View source for Astronomy:Moon

{{Short description|Natural satellite orbiting Earth}}
{{Pp-move}}
<!-- Please DO NOT add the name "Luna" anywhere in this article as an alternate English name. -->
{{Infobox planet
| name = Moon
| apsis = gee
| symbol = [[File:Moon decrescent symbol (bold).svg|24px|☾]] or [[File:Moon crescent symbol (bold).svg|24px|☽]]
| 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 = The [[Astronomy:Near side of the Moon|near side of the Moon]] with its [[Astronomy:Lunar north pole|north]] at top as seen from [[Astronomy:Earth|Earth]] in October 2010
| background = #ddd
| mpc_name = Earth I
| alt_names = {{hlist |Luna |{{nowrap|Selene (poetic)}}|{{nowrap|Cynthia (poetic)}}}}
| adjectives = {{hlist |Lunar |{{nowrap|Selenian (poetic)}}|{{nowrap|Cynthian (poetic)}}|{{nowrap|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)
| semimajor = {{val |384399 |u=km}}{{nbsp |2}}({{val |1.28 |u=[[Astronomy:Light-second|ls]]}}, {{val |0.00257 |u=[[Astronomy:Astronomical unit|AU]]}})<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 [[Astronomy:Ecliptic|ecliptic]]<ref name="Lang2011"/>{{efn|name=inclination|Between 18.29° and 28.58° to Earth's [[Astronomy:Equator|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 |[[Astronomy:Lunar precession#Nodal precession|Regressing]] by one revolution in 18.61&nbsp;years}}
| arg_peri = {{longitem |[[Astronomy:Lunar precession#Apsidal precession|Progressing]] by one<br/> revolution in 8.85&nbsp;years}}
| satellite_of = [[Astronomy:Earth|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=[[Earth:Journal of Geophysical Research|Journal of Geophysical Research]] |date=1 January 1997 |volume=102 |issue=E1 |page=1601 |doi=10.1029/96JE02940 |bibcode=1997JGR...102.1591S |hdl=2060/19980018849 |s2cid=17475023 |hdl-access=free }}</ref>
| circumference = {{val |10921 |u=km}}{{nbsp |2}}([[Astronomy:Equator|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 |7.342 |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 = {{val |1.622 |ul=m/s2}}{{nbsp |2}}{({{val |0.1654 |u=[[Physics:G-force|g]]}}; {{val |5.318 |ul=ft/s2}})<ref name="NSSDC"/>
| 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; [[Astronomy:Synodic day|synodic; solar day]]) ([[Astronomy: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 [[Astronomy:Ecliptic|ecliptic]]<ref name="SolarViews" /><!--1.533° according to Conn 2007-->|6.687° to [[Astronomy:Orbital plane|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 = [[Astronomy:J2000|J2000]]
| 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=24 September 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=4 March 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=26 September 2018 |archive-date=27 April 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 [[Astronomy:Daytime|daytime]])<ref name="surface-radiation"/>
| magnitude = {{ublist |−2.5 to −12.9{{efn |name=maxval}} |−12.74{{nbsp |2}}(mean [[Astronomy:Full moon|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=2023-06-01 | archive-date=21 March 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 [[Minute and second of arc|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 [[Bar (unit)|picobar]]){{nbsp |2}}(day) |10{{sup |−10}} Pa (1 femtobar) {{nbsp |2}} <br />(night){{efn |name=pressure explanation}}}}
| atmosphere_composition = {{hlist |[[Chemistry:Helium|He]] |[[Chemistry:Argon|Ar]] |[[Chemistry:Neon|Ne]] |[[Chemistry:Sodium|Na]] |[[Chemistry:Potassium|K]] |[[Chemistry:Hydrogen|H]] |[[Chemistry:Radon|Rn]]}}
}}

The '''Moon''' is [[Astronomy:Earth|Earth]]'s only [[Astronomy:Natural satellite|natural satellite]]. [[Astronomy:Orbit of the Moon|It orbits]] at [[Astronomy:Lunar distance|an average distance of]] {{cvt|384400|km|mi}}, about 30 times Earth's diameter. The Moon always presents [[Astronomy:Near side of the Moon|the same side]] to Earth, because [[Physics:Tidal force|gravitational pull]] has [[Astronomy:Tidal locking|locked its rotation]] to the planet. This results in the [[Astronomy:Lunar day|lunar day]] of 29.5 Earth days matching the [[Astronomy:Lunar month#Synodic month|lunar month]]. The Moon's gravitational pull{{snd}}and to a lesser extent the [[Astronomy:Sun|Sun]]'s{{snd}}are the main drivers of the [[Astronomy:Tide|tide]]s.

The Moon is in [[Astronomy:Geophysical definition of planet|geophysical terms]] a [[Astronomy:Planetary-mass object|planetary-mass object]] or satellite planet. It has a mass that amounts to 1.2% of Earth's, and a diameter that is roughly one-quarter of Earth's or with {{cvt|3474|km|mi}} about as wide as [[Earth:Australia (continent)|Australia]].<ref name="Australia"/> Within the [[Astronomy:Solar System|Solar System]] it is the [[Astronomy:List of Solar System objects by size|most massive and largest]] satellite in relation to its [[Astronomy:Primary body|parent planet]], the fifth most massive and largest moon overall, and more massive and larger than all known [[Astronomy:Dwarf planet|dwarf planet]]s.<ref name="Metzger2021"/> Its [[Physics:Surface gravity|surface gravity]] is about one sixth of Earth's, about half of that of [[Astronomy:Mars|Mars]], and after [[Astronomy:Jupiter|Jupiter]]'s moon [[Astronomy:Io (moon)|Io]] the second highest among all Solar System moons. The body of the Moon is [[Astronomy:Planetary differentiation|differentiated]] and [[Astronomy:Terrestrial planet|terrestrial]], with no significant [[Earth:Hydrosphere|hydrosphere]], [[Astronomy:Atmosphere of the Moon|atmosphere]], or [[Astronomy:Magnetic field of the Moon|magnetic field]]. It [[Astronomy:Origin of the Moon|formed]] 4.51&nbsp;billion years ago, not long after [[Earth:Age of the Earth|Earth's formation]], out of the debris from [[Astronomy:Giant-impact hypothesis|a giant impact]] between Earth and a hypothesized [[Astronomy:Mars|Mars]]-sized body called [[Astronomy:Theia (planet)|Theia]].

The lunar surface is covered in lunar dust and marked by [[Astronomy:List of mountains on the Moon|mountains]], [[Astronomy:Impact crater|impact crater]]s, their ejecta, [[Astronomy:Ray system|ray-like streaks]] and, mostly on the near side of the Moon, by dark [[Astronomy:Lunar mare|maria]] ("seas"), which are plains of [[Earth:Basalt|cooled magma]]. These maria were formed when molten lava flowed into ancient impact basins. The Moon is, beside when passing through [[Earth:Earth's shadow|Earth's shadow]] during a [[Astronomy:Lunar eclipse|lunar eclipse]], always illuminated by the Sun, but from Earth the visible illumination shifts during its orbit, producing the [[Astronomy:Lunar phase|lunar phase]]s.<ref>{{cite web |title=Is the 'full moon' merely a fallacy? |website=NBC News |date=28 February 2004 |url=https://www.nbcnews.com/id/wbna4402294 |access-date=2023-05-30 |language=en |archive-date=1 June 2023 |archive-url=https://web.archive.org/web/20230601085529/https://www.nbcnews.com/id/wbna4402294 |url-status=live }}</ref> The Moon is the brightest celestial object in Earth's [[Astronomy:Night sky|night sky]]. This is mainly due to its large [[Astronomy:Angular diameter|angular diameter]], while the [[Physics:Reflectance|reflectance]] of the lunar surface is comparable to that of [[Engineering:Asphalt concrete|asphalt]]. The apparent size is nearly the same as that of the Sun, allowing it to cover the Sun almost completely during a total [[Earth:Solar eclipse|solar eclipse]]. From Earth about 59% of the lunar surface is visible over time due to cyclical shifts in perspective ([[Astronomy:Libration|libration]]), making parts of the far side of the Moon visible.

For humans the Moon has been an important source of inspiration and knowledge, having been crucial to [[Astronomy:Cosmography|cosmography]], mythology, religion, art, time keeping, [[Natural science|natural science]], and [[Engineering:Spaceflight|spaceflight]]. On September 13, 1959, the first human-made object to [[Engineering:List of landings on extraterrestrial bodies|reach an extraterrestrial body]] arrived on the Moon, the [[Place:Soviet Union|Soviet Union]]'s [[Engineering:Luna 2|Luna 2]] impactor. In 1966, the Moon became the first extraterrestrial body where [[Engineering:Soft landing|soft landing]]s and orbital insertions were [[Astronomy:Timeline of Solar System exploration|achieved]]. On July 20, 1969, humans for the first time landed on the Moon and any extraterrestrial body, at [[Astronomy:Mare Tranquillitatis|Mare Tranquillitatis]] with the lander ''[[Engineering:Lunar Module Eagle|Eagle]]'' of the {{wipe|United States}}' [[Engineering:Apollo 11|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 [[Engineering:Apollo 17|Apollo 17]] crew. Since then, [[Astronomy:Exploration of the Moon|exploration of the Moon]] has continued robotically with crewed missions being [[Astronomy:Artemis program|planned to return]] beginning in the late 2020s.

== Names and etymology ==

The usual [[Social:English language|English]] proper name for Earth's natural satellite is simply ''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=[[Organization:International Astronomical Union|International Astronomical Union]] |access-date=6 April 2020 |url-status=dead |archive-url=https://web.archive.org/web/20081216024716/http://www.iau.org/public_press/themes/naming/#spelling |archive-date=16 December 2008 }}</ref><ref name="PN-FAQ" /> The noun ''moon'' is derived from [[Social:Old English|Old English]] ''mōna'', which (like all its Germanic cognates) 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=5 March 2020 | archive-date=17 June 2020 | archive-url=https://web.archive.org/web/20200617033731/https://archive.org/details/Orel-AHandbookOfGermanicEtymology/mode/2up/search/moon | url-status=live }}</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=22 May 2020 | access-date=30 July 2022 | archive-date=22 May 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>E.g.: {{cite book | first=James A. | last=Hall III | date=2016 | title=Moons of the Solar System | publisher=Springer International | 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 another poetic name, though rare, 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, ''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}} ''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 [[Chemistry:Selenium|selenium]].<ref>{{MW|selenic}}</ref> The element name ''selenium'' and the prefix ''seleno-'' (as in ''[[Astronomy:Selenography|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>

The Greek goddess of the wilderness and the hunt, [[Religion:Artemis|Artemis]], equated with the Roman [[Religion:Diana (mythology)|Diana]], one of whose symbols was the Moon and who was often regarded as the goddess of the Moon, was also called Cynthia, from her legendary 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 unipress GmbH |isbn=978-3-89971-640-5 |pages=96– |url-status=live |archive-url=https://web.archive.org/web/20160904223627/https://books.google.com/books?id=37CPbHwqPjwC&pg=PA96 |archive-date=4 September 2016}}</ref> These names – Luna, Cynthia and Selene – are reflected in technical terms for [[Astronomy:Lunar orbit|lunar orbit]]s such as ''apolune'', ''pericynthion'' and ''selenocentric''.

The astronomical symbol for the Moon is a crescent, [[File:Moon decrescent symbol (bold).svg|24px|☾]], for example in ''M''<sub>☾</sub> 'lunar mass' (also ''M<sub>L</sub>'').

