Moon#Physical characteristics

{{See also|Moon#Cultural representation}}

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

Occasionally, the name Luna {{IPAc-en|'|l|uː|n|ə}} is used in scientific writingFor example: {{cite book |first=James A. |last=Hall III |date=2016 |title=Moons of the Solar System |publisher=Springer |isbn=978-3-319-20636-3}} 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.{{OED|Luna}} Cynthia {{IPAc-en|ˈ|s|ɪ|n|θ|i|ə}} is a rare poetic name for the Moon personified as a goddess,{{OED|Cynthia}} while Selene {{IPAc-en|s|ə|ˈ|l|iː|n|iː}} (literally 'Moon') is the Greek goddess of the Moon.

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

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

The astronomical symbols for the Moon are the crescent File:Moon crescent symbol (bold).svg and decrescent File:Moon decrescent symbol (bold).svg, for example in M_☾ 'lunar mass'.

{{Main|Lunar geologic timescale}}

{{Timeline Lunar Geological Timescale}}

The lunar geological periods are named after their characteristic features, from most impact craters outside the dark mare, to the mare and later craters, and finally the young, still bright and therefore readily visible craters with ray systems like Copernicus or Tycho.

{{Main|Origin of the Moon |Giant-impact hypothesis|Circumplanetary disk}}

File:Far side of the Moon.png lacks the near side's characteristic large dark areas of maria. The near side of the Moon might have looked like this early in the Moon's history.{{cite web |title=The two-faced Moon |website=The Planetary Society |date=March 14, 2022 |url=https://www.planetary.org/articles/the-two-faced-moon |access-date=April 28, 2023 |archive-date=April 28, 2023 |archive-url=https://web.archive.org/web/20230428213253/https://www.planetary.org/articles/the-two-faced-moon |url-status=live}}{{cite web |website=explanet.info |url=https://explanet.info/Chapter04.htm |title=Exploring the Planets: Chapter 4. The Moon |access-date=April 28, 2023 |archive-date=April 28, 2023 |archive-url=https://web.archive.org/web/20230428213755/https://explanet.info/Chapter04.htm |url-status=live}}]]

Isotope dating of lunar samples suggests the Moon formed around 50 million years after the origin of the Solar System.{{cite journal |title=Early Moon formation inferred from hafnium-tungsten systematics |last1=Thiemens |first1=Maxwell M. |last2=Sprung |first2=Peter |last3=Fonseca |first3=Raúl O. C. |last4=Leitzke |first4=Felipe P. |last5=Münker |first5=Carsten |journal=Nature Geoscience |volume=12 |issue=9 |pages=696–700 |date=July 2019 |doi=10.1038/s41561-019-0398-3 |pmid=39649009 |bibcode=2019NatGe..12..696T |s2cid=198997377 |pmc=7617097}}{{cite news |url=https://www.universetoday.com/143025/the-moon-is-older-than-scientists-thought/ |title=The Moon is older than scientists thought |website=Universe Today |access-date=August 3, 2019 |archive-date=August 3, 2019 |archive-url=https://web.archive.org/web/20190803125139/https://www.universetoday.com/143025/the-moon-is-older-than-scientists-thought/ |url-status=live}} Historically, several formation mechanisms have been proposed,{{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}} but none satisfactorily explains the features of the Earth–Moon system. A fission of the Moon from Earth's crust through centrifugal force would require too great an initial rotation rate of Earth. Gravitational capture of a pre-formed Moon depends on an unfeasibly extended atmosphere of Earth to dissipate the energy of the passing Moon. A co-formation of Earth and the Moon together in the primordial accretion disk does not explain the depletion of metals in the Moon. None of these hypotheses can account for the high angular momentum of the Earth–Moon system.{{cite journal |last=Stevenson |first=D. J. |title=Origin of the moon–The collision hypothesis |journal=Annual Review of Earth and Planetary Sciences |date=1987 |volume=15 |issue=1 |pages=271–315 |bibcode=1987AREPS..15..271S |doi=10.1146/annurev.ea.15.050187.001415 |s2cid=53516498}}

The prevailing theory is that the Earth–Moon system formed after a giant impact of a Mars-sized body (named Theia) with the proto-Earth. The oblique impact blasted material into orbit about the Earth and the material accreted and formed the Moon{{cite web |url=http://news.nationalgeographic.com/2015/04/150416-asteroids-scars-moon-formation-space/ |title=Asteroids Bear Scars of Moon's Violent Formation |date=April 16, 2015 |url-status=dead |archive-url=https://web.archive.org/web/20161008160812/http://news.nationalgeographic.com/2015/04/150416-asteroids-scars-moon-formation-space/ |archive-date=October 8, 2016}} just beyond the Earth's Roche limit of ~{{val|2.56|ul=Earth radius}}.{{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}}

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.{{cite journal |last=Canup |first=R. |author1-link=Robin Canup |author2=Asphaug, E. |title=Origin of the Moon in a giant impact near the end of Earth's formation |journal=Nature |volume=412 |pages=708–712 |date=2001 |doi=10.1038/35089010 |pmid=11507633 |issue=6848 |bibcode=2001Natur.412..708C |s2cid=4413525}} However, models from 2007 and later suggest a larger fraction of the Moon derived from the proto-Earth.{{cite magazine |url=http://news.nationalgeographic.com/news/2007/12/071219-moon-collision.html |title=Earth–Asteroid Collision Formed Moon Later Than Thought |magazine=National Geographic |date=October 28, 2010 |access-date=May 7, 2012 |url-status=dead |archive-url=https://web.archive.org/web/20090418171528/http://news.nationalgeographic.com/news/2007/12/071219-moon-collision.html |archive-date=April 18, 2009}}{{cite journal |title=2008 Pellas-Ryder Award for Mathieu Touboul |journal=Meteoritics and Planetary Science |volume=43 |issue=S7 |pages=A11–A12 |date=2008 |url=http://digitalcommons.arizona.edu/objectviewer?o=uadc://azu_maps/Volume43/NumberSupplement/Touboul.pdf |bibcode=2008M&PS...43...11K |last1=Kleine |first1=Thorsten |doi=10.1111/j.1945-5100.2008.tb00709.x |s2cid=128609987 |access-date=April 8, 2020 |archive-url=https://web.archive.org/web/20180727164701/http://digitalcommons.arizona.edu/objectviewer?o=uadc%3A%2F%2Fazu_maps%2FVolume43%2FNumberSupplement%2FTouboul.pdf |archive-date=July 27, 2018 |url-status=dead}}{{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}}{{cite magazine |url=http://news.nationalgeographic.com/2015/04/150408-moon-form-giant-impact-earth |title=Flying Oceans of Magma Help Demystify the Moon's Creation |magazine=National Geographic |date=April 8, 2015 |url-status=dead |archive-url=https://web.archive.org/web/20150409220422/http://news.nationalgeographic.com/2015/04/150408-moon-form-giant-impact-earth/ |archive-date=April 9, 2015}} Other bodies of the inner Solar System such as Mars and Vesta have, according to meteorites from them, very different oxygen and tungsten 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, although this is debated.{{cite magazine |last=Nield |first=Ted |title=Moonwalk (summary of meeting at Meteoritical Society's 72nd Annual Meeting, Nancy, France) |magazine=Geoscientist |volume=19 |page=8 |date=2009 |url=http://www.geolsoc.org.uk/gsl/geoscientist/geonews/page6072.html |url-status=dead |archive-url=https://web.archive.org/web/20120927034348/http://www.geolsoc.org.uk/gsl/geoscientist/geonews/page6072.html |archive-date=September 27, 2012}}

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.{{cite journal |last=Tonks |first=W. Brian |author2=Melosh, H. Jay |date=1993 |title=Magma ocean formation due to giant impacts |journal=Journal of Geophysical Research |volume=98 |issue=E3 |pages=5319–5333 |bibcode=1993JGR....98.5319T |doi=10.1029/92JE02726}} The newly formed Moon would have had 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}}.

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

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

File:Archean.png. At that time the Moon orbited the Earth at a third of its current distance, making it appear 2.8 times larger in apparent size than it does today.]]

