breaking and soon widely discussed book {{lang|la |[[Sidereus Nuncius]]}}.

Later in the 17th century, the efforts of [[Giovanni Battista Riccioli]] and [[Francesco Maria Grimaldi]] led to the system of naming of lunar features in use today. The more exact 1834–1836 {{lang|la |Mappa Selenographica}} of [[Wilhelm Beer]] and [[Johann Heinrich von Mädler]], and their associated 1837 book {{lang|de |Der Mond}}, the first [[trigonometry|trigonometrically]] accurate study of lunar features, included the heights of more than a thousand mountains, and introduced the study of the Moon at accuracies possible in earthly geography.<ref>{{cite journal |last=Consolmagno |first=Guy J. |date=1996 |title=Astronomy, Science Fiction and Popular Culture: 1277 to 2001 (And beyond) |journal=[[Leonardo (journal)|Leonardo]] |volume=29 |issue=2 |pages=127–132 |jstor=1576348 |doi=10.2307/1576348 |s2cid=41861791}}</ref> Lunar craters, first noted by Galileo, were thought to be [[volcanic]] until the 1870s proposal of [[Richard Proctor]] that they were formed by collisions.<ref name="worldbook" /> This view gained support in 1892 from the experimentation of geologist [[Grove Karl Gilbert]], and from comparative studies from 1920 to the 1940s,<ref name="Hall1977" /> leading to the development of [[lunar geologic timescale|lunar stratigraphy]], which by the 1950s was becoming a new and growing branch of [[astrogeology]].<ref name="worldbook" />

===First missions to the Moon (1959–1976)===
{{See also|Space Race|Moon landing}}

After [[World War II]] the first [[launch system]]s were developed and by the end of the 1950s they reached capabilities that allowed the [[Soviet Union]] and the [[United States]] to launch [[spacecraft]] into space. The [[Cold War]] fueled a closely followed development of launch systems by the two states, resulting in the so-called [[Space Race]] and its later phase the Moon Race, accelerating efforts and interest in [[exploration of the Moon]].

[[File:Luna 3 moon.jpg|thumb|First view of the [[far side of the Moon]], taken by [[Luna 3]], October 7, 1959. Clearly visible is [[Mare Moscoviense]] (top right) and a mare triplet of [[Mare Crisium]], [[Mare Marginis]] and [[Mare Smythii]] (left center).]]

After the first spaceflight of [[Sputnik 1]] in 1957 during [[International Geophysical Year]] the spacecraft of the Soviet Union's [[Luna programme|''Luna'' program]] were the first to accomplish a number of goals. Following three unnamed failed missions in 1958,<ref>{{cite web |url=http://www.russianspaceweb.com/spacecraft_planetary_lunar.html |first=Anatoly |last=Zak |date=2009 |title=Russia's unmanned missions toward the Moon |access-date=April 20, 2010 |url-status=live |archive-url=https://web.archive.org/web/20100414115710/http://www.russianspaceweb.com/spacecraft_planetary_lunar.html |archive-date=April 14, 2010}}</ref> the first human-made object ''[[Luna 1]]'' escaped Earth's gravity and passed near the Moon in 1959. Later that year the first human-made object ''[[Luna 2]]'' reached the Moon's surface by [[Lander (spacecraft)#Impactors|intentionally impacting]]. By the end of the year ''[[Luna 3]]'' reached as the first human-made object the normally occluded [[far side of the Moon]], taking the first photographs of it.
The first spacecraft to perform a successful lunar [[lander (spacecraft)|soft landing]] was ''[[Luna 9]]'' and the first vehicle to orbit the Moon was ''[[Luna 10]]'', both in 1966.<ref name="worldbook" />

[[File:NASA-Apollo8-Dec24-Earthrise.jpg|thumb|''[[Earthrise]]'', the first color [[Timeline of first images of Earth from space|image of Earth]] taken by a human from the Moon, during [[Apollo 8]] (1968), the first time a crewed spacecraft left Earth orbit and reached another [[astronomical body]]|alt=The small blue-white semicircle of Earth, almost glowing with color in the blackness of space, rising over the limb of the desolate, cratered surface of the Moon.]]

Following President [[John F. Kennedy]]'s 1961 commitment to a crewed Moon landing before the end of the decade, the United States, under NASA leadership, launched a series of uncrewed probes to develop an understanding of the lunar surface in preparation for human missions: the [[Jet Propulsion Laboratory]]'s [[Ranger program]], the [[Lunar Orbiter program]] and the [[Surveyor program]]. The crewed [[Apollo program]] was developed in parallel; after a series of uncrewed and crewed tests of the Apollo spacecraft in Earth orbit, and spurred on by a potential [[Soviet human lunar programs|Soviet lunar human landing]], in 1968 [[Apollo 8]] made the first human mission to lunar orbit (the first Earthlings, two tortoises, had circled the Moon three months earlier on the Soviet Union's [[Zond 5]], followed by turtles on [[Zond 6]]).

The first time a person landed on the Moon and any extraterrestrial body was when [[Neil Armstrong]], the commander of the American mission [[Apollo 11]], set foot on the Moon at 02:56&nbsp;UTC on July 21, 1969.<ref>{{cite web |url=https://history.nasa.gov/ap11ann/ap11events.html |title=Record of Lunar Events, 24 July 1969 |work=Apollo 11 30th anniversary |publisher=NASA |access-date=April 13, 2010 |url-status=live |archive-url=https://web.archive.org/web/20100408213454/http://history.nasa.gov/ap11ann/ap11events.html |archive-date=April 8, 2010}}</ref> Considered the culmination of the [[Space Race]],<ref name="CNN" /> an estimated 500&nbsp;million people worldwide watched the transmission by the [[Apollo TV camera]], the largest television audience for a live broadcast at that time.<ref>{{cite web |title=Manned Space Chronology: Apollo_11 |url=http://www.spaceline.org/flightchron/apollo11.html |publisher=Spaceline.org |access-date=February 6, 2008 |url-status=dead |archive-url=https://web.archive.org/web/20080214213826/http://www.spaceline.org/flightchron/apollo11.html |archive-date=February 14, 2008}}</ref><ref>{{cite web |title=Apollo Anniversary: Moon Landing "Inspired World" |url=http://news.nationalgeographic.com/news/2004/07/0714_040714_moonlanding.html |work=National Geographic |access-date=February 6, 2008 |url-status=dead |archive-url=https://web.archive.org/web/20080209140059/http://news.nationalgeographic.com/news/2004/07/0714_040714_moonlanding.html |archive-date=February 9, 2008}}</ref> While at the same time another mission, the robotic sample return mission [[Luna 15]] by the Soviet Union had been in orbit around the Moon, becoming together with Apollo 11 the first ever case of two extraterrestrial missions being conducted at the same time.

The Apollo missions 11 to 17 (except [[Apollo 13]], which aborted its planned lunar landing) removed {{convert|837.87 |lb |kg |order=flip}} of lunar rock and soil in 2,196 [[moon rock|separate samples]].<ref>{{cite book |last=Orloff |first=Richard W. |title=NASA History Division, Office of Policy and Plans – Apollo by the Numbers: A Statistical Reference |url=https://history.nasa.gov/SP-4029/SP-4029.htm |chapter=Extravehicular Activity |chapter-url=https://history.nasa.gov/SP-4029/Apollo_18-30_Extravehicular_Activity.htm |access-date=August 1, 2013 |series=The NASA History Series |orig-year=First published 2000 |date=September 2004 |publisher=NASA |location=Washington, DC |isbn=978-0-16-050631-4 |lccn=00061677 |id=NASA SP-2000-4029 |ref=Orloff |url-status=live |archive-url=https://web.archive.org/web/20130606114042/http://history.nasa.gov/SP-4029/SP-4029.htm |archive-date=June 6, 2013}}</ref>
Scientific instrument packages were installed on the lunar surface during all the Apollo landings. Long-lived [[Apollo Lunar Surface Experiments Package|instrument stations]], including heat flow probes, [[seismometer]]s, and [[magnetometer]]s, were installed at the [[Apollo 12]], [[Apollo 14|14]], [[Apollo 15|15]], [[Apollo 16|16]], and [[Apollo 17|17]] landing sites. Direct transmission of data to Earth concluded in late 1977 because of budgetary considerations,<ref>{{cite press release |title=NASA news release 77-47 page 242 |date=September 1, 1977 |url=http://www.nasa.gov/centers/johnson/pdf/83129main_1977.pdf |access-date=March 16, 2010 |url-status=live |archive-url=https://web.archive.org/web/20110604114817/http://www.nasa.gov/centers/johnson/pdf/83129main_1977.pdf |archive-date=June 4, 2011}}</ref><ref>{{cite news |url=http://www.ast.cam.ac.uk/~ipswich/Miscellaneous/Archived_spaceflight_news.htm |access-date=August 29, 2007 |title=NASA Turns A Deaf Ear To The Moon |date=1977 |publisher=OASI Newsletters Archive |last=Appleton |first=James |author2=Radley, Charles |author3=Deans, John |author4=Harvey, Simon |author5=Burt, Paul |author6=Haxell, Michael |author7=Adams, Roy |author8=Spooner N. |author9=Brieske, Wayne |archive-url=https://web.archive.org/web/20071210143103/http://www.ast.cam.ac.uk/~ipswich/Miscellaneous/Archived_spaceflight_news.htm |archive-date=December 10, 2007 |url-status=dead}}</ref> but as the stations' [[lunar laser ranging]] corner-cube retroreflector arrays are passive instruments, they are still being used.<ref>{{cite journal |last1=Dickey |first1=J. |date=1994 |title=Lunar laser ranging: a continuing legacy of the Apollo program |journal=[[Science (journal)|Science]] |volume=265 |pages=482–490 |doi=10.1126/science.265.5171.482 |pmid=17781305 |issue=5171 |bibcode=1994Sci...265..482D |last2=Bender |first2=P. L. |last3=Faller |first3=J. E. |last4=Newhall |first4=X. X. |last5=Ricklefs |first5=R. L. |last6=Ries |first6=J. G. |last7=Shelus |first7=P. J. |last8=Veillet |first8=C. |last9=Whipple |first9=A. L. |s2cid=10157934}}</ref>
[[Apollo 17]] in 1972 remains the last crewed mission to the Moon. [[Explorer 49]] in 1973 was the last dedicated U.S. probe to the Moon until the 1990s.

The Soviet Union continued sending robotic missions to the Moon until 1976, deploying in 1970 with [[Luna 17]] the first remote controlled [[Rover (space exploration)|rover]] [[Lunokhod 1]] on an extraterrestrial surface, and collecting and returning 0.3&nbsp;kg of rock and soil samples with three ''Luna'' [[sample return mission]]s (''[[Luna 16]]'' in 1970, ''[[Luna 20]]'' in 1972, and ''[[Luna 24]]'' in 1976).<ref>{{cite web |url=http://curator.jsc.nasa.gov/lunar/index.cfm |title=Rocks and Soils from the Moon |publisher=NASA |access-date=April 6, 2010 |url-status=live |archive-url=https://web.archive.org/web/20100527085532/http://curator.jsc.nasa.gov/lunar/index.cfm |archive-date=May 27, 2010}}</ref>

=== Moon Treaty and explorational absence (1976–1990) ===
{{Main|Moon Treaty}}
Following the [[Luna 24|last Soviet mission to the Moon]] of 1976, there was little further lunar exploration for fourteen years. Astronautics had shifted its focus towards the exploration of the [[inner Solar System|inner]] (e.g. [[Venera program]]) and [[outer Solar System|outer]] (e.g. [[Pioneer 10]], 1972) [[Solar System]] [[planet]]s, but also towards [[Geocentric orbit|Earth orbit]], developing and continuously operating, beside [[communication satellite]]s, [[Earth observation satellite]]s (e.g. [[Landsat program]], 1972), [[space telescope]]s and particularly [[space station]]s (e.g. [[Salyut program]], 1971).

Negotiation in 1979 of [[Moon treaty]], and its subsequent ratification in 1984 was the only major activity regarding the Moon until 1990.