==Natural history==
===Lunar geologic timescale===
{{Main|Astronomy:Lunar geologic timescale}}

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

===Formation===
{{Main|Astronomy:Origin of the Moon |Astronomy:Giant-impact hypothesis|Astronomy:Circumplanetary disk}}
[[File:Far side of the Moon.png|thumb|The far side of the Moon, lacking the near side's characteristic large dark areas of maria, resembling how the near side of the Moon might have looked early in the Moon's history<ref name="The Planetary Society 2022">{{cite web | title=The two-faced Moon | website=The Planetary Society | date=2022-03-14 | url=https://www.planetary.org/articles/the-two-faced-moon | access-date=2023-04-28 | archive-date=28 April 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=2023-04-28 | archive-date=28 April 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 [[Astronomy:Formation and evolution of the Solar System|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 | bibcode=2019NatGe..12..696T | s2cid=198997377 }}</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=3 August 2019 |archive-date=3 August 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 [[Physics:Centrifugal force|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 [[Earth:Atmosphere of Earth|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 [[Astronomy:Circumplanetary disk|primordial]] [[Astronomy:Accretion disk|accretion disk]] does not explain the depletion of metals in the Moon.<ref name="BotM" /> None of these hypotheses can account for the high [[Physics:Angular momentum|angular momentum]] of the Earth–Moon system.<ref>{{cite journal |last=Stevenson |first=D.J. |title=Origin of the moon–The collision hypothesis |journal=[[Earth:Annual Review of Earth and Planetary Sciences|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 [[Astronomy:Mars|Mars]]-sized body (named ''[[Astronomy: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=16 April 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=8 October 2016}}</ref> just beyond the Earth's [[Physics:Roche limit|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. |author2=Asphaug, E. |title=Origin of the Moon in a giant impact near the end of Earth's formation |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=28 October 2010 |access-date=7 May 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=18 April 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=8 April 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=27 July 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 |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=8 April 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=9 April 2015}}</ref> Other bodies of the inner Solar System such as Mars and [[Astronomy:4 Vesta|Vesta]] have, according to meteorites from them, very different oxygen and tungsten [[Physics: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=[[Earth: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=27 September 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=[[Earth:Journal of Geophysical Research|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 [[Astronomy: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 |author=Daniel Clery |title=Impact Theory Gets Whacked |volume=342 |pages=183–185 |date=11 October 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=1 September 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> {{clarify span|text=Above a high resolution threshold for simulations,|explain=What does this even mean? It needs some form of clarification.|date=October 2023}} a study published in 2022 finds that giant impacts can immediately place a satellite with similar mass and iron content to the Moon into orbit far outside Earth's [[Physics:Roche limit|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=4 October 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 1 November 2023, scientists reported that, according to computer simulations, remnants of a [[Astronomy:Protoplanet|protoplanet]], named [[Astronomy:Theia (planet)|Theia]], could be inside the Earth, left over from a collision with the Earth in ancient times, and afterwards becoming the Moon.<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=1 November 2023 |work={{wipe|The New York Times}} |url-status=live |archiveurl=https://archive.today/20231101232849/https://www.nytimes.com/2023/11/01/science/moon-formation-theia.html |archivedate=1 November 2023 |accessdate=2 November 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=1 November 2023 |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 |archiveurl=https://archive.today/20231102061800/https://www.nature.com/articles/s41586-023-06589-1 |archivedate=2 November 2023 |accessdate=2 November 2023 }}</ref>

===Natural development===
[[File:Archean.png|thumb|upright=1.5|Artist's depiction of the Moon as it might have appeared in Earth's sky after the Late Heavy Bombardment around 4 billion years ago. At that time the Moon orbited the Earth at half its current distance, making it appear 2.8 times larger 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, [[Astronomy:Eclipse|eclipse]]s were more frequent, and tidal effects 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=7 September 2015 | archive-url=https://web.archive.org/web/20150907215806/https://www.lpi.usra.edu/exploration/training/illustrations/earthMoon/ | url-status=live }}</ref>
Due to [[Astronomy:Tidal acceleration|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 [[Astronomy: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=2017-10-09 | url=https://time.com/4974580/nasa-moon-had-atmosphere-volcanoes/ | access-date=2023-05-16 | archive-date=14 May 2023 | archive-url=https://web.archive.org/web/20230514100131/https://time.com/4974580/nasa-moon-had-atmosphere-volcanoes/ | url-status=live }}</ref> The lunar surface has since been shaped by large [[Astronomy:Impact event|impact event]]s and many small ones, forming a landscape featuring craters of all ages.

The Moon was volcanically active until 1.2&nbsp;billion years ago, which laid down the prominent lunar maria. Most of the [[Astronomy:Lunar mare|mare basalts]] erupted during the [[Earth: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 [[Astronomy: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=2 September 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|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 [[Astronomy:Hydrostatic equilibrium|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=12 April 2020 | archive-date=4 August 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|Astronomy: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 [[Astronomy:Hydrostatic equilibrium|to be round]], several having subsurface oceans 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 [[Astronomy:Planetary-mass moon|planetary-mass moon]]s, making it a satellite planet under the [[Astronomy:Geophysical definition of planet|geophysical definitions of the term]].<ref name="Metzger2021">{{Citation |last1=Metzger |first1=Philip |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 |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 and considerably larger than the largest [[Astronomy:Dwarf planet|dwarf planet]] of the Solar System, [[Astronomy:Pluto|Pluto]]. While the [[Astronomy:Minor-planet moon|minor-planet moon]] [[Astronomy:Charon (moon)|Charon]] of the Pluto-Charon system is larger relative to Pluto,{{efn|name=Moon vs. Charon}}<ref>{{cite web |url=http://www.planetary.org/explore/topics/pluto/ |title=Space Topics: Pluto and Charon |publisher=[[Organization:The Planetary Society|The Planetary Society]] |access-date=6 April 2010 |url-status=dead |archive-url=https://web.archive.org/web/20120218223842/http://www.planetary.org/explore/topics/pluto/ |archive-date=18 February 2012}}</ref> the Moon is the largest natural satellite of the Solar System relative to their [[Astronomy:Primary|primary]] planets.{{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.}}

The Moon's diameter is about 3,500&nbsp;km, more than a quarter of Earth's, with the face of the Moon comparable to the width of either {{wipe|Australia}},<ref name="Australia">{{cite web|url=https://theconversation.com/how-big-is-the-moon-let-me-compare-118840|date=18 July 2019|access-date=15 November 2020|title=How big is the Moon?|first=Jonti | last=Horner|archive-date=7 November 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 US without Alaska.<ref name="Dyches 2021 d923">{{cite web | last=Dyches | first=Preston | title=Five Things to Know about the Moon – NASA Solar System Exploration | website=NASA Solar System Exploration | date=2021-07-28 | url=https://solarsystem.nasa.gov/news/1946/five-things-to-know-about-the-moon/ | access-date=2023-09-24 | archive-date=18 July 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 million square kilometers, between the size of the [[Earth:Americas|Americas]] ([[Earth:North America|North]] and [[Earth:South America|South America]]) and [[Earth:Africa|Africa]].

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

===Structure===
{{Main|Astronomy:Internal structure of the Moon|Astronomy: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 [[Astronomy:Lunar mare|lunar mare]].]]
The Moon is a [[Astronomy:Planetary differentiation|differentiated]] body that was initially in [[Astronomy:Hydrostatic equilibrium|hydrostatic equilibrium]] but has since departed from this condition.<ref>{{cite journal | title=Interpretation of lunar potential fields | first=Stanley Keith | last=Runcorn | date=31 March 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 [[Chemistry:Geochemistry|geochemically]] distinct [[Earth:Crust (geology)|crust]], [[Earth:Mantle (geology)|mantle]], and [[Astronomy: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=6 January 2011 |url-status=live |archive-url=https://web.archive.org/web/20120111112210/http://www.nasa.gov/topics/moonmars/features/lunar_core.html |archive-date=11 January 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=21 January 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=15 October 2015 |bibcode=2011Sci...331..309W|s2cid=206530647 |access-date= 10 April 2017}}</ref> This structure is thought to have developed through the 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=[[Earth:Nature Geoscience|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 [[Earth:Mafic|mafic]] mantle from the [[Chemistry:Precipitation|precipitation]] and sinking of the minerals [[Chemistry:Olivine|olivine]], clinopyroxene, and orthopyroxene; after about three-quarters of the magma ocean had crystallized, lower-density [[Chemistry:Plagioclase|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 [[Chemistry:Compatibility (geochemistry)|incompatible]] and heat-producing elements.<ref name="W06" /> Consistent with this perspective, geochemical mapping made from orbit suggests a crust of mostly [[Earth:Anorthosite|anorthosite]].<ref name="L06" /> The [[Astronomy:Moon rock|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 [[Astronomy: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=[[Astronomy:Advances in Space Research|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|An astronaut jumping on the Moon, illustrating that the [[Physics: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=3 December 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=3 December 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 [[Physics:Surface gravity|surface gravity]] is {{val|1.62|ul=m/s2}}<ref name="NSSDC" /> ({{val|0.1654|u=[[Physics:G-force|g]]}}; {{val|5.318|ul=ft/s2}}), about half of the surface gravity of [[Astronomy:Mars|Mars]] and about a sixth of Earth's.

The [[Physics:Gravitation of the Moon|Moon's gravitational field]] is not uniform. The details of the gravitational field have been measured through tracking the [[Physics:Doppler effect|Doppler shift]] of radio signals emitted by orbiting spacecraft. The main lunar gravity features are [[Astronomy:Mass concentration|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 |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 |author=Richard A. Kerr |title=The Mystery of Our Moon's Gravitational Bumps Solved? |volume=340 |issue=6129 |pages=138–139 |date=12 April 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 |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=13 November 2004 |citeseerx=10.1.1.18.1930}}</ref>

=== Magnetic field ===
The Moon has [[Astronomy: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:Earth's magnetic field|that of Earth]]. The Moon does not have a global [[Physics:Dipole|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=[[Astronomy:Lunar Prospector|Lunar Prospector]] (NASA) |title=Magnetometer / Electron Reflectometer Results |date=2001 |access-date=17 March 2010 |url-status=dead |archive-url=https://web.archive.org/web/20100527121330/http://lunar.arc.nasa.gov/results/magelres.htm |archive-date=27 May 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 [[Earth:Antipodes|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=[[Earth:Journal of Geophysical Research|Journal of Geophysical Research]] |volume=96 |issue=B6 |pages=9837–9846 |date=1991 |doi=10.1029/91JB00308 |bibcode=1991JGR....96.9837H}}</ref>

=== Atmosphere ===
{{Main|Astronomy:Atmosphere of the Moon}}
[[File:Apollo 17 twilight ray sketch.jpg|thumb|The thin lunar atmosphere is visible on the Moon's surface at [[Astronomy:Sunrise|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=Aug 8, 2022 | archive-date=8 August 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=Sep 3, 2013 | url=https://science.nasa.gov/science-news/science-at-nasa/2013/03sep_ladee | access-date=Aug 8, 2022 | archive-date=3 July 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 of Aerospace Engineering - Vol 22, No 1 | journal=Journal of Aerospace Engineering | volume=22 | issue=1 | date=2009-01-01 | 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=2022-08-08 | archive-date=8 August 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=Apr 24, 2014 | url=https://earthsky.org/space/the-zodiacal-light-seen-from-the-moon/ | access-date=Aug 8, 2022 | archive-date=8 August 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 [[Astronomy:Atmosphere|atmosphere]] so tenuous as to be nearly [[Physics:Vacuum|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=17 March 2010 |url-status=dead |archive-url=https://web.archive.org/web/20100531205037/http://settlement.arc.nasa.gov/75SummerStudy/5appendJ.html |archive-date=31 May 2010 }}</ref> The surface pressure of this small mass is around 3 × 10<sup>−15</sup>&nbsp;[[Physics:Atmosphere (unit)|atm]] (0.3&nbsp;nPa); it varies with the lunar day. Its sources include [[Physics:Outgassing|outgassing]] and [[Physics:Sputtering|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=[[Astronomy:The Astrophysical 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=20 February 2009 |access-date=29 September 2009 }}</ref> Elements that have been detected include [[Chemistry:Sodium|sodium]] and [[Chemistry:Potassium|potassium]], produced by sputtering (also found in the atmospheres of [[Astronomy:Mercury (planet)|Mercury]] and [[Astronomy:Io (moon)|Io]]); [[Physics:Helium-4|helium-4]] and [[Chemistry:Neon|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=17 August 2015 |work=NASA |access-date=18 August 2015 |archive-date=19 August 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 [[Chemistry:Argon|argon-40]], [[Chemistry:Radon|radon-222]], and [[Physics:Polonium-210|polonium-210]], outgassed after their creation by [[Physics:Radioactive decay|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=[[Earth:Journal of Geophysical Research|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 [[Chemistry:Oxygen|oxygen]], [[Chemistry:Nitrogen|nitrogen]], [[Chemistry:Carbon|carbon]], [[Chemistry:Hydrogen|hydrogen]] and [[Chemistry:Magnesium|magnesium]], which are present in the regolith, is not understood.<ref name="Stern1999" /> Water vapor has been detected by ''[[Astronomy:Chandrayaan-1|Chandrayaan-1]]'' and found to vary with latitude, with a maximum at ~60–70&nbsp;degrees; it is possibly generated from the 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 [[Astronomy: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 [[Astronomy:Mars|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, [[Astronomy:Taurids|Northern Taurid]], and [[Astronomy:Omicron Centaurids|Omicron Centaurid]] [[Astronomy:Meteor shower|meteor shower]]s, when the Earth, and Moon pass through comet debris. The lunar dust cloud is asymmetric, being more dense 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=20 June 2015 |first1=Nadia |last1=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=19 June 2015 |date=17 June 2015}}</ref><ref>{{Cite journal |title=A permanent, asymmetric dust cloud around the Moon |journal=Nature |date=18 June 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|[[Biography:Gene Cernan|Gene Cernan]] with lunar dust stuck on his suit. Lunar dust is highly abrasive and can cause damage to human lungs, 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=8 December 2022 |archive-date=4 December 2021 |archive-url=https://web.archive.org/web/20211204004317/https://humanresearchroadmap.nasa.gov/evidence/reports/lunar%20dust.pdf |url-status=live }}</ref>]]
[[Physics:Ionizing radiation|Ionizing radiation]] from [[Astronomy:Cosmic ray|cosmic ray]]s, the Sun and the resulting [[Physics:Neutron radiation|neutron radiation]]<ref name="Science Mission Directorate 2005">{{cite web |date=2005-09-08 |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=live |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=2 November 2019 |access-date=2022-07-28 |website=Science Mission Directorate}}</ref> produce radiation levels on average of 1.369 millisieverts per day during lunar [[Astronomy:Daytime|daytime]],<ref name="surface-radiation"/> which is about 2.6 times more than on the [[Astronomy:International Space Station|International Space Station]] with 0.53 millisieverts per day at about 400&nbsp;km above Earth in orbit, 5-10 times more than during a trans-Atlantic flight, 200 times more than on Earth's surface.<ref name="ScienceAlert 2020">{{cite web |date=2020-09-26 |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=28 July 2022 |access-date=2022-07-28 |website=ScienceAlert}}</ref> For further comparison radiation on a [[Astronomy:Human mission to Mars|flight to Mars]] is about 1.84 millisieverts per day and on Mars on average 0.64 millisieverts per day, 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=2020-04-27 | class=astro-ph.EP | eprint=2004.13156v1 }}</ref><ref name="Wall 2013">{{cite web |last=Wall |first=Mike |date=2013-12-09 |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=2022-08-07 |website=Space.com |archive-date=15 December 2020 |archive-url=https://web.archive.org/web/20201215082045/https://www.space.com/23875-mars-radiation-life-manned-mission.html |url-status=live }}</ref>