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, eclipses were more frequent, and tidal effects were stronger.{{cite web |title=Earth-Moon Dynamics |website=Lunar and Planetary Institute |url=https://www.lpi.usra.edu/exploration/training/illustrations/earthMoon/ |access-date=September 2, 2022 |archive-date=September 7, 2015 |archive-url=https://web.archive.org/web/20150907215806/https://www.lpi.usra.edu/exploration/training/illustrations/earthMoon/ |url-status=live}}

Due to tidal acceleration, the Moon's orbit around Earth has become significantly larger, with a longer period.{{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}}

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

The Moon was volcanically active until 1.2 billion years ago, which laid down the prominent lunar maria. Most of the mare basalts erupted during the Imbrian period, 3.3–3.7 billion years ago, though some are as young as 1.2 billion years and some as old as 4.2 billion years. There are differing explanations for the eruption of mare basalts, particularly their uneven occurrence which mainly appear on the near-side. Causes of the distribution of the lunar highlands on the far side 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.{{cite web |title=Lunar Far Side Highlands |website=ESA Science & Technology |date=July 14, 2006 |url=https://sci.esa.int/web/smart-1/-/39791-lunar-far-side-highlands |access-date=September 2, 2022 |archive-date=September 2, 2022 |archive-url=https://web.archive.org/web/20220902221440/https://sci.esa.int/web/smart-1/-/39791-lunar-far-side-highlands |url-status=live}}

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

{{Further|List of natural satellites}}

File:Moons of solar system v7.jpg, 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 planetary-mass moons, making it a satellite planet under the geophysical definitions of the term.{{Citation |last1=Metzger |first1=Philip |author-link1=Philip T. Metzger |last2=Grundy |first2=Will |last3=Sykes |first3=Mark |last4=Stern |first4=Alan |last5=Bell |first5=James |last6=Detelich |first6=Charlene |last7=Runyon |first7=Kirby |last8=Summers |first8=Michael |date=2021 |title=Moons are planets: Scientific usefulness versus cultural teleology in the taxonomy of planetary science |journal=Icarus |volume=374 |page=114768 |doi=10.1016/j.icarus.2021.114768 |arxiv=2110.15285 |bibcode=2022Icar..37414768M |s2cid=240071005}} It is smaller than Mercury and considerably larger than the largest dwarf planet of the Solar System, Pluto. The Moon is the largest natural satellite in the Solar System relative to its primary planet.{{efn |There is no strong correlation between the sizes of planets and the sizes of their satellites. Larger planets tend to have more satellites, both large and small, than smaller planets.}}{{efn|name=Moon vs. Charon}}{{cite web |url=http://www.planetary.org/explore/topics/pluto/ |title=Space Topics: Pluto and Charon |publisher=The Planetary Society |access-date=April 6, 2010 |url-status=dead |archive-url=https://web.archive.org/web/20120218223842/http://www.planetary.org/explore/topics/pluto/ |archive-date=February 18, 2012}}

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

The Moon's mass is {{frac|1|81}} of Earth's, being the second densest among the planetary moons, and having the second highest surface gravity, after Io, at {{val |0.1654 |u=g}} and an escape velocity of {{convert|2.38|km/s|km/h mph|comma=gaps|abbr=on}}.

{{Main|Internal structure of the Moon|Geology of the Moon}}

File:Return of the moon diagram.svg.]]

The Moon is a differentiated body that was initially in hydrostatic equilibrium but has since departed from this condition.{{cite journal |title=Interpretation of lunar potential fields |first=Stanley Keith |last=Runcorn |date=March 31, 1977 |journal=Philosophical Transactions of the Royal Society of London. Series A, Mathematical and Physical Sciences |doi=10.1098/rsta.1977.0094 |bibcode=1977RSPTA.285..507R |volume=285 |issue=1327 |pages=507–516 |s2cid=124703189}} It has a geochemically distinct crust, mantle, and 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}}.{{cite web |last1=Brown |first1=D. |last2=Anderson |first2=J. |website=NASA |url=http://www.nasa.gov/topics/moonmars/features/lunar_core.html |title=NASA Research Team Reveals Moon Has Earth-Like Core |date=January 6, 2011 |url-status=live |archive-url=https://web.archive.org/web/20120111112210/http://www.nasa.gov/topics/moonmars/features/lunar_core.html |archive-date=January 11, 2012}}{{cite journal |last1=Weber |first1=R.C. |last2=Lin |first2=P.-Y. |last3=Garnero |first3=E.J. |last4=Williams |first4=Q. |last5=Lognonne |first5=P. |title=Seismic Detection of the Lunar Core |journal=Science |volume=331 |issue=6015 |date=January 21, 2011 |pages=309–312 |url=http://www.earth.northwestern.edu/people/seth/351/lunarcore.2011.pdf |doi=10.1126/science.1199375 |pmid=21212323 |url-status=dead |archive-url=https://web.archive.org/web/20151015035756/http://www.earth.northwestern.edu/people/seth/351/lunarcore.2011.pdf |archive-date=October 15, 2015 |bibcode=2011Sci...331..309W |s2cid=206530647 |access-date=April 10, 2017}} This structure is thought to have developed through the fractional crystallization of a global magma ocean shortly after the Moon's formation 4.5 billion years ago.{{cite journal |doi=10.1038/ngeo417 |title=Timing of crystallization of the lunar magma ocean constrained by the oldest zircon |date=2009 |last1=Nemchin |first1=A. |last2=Timms |first2=N. |last3=Pidgeon |first3=R. |last4=Geisler |first4=T. |last5=Reddy |first5=S. |last6=Meyer |first6=C. |journal=Nature Geoscience |volume=2 |issue=2 |pages=133–136 |bibcode=2009NatGe...2..133N |hdl=20.500.11937/44375 |hdl-access=free}}

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

The Moon is the second-densest satellite in the Solar System, after Io. However, the inner core of the Moon is small, with a radius of about {{convert|350|km}} or less, 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.{{cite journal |last1=Williams |first1=J.G. |last2=Turyshev |first2=S.G. |last3=Boggs |first3=D.H. |last4=Ratcliff |first4=J.T. |title=Lunar laser ranging science: Gravitational physics and lunar interior and geodesy |journal=Advances in Space Research |date=2006 |volume=37 |issue=1 |pages=67–71 |bibcode=2006AdSpR..37...67W |doi=10.1016/j.asr.2005.05.013 |arxiv=gr-qc/0412049 |s2cid=14801321}} The pressure at the lunar core is estimated to be {{cvt|5|GPa|atm}}.{{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}}

File:Youtubeastronautsonmoonot3.gif jumping on the Moon, illustrating that the 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.{{cite magazine |last=Kluger |first=Jeffrey |title=How Neil Armstrong's Moon Spacesuit Was Preserved for Centuries to Come |magazine=Time |date=October 12, 2018 |url=https://time.com/5422609/armstrong-spacesuit-smithsonian/ |access-date=November 29, 2023 |archive-date=December 3, 2023 |archive-url=https://web.archive.org/web/20231203061321/https://time.com/5422609/armstrong-spacesuit-smithsonian/ |url-status=live}}{{cite magazine |title=How Do You Pick Up Something on the Moon? |magazine=WIRED |date=December 9, 2013 |url=https://www.wired.com/2013/12/how-do-you-pick-up-something-on-the-moon/ |access-date=November 29, 2023 |archive-date=December 3, 2023 |archive-url=https://web.archive.org/web/20231203061321/https://www.wired.com/2013/12/how-do-you-pick-up-something-on-the-moon/ |url-status=live}}]]

On average the Moon's surface gravity is {{val|1.62|ul=m/s2}} ({{val|0.1654|u=g}}; {{val|5.318|ul=ft/s2}}), about half of the surface gravity of Mars and about a sixth of Earth's.

The Moon's gravitational field is not uniform. The details of the gravitational field have been measured through tracking the Doppler shift of radio signals emitted by orbiting spacecraft. The main lunar gravity features are 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.{{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}}{{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=April 12, 2013 |doi=10.1126/science.340.6129.138-a |pmid=23580504}} 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.{{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=November 13, 2004 |citeseerx=10.1.1.18.1930}}

The Moon has an external magnetic field of less than 0.2 nanoteslas,{{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}} or less than one hundred thousandth that of Earth. The Moon does not have a global dipolar magnetic field and only has crustal magnetization likely acquired early in its history when a dynamo was still operating.{{cite web |url=http://lunar.arc.nasa.gov/results/magelres.htm |publisher=Lunar Prospector (NASA) |title=Magnetometer / Electron Reflectometer Results |date=2001 |access-date=March 17, 2010 |url-status=dead |archive-url=https://web.archive.org/web/20100527121330/http://lunar.arc.nasa.gov/results/magelres.htm |archive-date=May 27, 2010}} Early in its history, 4 billion years ago, its magnetic field strength was likely close to that of Earth today. This early dynamo field apparently expired by about one billion years ago, after the lunar core had crystallized. Theoretically, some of the remnant magnetization may originate from transient magnetic fields generated during large impacts through the expansion of plasma clouds. These clouds are generated during large impacts in an ambient magnetic field. This is supported by the location of the largest crustal magnetizations situated near the antipodes of the giant impact basins.{{cite journal |last=Hood |first=L.L. |author2=Huang, Z. |title=Formation of magnetic anomalies antipodal to lunar impact basins: Two-dimensional model calculations |journal=Journal of Geophysical Research |volume=96 |issue=B6 |pages=9837–9846 |date=1991 |doi=10.1029/91JB00308 |bibcode=1991JGR....96.9837H}}