===Renewed exploration (1990–present)===
In 1990 ''[[Hiten (spacecraft)|Hiten]]'' – ''Hagoromo'',<ref>{{cite web |title=Hiten-Hagomoro |publisher=NASA |url=http://solarsystem.nasa.gov/missions/profile.cfm?MCode=Hiten&Display=ReadMore |access-date=March 29, 2010 |url-status=dead |archive-url=https://web.archive.org/web/20110614115823/http://solarsystem.nasa.gov/missions/profile.cfm?MCode=Hiten&Display=ReadMore |archive-date=June 14, 2011}}</ref> the first dedicated lunar mission since 1976, reached the Moon. Sent by [[Japan]], it became the first mission that was not a Soviet Union or U.S. mission to the Moon.

In 1994, the U.S. dedicated a mission to fly a spacecraft (''[[Clementine (spacecraft)|Clementine]]'') to the Moon again for the first time since 1973. This mission obtained the first near-global topographic map of the Moon, and the first global [[multispectral]] images of the lunar surface.<ref>{{cite web |title=Clementine information |publisher=NASA |date=1994 |url=http://nssdc.gsfc.nasa.gov/planetary/cleminfo.html |access-date=March 29, 2010 |url-status=live |archive-url=https://web.archive.org/web/20100925095846/http://nssdc.gsfc.nasa.gov/planetary/cleminfo.html |archive-date=September 25, 2010}}</ref> In 1998, this was followed by the ''[[Lunar Prospector]]'' mission, whose instruments indicated the presence of excess hydrogen at the lunar poles, which is likely to have been caused by the presence of water ice in the upper few meters of the regolith within permanently shadowed craters.<ref>{{cite web |title=Lunar Prospector: Neutron Spectrometer |publisher=NASA |url=http://lunar.arc.nasa.gov/results/neutron.htm |date=2001 |access-date=March 29, 2010 |url-status=dead |archive-url=https://web.archive.org/web/20100527105801/http://lunar.arc.nasa.gov/results/neutron.htm |archive-date=May 27, 2010}}</ref>

The next years saw a row of first missions to the Moon by a new group of states actively exploring the Moon.
Between 2004 and 2006 the first spacecraft by the [[European Space Agency]] (ESA) (''[[SMART-1]]'') reached the Moon, recording the first detailed survey of chemical elements on the lunar surface.<ref>{{cite web |url=http://www.esa.int/SPECIALS/SMART-1/SEMSDE1A6BD_0.html |title=SMART-1 factsheet |date=February 26, 2007 |publisher=[[European Space Agency]] |access-date=March 29, 2010 |url-status=live |archive-url=https://web.archive.org/web/20100323044139/http://www.esa.int/SPECIALS/SMART-1/SEMSDE1A6BD_0.html |archive-date=March 23, 2010}}</ref>
The [[Chinese Lunar Exploration Program]] reached the Moon for the first time with the orbiter ''[[Chang'e 1]]'' (2007–2009),<ref>{{cite web |title=Chang'e 1 |publisher=NASA |date=2019 |url=https://solarsystem.nasa.gov/missions/change-1/in-depth/ |access-date=October 3, 2021 |archive-date=November 22, 2021 |archive-url=https://web.archive.org/web/20211122070043/https://solarsystem.nasa.gov/missions/change-1/in-depth/ |url-status=live}}</ref> obtaining a full image map of the Moon.
[[Indian Space Research Organisation|India]] reached, orbited and impacted the Moon in 2008 for the first time with its ''[[Chandrayaan-1]]'' and [[Moon Impact Probe]], becoming the fifth and sixth state to do so, creating a high-resolution chemical, mineralogical and photo-geological map of the lunar surface, and confirming the presence of [[Lunar water|water molecules in lunar soil]].<ref>{{cite web |url=http://www.isro.org/Chandrayaan/htmls/mission_sequence.htm |title=Mission Sequence |date=November 17, 2008 |publisher=[[Indian Space Research Organisation]] |access-date=April 13, 2010 |url-status=live |archive-url=https://web.archive.org/web/20100706225136/http://www.isro.org/chandrayaan/htmls/mission_sequence.htm |archive-date=July 6, 2010}}</ref>

The U.S. launched the [[Lunar Reconnaissance Orbiter|''Lunar Reconnaissance Orbiter'' (LRO)]] and the ''[[LCROSS]]'' impactor on June 18, 2009. ''LCROSS'' completed its mission by making a planned and widely observed impact in the crater [[Cabeus]] on October 9, 2009,<ref>{{cite web |url=http://lcross.arc.nasa.gov/observation.htm |title=Lunar CRater Observation and Sensing Satellite (LCROSS): Strategy & Astronomer Observation Campaign |date=October 2009 |publisher=NASA |access-date=April 13, 2010 |url-status=dead |archive-url=https://web.archive.org/web/20120101191735/http://lcross.arc.nasa.gov/observation.htm |archive-date=January 1, 2012}}</ref> whereas ''LRO'' is currently in operation, obtaining precise lunar [[altimetry]] and high-resolution imagery.

China continued its lunar program in 2010 with ''[[Chang'e 2]]'', mapping the surface at a higher resolution over an eight-month period, and in 2013 with ''[[Chang'e 3]]'', a lunar [[lander (spacecraft)|lander]] along with a [[lunar rover]] named ''[[Yutu (rover)|Yutu]]'' ({{Lang-zh|c=玉兔|l=Jade Rabbit}}). This was the first lunar rover mission since ''[[Lunokhod 2]]'' in 1973 and the first lunar [[soft landing]] since ''[[Luna 24]]'' in 1976, making China the third country to achieve this.

In 2014 the first privately funded probe, the [[Manfred Memorial Moon Mission]], reached the Moon.

Another Chinese rover mission, ''[[Chang'e 4]]'', achieved the first landing on [[Far side of the Moon|the Moon's far side]] in early 2019.<ref>{{cite web |title=China Outlines New Rockets, Space Station and Moon Plans |url=http://www.space.com/28809-china-rocket-family-moon-plans.html |date=March 17, 2015 |first=Leonard |last=David |publisher=[[Space.com]] |access-date=June 29, 2016 |url-status=live |archive-url=https://web.archive.org/web/20160701055507/http://www.space.com/28809-china-rocket-family-moon-plans.html |archive-date=July 1, 2016}}</ref>

Also in 2019, India successfully sent its second probe, ''[[Chandrayaan-2]]'' to the Moon.

In 2020, China carried out its first robotic [[sample return mission]] (''[[Chang'e 5]]''), bringing back 1,731 grams of lunar material to Earth.<ref>{{cite news |title=China's Chang'e-5 brought 1,731 grams of samples from the moon |url=https://www.thehindu.com/sci-tech/science/chinas-change-5-brought-1731-grams-of-samples-from-the-moon/article33377559.ece |date=December 20, 2020 |work=[[The Hindu]] |access-date=October 15, 2021 |archive-date=October 29, 2021 |archive-url=https://web.archive.org/web/20211029180538/https://www.thehindu.com/sci-tech/science/chinas-change-5-brought-1731-grams-of-samples-from-the-moon/article33377559.ece |url-status=live}}</ref>

The U.S. [[Vision for Space Exploration|developed plans]] for returning to the Moon beginning in 2004,<ref>{{cite press release |url=http://www.nasa.gov/missions/solarsystem/bush_vision.html |title=President Bush Offers New Vision For NASA |date=December 14, 2004 |publisher=NASA |access-date=April 12, 2007 |url-status=live |archive-url=https://web.archive.org/web/20070510062228/http://www.nasa.gov/missions/solarsystem/bush_vision.html |archive-date=May 10, 2007}}</ref> and with the signing of the U.S.-led [[Artemis Accords]] in 2020, the [[Artemis program]] aims to return the astronauts to the Moon in the 2020s.<ref>{{Cite web |date=July 2019 |first=Adam |last=Mann |title=NASA's Artemis Program |url=https://www.space.com/artemis-program.html |access-date=April 19, 2021 |website=Space.com |language=en |archive-date=April 17, 2021 |archive-url=https://web.archive.org/web/20210417175557/https://www.space.com/artemis-program.html |url-status=live}}</ref> The Accords have been joined by a growing number of countries. The introduction of the Artemis Accords has fueled a renewed discussion about the international framework and cooperation of lunar activity, building on the [[Moon Treaty]] and the ESA-led [[Moon Village]] concept.<ref name="The Space Review 2020"/><ref name="Australian Institute of International Affairs 2021"/><ref name="The Space Treaty Institute – Dedicated to Peace and Sustainability in Outer Space. Our Mission"/>

2022 [[South Korea]] launched [[Danuri]] successfully, its first mission to the Moon, launched from the US.
2023 and 2024 [[India]] and Japan became the fourth and fifth country to [[Soft landing|soft land]] a spacecraft on the Moon, following the [[Soviet Union]] and [[United States]] in the 1960s, and [[China]] in the 2010s.<ref>{{Cite news |title=Japan makes contact with 'Moon Sniper' on lunar surface |url=https://www.bbc.co.uk/news/live/science-environment-68019846 |date=January 19, 2024 |access-date=January 19, 2024 |work=BBC News |language=en-gb |archive-date=January 19, 2024 |archive-url=https://web.archive.org/web/20240119143351/https://www.bbc.co.uk/news/live/science-environment-68019846 |url-status=live}}</ref> Notably, Japan's spacecraft, the [[Smart Lander for Investigating Moon]], survived 3 lunar nights.<ref>{{Cite web |author1=Robert Lea |date=April 24, 2024 |title=Japan's SLIM moon lander defies death to survive 3rd frigid lunar night (image) |url=https://www.space.com/japan-slim-moon-lander-survives-3rd-lunar-night |access-date=May 1, 2024 |website=Space.com |language=en |archive-date=April 30, 2024 |archive-url=https://web.archive.org/web/20240430163510/https://www.space.com/japan-slim-moon-lander-survives-3rd-lunar-night |url-status=live}}</ref> The [[IM-1]] lander became the first commercially built lander to land on the Moon in 2024.<ref>{{Cite web |title=Intuitive Machines' 'Odysseus' becomes first commercial lander to reach the Moon – Spaceflight Now |url=https://spaceflightnow.com/2024/02/22/live-coverage-intuitive-machines-aims-to-become-first-commercial-lander-to-safely-reach-the-moon/ |access-date=April 15, 2024 |language=en-US |archive-date=June 15, 2024 |archive-url=https://web.archive.org/web/20240615055824/https://spaceflightnow.com/2024/02/22/live-coverage-intuitive-machines-aims-to-become-first-commercial-lander-to-safely-reach-the-moon/ |url-status=live}}</ref>

China launched the [[Chang'e 6]] on May 3, 2024, which conducted another lunar sample return from the [[far side of the Moon]].<ref name="AJ_FI-20230425">{{cite tweet |author=Andrew Jones |user=AJ_FI |number=1650832520978526208 |title=China's Chang'e-6 sample return mission (a first ever lunar far side sample-return) is scheduled to launch in May 2024, and expected to take 53 days from launch to return module touchdown. Targeting southern area of Apollo basin (~43º S, 154º W) |date=April 25, 2023}}</ref> It also carried a Chinese rover to conduct [[Absorption spectroscopy|infrared spectroscopy]] of lunar surface.<ref>{{cite web |last1=Jones |first1=Andrew |title=China's Chang'e-6 is carrying a surprise rover to the moon |url=https://spacenews.com/chinas-change-6-is-carrying-a-surprise-rover-to-the-moon/ |website=SpaceNews |access-date=May 8, 2024 |date=May 6, 2024 |archive-date=May 8, 2024 |archive-url=https://web.archive.org/web/20240508193233/https://spacenews.com/chinas-change-6-is-carrying-a-surprise-rover-to-the-moon/ |url-status=live}}</ref> [[Pakistan]] sent a lunar orbiter called [[ICUBE-Q]] along with Chang'e 6.<ref>{{cite web |last=Jones |first=Andrew |url=https://spacenews.com/chinas-change-6-probe-arrives-at-spaceport-for-first-ever-lunar-far-side-sample-mission/ |title=China's Chang'e-6 probe arrives at spaceport for first-ever lunar far side sample mission |work=[[SpaceNews]] |date=January 10, 2024 |access-date=January 10, 2024 |archive-date=May 3, 2024 |archive-url=https://web.archive.org/web/20240503100724/https://spacenews.com/chinas-change-6-probe-arrives-at-spaceport-for-first-ever-lunar-far-side-sample-mission/ |url-status=live}}</ref>

[[IM-2|Nova-C 2]], [[Ispace (Japanese company)#Hakuto-R program|iSpace Lander]] and [[Blue Ghost]] were all launched to the Moon in 2024.