The Moon's [[Astronomy:Axial tilt|axial tilt]] with respect to the [[Astronomy:Ecliptic|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=30 July 2022 |access-date=30 July 2022 |s2cid=45209988}}</ref> much less than the 23.44° of Earth. Because of this small tilt, the Moon's solar illumination varies much less with [[Physics:Season|season]] than on Earth and it allows for the existence of some peaks of eternal light at the [[Astronomy:Lunar north pole|Moon's north pole]], at the rim of the crater [[Astronomy:Peary (crater)|Peary]].

The surface is exposed to drastic temperature differences ranging from {{val|140|u=°C}} to {{val|−171|u=°C}} depending on the [[Astronomy:Solar irradiance|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=21 May 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=27 May 2015 |website=PlanetFacts.org}}</ref> making topographical details play a decisive role on local [[Earth: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 "[[Astronomy: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=17 September 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=7 March 2010 |access-date=17 March 2010 |publisher=UCLA}}</ref> and just {{Convert |26 |K |4=0 |abbr=on}} close to the winter solstice in the north polar crater [[Astronomy:Hermite (crater)|Hermite]]. This is the coldest temperature in the Solar System ever measured by a spacecraft, colder even than the surface of [[Astronomy:Pluto|Pluto]].<ref name="bbc" />

Blanketed on top of the Moon's crust is a highly [[Engineering:Comminution|comminuted]] (broken into ever smaller particles) and impact gardened mostly gray surface layer called regolith, formed by impact processes. The finer regolith, the [[Astronomy:Lunar soil|lunar soil]] of [[Chemistry:Silicon dioxide|silicon dioxide]] glass, has a texture resembling snow and a scent resembling spent [[Chemistry:Gunpowder|gunpowder]].<ref>{{cite web |date=30 January 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=8 March 2010 |access-date=15 March 2010 |publisher=NASA}}</ref> The regolith of older surfaces is generally thicker than for younger surfaces: it varies in thickness from {{Convert|10 |- |15 |m |abbr=on}} in the highlands and {{Convert |4 |- |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={{wipe|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=17 December 2019 |editor2-last=French |editor2-first=B. |archive-url=https://web.archive.org/web/20200617181609/https://archive.org/details/lunarsourcebooku0000unse/page/736 |archive-date=17 June 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 |volume=313 |issue=5998 |pages=121–124 |bibcode=1985Natur.313..121R |doi=10.1038/313121a0 |s2cid=4245137}}</ref>

These extreme conditions for example are considered to make it unlikely for spacecraft to harbor bacterial spores at the Moon 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|Astronomy:Selenography|Chemistry:Lunar terrane|Astronomy:List of lunar features|Astronomy:List of quadrangles on the Moon}}
[[File:Apollo 17 AS17-140-21497.jpg|thumb|Apollo 17 astronaut Harrison H. Schmitt next to a large Moon boulder]]
The [[Astronomy:Topography of the Moon|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 topographic feature is the giant far-side [[Astronomy:South Pole–Aitken basin|South Pole–Aitken basin]], some {{Convert|2240 |km |abbr=on}} in diameter, the largest crater on the Moon and the second-largest confirmed impact 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=[[Earth:Geophysical Research Letters|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=17 July 1998 |journal=Planetary Science Research Discoveries |access-date=12 April 2007 |url-status=live |archive-url=https://web.archive.org/web/20070820042129/http://www.psrd.hawaii.edu/July98/spa.html |archive-date=20 August 2007 |bibcode=1998psrd.reptE..20T}}</ref> The highest elevations of the Moon's surface are located directly to the northeast, 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 [[Astronomy:Mare Imbrium|Imbrium]], [[Astronomy:Mare Serenitatis|Serenitatis]], [[Astronomy:Mare Crisium|Crisium]], [[Astronomy:Mare Smythii|Smythii]], and [[Astronomy: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 [[Earth:Fault scarp|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=19 August 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=21 August 2010}}</ref> Similar shrinkage features exist on 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=13 May 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>

==== Volcanic features ====
{{Main |Astronomy:Volcanism on the Moon}}
[[File:Moon names.svg|thumb|upright=1.35|The names of the main volcanic features the maria (blue) and some crater (brown) features 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 ''[[Astronomy:Lunar mare|maria]]'' (singular ''mare''; [[Social:Latin language|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=[[Company:Springer Science+Business Media|Springer]] |isbn=978-1-85233-193-1 |page=19}}</ref> are vast solidified pools of ancient [[Earth:Basalt|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=21 April 2004 |access-date=12 April 2007 |url-status=live |archive-url=https://web.archive.org/web/20070418152325/http://www.psrd.hawaii.edu/April04/lunarAnorthosites.html |archive-date=18 April 2007}}</ref> The majority of these lava deposits erupted or flowed into the depressions associated with [[Astronomy:Impact crater|impact basins]]. Several geologic provinces containing [[Earth:Shield volcano|shield volcano]]es and volcanic [[Astronomy: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=[[Earth:Journal of Geophysical Research|Journal of Geophysical Research]] |date=2003 |volume=108 |url=http://www.agu.org/pubs/crossref/2003/2002JE001909.shtml |access-date=12 April 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=12 March 2007}}</ref>

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 [[Chemistry: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 |volume=281 |issue=5382 |pages=1484–1489 |doi=10.1126/science.281.5382.1484 |date=11 August 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=31 August 2000 |access-date=12 April 2007 |url-status=live |archive-url=https://web.archive.org/web/20120301074958/http://www.psrd.hawaii.edu/Aug00/newMoon.html |archive-date=1 March 2012 |bibcode=2000psrd.reptE..41T}}</ref> Most of the Moon's [[Astronomy:Lunar mare|mare basalts]] erupted during the [[Earth: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 [[Earth:Basalt|hardened]] lava flows of Mare Imbrium forming wrinkle ridges]]

In 2006, a study of [[Astronomy:Ina (crater)|Ina]], a tiny depression in [[Astronomy:Lacus Felicitatis|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 |date=9 November 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=18 October 2014 |access-date=14 October 2014 }}</ref> Moonquakes and releases of gas indicate continued lunar activity.<ref name="Berardelli"/> Evidence of recent lunar volcanism has been identified at 70 [[Astronomy:Irregular mare patch|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=14 October 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=16 October 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=12 October 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=3 January 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 |date=12 October 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=14 October 2014}}</ref><ref>{{cite journal |title=Evidence for basaltic volcanism on the Moon within the past 100 million years |journal=[[Earth:Nature Geoscience|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=[[Earth:Journal of Geophysical Research|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=0 |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=[[Earth:Geophysical Research Letters|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 [[Chemistry:Plagioclase|plagioclase]] cumulates of the lunar magma ocean.<ref name="Papike" /><ref name="Hiesinger" /> 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=4 December 2006 |access-date=12 April 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=17 September 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=1 November 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=3 November 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=1 November 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=30 January 2013 }}</ref> Alternatively, it may be a consequence of asymmetrical [[Astronomy:Tidal heating|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 |Astronomy: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 [[Astronomy:Daedalus (crater)|Daedalus]] on the Moon's far side]]
A major geologic process that has affected the Moon's surface is [[Astronomy:Impact crater|impact crater]]ing,<ref>{{cite book |last=Melosh |first=H. J. |title=Impact cratering: A geologic process |date=1989 |publisher=[[Organization:Oxford University Press|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=[[Organization:European Space Agency|European Space Agency]] |date=2010 |access-date=12 May 2010 |archive-date=17 March 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> The [[Astronomy:Lunar geologic timescale|lunar geologic timescale]] is based on the most prominent impact events, including [[Earth:Nectarian|Nectaris]], Imbrium, and [[Astronomy:Mare Orientale|Orientale]]; structures characterized by multiple rings of uplifted material, between hundreds and thousands of kilometers in diameter and associated with a broad apron of ejecta deposits that form a regional [[Earth: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" /> 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 [[Astronomy:Late Heavy Bombardment|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 |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=13 October 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=13 October 2016 |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=13 Oct 2016 | publisher=NASA | url=https://www.nasa.gov/press-release/goddard/2016/lro-lunar-cratering | access-date=2021-05-21 | archive-date=2 July 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|Astronomy: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 [[Physics:Magnetic field|magnetic field]]s and many are located at the [[Antipodal point|antipodal point]] of major impacts. Well known swirls include the [[Astronomy:Reiner Gamma|Reiner Gamma]] feature and [[Astronomy:Mare Ingenii|Mare Ingenii]]. They are hypothesized to be areas that have been partially shielded from the [[Astronomy:Solar wind|solar wind]], resulting in slower [[Astronomy:Space weathering|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 ===
Liquid water cannot persist on the lunar surface. When exposed to solar radiation, water quickly decomposes through a process known as [[Astronomy:Photodissociation|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 [[Astronomy:Solar wind|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 |date=1 August 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 [[Astronomy: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 bistatic radar experiment located on the ''[[Engineering:Clementine (spacecraft)|Clementine]]'' spacecraft, indicated the existence of small, frozen pockets of water close to the surface. However, later radar observations by [[Astronomy: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=6 November 2006 |access-date=12 April 2007 |url-status=dead |archive-url=https://web.archive.org/web/20070222083000/http://www.thespacereview.com/article/740/1 |archive-date=22 February 2007 }}</ref> In 1998, the [[Astronomy: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 {{wipe|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 ''[[Astronomy:Chandrayaan-1|Chandrayaan-1]]'' spacecraft has since confirmed the existence of surface water ice, using the on-board [[Engineering:Moon Mineralogy Mapper|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, ''[[Astronomy:LCROSS|LCROSS]]'' sent a {{Convert|2300 |kg |abbr=on}} impactor into a [[Astronomy: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 [[Engineering:Apollo 17|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=21 August 2018 |work=BBC News |access-date=21 August 2018 |archive-date=21 August 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=21 August 2018 |archive-date=21 August 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=21 August 2018 |archive-date=21 August 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 [[Chemistry:Water|molecular water]] on the sunlit surface of the Moon by several independent spacecraft, including the [[Astronomy:Stratospheric Observatory for Infrared Astronomy|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=26 October 2020 |journal=[[Astronomy:Nature Astronomy|Nature Astronomy]] |volume=5 |issue=2 |pages=121–127 |doi=10.1038/s41550-020-01222-x |bibcode=2021NatAs...5..121H |s2cid=228954129 |access-date=26 October 2020 |archive-date=27 October 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=26 October 2020 |journal=[[Astronomy:Nature Astronomy|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=26 October 2020 |archive-date=27 October 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=26 October 2020 |newspaper={{wipe|The Washington Post}} |access-date=26 October 2020 |archive-date=26 October 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=26 October 2020 |work={{wipe|The New York Times}} |access-date=26 October 2020 |archive-date=26 October 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}}