{{Main|Atmosphere of the Moon}}

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

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

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

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, Northern Taurid, and Omicron Centaurid meteor showers, when the Earth, and Moon pass through comet debris. The lunar dust cloud is asymmetric, being denser near the boundary between the Moon's dayside and nightside.{{cite web |title=Lopsided Cloud of Dust Discovered Around the Moon |url=http://news.nationalgeographic.com/2015/06/150617-moon-dust-cloud-comet-space |website=National Geographic News |access-date=June 20, 2015 |first1=Nadia |last1=Drake |author1-link=Nadia Drake |url-status=dead |archive-url=https://web.archive.org/web/20150619052915/http://news.nationalgeographic.com/2015/06/150617-moon-dust-cloud-comet-space/ |archive-date=June 19, 2015 |date=June 17, 2015}}{{Cite journal |title=A permanent, asymmetric dust cloud around the Moon |journal=Nature |date=June 18, 2015 |pages=324–326 |volume=522 |issue=7556 |doi=10.1038/nature14479 |first1=M. |last1=Horányi |first2=J.R. |last2=Szalay |first3=S. |last3=Kempf |first4=J. |last4=Schmidt |first5=E. |last5=Grün |first6=R. |last6=Srama |first7=Z. |last7=Sternovsky |bibcode=2015Natur.522..324H |pmid=26085272 |s2cid=4453018}}

File:AS17-145-22224.jpg with lunar dust stuck on his suit. Lunar dust is highly abrasive and can cause damage to human lungs and nervous and cardiovascular systems.{{Cite web |last1=James |first1=John |last2=Kahn-Mayberry |first2=Noreen |date=Jan 2009 |title=Risk of Adverse Health Effects from Lunar Dust Exposure |url=https://humanresearchroadmap.nasa.gov/evidence/reports/lunar%20dust.pdf |access-date=December 8, 2022 |archive-date=December 4, 2021 |archive-url=https://web.archive.org/web/20211204004317/https://humanresearchroadmap.nasa.gov/evidence/reports/lunar%20dust.pdf |url-status=live}}]]

Ionizing radiation from cosmic rays, their resulting neutron radiation,{{cite web|date=September 8, 2005|title=Radioactive Moon|url=https://science.nasa.gov/science-news/science-at-nasa/2005/08sep_radioactivemoon#:~:text=Not%20so.,lunar%20surface%20itself%20is%20radioactive!|url-status=deviated|archive-url=https://web.archive.org/web/20191102123953/https://science.nasa.gov/science-news/science-at-nasa/2005/08sep_radioactivemoon/#:~:text=Not%20so.,lunar%20surface%20itself%20is%20radioactive!|archive-date=November 2, 2019|access-date=July 28, 2022|website=Science Mission Directorate}} and the Sun results in an average radiation level of 1.369 millisieverts per day during lunar daytime, which is about 2.6 times more than the level on the International Space Station, 5{{endash}}10 times more than the level during a trans-Atlantic flight, and 200 times more than the level on Earth's surface.{{cite web |date=September 26, 2020 |title=We Finally Know How Much Radiation There Is on The Moon, And It's Not Great News |url=https://www.sciencealert.com/scientists-predict-how-long-humans-can-survive-radiation-on-the-moon |url-status=live |archive-url=https://web.archive.org/web/20220728004319/https://www.sciencealert.com/scientists-predict-how-long-humans-can-survive-radiation-on-the-moon |archive-date=July 28, 2022 |access-date=July 28, 2022 |website=ScienceAlert}} For further comparison, radiation levels average about 1.84 millisieverts per day on a flight to Mars and about 0.64 millisieverts per day on Mars itself, with some locations on Mars possibly having levels as low as 0.342 millisieverts per day.{{cite arXiv |last1=Paris |first1=Antonio |last2=Davies |first2=Evan |last3=Tognetti |first3=Laurence |last4=Zahniser |first4=Carly |title=Prospective Lava Tubes at Hellas Planitia |date=April 27, 2020 |class=astro-ph.EP |eprint=2004.13156v1}}{{cite web |last=Wall |first=Mike |date=December 9, 2013 |title=Radiation on Mars 'Manageable' for Manned Mission, Curiosity Rover Reveals |url=https://www.space.com/23875-mars-radiation-life-manned-mission.html |access-date=August 7, 2022 |website=Space.com |archive-date=December 15, 2020 |archive-url=https://web.archive.org/web/20201215082045/https://www.space.com/23875-mars-radiation-life-manned-mission.html |url-status=live}}

Solar radiation also electrically charges the highly abrasive lunar dust and makes it levitate. This effect contributes to the easy spread of the sticky, lung- and gear-damaging lunar dust.{{cite web |title=The toxic side of the Moon |website=ESA |url=https://www.esa.int/Science_Exploration/Human_and_Robotic_Exploration/The_toxic_side_of_the_Moon |access-date=2025-01-07}}

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

The lunar surface is exposed to drastic temperature differences ranging from {{val|120|u=°C}} to {{val|−171|u=°C}} depending on the solar irradiance.

Because of the lack of atmosphere, temperatures of different areas vary particularly upon whether they are in sunlight or shadow,{{cite web |last=Rocheleau |first=Jake |date=May 21, 2012 |title=Temperature on the Moon – Surface Temperature of the Moon |url=http://planetfacts.org/temperature-on-the-moon/ |url-status=live |archive-url=https://web.archive.org/web/20150527194737/http://planetfacts.org/temperature-on-the-moon/ |archive-date=May 27, 2015 |website=PlanetFacts.org}} making topographical details play a decisive role on local surface temperatures.

Parts of many craters, particularly the bottoms of many polar craters, are permanently shadowed. These 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}}{{cite web |date=September 17, 2009 |title=Diviner News |url=http://www.diviner.ucla.edu/blog/?p=123 |url-status=dead |archive-url=https://web.archive.org/web/20100307031354/http://www.diviner.ucla.edu/blog/?p=123 |archive-date=March 7, 2010 |access-date=March 17, 2010 |publisher=UCLA}} and just {{Convert |26 |K |4=0 |abbr=on}} close to the winter solstice in the north polar crater Hermite. This is the coldest temperature in the Solar System ever measured by a spacecraft, colder even than the surface of Pluto.

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

These extreme conditions are considered to make it unlikely for spacecraft to harbor bacterial spores at the Moon for longer than just one lunar orbit.{{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}}

{{Main|Selenography|Lunar terrane|List of lunar features|List of quadrangles on the Moon}}

File:Apollo 17 AS17-140-21497.jpg astronaut Harrison H. Schmitt next to the large Moon boulder nicknamed "Tracy's Rock"]]

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

The discovery of fault scarp cliffs suggest that the Moon has shrunk by about 90 metres (300 ft) within the past billion years.{{cite web |publisher=NASA |title=NASA's LRO Reveals 'Incredible Shrinking Moon' |date=August 19, 2010 |url=http://www.nasa.gov/mission_pages/LRO/news/shrinking-moon.html |url-status=live |archive-url=https://web.archive.org/web/20100821124252/http://www.nasa.gov/mission_pages/LRO/news/shrinking-moon.html |archive-date=August 21, 2010}} 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.{{Cite journal |last1=Watters |first1=Thomas R. |last2=Weber |first2=Renee C. |last3=Collins |first3=Geoffrey C. |last4=Howley |first4=Ian J. |last5=Schmerr |first5=Nicholas C. |last6=Johnson |first6=Catherine L. |date=June 2019 |title=Shallow seismic activity and young thrust faults on the Moon |journal=Nature Geoscience |publication-date=May 13, 2019 |volume=12 |issue=6 |pages=411–417 |doi=10.1038/s41561-019-0362-2 |bibcode=2019NatGe..12..411W |s2cid=182137223 |issn=1752-0894}}

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

{{Main |Volcanism on the Moon}}

File:Moon names.svg (blue), and of some craters (brown) of the near side of the Moon]]

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

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

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

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

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

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

Almost all maria are on the near side of the Moon, and cover 31% of the surface of the near side compared with 2% of the far side.{{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}} This is likely due to a 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.{{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=August 11, 1998 |pmid=9727970 |bibcode=1998Sci...281.1484L |doi-access=free}}{{cite journal |url=http://www.psrd.hawaii.edu/Aug00/newMoon.html |title=A New Moon for the Twenty-First Century |page=41 |last=Taylor |first=G. J. |journal=Planetary Science Research Discoveries |date=August 31, 2000 |access-date=April 12, 2007 |url-status=live |archive-url=https://web.archive.org/web/20120301074958/http://www.psrd.hawaii.edu/Aug00/newMoon.html |archive-date=March 1, 2012 |bibcode=2000psrd.reptE..41T}} Most of the Moon's mare basalts erupted during the Imbrian period, 3.3–3.7 billion years ago, though some being as young as 1.2 billion years and as old as 4.2 billion years.