[[File:Artemis 2 Crew Portrait.jpg|thumb|[[Artemis II]] crew, with the [[Women in space|first woman]], person of color and non–US-citizen astronaut planned to go to the Moon, scheduled for 2026, returning humans to the Moon for the first time since [[Apollo 17]] in 1972. [[Clockwise]] from left: [[Christina Koch|Koch]], [[Victor J. Glover|Glover]], [[Jeremy Hansen|Hansen]] and [[Reid Wiseman|Wiseman]].]]

===Future===
{{See also|List of proposed missions to the Moon}}
Beside the progressing [[Artemis program]] and supporting [[Commercial Lunar Payload Services]], leading an international and commercial crewed opening up of the Moon and sending the [[Women in space|first woman]], person of color and non-US citizen to the Moon in the 2020s,<ref>{{Cite web |url=https://www.asianage.com/science/150519/nasa-plans-to-send-first-woman-on-moon-by-2024.html |title=NASA plans to send first woman on Moon by 2024 |date=May 15, 2019 |website=The Asian Age |access-date=May 15, 2019 |archive-date=April 14, 2020 |archive-url=https://web.archive.org/web/20200414162829/https://www.asianage.com/science/150519/nasa-plans-to-send-first-woman-on-moon-by-2024.html |url-status=live}}</ref> China is continuing its ambitious [[Chang'e program]], having announced with Russia's struggling ''[[Luna-Glob]]'' program joint missions.<ref name="TASS 2019 x202">{{cite web |title=Russia, China agree on joint Moon exploration |website=TASS |date=September 17, 2019 |url=https://tass.com/science/1078599 |access-date=April 16, 2024 |archive-date=July 22, 2023 |archive-url=https://web.archive.org/web/20230722101456/https://tass.com/science/1078599 |url-status=live}}</ref><ref>{{cite magazine |url=http://www.aviationnow.com/avnow/news/channel_awst_story.jsp?id=news/aw060506p2.xml |title=Russia Plans Ambitious Robotic Lunar Mission |last=Covault |first=C. |magazine=[[Aviation Week]] |date=June 4, 2006 |access-date=April 12, 2007 |url-status=live |archive-url=https://web.archive.org/web/20060612215659/http://www.aviationnow.com/avnow/news/channel_awst_story.jsp?id=news%2Faw060506p2.xml |archive-date=June 12, 2006}}</ref> Both the Chinese and US lunar programs have the goal to establish in the 2030s a [[lunar base]] with their international partners, though the US and its partners will first establish an orbital [[Lunar Gateway]] station in the 2020s, from which Artemis missions will land the [[Human Landing System]] to set up temporary surface camps.

While the Apollo missions were explorational in nature, the Artemis program plans to establish a more permanent presence. To this end, NASA is partnering with industry leaders to establish key elements such as modern communication infrastructure. A [[4G]] connectivity demonstration is to be launched aboard an [[Intuitive Machines Nova-C]] lander in 2024.<ref>{{Cite web |last=Bantock |first=Jack |date=April 24, 2024 |title=Streaming and texting on the Moon: Nokia and NASA are taking 4G into space {{!}} CNN Business |url=https://www.cnn.com/2024/04/24/tech/nokia-moon-4g-network-nasa-spc/index.html |access-date=April 27, 2024 |website=CNN |language=en |archive-date=April 27, 2024 |archive-url=https://web.archive.org/web/20240427205419/https://www.cnn.com/2024/04/24/tech/nokia-moon-4g-network-nasa-spc/index.html |url-status=live}}</ref> Another focus is on [[in situ resource utilization]], which is a key part of the [[DARPA lunar programs]]. [[DARPA]] has requested that industry partners develop a 10–year lunar architecture plan to enable the beginning of a lunar economy.<ref>{{Cite web |author1=Meredith Garofalo |date=December 8, 2023 |title=DARPA moon tech study selects 14 companies to develop a lunar economy |url=https://www.space.com/darpa-moon-tech-study-future-lunar-economy |access-date=April 27, 2024 |website=Space.com |language=en |archive-date=June 15, 2024 |archive-url=https://web.archive.org/web/20240615055827/https://www.space.com/darpa-moon-tech-study-future-lunar-economy |url-status=live}}</ref>

==Human presence==
{{See also|Human presence in space}}
[[File:Moon Soft Landings.svg|thumb|Map of all the sites of [[soft landing]]s on the Moon (2024)]]

In 1959 the first extraterrestrial probes reached the Moon ([[Luna program]]), just a year into the [[space age]], after the first ever orbital flight. Since then, humans have sent a range of probes and people to the Moon. The first stay of people on the Moon was conducted in 1969, in a series of crewed exploration missions (the [[Apollo Program]]), the last having taken place in 1972.

Uninterrupted presence has been the case through the [[List of artificial objects on the Moon|remains]] of impactors, landings and [[List of extraterrestrial orbiters#Moon|lunar orbiters]]. Some landings and orbiters have maintained a small lunar infrastructure, providing continuous observation and communication at the Moon.

Increasing human activity in [[cislunar space]] as well as on the Moon's surface, particularly missions at the far side of the Moon or the [[Lunar north pole|lunar north]] and [[Lunar south pole|south polar]] regions, are in need for a lunar infrastructure. For that purpose, orbiters in [[lunar orbit|orbits around the Moon]] or [[List of objects at Lagrange points#Earth–Moon Lagrange points|the Earth–Moon Lagrange points]], have since 2006 been operated. With highly [[Orbital eccentricity|eccentric orbits]] providing continuous communication, as with the orbit of [[Queqiao]] and [[Queqiao-2 relay satellite]] or the planned first extraterrestrial space station, the [[Lunar Gateway]].<ref name="Williams 2022">{{cite web |last=Williams |first=Matt |title=A CubeSat is Flying to the Moon to Make Sure Lunar Gateway's Orbit is Actually Stable |website=Universe Today |date=May 14, 2022 |url=https://www.universetoday.com/155842/a-cubesat-is-flying-to-the-moon-to-make-sure-lunar-gateways-orbit-is-actually-stable-1/ |access-date=December 17, 2022 |archive-date=December 17, 2022 |archive-url=https://web.archive.org/web/20221217015619/https://www.universetoday.com/155842/a-cubesat-is-flying-to-the-moon-to-make-sure-lunar-gateways-orbit-is-actually-stable-1/ |url-status=live}}</ref><ref name="Phys.org 2021">{{cite web |title=Queqiao: The bridge between Earth and the far side of the moon |website=Phys.org |date=June 11, 2021 |url=https://phys.org/news/2021-06-queqiao-bridge-earth-side-moon.html |access-date=December 17, 2022 |archive-date=December 17, 2022 |archive-url=https://web.archive.org/web/20221217015553/https://phys.org/news/2021-06-queqiao-bridge-earth-side-moon.html |url-status=live}}</ref>

=== Human impact ===
{{See also|Space debris|Space sustainability|List of artificial objects on the Moon|Space art#Art in space|Moonbase|Lunar resources #Mining|Tourism on the Moon|Space archaeology}}

[[File:ALSEP_AS17-134-20500.jpg|Artifacts of human activity, [[Apollo Lunar Surface Experiments Package|Apollo 17's Lunar Surface Experiments Package]]<ref name="Garber 2012" />|thumb|right]]

While the Moon has the lowest [[Planetary protection#Target categories|planetary protection target-categorization]], its degradation as a pristine body and scientific place has been discussed.<ref name="Vidaurri 2019">{{cite web |last=Vidaurri |first=Monica |title=Will people go to space—and then colonize it? |website=Quartz |date=October 24, 2019 |url=https://qz.com/1734103/will-people-go-to-space-and-then-colonize-it/ |access-date=November 9, 2021 |archive-date=November 9, 2021 |archive-url=https://web.archive.org/web/20211109040803/https://qz.com/1734103/will-people-go-to-space-and-then-colonize-it/ |url-status=live}}</ref> If there is [[#Astronomy from the Moon|astronomy performed from the Moon]], it will need to be free from any physical and [[radio pollution]]. While the Moon has no significant atmosphere, traffic and impacts on the Moon causes clouds of dust that can spread far and possibly contaminate the original state of the Moon and its special scientific content.<ref name="David 2020">{{cite web |last=David |first=Leonard |title=Cold as (lunar) ice: Protecting the moon's polar regions from contamination |website=Space.com |date=August 21, 2020 |url=https://www.space.com/moon-ice-mining-contamination-concerns.html |access-date=February 3, 2022 |archive-date=February 4, 2022 |archive-url=https://web.archive.org/web/20220204000406/https://www.space.com/moon-ice-mining-contamination-concerns.html |url-status=live}}</ref> Scholar [[Alice Gorman]] asserts that, although the Moon is inhospitable, it is not dead, and that sustainable human activity would require treating the Moon's ecology as a co-participant.<ref name="Gorman 2022">{{cite web |last=Gorman |first=Alice |title=#SpaceWatchGL Opinion: An ecofeminist approach to the sustainable use of the Moon |website=SpaceWatch.Global |date=July 1, 2022 |url=https://spacewatch.global/2022/07/spacewatchgl-opinion-an-ecofeminist-approach-to-the-sustainable-used-of-the-moon/ |access-date=July 3, 2022 |archive-date=July 4, 2022 |archive-url=https://web.archive.org/web/20220704024322/https://spacewatch.global/2022/07/spacewatchgl-opinion-an-ecofeminist-approach-to-the-sustainable-used-of-the-moon/ |url-status=live}} Note: see [[Val Plumwood]] which Alice Gorman cites regarding co-participation.</ref>

The so-called "[[Tardigrades on the Moon|Tardigrade affair]]" of the 2019 crashed [[Beresheet]] lander and its carrying of [[tardigrade]]s has been discussed as an example for lacking measures and lacking international regulation for [[planetary protection]].<ref name="Alvarez 2020 p."/>

[[Space debris]] beyond Earth around the Moon has been considered as a future challenge with increasing numbers of missions to the Moon, particularly as a danger for such missions.<ref name="Carter 2022">{{cite web |last=Carter |first=Jamie |title=As Chinese Rocket Strikes Moon This Week We Need To Act Now To Prevent New Space Junk Around The Moon Say Scientists |website=Forbes |date=February 27, 2022 |url=https://www.forbes.com/sites/jamiecartereurope/2022/02/27/as-chinese-rocket-strikes-moon-this-week-we-need-to-act-now-to-prevent-new-space-junk-around-the-moon-say-scientists/ |access-date=April 9, 2022 |archive-date=April 9, 2022 |archive-url=https://web.archive.org/web/20220409134704/https://www.forbes.com/sites/jamiecartereurope/2022/02/27/as-chinese-rocket-strikes-moon-this-week-we-need-to-act-now-to-prevent-new-space-junk-around-the-moon-say-scientists/ |url-status=live}}</ref><ref name="Nast 2013"/> As such lunar waste management has been raised as an issue which future lunar missions, particularly on the surface, need to tackle.<ref name="Pino Salmeri Hugo Hume p.">{{cite journal |last1=Pino |first1=Paolo |last2=Salmeri |first2=Antonino |last3=Hugo |first3=Adam |last4=Hume |first4=Shayna |title=Waste Management for Lunar Resources Activities: Toward a Circular Lunar Economy |journal=New Space |publisher=Mary Ann Liebert Inc |date=August 27, 2021 |issn=2168-0256 |doi=10.1089/space.2021.0012 |pages=274–283 |s2cid=233335692 |volume=10 |issue=3}}</ref><ref name="NASA/ADS">{{cite journal |title=1985lbsa.conf..423B Page 423 |journal=Lunar Bases and Space Activities of the 21st Century |bibcode=1985lbsa.conf..423B |url=https://adsabs.harvard.edu/full/1985lbsa.conf..423B |language=fi |access-date=May 26, 2022 |last1=Briggs |first1=Randall |last2=Sacco |first2=Albert |year=1985 |page=423 |archive-date=May 26, 2022 |archive-url=https://web.archive.org/web/20220526022021/https://adsabs.harvard.edu/full/1985lbsa.conf..423B |url-status=live}}</ref>