===Orbit===
{{Main|Astronomy:Orbit of the Moon|Physics:Lunar theory}}
[[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 [[Astronomy:Satellite system|satellite system]] with a shared center of mass, or [[Barycenter|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 [[Astronomy:Orbital eccentricity|orbital eccentricity]] of 0.055.<ref name="W06"/>
The semi-major axis of the geocentric lunar orbit, called the [[Astronomy:Lunar distance|lunar distance]], is approximately 400,000&nbsp;km (250,000 miles or 1.28 light-seconds), comparable to going 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=2023-07-20 | url=https://medium.com/the-aerospace-corporation/its-international-moon-day-let-s-talk-about-cislunar-space-9d108f1a1b0b | access-date=2023-11-07 | archive-date=8 November 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 at the same [[Astronomy:Lunar phase|lunar phase]], completing a full cycle, as seen from Earth. This synodic period or synodic month is commonly known as the [[Astronomy:Lunar month|lunar month]] and is equal to the length of the solar day on the Moon.<ref name="Day">{{cite web|url=https://www.universetoday.com/20524/how-long-is-a-day-on-the-moon-1/|date=10 July 2017|author=Matt Williams|title=How Long is a Day on the Moon?|access-date=5 December 2020|archive-date=29 November 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 [[Astronomy:Tidal locking|tidal locking]], the Moon has a 1:1 spin–orbit resonance. This [[Physics:Rotation|rotation]]–[[Physics:Orbit|orbit]] ratio makes the Moon's orbital periods around Earth equal to its corresponding [[Rotation period|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 [[Astronomy:Libration|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=30 March 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=22 May 2020 |access-date=11 February 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 [[Astronomy:Perturbation|perturbed]] by the Sun and Earth in many small, complex and interacting ways. For example, the plane of the Moon's orbit [[Astronomy: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=24 September 2019 |archive-date=12 December 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 [[Astronomy:Cassini's laws|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 |Physics:Tidal force |Astronomy:Tidal acceleration |Astronomy:Tide |Astronomy:Theory of tides}}
[[File:Tide animation.gif|thumb|Simplified diagram of the Moon's gravity tidal effect on the Earth]]
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. [[Astronomy:Tide|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 [[Astronomy:Libration|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:Earth's magnetic field|Earth's magnetic field]].<ref>{{cite web |author=Iain Todd |date=31 March 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=22 September 2020 |access-date=16 November 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 [[Earth:Seismometer|seismometer]]s placed on the Moon by [[Astronomy:Apollo program|Apollo]] [[Astronaut|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 are 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 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. As a result, 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 [[Physics:Inertia|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 |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.

Delays in the tidal peaks of both ocean and solid-body tides cause [[Physics:Torque|torque]] in opposition to the Earth's rotation. This "drains" [[Physics:Angular momentum|angular momentum]] and rotational [[Physics:Kinetic energy|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 [[Astronomy:Tidal acceleration|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 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=1 February 2011 |access-date=18 September 2015 |url-status=live |archive-url=https://web.archive.org/web/20150925185706/http://www.bbc.co.uk/news/science-environment-12311119 |archive-date=25 September 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=30 July 2022|archive-date=30 July 2022|archive-url=https://web.archive.org/web/20220730084922/https://link.springer.com/article/10.1007/s10569-016-9702-3|url-status=live}}</ref>
[[Engineering:Atomic clock|Atomic clock]]s show that Earth's day lengthens by about 17&nbsp;[[Microsecond|microsecond]]s every year,<ref>{{cite web |last=Ray |first=R. |date=15 May 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=17 March 2010 |url-status=dead |archive-url=https://web.archive.org/web/20100327084125/http://bowie.gsfc.nasa.gov/ggfc/tides/intro.html |archive-date=27 March 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 [[Physics:Coordinated Universal Time|UTC]] is adjusted by leap seconds.

This tidal drag makes the rotation of the Earth and the orbital period of the Moon very slowly match. This matching first results in [[Astronomy: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=2016-04-12 | url=https://www.universetoday.com/128350/will-earth-lock-moon/ | access-date=2022-01-05 | archive-date=28 May 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 [[Astronomy:Red giant#The Sun as a red giant|red giant]], engulfing the Earth-Moon system, long before then.<ref>{{cite book |author=Murray, C.D. |author2=Dermott, Stanley F. |title=Solar System Dynamics |date=1999 |publisher={{wipe|Cambridge University Press}} |isbn=978-0-521-57295-8 |page=184}}</ref><ref>{{cite book |last=Dickinson |first=Terence |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>

==Position and appearance==
{{anchor|Observation|Appearance from Earth}}
[[File:Lunar libration with phase Oct 2007 (continuous loop).gif|thumb |alt=Over one lunar month more than half of the Moon's surface can be seen from Earth's surface. |[[Astronomy:Libration|Libration]], the slight variation in the Moon's apparent size and viewing angle over a single lunar month as viewed from Earth's north]]

The Moon's highest altitude at [[Astronomy:Culmination|culmination]] varies by its [[Astronomy:Lunar phase|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 [[Earth:North Pole|North]] and [[Earth:South Pole|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 [[Astronomy:Tropical year|tropical year]]. [[Earth:Zooplankton|Zooplankton]] in the Arctic use [[Astronomy:Moonlight|moonlight]] when the Sun is [[Earth:Polar night|below the horizon]] for months on end.<ref>{{cite web |date=16 January 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=30 January 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=25 September 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=2022-01-02 |access-date=2022-01-02 |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. |date=18 October 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=16 October 2015 |access-date=28 September 2015 |publisher=Curious About Astronomy}}</ref>

The [[Astronomy:Lunar distance|distance between the Moon and Earth]] varies from around {{convert|356,400|km|mi|abbr=on}} ([[Astronomy:Apsis|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 [[Astronomy:Angular diameter|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 [[Astronomy:Moon illusion|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=[[Company:Routledge|Routledge]] |isbn=978-0-8058-0121-7 |page=5}}</ref>

Despite the Moon's tidal locking, the effect of [[Astronomy:Libration#Lunar libration|libration]] makes about 59% of the Moon's surface visible from Earth over the course of one month.<ref name="Liberation" /><ref name="worldbook" />

===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 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 [[Astronomy: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 [[Astronomy:Dark moon|dark moon]] to [[Astronomy:New moon|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=15 February 2010 |url-status=live |archive-url=https://web.archive.org/web/20100412192834/http://www.badastronomy.com/bad/misc/dark_side.html |archive-date=12 April 2010|}}</ref>

The Moon originally rotated at a faster rate, but early in its history its rotation slowed and became [[Astronomy:Tidal locking|tidally locked]] in this orientation as a result of [[Physics:Friction|friction]]al effects associated with [[Physics: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=[[Physics:Astrophysics and Space Science|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 ''[[Astronomy:Lunar Prospector|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=23 March 2016 |url-status=live |archive-url=https://web.archive.org/web/20160323203442/http://www.bbc.com/news/science-environment-35883576 |archive-date=23 March 2016 |work=BBC News |date=23 March 2016}}</ref>

===Illumination and phases===
[[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 [[Astronomy:Lunar phase|phases of the Moon]] that result, as viewed from the Northern Hemisphere. The Earth–Moon distance is not to scale.]]

Half of the Moon's surface is always illuminated by the Sun (except during a [[Astronomy:Lunar eclipse|lunar eclipse]]). Earth also reflects light onto the Moon, observable at times as [[Astronomy:Earthlight|Earthlight]] when it is reflected back to Earth from areas of the [[Astronomy:Near side of the Moon|near side of the Moon]] that are not illuminated by the Sun.

Since the Moon's axial tilt with respect to the ecliptic is 1.5427°, in every draconic year (346.62 days) the Sun moves from being 1.5427° north of the lunar equator to being 1.5427° south of it and then back, just as on Earth the Sun moves from the Tropic of Cancer to the Tropic of Capricorn and back once every [[Astronomy:Tropical year|tropical year]]. The poles of the Moon are therefore in the dark for half a draconic year (or with only part of the Sun visible) and then lit for half a draconic year. The amount of sunlight falling on horizontal areas near the poles depends on the altitude angle of the Sun. But these "seasons" have little effect in more equatorial areas.

With the different positions of the Moon, different areas of it are illuminated by the Sun. This illumination of different lunar areas, as viewed from Earth, produces the different [[Astronomy:Lunar phase|lunar phase]]s during the synodic month. The phase is equal to the area of the visible lunar sphere that is illuminated by the Sun. This area or ''degree of illumination'' is given by <math>(1-\cos e)/2=\sin^2(e/2)</math>, where <math>e</math> is the [[Astronomy:Elongation|elongation]] (i.e., the angle between Moon, the observer on Earth, and the Sun).

Brightness and apparent size of the Moon changes also due to its elliptic [[Astronomy: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|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=13 November 2016 |access-date=14 November 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=14 November 2016}}</ref> A full (or new) moon at such a position is called a [[Astronomy:Supermoon|supermoon]].<ref name="size1">{{cite web |title=Super Full Moon |date=16 March 2011 |author=Tony Phillips |publisher=NASA |access-date=19 March 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=7 May 2012 }}</ref><ref name="size2">{{cite news |title=Full moon tonight is as close as it gets |date=18 March 2011 |author=Richard K. De Atley |newspaper=The Press-Enterprise |access-date=19 March 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=22 March 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=19 March 2011 |access-date=19 March 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=25 December 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 [[Astronomy:Astronomical seeing|astronomical seeing]], or inadequate drawings. However, [[Physics:Outgassing|outgassing]] does occasionally occur and could be responsible for a minor percentage of the reported [[Astronomy:Transient lunar phenomenon|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=8 November 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=4 March 2007 |access-date=4 April 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 |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 [[Earth:Albedo|albedo]], giving it a [[Diffuse reflection|reflectance]] that is slightly brighter than that of worn [[Engineering:Asphalt concrete|asphalt]]. Despite this, it is the brightest object in the sky after the [[Astronomy:Sun|Sun]].<ref name="worldbook" />{{efn|name=brightness}} This is due partly to the brightness enhancement of the [[Physics:Opposition surge|opposition surge]]; the Moon at quarter phase is only one-tenth as bright, rather than half as bright, as at [[Astronomy:Full moon|full moon]].<ref name="Moon" /> Additionally, [[Physics:Color constancy|color constancy]] in the [[Biology:Visual system|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 [[Astronomy:Limb darkening|limb darkening]], because of the [[Lambert's cosine law#Lambertian scatterers and radiators|reflective properties]] of [[Astronomy:Lunar soil|lunar soil]], which [[Organization: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=2020-11-11 |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=2022-04-09 |access-date=2022-04-09 |website=Science Mission Directorate}}</ref>

At times, the Moon can appear red or blue.
It may appear red during a [[Astronomy:Lunar eclipse|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 colour, lunar eclipses are also sometimes called 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=2 November 2015 |access-date=4 November 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 [[Astronomy:Blue moon#Whole blue moon|blue moon]]. 