File:Lava flows in Mare Imbrium (AS15-M-1558).png lava flows of Mare Imbrium forming wrinkle ridges]]

In 2006, a study of Ina, a tiny depression in Lacus Felicitatis, found jagged, relatively dust-free features that, because of the lack of erosion by infalling debris, appeared to be only 2 million years old.{{cite journal |url=https://www.science.org/content/article/long-live-moon |title=Long Live the Moon! |journal=Science |date=November 9, 2006 |author=Phil Berardelli |url-status=live |archive-url=https://web.archive.org/web/20141018153016/http://news.sciencemag.org/2006/11/long-live-moon |archive-date=October 18, 2014 |access-date=October 14, 2014}} Moonquakes and releases of gas indicate continued lunar activity. Evidence of recent lunar volcanism has been identified at 70 irregular mare patches, 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.{{cite web |url=http://news.discovery.com/space/imps-reveal-volcanoes-erupted-recently-on-the-moon-141014.htm |title=Volcanoes Erupted 'Recently' on the Moon |publisher=Discovery News |date=October 14, 2014 |author=Jason Major |url-status=live |archive-url=https://web.archive.org/web/20141016190653/http://news.discovery.com/space/imps-reveal-volcanoes-erupted-recently-on-the-moon-141014.htm |archive-date=October 16, 2014}}{{cite web |url=http://www.nasa.gov/press/2014/october/nasa-mission-finds-widespread-evidence-of-young-lunar-volcanism/#.VDxNw0t3uxo |title=NASA Mission Finds Widespread Evidence of Young Lunar Volcanism |publisher=NASA |date=October 12, 2014 |url-status=live |archive-url=https://web.archive.org/web/20150103095208/http://www.nasa.gov/press/2014/october/nasa-mission-finds-widespread-evidence-of-young-lunar-volcanism/#.VDxNw0t3uxo |archive-date=January 3, 2015}}{{cite journal |url=https://www.science.org/content/article/recent-volcanic-eruptions-moon |title=Recent volcanic eruptions on the moon |journal=Science |date=October 12, 2014 |author=Eric Hand |url-status=live |archive-url=https://web.archive.org/web/20141014092239/http://news.sciencemag.org/space/2014/10/recent-volcanic-eruptions-moon |archive-date=October 14, 2014}}{{cite journal |title=Evidence for basaltic volcanism on the Moon within the past 100 million years |journal=Nature Geoscience |last1=Braden |first1=S.E. |last2=Stopar |first2=J.D. |last3=Robinson |first3=M.S. |last4=Lawrence |first4=S.J. |last5=van der Bogert |first5=C.H. |last6=Hiesinger |first6=H. |volume=7 |issue=11 |pages=787–791 |bibcode=2014NatGe...7..787B |doi=10.1038/ngeo2252 |year=2014}} Evidence has been found for 2–10 million years old basaltic volcanism within the crater Lowell,{{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}}{{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}} 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.{{cite journal |last1=Whitten |first1=Jennifer |last2=Head |first2=James W. |last3=Staid |first3=Matthew |last4=Pieters |first4=Carle M. |last5=Mustard |first5=John |last6=Clark |first6=Roger |last7=Nettles |first7=Jeff |last8=Klima |first8=Rachel L. |last9=Taylor |first9=Larry |year=2011 |title=Lunar mare deposits associated with the Orientale impact basin: New insights into mineralogy, history, mode of emplacement, and relation to Orientale Basin evolution from Moon Mineralogy Mapper (M3) data from Chandrayaan-1 |journal=Journal of Geophysical Research |volume=116 |page=E00G09 |doi=10.1029/2010JE003736 |bibcode=2011JGRE..116.0G09W |s2cid=7234547 |doi-access=free}}{{cite journal |last1=Cho |first1=Y. |display-authors=etal |year=2012 |title=Young mare volcanism in the Orientale region contemporary with the Procellarum KREEP Terrane (PKT) volcanism peak period 2 b.y. ago |journal=Geophysical Research Letters |volume=39 |issue=11 |page=L11203 |bibcode=2012GeoRL..3911203C |doi=10.1029/2012GL051838 |s2cid=134074700}}

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 billion years ago and may represent plagioclase cumulates of the lunar magma ocean. In contrast to Earth, no major lunar mountains are believed to have formed as a result of tectonic events.{{cite web |last=Munsell |first=K. |publisher=NASA |work=Solar System Exploration |title=Majestic Mountains |url=http://sse.jpl.nasa.gov/educ/themes/display.cfm?Item=mountains |date=December 4, 2006 |access-date=April 12, 2007 |url-status=dead |archive-url=https://web.archive.org/web/20080917055643/http://sse.jpl.nasa.gov/educ/themes/display.cfm?Item=mountains |archive-date=September 17, 2008}}

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.{{cite journal |author=Richard Lovett |url=http://www.nature.com/news/2011/110803/full/news.2011.456.html#B1 |title=Early Earth may have had two moons : Nature News |journal=Nature |access-date=November 1, 2012 |url-status=live |archive-url=https://web.archive.org/web/20121103145236/http://www.nature.com/news/2011/110803/full/news.2011.456.html#B1 |archive-date=November 3, 2012 |doi=10.1038/news.2011.456 |year=2011 |doi-access=free}}{{cite web |url=http://theconversation.edu.au/was-our-two-faced-moon-in-a-small-collision-2659 |title=Was our two-faced moon in a small collision? |publisher=Theconversation.edu.au |access-date=November 1, 2012 |url-status=dead |archive-url=https://web.archive.org/web/20130130004522/http://theconversation.edu.au/was-our-two-faced-moon-in-a-small-collision-2659 |archive-date=January 30, 2013}} Alternatively, it may be a consequence of asymmetrical tidal heating when the Moon was much closer to the Earth.{{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}}

{{Further |List of craters on the Moon}}

File:Daedalus crater AS11-41-6151.jpg on the Moon's far side]]

A major geologic process that has affected the Moon's surface is impact cratering,{{cite book |last=Melosh |first=H. J. |title=Impact cratering: A geologic process |date=1989 |publisher=Oxford University Press |isbn=978-0-19-504284-9}} 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.{{cite web |title=Moon Facts |url=http://planck.esa.int/science-e/www/object/index.cfm?fobjectid=31412 |work=SMART-1 |publisher=European Space Agency |date=2010 |access-date=May 12, 2010 |archive-date=March 17, 2012 |archive-url=https://web.archive.org/web/20120317004513/http://planck.esa.int/science-e/www/object/index.cfm?fobjectid=31412 |url-status=dead}} Lunar craters exhibit a variety of forms, depending on their size. In order of increasing diameter, the basic types are simple craters with smooth bowl shaped interiors and upturned rims, complex craters with flat floors, terraced walls and central peaks, peak ring basins, and multi-ring basins with two or more concentric rings of peaks.[https://www.lpi.usra.edu/exploration/education/hsResearch/moon_101/ImpactCratering.pdf Impact Cratering Notes (LPI)] The vast majority of impact craters are circular, but some, like Cantor and Janssen, have more polygonal outlines, possibly guided by underlying faults and joints. Others, such as the Messier pair, Schiller, and Daniell, are elongated. Such elongation can result from highly oblique impacts, binary asteroid impacts, fragmentation of impactors before surface strike, or closely spaced secondary impacts.{{cite journal |last1=Herrick |first1=R.R. |last2=Forsberg-Taylor |first2=N. K. |year=2003 |title=The shape and appearance of craters formed by oblique impact on the Moon and Venus |journal=Meteoritics & Planetary Science |volume=38 |issue=11 |pages=1551–1578 |doi=10.1111/j.1945-5100.2003.tb00001.x |bibcode=2003M&PS...38.1551H |url=https://onlinelibrary.wiley.com/doi/pdfdirect/10.1111/j.1945-5100.2003.tb00001.x}}

The lunar geologic timescale is based on the most prominent impact events, such as multi-ring formations like Nectaris, Imbrium, and Orientale that are between hundreds and thousands of kilometers in diameter and associated with a broad apron of ejecta deposits that form a regional stratigraphic horizon. 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.

However care needs to be exercised with the crater counting technique due to the potential presence of secondary craters. Ejecta from impacts can create secondary craters that often appear in clusters or chains but can also occur as isolated formations at a considerable distance from the impact. These can resemble primary craters, and may even dominate small crater populations, so their unidentified presence can distort age estimates.{{cite journal |last1=Xiao |first1=Z. |last2=Strom |first2=R.G. |year=2012 |title=Problems determining relative and absolute ages using the small crater population |journal=Icarus |volume=220 |issue=1 |pages=254–267 |doi=10.1016/j.icarus.2012.05.012 |bibcode=2012Icar..220..254X |url=https://www.uni-muenster.de/imperia/md/content/planetology/lectures/ss2015/143897-hottopics/xiao_and_strom_2012.pdf}}

The radiometric ages of impact-melted rocks collected during the Apollo missions cluster between 3.8 and 4.1 billion years old: this has been used to propose a Late Heavy Bombardment period of increased impacts.{{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}}

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.{{cite web |url=https://www.newscientist.com/article/2108929-the-moon-has-hundreds-more-craters-than-we-thought/ |title=The moon has hundreds more craters than we thought |first=Rebecca |last=Boyle |url-status=live |archive-url=https://web.archive.org/web/20161013143743/https://www.newscientist.com/article/2108929-the-moon-has-hundreds-more-craters-than-we-thought/ |archive-date=October 13, 2016}}{{cite journal |title=Quantifying crater production and regolith overturn on the Moon with temporal imaging |first1=Emerson J. |last1=Speyerer |first2=Reinhold Z. |last2=Povilaitis |first3=Mark S. |last3=Robinson |first4=Peter C. |last4=Thomas |first5=Robert V. |last5=Wagner |date=October 13, 2016 |journal=Nature |volume=538 |issue=7624 |pages=215–218 |doi=10.1038/nature19829 |pmid=27734864 |bibcode=2016Natur.538..215S |s2cid=4443574}} This rate is 100 times faster than the rate computed from models based solely on direct micrometeorite impacts.{{cite web |title=Earth's Moon Hit by Surprising Number of Meteoroids |date=October 13, 2016 |publisher=NASA |url=https://www.nasa.gov/press-release/goddard/2016/lro-lunar-cratering |access-date=May 21, 2021 |archive-date=July 2, 2022 |archive-url=https://web.archive.org/web/20220702225136/https://www.nasa.gov/press-release/goddard/2016/lro-lunar-cratering/ |url-status=live}}