Human remains have been transported to the Moon, including by private companies such as [[Celestis]] and [[Elysium Space]]. Because the Moon has been sacred or significant to many cultures, the practice of [[space burial]]s have attracted criticism from [[indigenous peoples]] leaders. For example, then{{endash}}[[Navajo Nation]] president [[Albert Hale]] criticized NASA for sending the [[cremated]] ashes of scientist [[Eugene Shoemaker]] to the Moon in 1998.<ref name="Magazine Sullivan 2024 a329">{{cite web |last1=Magazine |first1=Smithsonian |last2=Sullivan |first2=Will |title=Navajo Nation President Asks for Delay of Moon Mission Carrying Human Remains |website=Smithsonian Magazine |date=January 5, 2024 |url=https://www.smithsonianmag.com/smart-news/navajo-nation-president-asks-for-delay-of-moon-mission-carrying-human-remains-180983543/ |access-date=January 7, 2024 |archive-date=January 6, 2024 |archive-url=https://web.archive.org/web/20240106235545/https://www.smithsonianmag.com/smart-news/navajo-nation-president-asks-for-delay-of-moon-mission-carrying-human-remains-180983543/ |url-status=live}}</ref><ref name="web.archive.org 2011 c901">{{cite web |title=Celestis Memorial Spaceflights |date=August 8, 2011 |url=http://celestis.com/luna01Flight.asp |archive-url=https://web.archive.org/web/20140314165835/http://celestis.com/luna01Flight.asp |archive-date=March 14, 2014 |url-status=unfit |access-date=January 7, 2024}}</ref>

Beside the remains of human activity on the Moon, there have been some intended permanent installations like the ''[[Moon Museum]]'' art piece, [[Apollo 11 goodwill messages]], six [[lunar plaque]]s, the ''[[Fallen Astronaut]]'' memorial, and other artifacts.<ref name="Garber 2012">{{cite web |last=Garber |first=Megan |title=The Trash We've Left on the Moon |website=The Atlantic |date=December 19, 2012 |url=https://www.theatlantic.com/technology/archive/2012/12/the-trash-weve-left-on-the-moon/266465/ |access-date=April 11, 2022 |archive-date=April 9, 2022 |archive-url=https://web.archive.org/web/20220409080003/https://www.theatlantic.com/technology/archive/2012/12/the-trash-weve-left-on-the-moon/266465/ |url-status=live}}</ref>

Longterm missions continuing to be active are some orbiters such as the 2009-launched [[Lunar Reconnaissance Orbiter]] surveilling the Moon for future missions, as well as some Landers such as the 2013-launched [[Chang'e 3]] with its Lunar Ultraviolet Telescope still operational.<ref>{{cite web |url=https://www.space.com/china-change-3-moon-lander-lasts-7-years |author=Andrew Jones |title=China's Chang'e 3 lunar lander still going strong after 7 years on the moon |website=[[Space.com]] |date=September 23, 2020 |access-date=November 16, 2020 |archive-date=November 25, 2020 |archive-url=https://web.archive.org/web/20201125043612/https://www.space.com/china-change-3-moon-lander-lasts-7-years |url-status=live}}</ref>
Five retroreflectors have been installed on the Moon since the 1970s and since used for accurate measurements of the physical [[libration]]s through [[Lunar Laser Ranging experiment|laser ranging to the Moon]].

There are [[List of missions to the Moon#Future missions|several missions by different agencies and companies planned]] to establish a long-term human presence on the Moon, with the [[Lunar Gateway]] as the currently most advanced project as part of the [[Artemis program]].

===Astronomy from the Moon===
{{Further|Extraterrestrial sky#The Moon}}
[[File:Earth’s geocorona from the Moon.jpg|thumb|Earth's [[exosphere]] illuminated creating its [[geocorona]], visible in ultraviolet and viewed by the [[Far Ultraviolet Camera/Spectrograph]] of [[Apollo 16]] in 1972 from the Moon's surface]]
The Moon has been used as a site for astronomical and [[Earth observation]]s. The Earth appears in the [[Extraterrestrial sky#The Moon|Moon's sky]] with an [[apparent size]] of 1° 48{{prime}} to 2°,<ref name="Gorkavyi Krotkov Marshak 2023 pp. 1527–1537">{{cite journal |last1=Gorkavyi |first1=Nick |last2=Krotkov |first2=Nickolay |last3=Marshak |first3=Alexander |title=Earth observations from the Moon's surface: dependence on lunar libration |journal=Atmospheric Measurement Techniques |publisher=Copernicus GmbH |volume=16 |issue=6 |date=March 24, 2023 |issn=1867-8548 |doi=10.5194/amt-16-1527-2023 |pages=1527–1537 |bibcode=2023AMT....16.1527G |s2cid=257753776 |doi-access=free}}</ref> three to four times the size of the Moon or Sun in Earth's sky, or about the apparent width of two little fingers at an arm's length away. Observations from the Moon started as early as 1966 with the [[Timeline of first images of Earth from space|first images of Earth]] from the Moon, taken by [[Lunar Orbiter 1]]. Of particular cultural significance is the 1968 photograph called ''[[Earthrise]]'', taken by [[Bill Anders]] of [[Apollo 8]] in 1968. In April 1972 the [[Apollo 16]] mission set up the first dedicated telescope,<ref name="w422">{{cite web |last=Betz |first=Eric |title=The History and Future of Telescopes on the Moon |website=Astronomy Magazine |date=2020-06-03 |url=https://www.astronomy.com/observing/the-history-and-future-of-telescopes-on-the-moon/ |access-date=2024-10-22}}</ref><ref name="x909">{{cite web |title=Remembering the First Moon-Based Telescope |website=NASA |date=2019-07-15 |url=https://www.nasa.gov/solar-system/remembering-the-first-moon-based-telescope/ |access-date=2024-10-22}}</ref> the [[Far Ultraviolet Camera/Spectrograph]], recording various astronomical photos and spectra.<ref>{{cite web |url=http://www.lpi.usra.edu/lunar/missions/apollo/apollo_16/experiments/f_ultra/ |title=Far Ultraviolet Camera/Spectrograph |publisher=Lpi.usra.edu |access-date=October 3, 2013 |url-status=live |archive-url=https://web.archive.org/web/20131203010615/http://www.lpi.usra.edu/lunar/missions/apollo/apollo_16/experiments/f_ultra/ |archive-date=December 3, 2013}}</ref>

The Moon is recognized as an excellent site for telescopes.<ref>{{cite web |last=Takahashi |first=Yuki |title=Mission Design for Setting up an Optical Telescope on the Moon |publisher=[[California Institute of Technology]] |date=September 1999 |url=http://www.ugcs.caltech.edu/~yukimoon/MoonTelescope/ |access-date=March 27, 2011 |url-status=dead |archive-url=https://web.archive.org/web/20151106142659/http://www.ugcs.caltech.edu/~yukimoon/MoonTelescope/ |archive-date=November 6, 2015}}</ref> It is relatively nearby; certain craters near the poles are permanently dark and cold and especially useful for [[infrared telescope]]s; and [[radio telescope]]s on the far side would be shielded from the radio chatter of Earth.<ref>{{cite web |last=Chandler |first=David |title=MIT to lead development of new telescopes on moon |work=MIT News |date=February 15, 2008 |url=http://web.mit.edu/newsoffice/2008/moonscope-0215.html |access-date=March 27, 2011 |url-status=live |archive-url=https://web.archive.org/web/20090304062601/http://web.mit.edu/newsoffice/2008/moonscope-0215.html |archive-date=March 4, 2009}}</ref> The [[lunar soil]], although it poses a problem for any moving parts of [[telescope]]s, can be mixed with [[carbon nanotube]]s and [[Epoxy|epoxies]] and employed in the construction of mirrors up to 50 meters in diameter.<ref>{{cite web |last=Naeye |first=Robert |title=NASA Scientists Pioneer Method for Making Giant Lunar Telescopes |publisher=[[Goddard Space Flight Center]] |date=April 6, 2008 |url=http://www.nasa.gov/centers/goddard/news/topstory/2008/lunar_telescopes.html |access-date=March 27, 2011 |url-status=live |archive-url=https://web.archive.org/web/20101222142443/http://www.nasa.gov/centers/goddard/news/topstory/2008/lunar_telescopes.html |archive-date=December 22, 2010}}</ref> A lunar [[zenith telescope]] can be made cheaply with an [[ionic liquid]].<ref>{{cite web |last=Bell |first=Trudy |title=Liquid Mirror Telescopes on the Moon |work=Science News |publisher=NASA |date=October 9, 2008 |url=https://science.nasa.gov/science-news/science-at-nasa/2008/09oct_liquidmirror/ |access-date=March 27, 2011 |url-status=dead |archive-url=https://web.archive.org/web/20110323081215/http://science.nasa.gov/science-news/science-at-nasa/2008/09oct_liquidmirror/ |archive-date=March 23, 2011}}</ref>

===Living on the Moon===
{{Main|Lunar habitation}}
[[File:Aldrin Looks Back at Tranquility Base - GPN-2000-001102.jpg|thumb|Astronaut [[Buzz Aldrin]] in [[Apollo/Skylab spacesuit|life-supporting suit]] looking back at the first [[lunar base|lunar habitat and base]], the [[Lunar Module Eagle|Lunar Module ''Eagle'']] of [[Tranquility Base]], during [[Apollo 11]] (1969), the first crewed [[Moon landing]]]]
The only instances of [[Space habitat (facility)#Extraterrestrial surface habitat|humans living on the Moon]] have taken place in an [[Apollo Lunar Module]] for several days at a time (for example, during the [[Apollo 17]] mission).<ref>{{cite web |url=http://history.msfc.nasa.gov/saturn_apollo/documents/apollo17_overview.pdf |archive-url=https://web.archive.org/web/20060930204141/http://history.msfc.nasa.gov/saturn_apollo/documents/apollo17_overview.pdf |url-status=dead |archive-date=September 30, 2006 |title=Mission Report: Apollo 17 – The Most Productive Lunar Expedition |publisher=NASA |access-date=February 10, 2021}}</ref> One challenge to astronauts during their stay on the surface is that [[lunar dust]] sticks to their suits and is carried into their quarters. Astronauts could taste and smell the dust, which smells like gunpowder and was called the "Apollo aroma".<ref name="Aroma" /> This fine lunar dust can [[Lunar dust#Harmful effects of lunar dust|cause health issues]].<ref name="Aroma">{{cite web |url=https://www.space.com/moon-dust-problem-lunar-exploration.html |title=Moon Dust Could Be a Problem for Future Lunar Explorers |first=Leonard |last=David |website=[[Space.com]] |date=October 21, 2019 |access-date=November 26, 2020 |archive-date=December 1, 2020 |archive-url=https://web.archive.org/web/20201201103751/https://www.space.com/moon-dust-problem-lunar-exploration.html |url-status=live}}</ref>

In 2019, at least one plant seed sprouted in an experiment on the [[Change 4#Lunar lander|Chang'e 4 lander]]. It was carried from Earth along with other small life in its ''Lunar Micro Ecosystem''.<ref name="Seeds">{{cite web |url=https://www.scmp.com/news/china/science/article/2182111/chinese-lunar-landers-cotton-seeds-lead-way-plant-life-germinates |title=Chinese lunar lander's cotton seeds spring to life on far side of the moon |last1=Zheng |first1=William |date=January 15, 2019 |website=South China Morning Post |access-date=November 26, 2020 |archive-date=January 16, 2019 |archive-url=https://web.archive.org/web/20190116174611/https://www.scmp.com/news/china/science/article/2182111/chinese-lunar-landers-cotton-seeds-lead-way-plant-life-germinates |url-status=live}}</ref>

==Legal status==
{{See also|Space law|Politics of outer space|Space advocacy|Colonization of the Moon}}
Although ''[[Luna program|Luna]]'' landers scattered pennants of the [[Soviet Union]] on the Moon, and [[Lunar Flag Assembly|U.S. flags]] were symbolically planted at their landing sites by the [[Apollo astronauts]], no nation claims ownership of any part of the Moon's surface.<ref name="unoosa_q6" /> Likewise no [[Extraterrestrial real estate|private ownership of parts of the Moon, or as a whole]], is considered credible.<ref name="unoosa_q7" /><ref name="iisl_2004" /><ref name="iisl_2009" />

The 1967 [[Outer Space Treaty]] defines the Moon and all outer space as the "[[common heritage of mankind|province of all mankind]]".<ref name="unoosa_q6" /> It restricts the use of the Moon to peaceful purposes, explicitly banning military installations and [[weapons of mass destruction]].<ref name="unoosa_q5" /> A majority of countries are parties of this treaty.<ref name="unoosa_q4" />
The 1979 [[Moon Agreement]] was created to elaborate, and restrict the exploitation of the [[Lunar resources|Moon's resources]] by any single nation, leaving it to a yet unspecified international regulatory regime.<ref name="The Space Review 2021">{{cite web |title=The Space Review: Is outer space a de jure common-pool resource? |website=The Space Review |date=October 25, 2021 |url=https://www.thespacereview.com/article/4270/1 |access-date=April 9, 2022 |archive-date=November 2, 2021 |archive-url=https://web.archive.org/web/20211102004759/https://thespacereview.com/article/4270/1 |url-status=live}}</ref> As of January 2020, it has been signed and ratified by 18 nations,<ref name="unoosa_moon" /> none of which have [[human spaceflight]] capabilities.