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

=== Eclipses ===
{{Main |Earth:Solar eclipse |Astronomy:Lunar eclipse |Earth:Astronomy:Solar eclipses on the Moon|Astronomy: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 [[Earth:Solar eclipse|solar eclipse]] causes the Sun to be covered, revealing the white [[Astronomy:Stellar corona|corona]].
| caption2          = The Moon, tinted reddish, during a [[Astronomy:Lunar eclipse|lunar eclipse]]
}}

Eclipses only occur when the Sun, Earth, and Moon are all in a straight line (termed "[[Astronomy:Syzygy|syzygy]]"). [[Earth:Solar eclipse|Solar eclipse]]s occur at [[Astronomy:New moon|new moon]], when the Moon is between the Sun and Earth. In contrast, [[Astronomy:Lunar eclipse|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 (with the Moon appearing larger than the Sun) and 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=17 March 2010 |archive-date=24 May 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 [[Physics:Solar corona|solar corona]] becomes visible to the [[Astronomy:Naked eye|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 [[Astronomy:Red giant|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=10 July 2004 |access-date=25 December 2013 |url-status=live |archive-url=https://web.archive.org/web/20131208153430/http://www.fourmilab.ch/images/peri_apo/ |archive-date=8 December 2013}}</ref>

Because the Moon's orbit around Earth is inclined by about 5.145° (5° 9') to the [[Astronomy: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 [[Astronomy:Saros|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=17 March 2010 |url-status=dead |archive-url=https://web.archive.org/web/20071030225501/http://sunearth.gsfc.nasa.gov/eclipse/SEsaros/SEsaros.html |archive-date=30 October 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 |volume=55 |pages=200–203 |bibcode=1947PA.....55..200G}}</ref> the related phenomenon of [[Astronomy:Occultation|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 [[Physics:Precession|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=17 March 2010 |url-status=dead |archive-url=https://web.archive.org/web/20100223022627/http://occsec.wellington.net.nz/total/totoccs.htm |archive-date=23 February 2010}}</ref>

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

===Pre-telescopic observation (before 1609)===

It is believed by some that 20–30,000 year old [[Social:Tally stick|tally stick]]s were used to observe the phases of the Moon, keeping time using the waxing and waning of the Moon's phases.<ref name=Burton2011/>
One of the earliest-discovered possible depictions of the Moon is a 5000-year-old 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=18 September 2019 |archive-date=1 June 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=12 April 2007 |url-status=dead |archive-url=https://web.archive.org/web/20120305162253/http://www.spacetoday.org/SolSys/Earth/OldStarCharts.html |archive-date=5 March 2012 }}</ref>

The {{wipe|Ancient Greece}} philosopher [[Biography:Anaxagoras|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=[[Organization:University of St Andrews|University of St Andrews]] |access-date=12 April 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=12 January 2012}}</ref><ref name=Needham1986/>{{rp|page=227}} Elsewhere in the {{nowrap|5th century BC}} to {{nowrap|4th century BC}}, [[Astronomy:Babylonian astronomy|Babylonian astronomers]] had recorded the 18-year Saros cycle of [[Astronomy:Lunar eclipse|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 |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 [[Astronomy:Indian astronomy|Indian astronomers]] had described the Moon's monthly elongation.<ref name="Sarma-Ast-Ind" /> The [[Astronomy:Chinese astronomy|Chinese astronomer]] [[Biography:Shi Shen|Shi Shen]] {{nowrap|(fl. 4th century BC)}} gave instructions for predicting solar and lunar eclipses.<ref name=Needham1986/>{{rp|page=411}}

In [[Biography:Aristotle|Aristotle]]'s (384–322&nbsp;BC) [[Astronomy: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 [[Philosophy:Aether (classical element)|aether]], an [[Physics:Aristotelian physics|influential philosophy]] that would dominate for centuries.<ref>{{cite book |last=Lewis |first=C.S. |title=The Discarded Image |url=https://archive.org/details/discardedimagein0000lewi |url-access=registration |date=1964 |publisher={{wipe|Cambridge University Press}} |location=Cambridge |isbn=978-0-521-47735-2 |page=[https://archive.org/details/discardedimagein0000lewi/page/108 108] |access-date=11 November 2019 |archive-date=17 June 2020 |archive-url=https://web.archive.org/web/20200617181455/https://archive.org/details/discardedimagein0000lewi |url-status=live }}</ref> [[Biography:Archimedes|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=31 July 2008 |access-date=9 March 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=4 December 2013}}</ref> In the {{nowrap |2nd century BC}}, [[Biography:Seleucus of Seleucia|Seleucus of Seleucia]] correctly theorized that [[Astronomy:Tide|tide]]s were due to the attraction of the Moon, and that their height depends on the Moon's position relative to the [[Astronomy:Sun|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, [[Biography:Aristarchus of Samos|Aristarchus]] [[Astronomy:On the Sizes and Distances (Aristarchus)|computed the size and distance]] of the Moon from Earth, obtaining a value of about twenty times the [[Astronomy:Earth radius|radius of Earth]] for the distance.

Although the Chinese of the Han Dynasty believed the Moon to be energy equated to ''[[Philosophy:Qi|qi]]'', their 'radiating influence' theory recognized that the light of the Moon was merely a reflection of the Sun, and [[Biography:Jing Fang|Jing Fang]] (78–37&nbsp;BC) noted the sphericity of the Moon.<ref name=Needham1986/>{{rp|pages=413–414}} [[Biography:Ptolemy|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=[[Organization:Oxford University Press|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 499&nbsp;AD, the Indian astronomer Aryabhata mentioned in his ''[[Unsolved:Aryabhatiya|Aryabhatiya]]'' that reflected sunlight is the cause of the shining of the Moon.<ref>{{cite web |url=http://www-history.mcs.st-andrews.ac.uk/Biographies/Aryabhata_I.html |title=Aryabhata the Elder |last1=Robertson |first1=E.F. |date=November 2000 |publisher=School of Mathematics and Statistics, [[Organization:University of St Andrews|University of St Andrews]] |access-date=15 April 2010 |location=Scotland |url-status=live |archive-url=https://web.archive.org/web/20150711055702/http://www-history.mcs.st-andrews.ac.uk/Biographies/Aryabhata_I.html |archive-date=11 July 2015}}</ref> The astronomer and physicist Alhazen (965–1039) found that [[Astronomy:Sunlight|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> [[Biography:Shen Kuo|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 [[History:Middle Ages|Middle Ages]], before the invention of the telescope, the Moon was increasingly recognised 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=12 April 2007 |url-status=dead |archive-url=https://web.archive.org/web/20040623085326/http://galileo.rice.edu/sci/observations/Moon.html |archive-date=23 June 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]]

In 1609, [[Biography:Galileo Galilei|Galileo Galilei]] used an early telescope to make drawings of the Moon for his book {{lang|la |Sidereus Nuncius}}, and deduced that it was not smooth but had mountains and craters. [[Biography:Thomas Harriot|Thomas Harriot]] had made, but not published such drawings a few months earlier.

Telescopic mapping of the Moon followed: 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 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 |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 [[Astronomy: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 (1959–1990)===

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

[[File:Luna 3 moon.jpg|thumb|First view of the far side of the Moon, taken by Luna 3, 7 October 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 [[Engineering:Sputnik 1|Sputnik 1]] in 1957 during [[Earth:International Geophysical Year|International Geophysical Year]] the spacecraft of the Soviet Union's [[Astronomy: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=20 April 2010 |url-status=live |archive-url=https://web.archive.org/web/20100414115710/http://www.russianspaceweb.com/spacecraft_planetary_lunar.html |archive-date=14 April 2010}}</ref> the first human-made object ''[[Engineering:Luna 1|Luna 1]]'' escaped Earth's gravity and passed near the Moon in 1959. Later that year the first human-made object ''[[Engineering:Luna 2|Luna 2]]'' reached the Moon's surface by [[Engineering:Lander (spacecraft)#Impactors|intentionally impacting]]. By the end of the year ''[[Engineering:Luna 3|Luna 3]]'' reached as the first human-made object the normally occluded [[Astronomy:Far side of the Moon|far side of the Moon]], taking the first photographs of it.
The first spacecraft to perform a successful lunar [[Engineering:Lander (spacecraft)|soft landing]] was ''[[Astronomy:Luna 9|Luna 9]]'' and the first vehicle to orbit the Moon was ''[[Engineering:Luna 10|Luna 10]]'', both in 1966.<ref name="worldbook" />

[[File:NASA-Apollo8-Dec24-Earthrise.jpg|thumb|''Earthrise'', the first color 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 [[Biography:John F. Kennedy|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 [[Organization:Jet Propulsion Laboratory|Jet Propulsion Laboratory]]'s [[Engineering:Ranger program|Ranger program]], the [[Astronomy:Lunar Orbiter program|Lunar Orbiter program]] and the [[Astronomy:Surveyor program|Surveyor program]]. The crewed [[Astronomy:Apollo program|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 lunar human landing, in 1968 [[Engineering:Apollo 8|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 [[Astronomy:Zond 5|Zond 5]], followed by turtles on [[Astronomy:Zond 6|Zond 6]]). The subsequent landing of the first humans on the Moon in 1969 is seen by many as the culmination of the Space Race.<ref name="CNN" />

Neil Armstrong became the first person to walk on the Moon as the commander of the American mission [[Engineering:Apollo 11|Apollo 11]] by first setting foot on the Moon at 02:56&nbsp;UTC on 21 July 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=13 April 2010 |url-status=live |archive-url=https://web.archive.org/web/20100408213454/http://history.nasa.gov/ap11ann/ap11events.html |archive-date=8 April 2010}}</ref> An estimated 500&nbsp;million people worldwide watched the transmission by the [[Engineering:Apollo TV camera|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=6 February 2008 |url-status=dead |archive-url=https://web.archive.org/web/20080214213826/http://www.spaceline.org/flightchron/apollo11.html |archive-date=14 February 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=6 February 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=9 February 2008}}</ref> The Apollo missions 11 to 17 (except [[Engineering:Apollo 13|Apollo 13]], which aborted its planned lunar landing) removed {{convert|837.87 |lb |kg |order=flip}} of lunar rock and soil in 2,196 [[Astronomy: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=1 August 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=6 June 2013}}</ref>

Scientific instrument packages were installed on the lunar surface during all the Apollo landings. Long-lived [[Astronomy:Apollo Lunar Surface Experiments Package|instrument stations]], including heat flow probes, [[Earth:Seismometer|seismometer]]s, and [[Physics:Magnetometer|magnetometer]]s, were installed at the [[Engineering:Apollo 12|Apollo 12]], [[Engineering:Apollo 14|14]], [[Engineering:Apollo 15|15]], [[Engineering:Apollo 16|16]], and [[Engineering: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=1 September 1977 |url=http://www.nasa.gov/centers/johnson/pdf/83129main_1977.pdf |access-date=16 March 2010 |url-status=live |archive-url=https://web.archive.org/web/20110604114817/http://www.nasa.gov/centers/johnson/pdf/83129main_1977.pdf |archive-date=4 June 2011}}</ref><ref>{{cite news |url=http://www.ast.cam.ac.uk/~ipswich/Miscellaneous/Archived_spaceflight_news.htm |access-date=29 August 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=10 December 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 |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>
[[Engineering:Apollo 17|Apollo 17]] in 1972 remains the last crewed mission to the Moon. [[Astronomy:Explorer 49|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 [[Engineering:Luna 17|Luna 17]] the first remote controlled [[Astronomy:Rover (space exploration)|rover]] [[Astronomy:Lunokhod 1|Lunokhod 1]] on an extraterrestrial surface, and collecting and returning 0.3&nbsp;kg of rock and soil samples with three ''Luna'' sample return missions (''[[Astronomy:Luna 16|Luna 16]]'' in 1970, ''[[Astronomy:Luna 20|Luna 20]]'' in 1972, and ''[[Astronomy:Luna 24|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=6 April 2010 |url-status=live |archive-url=https://web.archive.org/web/20100527085532/http://curator.jsc.nasa.gov/lunar/index.cfm |archive-date=27 May 2010}}</ref>

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

The until 1979 negotiated Moon treaty, with its ratification in 1984 by its few signatories was about the only major activity regarding the Moon until 1990.