{{Main|Lunar swirls}}

File:Reiner-gamma-clem1.jpg]]

Lunar swirls are enigmatic features found across the Moon's surface. They are characterized by a high albedo, appear optically immature (i.e. the optical characteristics of a relatively young regolith), and often have a sinuous shape. Their shape is often accentuated by low albedo regions that wind between the bright swirls. They are located in places with enhanced surface magnetic fields and many are located at the antipodal point of major impacts. Well known swirls include the Reiner Gamma feature and Mare Ingenii. They are hypothesized to be areas that have been partially shielded from the solar wind, resulting in slower space weathering.{{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}}

{{Main|2 = Lunar water}}

Liquid water cannot persist on the lunar surface. When exposed to solar radiation, water quickly decomposes through a process known as photodissociation and is lost to space. However, since the 1960s, scientists have hypothesized that water ice may be deposited by impacting comets or possibly produced by the reaction of oxygen-rich lunar rocks, and hydrogen from solar wind, leaving traces of water which could possibly persist in cold, permanently shadowed craters at either pole on the Moon.

{{cite journal |first=William R. |last=Ward |title=Past Orientation of the Lunar Spin Axis |journal=Science |date=August 1, 1975 |volume=189 |issue=4200 |pages=377–379 |doi=10.1126/science.189.4200.377 |pmid=17840827 |bibcode=1975Sci...189..377W |s2cid=21185695}} Computer simulations suggest that up to {{Convert |14000 |km2 |abbr=on}} of the surface may be in permanent shadow. The presence of usable quantities of water on the Moon is an important factor in rendering lunar habitation as a cost-effective plan; the alternative of transporting water from Earth would be prohibitively expensive.

In years since, signatures of water have been found to exist on the lunar surface. In 1994, the bistatic radar experiment located on the Clementine spacecraft, indicated the existence of small, frozen pockets of water close to the surface. However, later radar observations by Arecibo, suggest these findings may rather be rocks ejected from young impact craters.{{cite web |last=Spudis |first=P. |title=Ice on the Moon |url=http://www.thespacereview.com/article/740/1 |publisher=The Space Review |date=November 6, 2006 |access-date=April 12, 2007 |url-status=dead |archive-url=https://web.archive.org/web/20070222083000/http://www.thespacereview.com/article/740/1 |archive-date=February 22, 2007}} In 1998, the 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. Volcanic lava beads, brought back to Earth aboard Apollo 15, showed small amounts of water in their interior.

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

The 2008 Chandrayaan-1 spacecraft has since confirmed the existence of surface water ice, using the on-board Moon Mineralogy Mapper. The spectrometer observed absorption lines common to hydroxyl, in reflected sunlight, providing evidence of large quantities of water ice, on the lunar surface. The spacecraft showed that concentrations may possibly be as high as 1,000 ppm. Using the mapper's reflectance spectra, indirect lighting of areas in shadow confirmed water ice within 20° latitude of both poles in 2018.{{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}} In 2009, LCROSS sent a {{Convert|2300 |kg |abbr=on}} impactor into a permanently shadowed polar crater, and detected at least {{Convert |100 |kg |abbr=on}} of water in a plume of ejected material. Another examination of the LCROSS data showed the amount of detected water to be closer to {{Convert |155 |± |12 |kg |abbr=on}}.

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

Analysis of the findings of the Moon Mineralogy Mapper (M3) revealed in August 2018 for the first time "definitive evidence" for water-ice on the lunar surface.{{Cite news |url=https://www.bbc.co.uk/news/science-environment-45251370 |title=Water ice 'detected on Moon's surface' |last=Rincon |first=Paul |date=August 21, 2018 |work=BBC News |access-date=August 21, 2018 |archive-date=August 21, 2018 |archive-url=https://web.archive.org/web/20180821151638/https://www.bbc.co.uk/news/science-environment-45251370 |url-status=live}}{{Cite news |url=https://www.scientificamerican.com/article/beyond-the-shadow-of-a-doubt-water-ice-exists-on-the-moon/ |title=Beyond the Shadow of a Doubt, Water Ice Exists on the Moon |last=David |first=Leonard |work=Scientific American |access-date=August 21, 2018 |archive-date=August 21, 2018 |archive-url=https://web.archive.org/web/20180821125629/https://www.scientificamerican.com/article/beyond-the-shadow-of-a-doubt-water-ice-exists-on-the-moon/ |url-status=live}} The data revealed the distinct reflective signatures of water-ice, as opposed to dust and other reflective substances.{{Cite news |url=https://www.space.com/41554-water-ice-moon-surface-confirmed.html |title=Water Ice Confirmed on the Surface of the Moon for the 1st Time! |work=Space.com |access-date=August 21, 2018 |archive-date=August 21, 2018 |archive-url=https://web.archive.org/web/20180821134450/https://www.space.com/41554-water-ice-moon-surface-confirmed.html |url-status=live}} 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.

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

{{anchor|Orbit and relationship to Earth|Relationship to Earth}}

{{See also|Satellite system (astronomy)|Claimed moons of Earth|Double planet}}

{{Main|Orbit of the Moon|Lunar theory|Lunar orbit|Cislunar space}}

File:Dscovrepicmoontransitfull.gif as the Moon passes on its orbit in between the observing DSCOVR satellite and Earth]]

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

The Moon's orbit is slightly elliptical, with an orbital eccentricity of 0.055.

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

The Moon makes a complete orbit around Earth with respect to the fixed stars, its sidereal period, about once every 27.3 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 days,{{Efn |name=synpd}} to return to the same lunar phase, completing a full cycle, as seen from Earth. This synodic period or synodic month is commonly known as the lunar month and is equal to the length of the solar day on the Moon.{{cite news |url=https://www.universetoday.com/20524/how-long-is-a-day-on-the-moon-1/ |date=July 10, 2017 |author=Matt Williams |title=How Long is a Day on the Moon? |newspaper=Universe Today |access-date=December 5, 2020 |archive-date=November 29, 2020 |archive-url=https://web.archive.org/web/20201129020253/https://www.universetoday.com/20524/how-long-is-a-day-on-the-moon-1/ |url-status=live}}

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

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

File:Moon distance range to scale.svg

{{Main |Tidal force |Tidal acceleration |Tide |Theory of tides}}

File:Tide animation.gifs. The Ocean and Earth are being pulled more where it is closer to the Moon, causing tidal forces to be weaker at the far-side of Earth creating a second bulge and high-tide. The animation shows the change of the Moon's position on its inclined orbit.]]

The gravitational attraction that Earth and the Moon (as well as the Sun) exert on each other manifests in a slightly greater attraction on the sides closest to each other, resulting in tidal forces. Ocean tides are the most widely experienced result of this, but tidal forces also considerably affect other mechanics of Earth, as well as the Moon and their system.

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

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 – significantly longer than terrestrial quakes – because of scattering of the seismic vibrations in the dry fragmented upper crust. The existence of moonquakes was an unexpected discovery from seismometers placed on the Moon by Apollo astronauts from 1969 through 1972.{{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}}

The most commonly known effect of tidal forces is elevated sea levels called ocean tides. 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.

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

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

If the Earth were a water world (one with no continents) it would produce a tide of only one meter, and that tide would be very predictable, but the ocean tides are greatly modified by other effects:

• the frictional coupling of water to Earth's rotation through the ocean floors
• the inertia of water's movement
• ocean basins that grow shallower near land
• the sloshing of water between different ocean basins{{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}}

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 torque in opposition to the Earth's rotation. This "drains" angular momentum and rotational kinetic energy from Earth's rotation, slowing the Earth's rotation. That angular momentum, lost from the Earth, is transferred to the Moon in a process known as tidal acceleration, which lifts the Moon into a higher orbit while lowering orbital speed around the Earth.