Since 2020, countries have joined the U.S. in their [[Artemis Accords]], which are challenging the treaty. The U.S. has furthermore emphasized in a presidential [[executive order]] ("Encouraging International Support for the Recovery and Use of Space Resources.") that "the United States does not view outer space as a 'global commons{{' "}} and calls the Moon Agreement "a failed attempt at constraining free enterprise."<ref>{{cite web |first=Kiran |last=Vazhapully |title=Space Law at the Crossroads: Contextualizing the Artemis Accords and the Space Resources Executive Order |date=July 22, 2020 |website=OpinioJuris |access-date=May 10, 2021 |url=http://opiniojuris.org/2020/07/22/space-law-at-the-crossroads-contextualizing-the-artemis-accords-and-the-space-resources-executive-order/ |archive-date=May 10, 2021 |archive-url=https://web.archive.org/web/20210510140033/http://opiniojuris.org/2020/07/22/space-law-at-the-crossroads-contextualizing-the-artemis-accords-and-the-space-resources-executive-order/ |url-status=live}}</ref><ref>{{Cite press release |url=https://spaceref.com/press-release/administration-statement-on-executive-order-on-encouraging-international-support-for-the-recovery-and-use-of-space-resources/ |archive-url=https://archive.today/20240201151140/https://spaceref.com/press-release/administration-statement-on-executive-order-on-encouraging-international-support-for-the-recovery-and-use-of-space-resources/ |archive-date=February 1, 2024 |url-status=live |title=Administration Statement on Executive Order on Encouraging International Support for the Recovery and Use of Space Resources |via=SpaceRef |date=April 6, 2020 |publisher=White House |access-date=June 17, 2020}}</ref>

With Australia signing and ratifying both the Moon Treaty in 1986 as well as the Artemis Accords in 2020, there has been a discussion if they can be harmonized.<ref name="Australian Institute of International Affairs 2021">{{cite web |title=Australia Between the Moon Agreement and the Artemis Accords |website=Australian Institute of International Affairs |date=June 2, 2021 |url=https://www.internationalaffairs.org.au/australianoutlook/australia-between-the-moon-agreement-and-the-artemis-accords/ |access-date=February 1, 2022 |archive-date=February 1, 2022 |archive-url=https://web.archive.org/web/20220201052259/https://www.internationalaffairs.org.au/australianoutlook/australia-between-the-moon-agreement-and-the-artemis-accords/ |url-status=live}}</ref> In this light an ''Implementation Agreement'' for the Moon Treaty has been advocated for, as a way to compensate for the shortcomings of the Moon Treaty and to harmonize it with other laws and agreements such as the Artemis Accords, allowing it to be more widely accepted.<ref name="The Space Review 2020">{{cite web |title=The Space Review: The Artemis Accords: repeating the mistakes of the Age of Exploration |website=The Space Review |date=June 29, 2020 |url=https://www.thespacereview.com/article/3975/1 |access-date=February 1, 2022 |archive-date=January 25, 2022 |archive-url=https://web.archive.org/web/20220125075833/https://www.thespacereview.com/article/3975/1 |url-status=live}}</ref><ref name="The Space Treaty Institute – Dedicated to Peace and Sustainability in Outer Space. Our Mission">{{cite web |title=The Space Treaty Institute – Dedicated to Peace and Sustainability in Outer Space. Our Mission: To give people Hope and Inspiration by helping the nations of Earth to build a Common Future |website=The Space Treaty Institute – Dedicated to Peace and Sustainability in Outer Space. Our Mission |url=http://www.spacetreaty.org/ |access-date=February 1, 2022 |archive-date=February 1, 2022 |archive-url=https://web.archive.org/web/20220201060827/http://www.spacetreaty.org/ |url-status=live}}</ref>

In the face of such increasing commercial and national interest, particularly prospecting territories, U.S. lawmakers have introduced in late 2020 specific regulation for the conservation of historic landing sites<ref name="HowStuffWorks 2021">{{cite web |title='One Small Step' Act Encourages Protection of Human Heritage in Space |website=HowStuffWorks |date=January 12, 2021 |url=https://science.howstuffworks.com/us-law-protect-lunar-landing-sites.htm |access-date=November 1, 2021 |archive-date=November 1, 2021 |archive-url=https://web.archive.org/web/20211101214329/https://science.howstuffworks.com/us-law-protect-lunar-landing-sites.htm |url-status=live}}</ref> and interest groups have argued for making such sites [[World Heritage Site]]s<ref name="For All Moonkind">{{cite web |title=Moonkind – Human Heritage in Outer Space |website=For All Moonkind |url=https://www.forallmoonkind.org/moonkind-mission/human-heritage-in-outer-space/ |access-date=November 1, 2021 |archive-date=November 1, 2021 |archive-url=https://web.archive.org/web/20211101214336/https://www.forallmoonkind.org/moonkind-mission/human-heritage-in-outer-space/ |url-status=live}}</ref> and zones of scientific value protected zones, all of which add to the legal availability and territorialization of the Moon.<ref name="Alvarez 2020 p.">{{cite thesis |last=Alvarez |first=Tamara |title=The Eighth Continent: An Ethnography of Twenty-First Century Euro-American Plans to Settle the Moon |date=January 1, 2020 |url=https://www.academia.edu/43890727 |access-date=November 1, 2021 |page=109-115, 164–167, 176 |archive-date=February 5, 2022 |archive-url=https://web.archive.org/web/20220205171101/https://www.academia.edu/43890727 |url-status=live}}</ref>

In 2021, the ''Declaration of the Rights of the Moon''<ref name="Declaration">{{cite web |title=Declaration of the Rights of the Moon |date=February 11, 2021 |publisher=Australian Earth Laws Alliance |url=https://www.earthlaws.org.au/moon-declaration/ |access-date=May 10, 2021 |archive-date=April 23, 2021 |archive-url=https://web.archive.org/web/20210423050426/https://www.earthlaws.org.au/moon-declaration/ |url-status=live}}</ref> was created by a group of "lawyers, space archaeologists and concerned citizens", drawing on precedents in the [[Rights of Nature]] movement and the concept of legal personality for non-human entities in space.<ref>{{Cite journal |last1=Tepper |first1=Eytan |last2=Whitehead |first2=Christopher |date=December 1, 2018 |title=Moon, Inc.: The New Zealand Model of Granting Legal Personality to Natural Resources Applied to Space |url=https://www.liebertpub.com/doi/abs/10.1089/space.2018.0025 |journal=New Space |volume=6 |issue=4 |pages=288–298 |doi=10.1089/space.2018.0025 |bibcode=2018NewSp...6..288T |s2cid=158616075 |issn=2168-0256 |access-date=July 30, 2022 |archive-date=June 28, 2021 |archive-url=https://web.archive.org/web/20210628015902/https://www.liebertpub.com/doi/abs/10.1089/space.2018.0025 |url-status=live}}</ref><ref name="Evans 2021">{{cite web |last=Evans |first=Kate |title=Hear Ye! Hear Ye! A Declaration of the Rights of the Moon |website=Eos |date=July 20, 2021 |url=http://eos.org/features/hear-ye-hear-ye-a-declaration-of-the-rights-of-the-moon |access-date=April 9, 2022 |archive-date=February 6, 2022 |archive-url=https://web.archive.org/web/20220206102833/https://eos.org/features/hear-ye-hear-ye-a-declaration-of-the-rights-of-the-moon |url-status=live}}</ref>

===Coordination and regulation===
Increasing human activity at the Moon has raised the need for coordination to safeguard international and commercial lunar activity. Issues from cooperation to mere coordination, through for example the development of a shared [[Lunar time]], have been raised.

In particular the establishment of an [[Internationalism (politics)|international]] or [[United Nations]] regulatory regime for lunar human activity has been called for by the [[Moon Treaty]] and suggested through an ''Implementation Agreement'',<ref name="The Space Review 2020"/><ref name="The Space Treaty Institute – Dedicated to Peace and Sustainability in Outer Space. Our Mission"/> but remains contentious. Current lunar programs are [[Multilateralism|multilateral]], with the US-led [[Artemis program]] and the China-led [[International Lunar Research Station]]. For broader international cooperation and coordination, the [[International Lunar Exploration Working Group]] (ILEWG), the [[Moon Village|Moon Village Association]] (MVA) and more generally the International Space Exploration Coordination Group (ISECG) has been established.

==In culture and life==
===Timekeeping===
{{Further|Lunar calendar |Lunisolar calendar |Metonic cycle }}
[[File:Venus-de-Laussel-detail-corne.jpg|thumb|right|The [[Venus of Laussel]] (c. 25,000 [[Before present|BP]]) holding a crescent shaped horn. The 13 notches on the horn may symbolize the average number of days from menstruation to an [[ovulation]], or the approximate number of full [[menstrual cycle]]s and [[lunar cycle]]s per year (although these two phenomena are unrelated).<ref name=":0b">{{Cite book |last=Thompson, William Irwin. |url=https://www.worldcat.org/oclc/6890108 |title=The time falling bodies take to light : mythology, sexuality, and the origins of culture |date=1981 |publisher=St. Martin's Press |isbn=0-312-80510-1 |location=New York |pages=105 |oclc=6890108 |access-date=July 30, 2022 |archive-url=https://web.archive.org/web/20211003030402/https://www.worldcat.org/title/time-falling-bodies-take-to-light-mythology-sexuality-and-the-origins-of-culture/oclc/6890108 |archive-date=October 3, 2021 |url-status=live}}</ref><ref name="Boyle 2019">{{cite web |last=Boyle |first=Rebecca |date=July 9, 2019 |title=Ancient humans used the moon as a calendar in the sky |url=https://www.sciencenews.org/article/moon-time-calendar-ancient-human-art |url-status=live |archive-url=https://web.archive.org/web/20211104145754/https://www.sciencenews.org/article/moon-time-calendar-ancient-human-art |archive-date=November 4, 2021 |access-date=November 4, 2021 |website=Science News}}</ref>]]Since pre-historic times people have taken note of [[Lunar phases|the Moon's phases]] and its [[Lunar cycle|waxing and waning cycle]] and used it to keep record of time. [[Tally stick]]s, notched bones dating as far back as 20–30,000 years ago, are believed by some to mark the phases of the Moon.<ref name="Burton2011" /><ref>{{cite journal |last1=Brooks |first1=A. S. |last2=Smith |first2=C. C. |date=1987 |title=Ishango revisited: new age determinations and cultural interpretations |journal=The African Archaeological Review |volume=5 |issue=1 |pages=65–78 |doi=10.1007/BF01117083 |jstor=25130482 |s2cid=129091602}}</ref><ref>{{cite book |last=Duncan |first=David Ewing |title=The Calendar |date=1998 |publisher=Fourth Estate Ltd. |isbn=978-1-85702-721-1 |pages=[https://archive.org/details/calendar5000year0000dunc_l8r5/page/10 10–11] |url=https://archive.org/details/calendar5000year0000dunc_l8r5}}</ref> The counting of the days between the Moon's phases eventually gave rise to generalized [[Unit of time|time period]]s of lunar cycles as [[month]]s, and possibly of its phases as [[week]]s.<ref name="Zerubavel 1989 p. 9">{{cite book |last=Zerubavel |first=E. |title=The Seven Day Circle: The History and Meaning of the Week |publisher=University of Chicago Press |year=1989 |isbn=978-0-226-98165-9 |url=https://books.google.com/books?id=Cd5ZjRsNj4sC&pg=PA9 |access-date=February 25, 2022 |page=9 |archive-date=July 25, 2022 |archive-url=https://web.archive.org/web/20220725234921/https://books.google.com/books?id=Cd5ZjRsNj4sC&pg=PA9 |url-status=live}}</ref>