===Renewed exploration (1990–present)===
[[File:Moon landing sites.svg|thumb|Map of all soft landing sites on the near side of the Moon (2020)|450x450px]]
In 1990 ''[[Engineering: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=29 March 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=14 June 2011}}</ref> the first dedicated lunar mission since 1976, reached the Moon. Sent by {{wipe|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 (''[[Engineering: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=29 March 2010 |url-status=live |archive-url=https://web.archive.org/web/20100925095846/http://nssdc.gsfc.nasa.gov/planetary/cleminfo.html |archive-date=25 September 2010}}</ref> In 1998, this was followed by the ''[[Astronomy:Lunar Prospector|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=29 March 2010 |url-status=dead |archive-url=https://web.archive.org/web/20100527105801/http://lunar.arc.nasa.gov/results/neutron.htm |archive-date=27 May 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 [[Organization:European Space Agency|European Space Agency]] (ESA) (''[[Astronomy:SMART-1|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=26 February 2007 |publisher=[[Organization:European Space Agency|European Space Agency]] |access-date=29 March 2010 |url-status=live |archive-url=https://web.archive.org/web/20100323044139/http://www.esa.int/SPECIALS/SMART-1/SEMSDE1A6BD_0.html |archive-date=23 March 2010}}</ref>
The [[Astronomy:Chinese Lunar Exploration Program|Chinese Lunar Exploration Program]] began with ''[[Astronomy:Chang'e 1|Chang'e 1]]'' between 2007 and 2009,<ref>{{cite web |title=Chang'e 1 |publisher=NASA |date=2019 |url=https://solarsystem.nasa.gov/missions/change-1/in-depth/ |access-date=3 October 2021 |archive-date=22 November 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.
[[Astronomy:Indian Space Research Organisation|India]] reached the Moon in 2008 for the first time with its ''[[Astronomy:Chandrayaan-1|Chandrayaan-1]]'', creating a high-resolution chemical, mineralogical and photo-geological map of the lunar surface, and confirming the presence of [[Astronomy:Lunar water|water molecules in lunar soil]].<ref>{{cite web |url=http://www.isro.org/Chandrayaan/htmls/mission_sequence.htm |title=Mission Sequence |date=17 November 2008 |publisher=[[Astronomy:Indian Space Research Organisation|Indian Space Research Organisation]] |access-date=13 April 2010 |url-status=live |archive-url=https://web.archive.org/web/20100706225136/http://www.isro.org/chandrayaan/htmls/mission_sequence.htm |archive-date=6 July 2010}}</ref>

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

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

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

Another Chinese rover mission, ''[[Astronomy:Chang'e 4|Chang'e 4]]'', achieved the first landing on [[Astronomy: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=17 March 2015 |first=Leonard | last=David |publisher=Space.com |access-date=29 June 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=1 July 2016}}</ref>

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

In 2020, China carried out its first robotic sample return mission (''[[Astronomy:Chang'e 5|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=20 December 2020 |work=The Hindu |access-date=15 October 2021 |archive-date=29 October 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>

With the signing of the U.S.-led [[Astronomy:Artemis Accords|Artemis Accords]] in 2020, the [[Astronomy:Artemis program|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=2021-04-19|website=Space.com|language=en|archive-date=2021-04-17|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 [[Astronomy:Moon Treaty|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"/> The U.S. [[Astronomy: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=14 December 2004 |publisher=NASA |access-date=12 April 2007 |url-status=live |archive-url=https://web.archive.org/web/20070510062228/http://www.nasa.gov/missions/solarsystem/bush_vision.html |archive-date=10 May 2007}}</ref> which resulted in several programs. The Artemis program has advanced the farthest, and includes plans to send the first woman to the Moon<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=15 May 2019 |website=The Asian Age |access-date=15 May 2019 |archive-date=14 April 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> as well as build an international lunar space station called [[Astronomy:Lunar Gateway|Lunar Gateway]].

On 19 January 2024, Japan became the fifth country to land a spacecraft on the moon, following the [[Place:Soviet Union|Soviet Union]], {{wipe|United States}}, {{wipe|China}}, and {{wipe|India}}.<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=19 January 2024 |access-date=19 January 2024 |work=BBC News |language=en-gb}}</ref>

===Future===
[[File:Orion and the Moon (art001e000269).jpg|thumb|[[Engineering:Orion (spacecraft)|Orion spacecraft]]'s flyby of the Moon in the Artemis 1 mission]]
Upcoming lunar missions include the [[Astronomy:Artemis program|Artemis program]] missions and Russia's first lunar mission, ''[[Astronomy:Luna-Glob|Luna-Glob]]'': an uncrewed lander with a set of seismometers, and an orbiter based on its failed Martian ''[[Astronomy:Fobos-Grunt|Fobos-Grunt]]'' mission.<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=4 June 2006 |access-date=12 April 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=12 June 2006}}</ref>

In 2021, China announced a plan with Russia to develop and construct an [[Astronomy:International Lunar Research Station|International Lunar Research Station]] in the 2030s.

==Human presence==
{{See also|Human presence in space}} Humans last landed on the Moon during the Apollo Program, a series of crewed exploration missions carried out from 1969 to 1972. [[Astronomy:Lunar orbit|Lunar orbit]] has seen uninterrupted [[Astronomy:List of extraterrestrial orbiters#Moon|presence of orbiters since 2006]], performing mainly [[Astronomy:Lunar observation|lunar observation]] and providing relayed communication for robotic missions on the lunar surface.

Lunar orbits and [[Astronomy:List of objects at Lagrange points#Earth–Moon Lagrange points|orbits around Earth–Moon Lagrange points]] are used to establish a near-lunar infrastructure to enable increasing human activity in cislunar space as well as on the Moon's surface. Missions at the far side of the Moon or the [[Astronomy:Lunar north pole|lunar north]] and [[Astronomy:Lunar south pole|south polar]] regions need spacecraft with special orbits, such as the [[Astronomy:Queqiao relay satellite|Queqiao relay satellite]] or the planned first extraterrestrial space station, the [[Astronomy:Lunar Gateway|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=2022-05-14 | 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=2022-12-17 | archive-date=17 December 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=17 December 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 ===

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

While the Moon has the lowest [[Astronomy: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=2019-10-24 | url=https://qz.com/1734103/will-people-go-to-space-and-then-colonize-it/ | access-date=2021-11-09 | archive-date=2021-11-09 | 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 performed from the Moon, it will need to be free from any physical and [[Astronomy:Radio spectrum pollution|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=21 August 2020 | url=https://www.space.com/moon-ice-mining-contamination-concerns.html | access-date=3 February 2022 | archive-date=4 February 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=2022-07-01 | url=https://spacewatch.global/2022/07/spacewatchgl-opinion-an-ecofeminist-approach-to-the-sustainable-used-of-the-moon/ | access-date=2022-07-03 | archive-date=2022-07-04 | 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 [[Biography:Val Plumwood|Val Plumwood]] which Alice Gorman cites regarding co-participation.</ref>

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

[[Astronomy:Space debris|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=2022-02-27 | 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=2022-04-09 | archive-date=2022-04-09 | 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=2021-08-27 | 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=2022-05-26 | last1=Briggs | first1=Randall | last2=Sacco | first2=Albert | year=1985 | page=423 | archive-date=2022-05-26 | archive-url=https://web.archive.org/web/20220526022021/https://adsabs.harvard.edu/full/1985lbsa.conf..423B | url-status=live }}</ref>

Human remains on the Moon, particularly of deceased humans, have been an issue of [[Religion:Desecration|desecration]] of the venerated Moon. Raised by indigenous peoples at least since the first extraterrestrial space burial, the crashing of remains of Eugene Shoemaker with the [[Astronomy:Lunar Prospector|Lunar Prospector]] probe in 1999 at the [[Astronomy:Shoemaker (lunar crater)|Shoemaker crater]] of the [[Astronomy:Lunar south pole|lunar south pole]] region.<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=2024-01-05 | url=https://www.smithsonianmag.com/smart-news/navajo-nation-president-asks-for-delay-of-moon-mission-carrying-human-remains-180983543/ | access-date=2024-01-07}}</ref><ref name="web.archive.org 2011 c901">{{cite web | title=Celestis Memorial Spaceflights | date=2011-08-08 | url=http://celestis.com/luna01Flight.asp | archive-url=https://web.archive.org/web/20140314165835/http://celestis.com/luna01Flight.asp | archive-date=2014-03-14 | url-status=unfit | access-date=2024-01-07}}</ref>

Beside the remains of human activity on the Moon, there have been some intended permanent installations like the ''[[Astronomy:Moon Museum|Moon Museum]]'' art piece, [[Astronomy:Apollo 11 goodwill messages|Apollo 11 goodwill messages]], six [[Astronomy:Lunar plaque|lunar plaque]]s, the ''[[Astronomy:Fallen Astronaut|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=2012-12-19 | url=https://www.theatlantic.com/technology/archive/2012/12/the-trash-weve-left-on-the-moon/266465/ | access-date=2022-04-11 | archive-date=2022-04-09 | 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 [[Astronomy:Lunar Reconnaissance Orbiter|Lunar Reconnaissance Orbiter]] surveilling the Moon for future missions, as well as some Landers such as the 2013-launched [[Astronomy:Chang'e 3|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=23 September 2020|access-date=16 November 2020|archive-date=25 November 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 [[Astronomy:Libration|libration]]s through [[Astronomy:Lunar Laser Ranging experiment|laser ranging to the Moon]].

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

===Astronomy from the Moon===
[[File:Niac2020 bandyopadhyay.jpg|thumb|The [[Astronomy:Lunar Crater Radio Telescope|LCRT]] concept for a radio telescope on the Moon]]
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=[[Organization:California Institute of Technology|California Institute of Technology]] |date=September 1999 |url=http://www.ugcs.caltech.edu/~yukimoon/MoonTelescope/ |access-date=27 March 2011 |url-status=dead |archive-url=https://web.archive.org/web/20151106142659/http://www.ugcs.caltech.edu/~yukimoon/MoonTelescope/ |archive-date=6 November 2015 }}</ref> It is relatively nearby; certain craters near the poles are permanently dark and cold and especially useful for [[Astronomy:Infrared telescope|infrared telescope]]s; and [[Astronomy:Radio telescope|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=15 February 2008 |url=http://web.mit.edu/newsoffice/2008/moonscope-0215.html |access-date=27 March 2011 |url-status=live |archive-url=https://web.archive.org/web/20090304062601/http://web.mit.edu/newsoffice/2008/moonscope-0215.html |archive-date=4 March 2009}}</ref> The [[Astronomy:Lunar soil|lunar soil]], although it poses a problem for any moving parts of [[Astronomy:Telescope|telescope]]s, can be mixed with [[Physics:Carbon nanotube|carbon nanotube]]s and [[Chemistry: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=[[Organization:Goddard Space Flight Center|Goddard Space Flight Center]] |date=6 April 2008 |url=http://www.nasa.gov/centers/goddard/news/topstory/2008/lunar_telescopes.html |access-date=27 March 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=22 December 2010}}</ref> A lunar [[Astronomy:Zenith telescope|zenith telescope]] can be made cheaply with an [[Physics:Ionic liquid|ionic liquid]].<ref>{{cite web |last=Bell |first=Trudy |title=Liquid Mirror Telescopes on the Moon |work=Science News |publisher=NASA |date=9 October 2008 |url=https://science.nasa.gov/science-news/science-at-nasa/2008/09oct_liquidmirror/ |access-date=27 March 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=23 March 2011 }}</ref>

In April 1972, the [[Engineering:Apollo 16|Apollo 16]] mission recorded various astronomical photos and spectra in ultraviolet with the Far Ultraviolet Camera/Spectrograph.<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=3 October 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=3 December 2013}}</ref>

The Moon has been also a site of [[Earth:Earth observation|Earth observation]], particularly culturally as in the photograph called ''[[Astronomy:Earthrise|Earthrise]]''. The Earth appears in the [[Astronomy: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=2023-03-24 | 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.

===Living on the Moon===
{{Main|Astronomy:Lunar habitation}}
[[File:Aldrin Looks Back at Tranquility Base - GPN-2000-001102.jpg|thumb|Astronaut [[Biography:Buzz Aldrin|Buzz Aldrin]] in life-supporting suit looking back at the first lunar habitat and base, the Lunar Module ''Eagle'' of Tranquility Base, during Apollo 11 (1969), the first crewed Moon landing]]
The only instances of [[Engineering:Space habitat (facility)#Extraterrestrial surface habitat|humans living on the Moon]] have taken place in an [[Engineering:Apollo Lunar Module|Apollo Lunar Module]] for several days at a time (for example, during the [[Engineering:Apollo 17|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=30 September 2006|title=Mission Report: Apollo 17 – The Most Productive Lunar Expedition|publisher=NASA|access-date=10 February 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, calling it the "Apollo aroma".<ref name="Aroma" /> This fine lunar dust can 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=21 October 2019|access-date=26 November 2020|archive-date=1 December 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 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=15 January 2019|website=South China Morning Post|access-date=26 November 2020|archive-date=16 January 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==
Although ''Luna'' landers scattered pennants of the [[Place:Soviet Union|Soviet Union]] on the Moon, and [[Engineering:Lunar Flag Assembly|U.S. flags]] were symbolically planted at their landing sites by the [[Astronomy:List of Apollo astronauts|Apollo astronauts]], no nation claims ownership of any part of the Moon's surface.<ref name="unoosa_q6" /> Likewise no [[Astronomy: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 [[Engineering:Outer Space Treaty|Outer Space Treaty]] defines the Moon and all outer space as the "[[Social: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 [[Astronomy:Moon Treaty|Moon Agreement]] was created to elaborate, and restrict the exploitation of the [[Astronomy: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=2021-10-25 | url=https://www.thespacereview.com/article/4270/1 | access-date=2022-04-09 | archive-date=2021-11-02 | 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 [[Astronomy:Human spaceflight|human spaceflight]] capabilities.