Thus the distance between Earth and Moon is increasing, and the Earth's rotation is slowing in reaction. 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).{{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}}{{cite news |url=https://www.bbc.co.uk/news/science-environment-12311119 |title=Why the Moon is getting further away from Earth |newspaper=BBC News |date=February 1, 2011 |access-date=September 18, 2015 |url-status=live |archive-url=https://web.archive.org/web/20150925185706/http://www.bbc.co.uk/news/science-environment-12311119 |archive-date=September 25, 2015}}{{Cite journal |last1=Williams |first1=James G. |last2=Boggs |first2=Dale H. |date=2016 |title=Secular tidal changes in lunar orbit and Earth rotation |url=https://doi.org/10.1007/s10569-016-9702-3 |journal=Celestial Mechanics and Dynamical Astronomy |language=en |volume=126 |issue=1 |pages=89–129 |doi=10.1007/s10569-016-9702-3 |bibcode=2016CeMDA.126...89W |s2cid=124256137 |issn=1572-9478 |access-date=July 30, 2022 |archive-date=July 30, 2022 |archive-url=https://web.archive.org/web/20220730084922/https://link.springer.com/article/10.1007/s10569-016-9702-3 |url-status=live}}

Atomic clocks show that Earth's Day lengthens by about 17 microseconds every year,{{cite web |last=Ray |first=R. |date=May 15, 2001 |url=http://bowie.gsfc.nasa.gov/ggfc/tides/intro.html |title=Ocean Tides and the Earth's Rotation |publisher=IERS Special Bureau for Tides |access-date=March 17, 2010 |url-status=dead |archive-url=https://web.archive.org/web/20100327084125/http://bowie.gsfc.nasa.gov/ggfc/tides/intro.html |archive-date=March 27, 2010}}{{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}}{{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}} slowly increasing the rate at which 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 tidally locking the lighter body of the orbital system, as is already the case with the Moon. Theoretically, in 50 billion years,{{cite web |title=When Will Earth Lock to the Moon? |website=Universe Today |date=April 12, 2016 |url=https://www.universetoday.com/128350/will-earth-lock-moon/ |access-date=January 5, 2022 |archive-date=May 28, 2022 |archive-url=https://web.archive.org/web/20220528015905/https://www.universetoday.com/128350/will-earth-lock-moon/ |url-status=live}} the Earth's rotation will have slowed to the point of matching the Moon's orbital period, causing the Earth to always present the same side to the Moon. However, the Sun will become a red giant, most likely engulfing the Earth–Moon system long before then.{{cite book |last1=Murray |first1=C.D. |last2=Dermott |first2=Stanley F. |title=Solar System Dynamics |date=1999 |publisher=Cambridge University Press |isbn=978-0-521-57295-8 |page=184}}{{cite book |last=Dickinson |first=Terence |author-link=Terence Dickinson |title=From the Big Bang to Planet X |date=1993 |publisher=Camden House |location=Camden East, Ontario |isbn=978-0-921820-71-0 |pages=79–81}}

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

{{anchor|Observation|Appearance from Earth}}

{{See also|Lunar observation}}

File:Lunar libration with phase Oct 2007 HD.gif, the slight variation in the Moon's apparent size and viewing angle over a single lunar month as viewed from somewhere on the Earth's northern hemisphere.]]

The Moon's highest altitude at culmination varies by its lunar phase, or more correctly its orbital position, and time of the year, or more correctly the position of the Earth's axis. The full moon is highest in the sky during winter and lowest during summer (for each hemisphere respectively), with its altitude changing towards dark moon to the opposite.

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

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.{{cite web |last=Howells |first=Kate |date=September 25, 2020 |title=Can the Moon be upside down? |url=https://www.planetary.org/articles/can-the-moon-be-upside-down |url-status=live |archive-url=https://web.archive.org/web/20220102132012/https://www.planetary.org/articles/can-the-moon-be-upside-down |archive-date=January 2, 2022 |access-date=January 2, 2022 |publisher=The Planetary Society}} 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.{{cite web |last=Spekkens |first=K. |author1-link=Kristine Spekkens |date=October 18, 2002 |title=Is the Moon seen as a crescent (and not a "boat") all over the world? |url=http://curious.astro.cornell.edu/our-solar-system/46-our-solar-system/the-moon/observing-the-moon/124-is-the-moon-seen-as-a-crescent-and-not-a-boat-all-over-the-world-is-the-same-phase-of-the-moon-visible-from-the-northern-and-southern-hemispheres-advanced |url-status=live |archive-url=https://web.archive.org/web/20151016011356/http://curious.astro.cornell.edu/our-solar-system/46-our-solar-system/the-moon/observing-the-moon/124-is-the-moon-seen-as-a-crescent-and-not-a-boat-all-over-the-world-is-the-same-phase-of-the-moon-visible-from-the-northern-and-southern-hemispheres-advanced |archive-date=October 16, 2015 |access-date=September 28, 2015 |publisher=Curious About Astronomy}}

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

File:Tidal locking of the Moon with the Earth.gif

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 far side. The far side is often inaccurately called the "dark side", but it is in fact illuminated as often as the near side: once every 29.5 Earth days. During dark moon to new moon, the near side is dark.{{cite web |title=Dark Side of the Moon |author=Phil Plait |publisher=Bad Astronomy: Misconceptions |url=http://www.badastronomy.com/bad/misc/dark_side.html |access-date=February 15, 2010 |url-status=live |archive-url=https://web.archive.org/web/20100412192834/http://www.badastronomy.com/bad/misc/dark_side.html |archive-date=April 12, 2010 |author-link=Phil Plait}}

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

{{See also|Lunar phase|Moonlight|Halo (optical phenomenon)}}

File:Moon phases en.jpg that result, as viewed from the Northern Hemisphere. The Earth–Moon distance is not to scale.]]

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

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

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

There has been historical controversy over whether observed features on the Moon's surface change over time. Today, many of these claims are thought to be illusory, resulting from observation under different lighting conditions, poor astronomical seeing, or inadequate drawings. However, outgassing does occasionally occur and could be responsible for a minor percentage of the reported lunar transient phenomena. Recently, it has been suggested that a roughly {{convert|3|km|abbr=on}} diameter region of the lunar surface was modified by a gas release event about a million years ago.{{cite journal |last=Taylor |first=G. J. |date=November 8, 2006 |title=Recent Gas Escape from the Moon |url=http://www.psrd.hawaii.edu/Nov06/MoonGas.html |url-status=dead |journal=Planetary Science Research Discoveries |page=110 |bibcode=2006psrd.reptE.110T |archive-url=https://web.archive.org/web/20070304055515/http://www.psrd.hawaii.edu/Nov06/MoonGas.html |archive-date=March 4, 2007 |access-date=April 4, 2007}}{{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}}

File:Two Lunar Phases.jpg

The Moon has an exceptionally low albedo, giving it a reflectance that is slightly brighter than that of worn asphalt. Despite this, it is the brightest object in the sky after the Sun.{{efn|name=brightness}} This is due partly to the brightness enhancement of the opposition surge; the Moon at quarter phase is only one-tenth as bright, rather than half as bright, as at full moon. Additionally, color constancy in the visual system recalibrates the relations between the colors of an object and its surroundings, and because the surrounding sky is comparatively dark, the sunlit Moon is perceived as a bright object. The edges of the full moon seem as bright as the center, without limb darkening, because of the reflective properties of lunar soil, which 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.{{cite web |date=November 11, 2020 |title=Colors of the Moon |url=https://science.nasa.gov/colors-moon |url-status=live |archive-url=https://web.archive.org/web/20220409212600/https://science.nasa.gov/colors-moon |archive-date=April 9, 2022 |access-date=April 9, 2022 |website=Science Mission Directorate}}

At times, the Moon can appear red or blue.

It may appear red during a lunar eclipse, because of the red spectrum of the Sun's light being refracted onto the Moon by Earth's atmosphere. Because of this red color, lunar eclipses are also sometimes called blood 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, such as volcanic particles,{{cite web |last=Gibbs |first=Philip |date=May 1997 |title=Why is the sky blue? |url=http://math.ucr.edu/home/baez/physics/General/BlueSky/blue_sky.html |url-status=live |archive-url=https://web.archive.org/web/20151102085211/http://math.ucr.edu/home/baez/physics/General/BlueSky/blue_sky.html |archive-date=November 2, 2015 |access-date=November 4, 2015 |website=math.ucr.edu |quote=... may cause the moon to have a blue tinge since the red light has been scattered out.}} in which case it can be called a blue moon.

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

{{Main |Solar eclipse |Lunar eclipse |Solar eclipses on the Moon|Eclipse cycle}}

{{multiple image

| total_width = 330

| image1 = Solar_eclipse_1999_4_NR.jpg

| image2 = Full Eclipse of the Moon as seen in from Irvine, CA, USA (52075715442) (cropped).jpg

| caption1 = A solar eclipse causes the Sun to be covered, revealing the white corona.

| caption2 = The Moon, tinted reddish, during a lunar eclipse

}}

Eclipses only occur when the Sun, Earth, and Moon are all in a straight line (termed "syzygy"). Solar eclipses occur at new moon, when the Moon is between the Sun and Earth. In contrast, lunar eclipses 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.{{cite web |first=F. |last=Espenak |date=2000 |url=http://www.mreclipse.com/Special/SEprimer.html |title=Solar Eclipses for Beginners |publisher=MrEclip |access-date=March 17, 2010 |archive-date=May 24, 2015 |archive-url=https://web.archive.org/web/20150524172606/http://www.mreclipse.com/Special/SEprimer.html |url-status=dead}} In a total eclipse, the Moon completely covers the disc of the Sun and the solar corona becomes visible to the naked eye.