The words for the month in a range of different languages carry this relation between the period of the month and the Moon etymologically. The English ''month'' as well as ''moon'', and its cognates in other Indo-European languages (e.g. the [[Latin]] {{lang|la |mensis}} and [[Ancient Greek]] {{lang|grc |μείς}} (''meis'') or {{lang |grc |μήν}} (mēn), meaning "month")<ref>{{cite book |author=Smith, William George |title=Dictionary of Greek and Roman Biography and Mythology: Oarses-Zygia |url=https://books.google.com/books?id=PJ0YAAAAIAAJ |access-date=March 29, 2010 |volume=3 |date=1849 |publisher=J. Walton |page=768 |archive-date=November 26, 2020 |archive-url=https://web.archive.org/web/20201126140722/https://books.google.com/books?id=PJ0YAAAAIAAJ |url-status=live}}</ref><ref>{{cite book |author=Estienne, Henri |title=Thesaurus graecae linguae |url=https://books.google.com/books?id=0qQ_AAAAcAAJ |access-date=March 29, 2010 |volume=5 |date=1846 |publisher=Didot |page=1001 |archive-date=July 28, 2020 |archive-url=https://web.archive.org/web/20200728014911/https://books.google.com/books?id=0qQ_AAAAcAAJ |url-status=live}}</ref><ref>{{L&S |mensis |ref}}</ref><ref>{{LSJ |mei/s |μείς |shortref}}.</ref> stem from the [[Proto-Indo-European]] (PIE) root of ''moon'', *''méh<sub>1</sub>nōt'', derived from the PIE verbal root *''meh<sub>1</sub>''-, "to measure", "indicat[ing] a functional conception of the Moon, i.e. marker of the month" ([[cf.]] the English words ''measure'' and ''menstrual'').<ref>{{cite book |title=The Oxford Introduction to Proto-Indo-European and the Proto-Indo-European World |series=Oxford Linguistics |author1-first=J.P. |author1-last=Mallory |author2-first=D.Q. |author2-last=Adams |date=2006 |pages=98, 128, 317 |publisher=[[Oxford University Press]] |isbn=978-0-19-928791-8}}</ref><ref>{{OEtymD |measure |}}</ref><ref>{{OEtymD |menstrual |}}</ref> To give another example from a different [[language family]], the [[Chinese language]] uses the same word ({{lang|zh |{{linktext|月}}}}) for ''moon'' as for ''month'', which furthermore can be found in the symbols for the word ''week'' ({{lang|zh |{{linktext|星期}}}}).

This lunar timekeeping gave rise to the historically dominant, but varied, [[lunisolar calendar]]s. The 7th-century [[Islamic calendar]] is an example of a purely [[lunar calendar]], where months are traditionally determined by the visual sighting of the hilal, or earliest crescent moon, over the horizon.<ref>{{cite journal |title=Lunar Crescent Visibility Criterion and Islamic Calendar |last=Ilyas |first=Mohammad |journal=Quarterly Journal of the Royal Astronomical Society |volume=35 |page=425 |date=March 1994 |bibcode=1994QJRAS..35..425I}}</ref>

Of particular significance has been the occasion of [[full moon]], highlighted and celebrated in a range of calendars and cultures, an example being the Buddhist [[Vesak]]. The full moon around the [[March equinox|southern]] or [[September equinox|northern autumnal equinox]] is often called the [[harvest moon]] and is celebrated with festivities such as the [[Harvest Moon Festival]] of the [[Chinese lunar calendar]], its second most important celebration after [[Chinese New Year|the Chinese]] lunisolar [[Lunar New Year]].<ref name="Confucius Institute for Scotland 2022">{{cite web |title=Mid-Autumn Festival Celebration |website=Confucius Institute for Scotland |date=August 30, 2022 |url=https://www.confuciusinstitute.ac.uk/events/mid-autumn-festival-activities-10-september/ |access-date=November 22, 2022 |archive-date=November 22, 2022 |archive-url=https://web.archive.org/web/20221122172612/https://www.confuciusinstitute.ac.uk/events/mid-autumn-festival-activities-10-september/ |url-status=live}}</ref>

Furthermore, association of time with the Moon can also be found in religion, such as the ancient Egyptian temporal and lunar deity [[Khonsu]].

===Cultural representation===
{{Further|Cultural astronomy|Archaeoastronomy|Lunar deity |Selene |Luna (goddess) |Crescent |Man in the Moon }}
{{see also|Nocturne (painting)|Moon magic}}

{{multiple image
| title             = Recurring lunar [[aspect (religion)|aspects]] of [[lunar deities]]
| align             = right
| direction         = vertical
| image1            = Sumerian_Cylinder_Seal_of_King_Ur-Nammu.jpg
| alt1              = [[Sumeria]]n [[cylinder seal]] and impression, dated {{circa|2100}} BC, of Ḫašḫamer, [[ensi (Sumerian)|ensi]] (governor) of Iškun-Sin c. 2100 BC. The seated figure is probably king [[Ur-Nammu]], bestowing the governorship on Ḫašḫamer, who is led before him by [[Lamassu|Lamma]] (protective goddess).<ref name="Collections Search – Museum of Fine Arts, Boston 1987">{{cite web |title=Cylinder vase |website=Collections Search – Museum of Fine Arts, Boston |date=May 20, 1987 |url=https://collections.mfa.org/objects/6027/cylinder-vase;jsessionid=F2E906D47F69B2A85DB31D259E691783 |access-date=November 11, 2021 |archive-date=November 11, 2021 |archive-url=https://web.archive.org/web/20211111060850/https://collections.mfa.org/objects/6027/cylinder-vase;jsessionid=F2E906D47F69B2A85DB31D259E691783 |url-status=live}}</ref>
| caption1          = The [[crescent]] of [[Sin (mythology)|Nanna/Sîn]], {{circa|2100}} BC
| image2            = Patera di Parabiago - MI - Museo archeologico - Diana - Luna - 25-7-2003 - Foto Giovanni Dall'Orto - 25-7-2003.jpg
| alt2              = [[Luna (goddess)|Luna]] on the [[Parabiago plate]] (2nd–5th century), featuring the crescent crown, [[Luna (goddess)#Chariot of the Moon|chariot]] and [[velificatio]] as lunar [[aspect (religion)|aspect]] found in different cultures.
| caption2          = Crescent headgear, [[Luna (goddess)#Chariot of the Moon|chariot]] and [[velificatio]] of [[Luna (goddess)|Luna]], 2nd–5th century
| image3            = Goddess O Ixchel.jpg
| alt3              = Rabbits are in a range of cultures identified with the Moon, from China to the [[Indigenous peoples of the Americas]], as with the rabbit (on the left) of the [[Maya moon goddess]] (6th–9th century).
| caption3          = A [[Moon rabbit]] of the [[Maya moon goddess|Mayan moon goddess]], 6th–9th century
| image4            =
| caption4          =
}}

Humans have not only observed the Moon since [[prehistoric times]], but have also developed intricate perceptions of the Moon. Over time the Moon has been characterized and associated in many different ways, from having a [[Spirit (vital essence)|spirit]] or being [[Lunar deity|a deity]], and an [[aspect (religion)|aspect]] thereof or an aspect [[Moon (astrology)|in astrology]], being made an important part of many [[cosmology|cosmologies]].

This rich history of humans viewing the Moon has been evidenced starting with depictions from 40,000 [[Before present|BP]] and in written form from the [[4th millennium BCE]] in the earliest cases of [[writing]]. The oldest named astronomer and poet [[Enheduanna]], [[Akkadian Empire|Akkadian]] high priestess to the lunar deity [[Sin (mythology)|Nanna/Sin]] and pricess, daughter of [[Sargon the Great]] ({{circa|2334}} &ndash; {{circa|2279}} BCE), tracked the Moon and wrote poems about her divine Moon.<ref name="c099"/>

====Crescent====
For the representation of the Moon, especially its [[lunar phase]]s, the [[crescent]] (🌙) has been a recurring symbol in a range of cultures since at least 3,000 BCE or possibly earlier with bull horns dating to the earliest [[cave painting]]s at 40,000 [[Before present|BP]].<ref name="e093"/><ref name="k874"/> In [[writing system]]s such as Chinese the crescent has developed into the symbol {{lang|zh |{{linktext|月}}}}, the word for Moon, and in ancient Egyptian it was the symbol {{linktext|𓇹}}, meaning Moon and spelled like the ancient Egyptian lunar deity ''[[Iah]]'',<ref name="Hart 2005 p. 77">{{cite book |last=Hart |first=G. |title=The Routledge Dictionary of Egyptian Gods and Goddesses |publisher=Taylor & Francis |series=Routledge Dictionaries |year=2005 |isbn=978-1-134-28424-5 |url=https://books.google.com/books?id=Q1LAiPylZm4C&pg=PA77 |access-date=February 23, 2022 |page=77 |archive-date=July 25, 2022 |archive-url=https://web.archive.org/web/20220725234921/https://books.google.com/books?id=Q1LAiPylZm4C&pg=PA77 |url-status=live}}</ref> which the other ancient Egyptian lunar deities [[Khonsu]] and [[Thoth]] were associated with.

Iconographically the crescent was used in [[Mesopotamia]] as the primary symbol of [[Sin (mythology)|Nanna/Sîn]],<ref name=BlackGreen1992/> the ancient [[Sumeria]]n lunar deity,<ref name=Nemet1998>{{citation |last=Nemet-Nejat |first=Karen Rhea |date=1998 |title=Daily Life in Ancient Mesopotamia |publisher=Greenwood |isbn=978-0-313-29497-6 |page=[https://archive.org/details/dailylifeinancie00neme/page/203 203] |url=https://archive.org/details/dailylifeinancie00neme |access-date=June 11, 2019 |archive-date=June 16, 2020 |archive-url=https://web.archive.org/web/20200616064441/https://archive.org/details/dailylifeinancie00neme/page/203 |url-status=live}}</ref><ref name=BlackGreen1992>{{cite book |last1=Black |first1=Jeremy |first2=Anthony |last2=Green |title=Gods, Demons and Symbols of Ancient Mesopotamia: An Illustrated Dictionary |url=https://books.google.com/books?id=05LXAAAAMAAJ |publisher=The British Museum Press |year=1992 |isbn=978-0-7141-1705-8 |pages=54, 135 |access-date=October 28, 2017 |archive-date=August 19, 2020 |archive-url=https://web.archive.org/web/20200819021935/https://books.google.com/books?id=05LXAAAAMAAJ&hl=en |url-status=live}}</ref> who was the father of [[Inanna|Inanna/Ishtar]], the goddess of the planet [[Venus]] (symbolized as the [[Octagram|eight pointed]] [[Star of Ishtar]]),<ref name="Nemet1998"/><ref name=BlackGreen1992/> and [[Utu|Utu/Shamash]], the god of the Sun ([[Solar symbol|symbolized as a disc, optionally with eight rays]]),<ref name="Nemet1998"/><ref name=BlackGreen1992/> all three often depicted next to each other. Nanna/Sîn is, like some other lunar deities, for example Iah and Khonsu of ancient Egypt, [[Mene (goddess)|Mene]]/[[Selene]] of ancient Greece and [[Luna (mythology)|Luna]] of ancient Rome, depicted as a [[horned deity]], featuring crescent shaped headgears or crowns.<ref>{{cite book |last=Zschietzschmann |first=W. |date=2006 |title=Hellas and Rome: The Classical World in Pictures |location=Whitefish, Montana |publisher=Kessinger Publishing |isbn=978-1-4286-5544-7 |page=23}}</ref><ref>{{cite book |last=Cohen |first=Beth |date=2006 |article=Outline as a Special Technique in Black- and Red-figure Vase-painting |url=https://books.google.com/books?id=YyufPUA_S74C&pg=PA178 |title=The Colors of Clay: Special Techniques in Athenian Vases |location=Los Angeles |publisher=Getty Publications |isbn=978-0-89236-942-3 |pages=178–179 |access-date=April 28, 2020 |archive-date=August 19, 2020 |archive-url=https://web.archive.org/web/20200819021937/https://books.google.com/books?id=YyufPUA_S74C&pg=PA178&hl=en |url-status=live}}</ref>