Since 2020, countries have joined the U.S. in their [[Astronomy:Artemis Accords|Artemis Accords]], which are challenging the treaty. The U.S. has furthermore emphasized in a presidential [[Social:Executive order|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=22 July 2020 | website=OpinioJuris | access-date=2021-05-10 | url=http://opiniojuris.org/2020/07/22/space-law-at-the-crossroads-contextualizing-the-artemis-accords-and-the-space-resources-executive-order/ | archive-date=2021-05-10 | 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 web |url=http://www.spaceref.com/news/viewpr.html?pid=55513 |title=Administration Statement on Executive Order on Encouraging International Support for the Recovery and Use of Space Resources |website=SpaceRef.com |date=6 April 2020 |publisher=White House |access-date=17 June 2020 }}{{Dead link|date=September 2023 |bot=InternetArchiveBot |fix-attempted=yes }}</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=Jun 2, 2021 | url=https://www.internationalaffairs.org.au/australianoutlook/australia-between-the-moon-agreement-and-the-artemis-accords/ | access-date=Feb 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=Jun 29, 2020 | url=https://www.thespacereview.com/article/3975/1 | access-date=Feb 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=Feb 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=12 Jan 2021 | url=https://science.howstuffworks.com/us-law-protect-lunar-landing-sites.htm | access-date=1 Nov 2021 | archive-date=1 November 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 Sites<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=1 Nov 2021 | archive-date=1 November 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=1 Jan 2020 | url=https://www.academia.edu/43890727 | access-date=1 Nov 2021 | page=109-115, 164–167, 176 | archive-date=5 February 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=11 February 2021 | publisher=Australian Earth Laws Alliance | url=https://www.earthlaws.org.au/moon-declaration/ | access-date=2021-05-10 | archive-date=2021-04-23 | 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=2018-12-01|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=2022-07-30|archive-date=2021-06-28|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=2021-07-20 | url=http://eos.org/features/hear-ye-hear-ye-a-declaration-of-the-rights-of-the-moon | access-date=2022-04-09 | archive-date=2022-02-06 | 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===
In light of future development on the Moon some international and multi-space agency organizations have been created:

* [[Astronomy:International Lunar Exploration Working Group|International Lunar Exploration Working Group]] (ILEWG)
* [[Astronomy:Moonbase#Moon Village|Moon Village Association]] (MVA)
* International Space Exploration Coordination Group (ISECG)

==In culture and life==
===Timekeeping===
[[File:Venus-de-Laussel-detail-corne.jpg|thumb|right|The Venus of Laussel (c. 25,000 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 cycles and lunar cycles 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=2022-07-30 |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=2021-10-03 |url-status=live}}</ref><ref name="Boyle 2019">{{cite web |last=Boyle |first=Rebecca |date=2019-07-09 |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=2021-11-04 |access-date=2021-11-04 |website=Science News}}</ref>]]Since pre-historic times people have taken note of the Moon's phases and its waxing and waning cycle, and used it to keep record of time. Tally sticks, 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 gave eventually rise to generalized time periods of lunar cycles as [[Month|month]]s, and possibly of its phases as [[Physics:Week|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=2022-02-25 | page=9 | archive-date=2022-07-25 | 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 [[Social:Latin|Latin]] {{lang|la |mensis}} and [[Social:Ancient Greek|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=29 March 2010 |volume=3 |date=1849 |publisher=J. Walton |page=768 |archive-date=26 November 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=29 March 2010 |volume=5 |date=1846 |publisher=Didot |page=1001 |archive-date=28 July 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=[[Organization:Oxford University Press|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 [[Social:Language family|language family]], the [[Social:Chinese language|Chinese language]] uses the same word ({{lang|zh |{{linktext|月}}}}) for ''moon'' as well 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, [[Astronomy:Lunisolar calendar|lunisolar calendar]]s. The 7th-century [[Engineering:Islamic calendar|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 [[Astronomy:Full moon|full moon]], highlighted and celebrated in a range of calendars and cultures, an example being the Buddhist [[Astronomy:Vesak|Vesak]]. The full moon around the [[Astronomy:March equinox|southern]] or [[Astronomy: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 [[Place: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=2022-08-30 | url=https://www.confuciusinstitute.ac.uk/events/mid-autumn-festival-activities-10-september/ | access-date=2022-11-22 | archive-date=22 November 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===

{{multiple image
| title             = Recurring lunar [[Religion:Aspect|aspects]] of lunar deities
| align             = right
| direction         = vertical
| image1            = Sumerian_Cylinder_Seal_of_King_Ur-Nammu.jpg
| alt1              = Sumerian cylinder seal and impression, dated {{circa|2100}} BC, of Ḫašḫamer, 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 [[Unsolved: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=1987-05-20 | url=https://collections.mfa.org/objects/6027/cylinder-vase;jsessionid=F2E906D47F69B2A85DB31D259E691783 | access-date=2021-11-11 | archive-date=2021-11-11 | 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|crescent]] ([[Religion: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 on the Parabiago plate (2nd–5th century), featuring the crescent crown and chariot lunar [[Religion:Aspect|aspect]] found in different cultures.
| caption2          = Crescent headgear and chariot (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 [[Unsolved:Moon rabbit|Moon rabbit]] (Mayan moon goddess, 6th–9th century)
| image4            = 
| caption4          = 
}}

Since prehistoric and ancient times humans have drawn the Moon and have described a range of understandings of it, having prominent importance in different [[Astronomy:Cosmology|cosmologies]], often exhibiting a [[Philosophy:Spirit (vital essence)|spirit]], being a deity or an [[Religion:Aspect|aspect]], particularly in astrology.

For the representation of the Moon, especially its lunar phases, the [[Crescent|crescent]] symbol (🌙) has been particularly used by many cultures. In [[Social:Writing system|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}}, which is spelled like the ancient Egyptian lunar deity ''Iah'', meaning Moon.<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=2022-02-23 | page=77 | archive-date=2022-07-25 | archive-url=https://web.archive.org/web/20220725234921/https://books.google.com/books?id=Q1LAiPylZm4C&pg=PA77 | url-status=live }}</ref>

Iconographically the crescent was used in [[Place:Mesopotamia|Mesopotamia]] as the primary symbol of [[Religion:Sin (mythology)|Nanna/Sîn]],<ref name=BlackGreen1992/> the ancient Sumerian 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=11 June 2019 |archive-date=16 June 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 |page=135 |access-date=28 October 2017 |archive-date=19 August 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 Innana/Ishtar, the goddess of the planet [[Astronomy:Venus|Venus]] (symbolized as the [[Octagram|eight pointed]] [[Star of Ishtar]]),<ref name="Nemet1998"/><ref name=BlackGreen1992/> and [[Religion:Utu|Utu/Shamash]], the god of the Sun ([[Astronomy: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 was later known as Sîn,<ref name=BlackGreen1992/><ref name="Nemet1998"/> and was particularly associated with magic and sorcery.<ref name="Nemet1998"/>

The crescent was further used as an element of lunar deities wearing headgears or crowns in an arrangement reminiscent of horns, as in the case of the ancient Greek Selene<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=28 April 2020 |archive-date=19 August 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> or the ancient Egyptian Khonsu. Selene is associated with [[Religion:Artemis|Artemis]] and paralleled by the Roman Luna, which both are occasionally depicted driving a chariot, like the Hindu lunar deity Chandra. The different or sharing [[Religion:Aspect|aspect]]s of deities within [[Religion:Pantheon|pantheon]]s has been observed in many cultures, especially by later or contemporary culture, particularly forming [[Religion:Triple deity|triple deities]]. The Moon in Roman mythology for example has been associated with Juno and Diana, while Luna being identified as their byname and as part of a triplet (''diva triformis'') with Diana and Proserpina, [[Religion:Hecate|Hecate]] being identified as their binding manifestation as ''trimorphos''.

The [[Star and crescent|star and crescent]] (☪️) arrangement goes back to the Bronze Age, representing either the Sun and Moon, or the Moon and planet [[Astronomy:Venus|Venus]], in combination. It came to represent the goddess Artemis or Hecate, and via the patronage of Hecate came to be used as a symbol of Byzantium, 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>
Since then the heraldric use of the star and crescent proliferated becoming a popular symbol for Islam (as the ''hilal'' of the [[Engineering:Islamic calendar|Islamic calendar]]) and [[Star and crescent#Contemporary use|for a range of nations]].<ref name="Kadoi 2014">{{cite web | last=Kadoi | first=Yuka | title=Crescent (symbol of Islam) | website=Brill Encyclopedia of Islam Online | date=2014-10-01 | url=https://referenceworks.brillonline.com/entries/encyclopaedia-of-islam-3/crescent-symbol-of-islam-COM_25588?s.num=27&s.start=20 | access-date=2022-04-08 | archive-date=2022-04-08 | archive-url=https://web.archive.org/web/20220408190925/https://referenceworks.brillonline.com/entries/encyclopaedia-of-islam-3/crescent-symbol-of-islam-COM_25588?s.num=27&s.start=20 | url-status=live }}</ref>

In Roman Catholic Marian veneration, the Virgin Mary ([[Unsolved:Queen of Heaven|Queen of Heaven]]) has been depicted since the [[History:Late Middle Ages|late Middle Ages]] on a crescent and adorned with stars. In [[Religion:Islam|Islam]] [[Biography:Muhammad|Muhammad]] is particularly attributed with the Moon through the so-called [[Religion:Splitting of the Moon|splitting of the Moon]] ({{lang-ar|انشقاق القمر}}) miracle.<ref>"Muhammad." ''[[Encyclopædia Britannica]]''. 2007. Encyclopædia Britannica Online, p.13</ref>

The contrast between the brighter highlands and the darker maria have been seen by different cultures forming abstract shapes, which are among others the Man in the Moon or the Moon Rabbit (e.g. the Chinese [[Religion:Tu'er Ye|Tu'er Ye]] or in Indigenous American mythologies, as with the aspect of the Mayan Moon goddess).<ref name="Collections Search – Museum of Fine Arts, Boston 1987"/>

In Western [[Philosophy:Alchemy|alchemy]] [[Chemistry:Silver|silver]] is associated with the Moon, and gold 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=2019-08-30 | issn=2532-3997 | doi=10.13128/Substantia-603 | pages=39–44 | url=https://riviste.fupress.net/index.php/subs/article/view/603 | access-date=2022-04-08 | archive-date=2022-06-17 | archive-url=https://web.archive.org/web/20220617041849/https://riviste.fupress.net/index.php/subs/article/view/603 | url-status=live }}</ref>
{{clear}}

=== Modern culture representation ===

{{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''.
| 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), inspired by a history of literature about going to the Moon.
}}

The perception of the Moon in modern times has been informed by [[Astronomy:Telescope|telescope]] enabled modern astronomy and later by [[Engineering:Spaceflight|spaceflight]] enabled actual human activity at the Moon, particularly the [[Astronomy: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=29 Sep 2020 | url=https://thereader.mitpress.mit.edu/moon-of-science-vs-moon-of-lovers/ | access-date=1 Nov 2021 | archive-date=1 November 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=2019-07-09 | 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=2019-07-09 |url-access=subscription |url-status=live | access-date=2021-11-04}}</ref><ref name="Nature 2019">{{cite journal | title=Moon on the mind: two millennia of lunar literature | journal=Nature | date=9 Jul 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 economic expansion into space, with missions prospecting for [[Astronomy:Lunar resources|lunar resources]]. This has been accompanied with renewed public and critical reflection on humanity's cultural and legal relation to the celestial body, especially regarding [[Social:Colonialism|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=2013-07-15 | url=https://www.wired.com/2013/07/space-environmentalism/ | access-date=2022-04-09 | archive-date=2021-07-14 | archive-url=https://web.archive.org/web/20210714235012/https://www.wired.com/2013/07/space-environmentalism/ | url-status=live }}</ref> and as a common.<ref name="Open Lunar Foundation 2022">{{cite web | title=Polycentricity for Governance of the Moon as a Commons | website=Open Lunar Foundation | date=2022-03-22 | url=https://www.openlunar.org/library/polycentricity-for-governance-of-the-moon-as-a-commons | access-date=2022-04-09 | archive-date=2022-04-20 | 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 the 20th of July, the date of the [[Engineering:Apollo 11#Landing|first crewed moon landing]], became the annual ''International Moon Day''.<ref name="Nations 1967 a849">{{cite web | last=Nations | first=United | title=International Moon Day | publisher=United Nations | date=1967-10-10 | url=https://www.un.org/en/observances/moon-day | access-date=2023-11-08 | archive-date=27 June 2023 | archive-url=https://web.archive.org/web/20230627042218/https://www.un.org/en/observances/moon-day | url-status=live }}</ref>