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

As the Moon's orbit around Earth is inclined by about 5.145° (5° 9') to the 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. The periodicity and recurrence of eclipses of the Sun by the Moon, and of the Moon by Earth, is described by the saros, which has a period of approximately 18 years.{{cite web |url=http://sunearth.gsfc.nasa.gov/eclipse/SEsaros/SEsaros.html |last=Espenak |first=F. |title=Saros Cycle |publisher=NASA |access-date=March 17, 2010 |url-status=dead |archive-url=https://web.archive.org/web/20071030225501/http://sunearth.gsfc.nasa.gov/eclipse/SEsaros/SEsaros.html |archive-date=October 30, 2007}}

Because the Moon continuously blocks the view of a half-degree-wide circular area of the sky,{{Efn |name=area}}{{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}} the related phenomenon of occultation occurs when a bright star or planet passes behind the Moon and is occulted: hidden from view. In this way, a solar eclipse is an occultation of the Sun. Because the Moon is comparatively close to Earth, occultations of individual stars are not visible everywhere on the planet, nor at the same time. Because of the precession of the lunar orbit, each year different stars are occulted.{{cite web |url=http://occsec.wellington.net.nz/total/totoccs.htm |title=Total Lunar Occultations |publisher=Royal Astronomical Society of New Zealand |access-date=March 17, 2010 |url-status=dead |archive-url=https://web.archive.org/web/20100223022627/http://occsec.wellington.net.nz/total/totoccs.htm |archive-date=February 23, 2010}}

{{anchor |Exploration}}

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

It is believed by some that the oldest cave paintings from up to 40,000 BP of bulls and geometric shapes,{{cite web |last=Boyle |first=Rebecca |title=Ancient humans used the moon as a calendar in the sky |website=Science News |date=July 9, 2019 |url=https://www.sciencenews.org/article/moon-time-calendar-ancient-human-art |access-date=May 26, 2024 |archive-date=November 4, 2021 |archive-url=https://web.archive.org/web/20211104145754/https://www.sciencenews.org/article/moon-time-calendar-ancient-human-art |url-status=live}} or 20–30,000 year old tally sticks were used to observe the phases of the Moon, keeping time using the waxing and waning of the Moon's phases.

Aspects of the Moon were identified and aggregated in lunar deities from prehistoric times and were eventually documented and put into symbols from the very first instances of writing in the 4th millennium BC. One of the earliest-discovered possible depictions of the Moon is a 3,000 BCE rock carving Orthostat 47 at Knowth, Ireland.{{cite web |url=https://www.knowth.com/lunar-maps.htm |title=Lunar maps |access-date=September 18, 2019 |archive-date=June 1, 2019 |archive-url=https://web.archive.org/web/20190601184833/https://www.knowth.com/lunar-maps.htm |url-status=live}}{{cite web |url=http://www.spacetoday.org/SolSys/Earth/OldStarCharts.html |title=Carved and Drawn Prehistoric Maps of the Cosmos |publisher=Space Today |date=2006 |access-date=April 12, 2007 |url-status=dead |archive-url=https://web.archive.org/web/20120305162253/http://www.spacetoday.org/SolSys/Earth/OldStarCharts.html |archive-date=March 5, 2012}} The crescent depicting the Moon as with the lunar deity Nanna/Sin have been found from the 3rd millennium BCE.

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

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

The ancient Greek philosopher Anaxagoras ({{died-in|428 BC}}) reasoned that the Sun and Moon were both giant spherical rocks, and that the latter reflected the light of the former.{{cite web |last=O'Connor |first=J.J. |author2=Robertson, E.F. |date=February 1999 |url=http://www-history.mcs.st-andrews.ac.uk/Biographies/Anaxagoras.html |title=Anaxagoras of Clazomenae |publisher=University of St Andrews |access-date=April 12, 2007 |url-status=live |archive-url=https://web.archive.org/web/20120112072236/http://www-history.mcs.st-andrews.ac.uk/Biographies/Anaxagoras.html |archive-date=January 12, 2012}}{{rp|page=227}} Elsewhere in the {{nowrap|5th century BC}} to {{nowrap|4th century BC}}, Babylonian astronomers had recorded the 18-year Saros cycle of lunar eclipses,{{cite journal |doi=10.2307/1006543 |title=Saros Cycle Dates and Related Babylonian Astronomical Texts |first1=A. |last1=Aaboe |first2=J.P. |last2=Britton |first3=J.A. |last3=Henderson |first4=Otto |last4=Neugebauer |author-link4=Otto Neugebauer |first5=A.J. |last5=Sachs |journal=Transactions of the American Philosophical Society |volume=81 |issue=6 |pages=1–75 |date=1991 |quote=One comprises what we have called "Saros Cycle Texts", which give the months of eclipse possibilities arranged in consistent cycles of 223 months (or 18 years). |jstor=1006543}} and Indian astronomers had described the Moon's monthly elongation. The Chinese astronomer Shi Shen {{nowrap|(fl. 4th century BC)}} gave instructions for predicting solar and lunar eclipses.{{rp|page=411}}

In Aristotle's (384–322 BC) description of the universe, the Moon marked the boundary between the spheres of the mutable elements (earth, water, air and fire), and the imperishable stars of aether, an influential philosophy that would dominate for centuries.{{cite book |last=Lewis |first=C.S. |author-link=C. S. Lewis |title=The Discarded Image |url=https://archive.org/details/discardedimagein0000lewi |url-access=registration |date=1964 |publisher=Cambridge University Press |location=Cambridge |isbn=978-0-521-47735-2 |page=[https://archive.org/details/discardedimagein0000lewi/page/108 108] |access-date=November 11, 2019 |archive-date=June 17, 2020 |archive-url=https://web.archive.org/web/20200617181455/https://archive.org/details/discardedimagein0000lewi |url-status=live}} Archimedes (287–212 BC) designed a planetarium that could calculate the motions of the Moon and other objects in the Solar System.{{cite news |url=https://www.nytimes.com/2008/07/31/science/31computer.html?hp |work=The New York Times |title=Discovering How Greeks Computed in 100 B.C. |date=July 31, 2008 |access-date=March 9, 2014 |url-status=live |archive-url=https://web.archive.org/web/20131204053238/http://www.nytimes.com/2008/07/31/science/31computer.html?hp |archive-date=December 4, 2013}} In the {{nowrap |2nd century BC}}, Seleucus of Seleucia correctly thought that tides were due to the attraction of the Moon, and that their height depends on the Moon's position relative to the Sun.{{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}} In the same century, Aristarchus computed the size and distance of the Moon from Earth, obtaining a value of about twenty times the radius of Earth for the distance.

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

File:Galileo's sketches of the moon.png's sketches of the Moon from the ground-breaking Sidereus Nuncius (1610), publishing among other findings the first descriptions of the Moon's topography]]

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

Later in the 17th century, the efforts of Giovanni Battista Riccioli and Francesco Maria Grimaldi led to the system of naming of lunar features in use today. The more exact 1834–1836 {{lang|la |Mappa Selenographica}} of Wilhelm Beer and Johann Heinrich von Mädler, and their associated 1837 book {{lang|de |Der Mond}}, the first 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.{{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}} Lunar craters, first noted by Galileo, were thought to be volcanic until the 1870s proposal of Richard Proctor that they were formed by collisions. This view gained support in 1892 from the experimentation of geologist Grove Karl Gilbert, and from comparative studies from 1920 to the 1940s, leading to the development of lunar stratigraphy, which by the 1950s was becoming a new and growing branch of astrogeology.

{{See also|Space Race|Moon landing}}

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

File:Luna 3 moon.jpg, taken by Luna 3, October 7, 1959. Clearly visible is Mare Moscoviense (top right) and a mare triplet of Mare Crisium, Mare Marginis and Mare Smythii (left center).]]

After the first spaceflight of Sputnik 1 in 1957 during International Geophysical Year the spacecraft of the Soviet Union's Luna program were the first to accomplish a number of goals. Following three unnamed failed missions in 1958,{{cite web |url=http://www.russianspaceweb.com/spacecraft_planetary_lunar.html |first=Anatoly |last=Zak |date=2009 |title=Russia's unmanned missions toward the Moon |access-date=April 20, 2010 |url-status=live |archive-url=https://web.archive.org/web/20100414115710/http://www.russianspaceweb.com/spacecraft_planetary_lunar.html |archive-date=April 14, 2010}} the first human-made object Luna 1 escaped Earth's gravity and passed near the Moon in 1959. Later that year the first human-made object Luna 2 reached the Moon's surface by intentionally impacting. By the end of the year Luna 3 reached as the first human-made object the normally occluded far side of the Moon, taking the first photographs of it.

The first spacecraft to perform a successful lunar soft landing was Luna 9 and the first vehicle to orbit the Moon was Luna 10, both in 1966.

File:NASA-Apollo8-Dec24-Earthrise.jpg, 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 John F. Kennedy's 1961 commitment to a crewed Moon landing before the end of the decade, the United States, under NASA leadership, launched a series of uncrewed probes to develop an understanding of the lunar surface in preparation for human missions: the Jet Propulsion Laboratory's Ranger program, the Lunar Orbiter program and the Surveyor program. The crewed Apollo program was developed in parallel; after a series of uncrewed and crewed tests of the Apollo spacecraft in Earth orbit, and spurred on by a potential Soviet lunar human landing, in 1968 Apollo 8 made the first human mission to lunar orbit (the first Earthlings, two tortoises, had circled the Moon three months earlier on the Soviet Union's Zond 5, followed by turtles on Zond 6).