The particular arrangement of the crescent with a star known as the [[star and crescent]] (☪️) goes back to the Bronze Age, representing either the Sun and Moon, or the Moon and the planet Venus, in combination. It came to represent the selene goddess [[Artemis]], and via the patronage of [[Hecate]], which as [[triple deity]] under the [[epithet]] ''trimorphos''/''trivia'' included aspects of Artemis/[[Diana (mythology)|Diana]], came to be used as a [[Byzantine flags and insignia|symbol of Byzantium]], with [[Virgin Mary]] ([[Queen of Heaven]]) later taking her place, becoming depicted in [[Marian veneration]] on a crescent and adorned with stars. Since then the [[heraldry|heraldric]] use of the star and crescent proliferated, Byzantium's symbolism possibly influencing the development of the [[Ottoman flag]], specifically the combination of the Turkish crescent with a star,<ref>"It seems possible, though not certain, that after the conquest Mehmed took over the crescent ''and'' star as an emblem of sovereignty from the Byzantines. The half-moon alone on a blood red flag, allegedly conferred on the Janissaries by Emir Orhan, was much older, as is demonstrated by numerous references to it dating from before 1453. But since these flags lack the star, which along with the half-moon is to be found on Sassanid and Byzantine municipal coins, it may be regarded as an innovation of Mehmed. It seems certain that in the interior of Asia tribes of Turkish nomads had been using the half-moon alone as an emblem for some time past, but it is equally certain that crescent and star ''together'' are attested only for a much later period. There is good reason to believe that old Turkish and Byzantine traditions were combined in the emblem of Ottoman and, much later, present-day Republican Turkish sovereignty." Franz Babinger (William C. Hickman Ed., Ralph Manheim Trans.), ''Mehmed the Conqueror and His Time'', Princeton University Press, 1992, p 108</ref> and becoming a popular [[Symbols of Islam|symbol for Islam]] (as the ''[[wikt:hilal#Noun|hilal]]'' of the [[Islamic calendar]]) and [[Star and crescent#Contemporary use|for a range of nations]].<ref name="Kadoi 2014">{{cite encyclopedia |last=Kadoi |first=Yuka |title=Crescent (symbol of Islam) |encyclopedia=Encyclopedia of Islam Online |date=October 1, 2014 |url=https://referenceworks.brillonline.com/entries/encyclopaedia-of-islam-3/crescent-symbol-of-islam-COM_25588?s.num=27&s.start=20}}</ref>

====Other association====
The features of the Moon, the contrasting brighter highlands and darker maria, have been seen by different cultures [[Lunar pareidolia|forming abstract shapes]]. Such shapes are among others the [[Man in the Moon]] (e.g. [[Coyolxāuhqui]]) or the [[Moon Rabbit]] (e.g. the Chinese [[Tu'er Ye]] or in [[Mythologies of the indigenous peoples of the Americas|Indigenous American mythologies]] the aspect of the [[Maya moon goddess|Mayan Moon goddess]], from which possibly [[Awilix]] is derived, or of [[Metztli]]/[[Tēcciztēcatl]]).<ref name="Collections Search – Museum of Fine Arts, Boston 1987"/>

Occasionally some lunar deities have been also depicted [[Luna (goddess)#Chariot of the Moon|driving a chariot across the sky]], such as the Hindu [[Chandra|Chandra/Soma]], the Greek Artemis, which is associated with Selene, or Luna, Selene's ancient Roman equivalent.

Color and material wise the Moon has been associated in Western [[alchemy]] with [[silver]], while gold is associated with the Sun.<ref name="Abbri 2019 pp. 39–44">{{cite journal |last=Abbri |first=Ferdinando |title=Gold and silver: perfection of metals in medieval and early modern alchemy |journal=Substantia |date=August 30, 2019 |issn=2532-3997 |doi=10.13128/Substantia-603 |pages=39–44 |url=https://riviste.fupress.net/index.php/subs/article/view/603 |access-date=April 8, 2022 |archive-date=June 17, 2022 |archive-url=https://web.archive.org/web/20220617041849/https://riviste.fupress.net/index.php/subs/article/view/603 |url-status=live}}</ref>

Through a miracle, the so-called [[splitting of the Moon]] ({{langx|ar|انشقاق القمر}}) in [[Islam]], association with the Moon applies also to [[Muhammad]].<ref>"Muhammad." ''[[Encyclopædia Britannica]]''. 2007. Encyclopædia Britannica Online, p.13</ref>{{clear}}

=== Representation in modern culture ===
{{See also|Moon in science fiction|List of appearances of the Moon in fiction}}

{{Multiple images
| align             = right
| total_width       = 410
| image1            = Van Gogh - Starry Night - Google Art Project.jpg
| image2            = Melies_color_Voyage_dans_la_lune.jpg
| caption1 = The Moon is prominently featured in [[Vincent van Gogh]]'s 1889 painting ''[[The Starry Night]]''.<ref name="The New York Times 2019"/>
| caption2 = An iconic image of the [[Man in the Moon]] from the first [[science-fiction film]] set in space, ''[[A Trip to the Moon]]'' (1902, [[Georges Méliès]]), inspired by a history of literature about going to the Moon.
}}

The perception of the Moon in the [[modern era]] has been informed by [[telescope]]-enabled [[modern astronomy]] and later by [[spaceflight]] which enabled actual human activity at the Moon, particularly the [[Apollo program#Cultural impact|culturally impactful lunar landing]]s. These new insights inspired cultural references, connecting romantic reflections about the Moon<ref name="The MIT Press Reader 2020">{{cite web |title=The Moon of Science or the Moon of Lovers? |website=The MIT Press Reader |date=September 29, 2020 |url=https://thereader.mitpress.mit.edu/moon-of-science-vs-moon-of-lovers/ |access-date=November 1, 2021 |archive-date=November 1, 2021 |archive-url=https://web.archive.org/web/20211101231807/https://thereader.mitpress.mit.edu/moon-of-science-vs-moon-of-lovers/ |url-status=live}}</ref> and speculative fiction such as science-fiction dealing with the Moon.<ref name="The New York Times 2019">{{cite web |title=Imagining the Moon |website=The New York Times |date=July 9, 2019 |url=https://www.nytimes.com/2019/07/09/science/moon-art-culture.html |archive-url=https://web.archive.org/web/20190709091131/https://www.nytimes.com/2019/07/09/science/moon-art-culture.html |archive-date=July 9, 2019 |url-access=subscription |url-status=live |access-date=November 4, 2021}}</ref><ref name="Nature 2019">{{cite journal |title=Moon on the mind: two millennia of lunar literature |journal=Nature |date=July 9, 2019 |doi=10.1038/d41586-019-02090-w |last1=Seed |first1=David |volume=571 |issue=7764 |pages=172–173 |bibcode=2019Natur.571..172S |s2cid=195847287 |doi-access=free}}</ref>

Contemporarily the Moon has been seen as a place for [[commercialization of space|economic expansion into space]], with missions prospecting for [[lunar resources]]. This has been accompanied with renewed public and critical reflection on humanity's cultural and [[#Legal status|legal relation to the celestial body]], especially regarding [[colonialism]],<ref name="Alvarez 2020 p."/> as in the 1970 poem "[[Whitey on the Moon]]". In this light the Moon's nature has been invoked,<ref name="Declaration"/> particularly for lunar conservation<ref name="Nast 2013">{{cite magazine |title=Space: The Final Frontier of Environmental Disasters? |magazine=Wired |date=July 15, 2013 |url=https://www.wired.com/2013/07/space-environmentalism/ |access-date=April 9, 2022 |archive-date=July 14, 2021 |archive-url=https://web.archive.org/web/20210714235012/https://www.wired.com/2013/07/space-environmentalism/ |url-status=live}}</ref> and as a [[commons|common]].<ref name="Open Lunar Foundation 2022">{{cite web |title=Polycentricity for Governance of the Moon as a Commons |website=Open Lunar Foundation |date=March 22, 2022 |url=https://www.openlunar.org/library/polycentricity-for-governance-of-the-moon-as-a-commons |access-date=April 9, 2022 |archive-date=April 20, 2022 |archive-url=https://web.archive.org/web/20220420015444/https://www.openlunar.org/library/polycentricity-for-governance-of-the-moon-as-a-commons |url-status=live}}</ref><ref name="The Space Review 2021"/><ref name="Evans 2021"/>

In 2021 20 July, the date of the [[Apollo 11#Landing|first crewed Moon landing]], became the annual ''International Moon Day''.<ref name="Nations 1967 a849">{{cite web |author= United Nations |title=International Moon Day |publisher=United Nations |date=July 20, 2021 |url=https://www.un.org/en/observances/moon-day |access-date=November 8, 2023 |archive-date=June 27, 2023 |archive-url=https://web.archive.org/web/20230627042218/https://www.un.org/en/observances/moon-day |url-status=live}}</ref>

===Lunar effect===
{{Main|Lunar effect}}
The lunar effect is a purported unproven correlation between specific stages of the roughly 29.5-day lunar cycle and behavior and physiological changes in living beings on Earth, including humans. The Moon has long been associated with insanity and irrationality; the words ''lunacy'' and ''[[lunatic]]'' are derived from the Latin name for the Moon, ''Luna''. Philosophers [[Aristotle]] and [[Pliny the Elder]] argued that the full moon induced insanity in susceptible individuals, believing that the brain, which is mostly water, must be affected by the Moon and its power over the tides, but the Moon's gravity is too slight to affect any single person.<ref name="sciam"/> Even today, people who believe in a lunar effect claim that admissions to psychiatric hospitals, traffic accidents, homicides or suicides increase during a full moon, but dozens of studies invalidate these claims.<ref name="sciam"/><ref name="RottonKelly1985"/><ref name="MartensKelly1988"/><ref name="kelly"/><ref name="FosterRoenneberg2008"/>

== See also ==
*[[List of natural satellites]]
*[[Selenography]] (geography of the Moon)
*[[Timekeeping on the Moon]]

== Explanatory notes ==
{{Notelist
 |notes=
{{Efn|name=maxval
 |The ''maximum value'' is given based on scaling of the brightness from the value of −12.74 given for an equator to Moon-centre distance of 378&nbsp;000&nbsp;km in the NASA factsheet reference to the minimum Earth–Moon distance given there, after the latter is corrected for Earth's equatorial radius of 6&nbsp;378&nbsp;km, giving 350&nbsp;600&nbsp;km. The ''minimum value'' (for a distant [[new moon]]) is based on a similar scaling using the maximum Earth–Moon distance of 407&nbsp;000&nbsp;km (given in the factsheet) and by calculating the brightness of the [[earthshine]] onto such a new moon. The brightness of the earthshine is {{nowrap|[ Earth [[albedo]] ×}} {{nowrap|([[Earth radius]] /}} Radius of [[Moon's orbit]])<sup>2</sup>&nbsp;] relative to the direct solar illumination that occurs for a full moon. ({{nowrap |Earth albedo {{=}} 0.367}}; {{nowrap |Earth radius {{=}} (polar}} radius&nbsp;× equatorial {{nowrap |radius)<sup>½</sup> {{=}} 6 367 km}}.)
}}
{{Efn |name=angular size
 |The range of angular size values given are based on simple scaling of the following values given in the fact sheet reference: at an Earth-equator to Moon-centre distance of 378&nbsp;000&nbsp;km, the [[angular size]] is 1896&nbsp;[[arcsecond]]s. The same fact sheet gives extreme Earth–Moon distances of 407&nbsp;000&nbsp;km and 357&nbsp;000&nbsp;km. For the maximum angular size, the minimum distance has to be corrected for Earth's equatorial radius of 6&nbsp;378&nbsp;km, giving 350&nbsp;600&nbsp;km.
}}
{{Efn|name=pressure explanation
 |Lucey et al. (2006) give {{nowrap |10<sup>7</sup> particles cm<sup>−3</sup>}} by day and {{nowrap |10<sup>5</sup> particles cm<sup>−3</sup>}} by night. Along with equatorial surface temperatures of 390&nbsp;[[Kelvin|K]] by day and 100&nbsp;K by night, the [[ideal gas law]] yields the pressures given in the infobox (rounded to the nearest [[order of magnitude]]): 10<sup>−7</sup>&nbsp;[[Pascal (unit)|Pa]] by day and 10<sup>−10</sup>&nbsp;Pa by night.
}}
{{Efn |name=near-Earth asteroids
 |There are a number of [[near-Earth asteroid]]s, including [[3753 Cruithne]], that are [[co-orbital]] with Earth: their orbits bring them close to Earth for periods of time but then alter in the long term (Morais et al, 2002). These are [[quasi-satellite]]s&nbsp;– they are not moons as they do not orbit Earth. For more information, see [[Other moons of Earth]].
}}
{{Efn|name=Moon vs. Charon
 |With 27% the diameter and 60% the density of Earth, the Moon has 1.23% of the mass of Earth. The moon [[Charon (moon)|Charon]] is larger relative to its primary [[Pluto]], but Earth and the Moon are different since Pluto is considered a [[dwarf planet]] and not a planet, unlike Earth.
}}
{{Efn |name=orbpd
 |More accurately, the Moon's mean sidereal period (fixed star to fixed star) is 27.321661&nbsp;days {{nowrap |(27 d 07 h 43 min 11.5 s)}}, and its mean tropical orbital period (from equinox to equinox) is 27.321582&nbsp;days {{nowrap |(27 d 07 h 43 min 04.7 s)}} (''Explanatory Supplement to the Astronomical Ephemeris'', 1961, at p.107).
}}
{{Efn |name=synpd
 |More accurately, the Moon's mean synodic period (between mean solar conjunctions) is 29.530589&nbsp;days {{nowrap |(29 d 12 h 44 min 02.9 s)}} (''Explanatory Supplement to the Astronomical Ephemeris'', 1961, at p.107).
}}
{{Efn |name=brightness
 |The Sun's [[apparent magnitude]] is −26.7, while the full moon's apparent magnitude is −12.7.
}}
{{Efn|name=area
 |On average, the Moon covers an area of {{nowrap |0.21078 square degrees}} on the night sky.
}}
{{Efn |name=size changes
 |See graph in [[Sun#Life phases]]. At present, the diameter of the Sun is increasing at a rate of about five percent per billion years. This is very similar to the rate at which the apparent angular diameter of the Moon is decreasing as it recedes from Earth.
}}
}}