===Lunar effect===
{{Main|Biology: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 ''[[Astronomy:Lunatic|lunatic]]'' are derived from the Latin name for the Moon, ''Luna''. Philosophers [[Biography:Aristotle|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 ==
*[[Astronomy:List of natural satellites|List of natural satellites]]
*[[Astronomy:Selenography|Selenography]] (geography of 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 [[Astronomy:New moon|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 [[Earth:Albedo|albedo]] ×}} {{nowrap|([[Astronomy:Earth radius|Earth radius]] /}} Radius of [[Astronomy:Orbit of the Moon|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 [[Astronomy:Angular diameter|angular size]] is 1896&nbsp;[[Arcsecond|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 [[Physics:Ideal gas law|ideal gas law]] yields the pressures given in the infobox (rounded to the nearest [[Order of magnitude|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 [[Astronomy:Near-Earth asteroid|near-Earth asteroid]]s, including [[Astronomy:3753 Cruithne|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 [[Astronomy:Quasi-satellite|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 [[Astronomy:Charon (moon)|Charon]] is larger relative to its primary [[Astronomy:Pluto|Pluto]], but Earth and the Moon are different since Pluto is considered a [[Astronomy:Dwarf planet|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 [[Astronomy:Apparent magnitude|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 [[Astronomy:Sun#Life phases|Sun]]. 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="unoosa_q5">{{cite web |url=http://www.unoosa.org/oosa/en/FAQ/splawfaq.html#Q5 |title=Do the five international treaties regulate military activities in outer space? |publisher=[[Organization:United Nations Office for Outer Space Affairs|United Nations Office for Outer Space Affairs]] |access-date=28 March 2010 |url-status=live |archive-url=https://web.archive.org/web/20100421232450/http://www.unoosa.org/oosa/en/FAQ/splawfaq.html#Q5 |archive-date=21 April 2010}}</ref>

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<!-- <ref name="barnhart-and-germania">For etymology, see {{cite book |last=Barnhart |first=Robert K. |title=The Barnhart Concise Dictionary of Etymology |date=1995 |publisher=Harper Collins |isbn=978-0-06-270084-1 |page=487}}. For the lunar calendar of the Germanic peoples, see {{cite book |last=Birley |first=A. R. (Trans.) |title=Agricola and Germany |series=Oxford World's Classics |date=1999 |publisher=[[Organization:Oxford University Press|Oxford University Press]] |location=US |isbn=978-0-19-283300-6 |page=[https://archive.org/details/agricolagermany00taci/page/108 108] |url=https://archive.org/details/agricolagermany00taci/page/108 |access-date=11 June 2019 |archive-date=17 June 2020 |archive-url=https://web.archive.org/web/20200617081723/https://archive.org/details/agricolagermany00taci/page/108 |url-status=live }}</ref> -->

<ref name="sciam">{{cite magazine |title=Lunacy and the Full Moon |magazine=Scientific American |date=2009 |first1=Scott O. |last1=Lilienfeld |first2=Hal |last2=Arkowitz |url=http://www.scientificamerican.com/article.cfm?id=lunacy-and-the-full-moon |access-date=13 April 2010 |url-status=live |archive-url=https://web.archive.org/web/20091016163312/http://www.scientificamerican.com/article.cfm?id=lunacy-and-the-full-moon |archive-date=16 October 2009}}
</ref>

<ref name="Williams1996">{{cite journal |last1=Williams |first1=James G. |last2=Newhall |first2=XX |last3=Dickey |first3=Jean O. |title=Lunar moments, tides, orientation, and coordinate frames |journal=Planetary and Space Science |volume=44 |issue=10 |date=1996 |pages=1077–1080 |doi=10.1016/0032-0633(95)00154-9 |bibcode=1996P&SS...44.1077W}}</ref>

<ref name="MartensKelly1988">{{cite journal |last1=Martens |first1=R. |last2=Kelly |first2=I.W. |last3=Saklofske |first3=D.H. |title=Lunar Phase and Birthrate: A 50-year Critical Review |journal=Psychological Reports |volume=63 |issue=3 |date=1988 |pages=923–934 |doi=10.2466/pr0.1988.63.3.923|pmid=3070616 |s2cid=34184527 }}</ref>

<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=[[Biology:Current Biology|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 }}</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=[[Unsolved:Skeptical Inquirer|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 [[Biography:Joe Nickell|Joe Nickell]], [[Biography:Barry Karr|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 Books |isbn=978-0-521-05801-8 |place=Taipei |access-date=22 August 2020 |archive-date=22 June 2019 |archive-url=https://web.archive.org/web/20190622004236/https://books.google.com/books?id=jfQ9E0u4pLAC |url-status=live }}</ref>

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

==Further reading==
{{Refbegin}}
* {{cite news |last=Angier |first=Natalie |date=7 September 2014 |title=The Moon Comes Around Again |url=https://www.nytimes.com/2014/09/09/science/revisiting-the-moon.html |work={{wipe|The New York Times}} |access-date=8 September 2014 |archive-date=8 September 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=http://www.bbc.co.uk/worldservice/specials/948_discovery_2008/page4.shtml | title=The Moon | work=Discovery 2008 | publisher=BBC World Service | access-date=2021-05-09 | archive-date=2011-03-11 | 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. |title=The Clementine Atlas of the Moon |date=2004 |publisher={{wipe|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=2021-05-09 |archive-date=2021-05-10 |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=12 April 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=[[Chemistry:Reviews in Mineralogy and Geochemistry|Reviews in Mineralogy and Geochemistry]] |bibcode=2006RvMG...60D...5J |archive-date=27 June 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=2021-05-09 |archive-date=2021-05-08 |archive-url=https://web.archive.org/web/20210508133136/https://www.hq.nasa.gov/alsj/ |url-status=live }}
* {{cite web | title=Exploring the Moon | publisher=[[Organization:Lunar and Planetary Institute|Lunar and Planetary Institute]] | url=https://www.lpi.usra.edu/lunar/missions/ | access-date=2021-05-09 | archive-date=2021-05-10 | 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={{wipe|John Wiley & Sons}} |location=Hoboken, NJ |isbn=978-0-471-15057-2 |url=https://archive.org/details/bigsplatorhowour00mack |access-date=11 June 2019 |archive-date=17 June 2020 |archive-url=https://web.archive.org/web/20200617181357/https://archive.org/details/bigsplatorhowour00mack |url-status=live }}
* {{cite book |last=Moore, P. |title=On the Moon |date=2001 |publisher=Sterling Publishing Co. |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=http://www.psrd.hawaii.edu/Archive/Archive-Moon.html |access-date=18 November 2006 |archive-date=17 November 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=[[Company:Smithsonian Institution Press|Smithsonian Institution Press]] |isbn=978-1-56098-634-8 |url=https://archive.org/details/oncefuturemoon0000spud |access-date=11 June 2019 |archive-date=17 June 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={{wipe|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=http://www.apolloarchive.com/apollo_archive.html |access-date=12 April 2007 |archive-date=4 April 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=12 April 2007 |doi=10.3133/pp1348 |series=Professional Paper |doi-access=free |archive-date=23 February 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=10 March 2009 |date=1993 |publisher=University of Arizona Press |location=Tucson |isbn=978-0-8165-1065-8 |url-access=registration |archive-date=17 June 2020 |archive-url=https://web.archive.org/web/20200617181456/https://archive.org/details/torockymoongeolo0000wilh |url-status=live }}
{{Refend}}

==External links==
* [https://www.nasa.gov/moon NASA images and videos about the Moon]
* Albums of images and high-resolution overflight videos by Seán Doran, based on LROC data, on [https://www.flickr.com/photos/136797589@N04/albums/72157686992929766/with/35498090194/ Flickr] and [https://www.youtube.com/playlist?list=PLbdt9s6ywoD_62doBvzu9pSLDSY1TYtX_ YouTube]

===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.google.com/maps/space/moon/@6.1467095,139.2754359,23010541m/data=!3m1!1e3 The Moon] on [[Software:Google Maps|Google Maps]], a 3-D rendition of the Moon akin to Google Earth
* {{cite web |title=Consolidated Lunar Atlas |publisher=[[Organization:Lunar and Planetary Institute|Lunar and Planetary Institute]] |url=http://www.lpi.usra.edu/resources/cla/ |access-date=26 February 2012}}
* [http://planetarynames.wr.usgs.gov/jsp/FeatureTypes2.jsp?system=Earth&body=Moon&systemID=3&bodyID=11 Gazetteer of Planetary Nomenclature (USGS)] List of feature names.
* {{cite web |title=Clementine Lunar Image Browser |publisher=U.S. Navy |date=15 October 2003 |url=http://www.cmf.nrl.navy.mil/clementine/clib/ |access-date=12 April 2007 |archive-date=7 April 2007 |archive-url=https://web.archive.org/web/20070407000411/http://www.cmf.nrl.navy.mil/clementine/clib/ |url-status=dead }}
* 3D zoomable globes:
** {{cite web |title=Google Moon |date=2007 |url=http://moon.google.com |access-date=12 April 2007}}
** {{cite web |title=Moon |work=World Wind Central |publisher=NASA |date=2007 |url=http://www.worldwindcentral.com/wiki/Moon |access-date=12 April 2007}}
* {{cite web |last=Aeschliman |first=R |title=Lunar Maps |work=Planetary Cartography and Graphics |url=http://ralphaeschliman.com/id26.htm |access-date=12 April 2007 |archive-date=29 May 2015 |archive-url=https://web.archive.org/web/20150529090138/http://ralphaeschliman.com/id26.htm |url-status=dead }} Maps and panoramas at Apollo landing sites
* [https://web.archive.org/web/20120305055023/https://wms.selene.jaxa.jp/index_e.html Japan Aerospace Exploration Agency (JAXA)] Kaguya (Selene) images
* [https://earthlymission.com/wp-content/uploads/2016/10/moon-earthside-map.jpg Lunar Earthside chart (4497 x 3150px)]
* [http://home.bt.com/techgadgets/technews/explore-the-lunar-north-pole-11363885909226?s_intcid=con_RL_LunarNorthPole Large image of the Moon's north pole area] {{Webarchive|url=https://web.archive.org/web/20160823192057/http://home.bt.com/techgadgets/technews/explore-the-lunar-north-pole-11363885909226?s_intcid=con_RL_LunarNorthPole |date=23 August 2016 }}

===Observation tools===
* {{cite web |title=NASA's SKYCAL – Sky Events Calendar |publisher=NASA |url=http://sunearth.gsfc.nasa.gov/eclipse/SKYCAL/SKYCAL.html |access-date=27 August 2007 |url-status=dead |archive-url=https://web.archive.org/web/20070820075142/http://sunearth.gsfc.nasa.gov/eclipse/SKYCAL/SKYCAL.html |archive-date=20 August 2007}}
* {{cite web |title=Find moonrise, moonset and moonphase for a location |date=2008 |url=http://www.timeanddate.com/worldclock/moonrise.html |access-date=18 February 2008}}
* {{cite web |title=HMNAO's Moon Watch |date=2005 |url=http://www.crescentmoonwatch.org/nextnewmoon.htm |access-date=24 May 2009 |archive-date=4 February 2009 |archive-url=https://web.archive.org/web/20090204002746/http://www.crescentmoonwatch.org/nextnewmoon.htm |url-status=dead }} See when the next new crescent moon is visible for any location.

{{The Moon}}
{{Earth}}
{{Solar System moons (compact)}}
{{Solar System}}

[[Category:Moon| ]]
[[Category:Moons|*]]
[[Category:Astronomical objects known since antiquity]]
[[Category:Planetary satellite systems]]

{{Sourceattribution|Moon}}