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<ref name="RottonKelly1985">{{cite journal |last1=Rotton |first1=James |last2=Kelly |first2=I.W. |title=Much ado about the full moon: A meta-analysis of lunar-lunacy research |journal=[[Psychological Bulletin]] |volume=97 |issue=2 |date=1985 |pages=286–306 |doi=10.1037/0033-2909.97.2.286 |pmid=3885282}}</ref>

<ref name="FosterRoenneberg2008">{{cite journal |last1=Foster |first1=Russell G. |last2=Roenneberg |first2=Till |title=Human Responses to the Geophysical Daily, Annual and Lunar Cycles |journal=[[Current Biology]] |volume=18 |issue=17 |date=2008 |pages=R784–R794 |doi=10.1016/j.cub.2008.07.003 |pmid=18786384 |s2cid=15429616 |doi-access=free |bibcode=2008CBio...18.R784F}}</ref>

<ref name="kelly">{{Citation |last1=Kelly |first1=Ivan |last2=Rotton |first2=James |last3=Culver |first3=Roger |date=1986 |title=The Moon Was Full and Nothing Happened: A Review of Studies on the Moon and Human Behavior |journal=[[Skeptical Inquirer]] |volume=10 |issue=2 |pages=129–143}} Reprinted in ''The Hundredth Monkey – and other paradigms of the paranormal'', edited by Kendrick Frazier, Prometheus Books. Revised and updated in ''The Outer Edge: Classic Investigations of the Paranormal'', edited by [[Joe Nickell]], [[Barry Karr]], and Tom Genoni, 1996, [[CSICOP]].</ref>

<ref name=Needham1986>{{cite book |last=Needham |first=Joseph |title=Science and Civilization in China, Volume III: Mathematics and the Sciences of the Heavens and Earth |url=https://books.google.com/books?id=jfQ9E0u4pLAC |date=1986 |publisher=Caves |isbn=978-0-521-05801-8 |place=Taipei |access-date=August 22, 2020}}</ref>

}}<!--(end {{Notelist}})-->

==Further reading==
{{Refbegin}}
* {{cite news |last=Angier |first=Natalie |date=September 7, 2014 |title=The Moon Comes Around Again |url=https://www.nytimes.com/2014/09/09/science/revisiting-the-moon.html |work=[[The New York Times]] |access-date=September 8, 2014 |archive-date=September 8, 2014 |archive-url=https://web.archive.org/web/20140908072715/http://www.nytimes.com/2014/09/09/science/revisiting-the-moon.html |url-status=live}}
* {{cite web |url=https://www.bbc.co.uk/worldservice/specials/948_discovery_2008/page4.shtml |title=The Moon |work=Discovery 2008 |publisher=BBC World Service |access-date=May 9, 2021 |archive-date=March 11, 2011 |archive-url=https://web.archive.org/web/20110311073446/http://www.bbc.co.uk/worldservice/specials/948_discovery_2008/page4.shtml |url-status=live}}
* {{cite book |last=Bussey |first=B. |author2=Spudis, P.D. |author-link2=Paul Spudis |title=The Clementine Atlas of the Moon |date=2004 |publisher=[[Cambridge University Press]] |isbn=978-0-521-81528-4}}
* {{cite news |last=Cain |first=Fraser |title=Where does the Moon Come From? |work=[[Universe Today]] |url=https://www.universetoday.com/1143/podcast-where-does-the-moon-come-from/ |access-date=May 9, 2021 |archive-date=May 10, 2021 |archive-url=https://web.archive.org/web/20210510142948/https://www.universetoday.com/1143/podcast-where-does-the-moon-come-from/ |url-status=live}} (podcast and transcript)
* {{cite journal |last=Jolliff |first=B. |editor1-last=Wieczorek |editor1-first=M. |editor2-last=Shearer |editor2-first=C. |editor3-last=Neal |editor3-first=C. |title=New views of the Moon |url=http://www.minsocam.org/msa/RIM/Rim60.html |access-date=April 12, 2007 |volume=60 |date=2006 |publisher=Mineralogy Society of America |location=Chantilly, Virginia |isbn=978-0-939950-72-0 |doi=10.2138/rmg.2006.60.0 |page=721 |issue=1 |journal=[[Reviews in Mineralogy and Geochemistry]] |bibcode=2006RvMG...60D...5J |archive-date=June 27, 2007 |archive-url=https://web.archive.org/web/20070627165803/http://www.minsocam.org/MSA/RIM/Rim60.html |url-status=live}}
* {{cite web |last=Jones |first=E. M. |title=Apollo Lunar Surface Journal |publisher=NASA |date=2006 |url=https://www.hq.nasa.gov/alsj/ |access-date=May 9, 2021 |archive-date=May 8, 2021 |archive-url=https://web.archive.org/web/20210508133136/https://www.hq.nasa.gov/alsj/ |url-status=live}}
* {{cite web |title=Exploring the Moon |publisher=[[Lunar and Planetary Institute]] |url=https://www.lpi.usra.edu/lunar/missions/ |access-date=May 9, 2021 |archive-date=May 10, 2021 |archive-url=https://web.archive.org/web/20210510141741/https://www.lpi.usra.edu/lunar/missions/ |url-status=live}}
* {{cite book |last=Mackenzie |first=Dana |title=The Big Splat, or How Our Moon Came to Be |date=2003 |publisher=[[John Wiley & Sons]] |location=Hoboken, NJ |isbn=978-0-471-15057-2 |url=https://archive.org/details/bigsplatorhowour00mack |access-date=June 11, 2019 |archive-date=June 17, 2020 |archive-url=https://web.archive.org/web/20200617181357/https://archive.org/details/bigsplatorhowour00mack |url-status=live}}
* {{cite book |last=Moore |first=P. |title=On the Moon |date=2001 |publisher=Sterling |location=Tucson, Arizona |isbn=978-0-304-35469-6 |url=https://archive.org/details/patrickmooreonmo00patr}}
* {{cite web |title=Moon Articles |work=Planetary Science Research Discoveries |publisher=Hawai'i Institute of Geophysics and Planetology |url=https://www.psrd.hawaii.edu/Archive/Archive-Moon.html |access-date=November 18, 2006 |archive-date=November 17, 2015 |archive-url=https://web.archive.org/web/20151117030432/http://www.psrd.hawaii.edu/Archive/Archive-Moon.html |url-status=live}}
* {{cite book |last=Spudis |first=P. D. |title=The Once and Future Moon |date=1996 |publisher=[[Smithsonian Institution Press]] |isbn=978-1-56098-634-8 |url=https://archive.org/details/oncefuturemoon0000spud |access-date=June 11, 2019 |archive-date=June 17, 2020 |archive-url=https://web.archive.org/web/20200617181602/https://archive.org/details/oncefuturemoon0000spud |url-status=live}}
* {{cite book |last=Taylor |first=S. R. |title=Solar system evolution |publisher=[[Cambridge University Press]] |page=[https://archive.org/details/isbn_9780521372121/page/307 307] |date=1992 |isbn=978-0-521-37212-1 |url=https://archive.org/details/isbn_9780521372121}}
* {{cite web |last=Teague |first=K. |title=The Project Apollo Archive |date=2006 |url=https://www.apolloarchive.com/apollo_archive.html |access-date=April 12, 2007 |archive-date=April 4, 2007 |archive-url=https://web.archive.org/web/20070404042710/http://www.apolloarchive.com/apollo_archive.html |url-status=live}}
* {{cite journal |last=Wilhelms |first=D. E. |title=Geologic History of the Moon |journal=U.S. Geological Survey Professional Paper |date=1987 |volume=1348 |url=http://ser.sese.asu.edu/GHM/ |access-date=April 12, 2007 |doi=10.3133/pp1348 |series=Professional Paper |doi-access=free |bibcode=1987ghm..book.....W |archive-date=February 23, 2019 |archive-url=https://web.archive.org/web/20190223214805/http://ser.sese.asu.edu/GHM/ |url-status=live}}
* {{cite book |last=Wilhelms |first=D. E. |title=To a Rocky Moon: A Geologist's History of Lunar Exploration |url=https://archive.org/details/torockymoongeolo0000wilh |access-date=March 10, 2009 |date=1993 |publisher=[[University of Arizona Press]] |location=Tucson |isbn=978-0-8165-1065-8 |url-access=registration |archive-date=June 17, 2020 |archive-url=https://web.archive.org/web/20200617181456/https://archive.org/details/torockymoongeolo0000wilh |url-status=live}}
{{Refend}}

==External links==
{{Sister project links |Moon |voy=Moon}}
* [https://www.nasa.gov/moon NASA images and videos about the Moon]
* {{youTube|nr5Pj6GQL2o|time=0s|Video (04:56) – The Moon in 4K (NASA, April 2018)}}
* [https://www.timeanddate.com/worldclock/moonrise.html Find moonrise, moonset and moon phase for a location]

===Cartographic resources===
*[https://web.archive.org/web/20200421114248/https://astrogeology.usgs.gov/search/map/Moon/Geology/Unified_Geologic_Map_of_the_Moon_GIS_v2 Unified Geologic Map of the Moon] – [[United States Geological Survey]]
* [https://trek.nasa.gov/moon/ Moon Trek – An integrated map browser of datasets and maps for the Moon]
* [https://www.lpi.usra.edu/resources/cla/ Consolidated Lunar Atlas]
* 3D zoomable globes:
** [https://www.google.com/maps/space/moon/ The Moon] on [[Google Maps]], a 3-D rendition of the Moon akin to Google Earth
** [https://www.worldwindcentral.com/wiki/Moon World Wind Central on Moon] {{Webarchive|url=https://web.archive.org/web/20070515064406/http://www.worldwindcentral.com/wiki/Moon |date=May 15, 2007 }}
* [https://web.archive.org/web/20150529090138/http://ralphaeschliman.com/id26.htm Maps and panoramas at Apollo landing sites]
* [https://web.archive.org/web/20201030074615/https://earthlymission.com/wp-content/uploads/2016/10/moon-earthside-map.jpg earthly mission] 
* [https://web.archive.org/web/20160818143433/http://lroc.sese.asu.edu/images/gigapan Large image of the Moon's north pole area]

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