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

The Apollo missions 11 to 17 (except Apollo 13, which aborted its planned lunar landing) removed {{convert|837.87 |lb |kg |order=flip}} of lunar rock and soil in 2,196 separate samples.{{cite book |last=Orloff |first=Richard W. |title=NASA History Division, Office of Policy and Plans – Apollo by the Numbers: A Statistical Reference |url=https://history.nasa.gov/SP-4029/SP-4029.htm |chapter=Extravehicular Activity |chapter-url=https://history.nasa.gov/SP-4029/Apollo_18-30_Extravehicular_Activity.htm |access-date=August 1, 2013 |series=The NASA History Series |orig-year=First published 2000 |date=September 2004 |publisher=NASA |location=Washington, DC |isbn=978-0-16-050631-4 |lccn=00061677 |id=NASA SP-2000-4029 |ref=Orloff |url-status=live |archive-url=https://web.archive.org/web/20130606114042/http://history.nasa.gov/SP-4029/SP-4029.htm |archive-date=June 6, 2013}}

Scientific instrument packages were installed on the lunar surface during all the Apollo landings. Long-lived instrument stations, including heat flow probes, seismometers, and magnetometers, were installed at the Apollo 12, 14, 15, 16, and 17 landing sites. Direct transmission of data to Earth concluded in late 1977 because of budgetary considerations,{{cite press release |title=NASA news release 77-47 page 242 |date=September 1, 1977 |url=http://www.nasa.gov/centers/johnson/pdf/83129main_1977.pdf |access-date=March 16, 2010 |url-status=live |archive-url=https://web.archive.org/web/20110604114817/http://www.nasa.gov/centers/johnson/pdf/83129main_1977.pdf |archive-date=June 4, 2011}}{{cite news |url=http://www.ast.cam.ac.uk/~ipswich/Miscellaneous/Archived_spaceflight_news.htm |access-date=August 29, 2007 |title=NASA Turns A Deaf Ear To The Moon |date=1977 |publisher=OASI Newsletters Archive |last=Appleton |first=James |author2=Radley, Charles |author3=Deans, John |author4=Harvey, Simon |author5=Burt, Paul |author6=Haxell, Michael |author7=Adams, Roy |author8=Spooner N. |author9=Brieske, Wayne |archive-url=https://web.archive.org/web/20071210143103/http://www.ast.cam.ac.uk/~ipswich/Miscellaneous/Archived_spaceflight_news.htm |archive-date=December 10, 2007 |url-status=dead}} but as the stations' lunar laser ranging corner-cube retroreflector arrays are passive instruments, they are still being used.{{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}}

Apollo 17 in 1972 remains the last crewed mission to the Moon. Explorer 49 in 1973 was the last dedicated U.S. probe to the Moon until the 1990s.

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

{{Main|Moon Treaty}}

Following the last Soviet mission to the Moon of 1976, there was little further lunar exploration for fourteen years. Astronautics had shifted its focus towards the exploration of the inner (e.g. Venera program) and outer (e.g. Pioneer 10, 1972) Solar System planets, but also towards Earth orbit, developing and continuously operating, beside communication satellites, Earth observation satellites (e.g. Landsat program, 1972), space telescopes and particularly space stations (e.g. Salyut program, 1971).

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

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

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

The next years saw a row of first missions to the Moon by a new group of states actively exploring the Moon.

Between 2004 and 2006 the first spacecraft by the European Space Agency (ESA) (SMART-1) reached the Moon, recording the first detailed survey of chemical elements on the lunar surface.{{cite web |url=http://www.esa.int/SPECIALS/SMART-1/SEMSDE1A6BD_0.html |title=SMART-1 factsheet |date=February 26, 2007 |publisher=European Space Agency |access-date=March 29, 2010 |url-status=live |archive-url=https://web.archive.org/web/20100323044139/http://www.esa.int/SPECIALS/SMART-1/SEMSDE1A6BD_0.html |archive-date=March 23, 2010}}

The Chinese Lunar Exploration Program reached the Moon for the first time with the orbiter Chang'e 1 (2007–2009),{{cite web |title=Chang'e 1 |publisher=NASA |date=2019 |url=https://solarsystem.nasa.gov/missions/change-1/in-depth/ |access-date=October 3, 2021 |archive-date=November 22, 2021 |archive-url=https://web.archive.org/web/20211122070043/https://solarsystem.nasa.gov/missions/change-1/in-depth/ |url-status=live}} obtaining a full image map of the Moon.

India reached, orbited and impacted the Moon in 2008 for the first time with its Chandrayaan-1 and Moon Impact Probe, becoming the fifth and sixth state to do so, creating a high-resolution chemical, mineralogical and photo-geological map of the lunar surface, and confirming the presence of water molecules in lunar soil.{{cite web |url=http://www.isro.org/Chandrayaan/htmls/mission_sequence.htm |title=Mission Sequence |date=November 17, 2008 |publisher=Indian Space Research Organisation |access-date=April 13, 2010 |url-status=live |archive-url=https://web.archive.org/web/20100706225136/http://www.isro.org/chandrayaan/htmls/mission_sequence.htm |archive-date=July 6, 2010}}

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

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

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

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

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

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

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

2022 South Korea launched Danuri successfully, its first mission to the Moon, launched from the US.

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

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

Nova-C 2, iSpace Lander and Blue Ghost were all launched to the Moon in 2024.

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

{{See also|List of proposed missions to the Moon}}

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

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

{{See also|Human presence in space}}

File:Moon Soft Landings.svgs on the Moon (2024)]]

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

Uninterrupted presence has been the case through the remains of impactors, landings and lunar orbiters. Some landings and orbiters have maintained a small lunar infrastructure, providing continuous observation and communication at the Moon.

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

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

File:ALSEP_AS17-134-20500.jpg|thumb|right]]

While the Moon has the lowest planetary protection target-categorization, its degradation as a pristine body and scientific place has been discussed.{{cite web |last=Vidaurri |first=Monica |title=Will people go to space—and then colonize it? |website=Quartz |date=October 24, 2019 |url=https://qz.com/1734103/will-people-go-to-space-and-then-colonize-it/ |access-date=November 9, 2021 |archive-date=November 9, 2021 |archive-url=https://web.archive.org/web/20211109040803/https://qz.com/1734103/will-people-go-to-space-and-then-colonize-it/ |url-status=live}} If there is astronomy performed from the Moon, it will need to be free from any physical and radio pollution. While the Moon has no significant atmosphere, traffic and impacts on the Moon causes clouds of dust that can spread far and possibly contaminate the original state of the Moon and its special scientific content.{{cite web |last=David |first=Leonard |title=Cold as (lunar) ice: Protecting the moon's polar regions from contamination |website=Space.com |date=August 21, 2020 |url=https://www.space.com/moon-ice-mining-contamination-concerns.html |access-date=February 3, 2022 |archive-date=February 4, 2022 |archive-url=https://web.archive.org/web/20220204000406/https://www.space.com/moon-ice-mining-contamination-concerns.html |url-status=live}} 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.{{cite web |last=Gorman |first=Alice |title=#SpaceWatchGL Opinion: An ecofeminist approach to the sustainable use of the Moon |website=SpaceWatch.Global |date=July 1, 2022 |url=https://spacewatch.global/2022/07/spacewatchgl-opinion-an-ecofeminist-approach-to-the-sustainable-used-of-the-moon/ |access-date=July 3, 2022 |archive-date=July 4, 2022 |archive-url=https://web.archive.org/web/20220704024322/https://spacewatch.global/2022/07/spacewatchgl-opinion-an-ecofeminist-approach-to-the-sustainable-used-of-the-moon/ |url-status=live}} Note: see Val Plumwood which Alice Gorman cites regarding co-participation.

The so-called "Tardigrade affair" of the 2019 crashed Beresheet lander and its carrying of tardigrades has been discussed as an example for lacking measures and lacking international regulation for planetary protection.

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

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

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

Longterm missions continuing to be active are some orbiters such as the 2009-launched Lunar Reconnaissance Orbiter surveilling the Moon for future missions, as well as some Landers such as the 2013-launched Chang'e 3 with its Lunar Ultraviolet Telescope still operational.{{cite web |url=https://www.space.com/china-change-3-moon-lander-lasts-7-years |author=Andrew Jones |title=China's Chang'e 3 lunar lander still going strong after 7 years on the moon |website=Space.com |date=September 23, 2020 |access-date=November 16, 2020 |archive-date=November 25, 2020 |archive-url=https://web.archive.org/web/20201125043612/https://www.space.com/china-change-3-moon-lander-lasts-7-years |url-status=live}}

Five retroreflectors have been installed on the Moon since the 1970s and since used for accurate measurements of the physical librations through laser ranging to the Moon.

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

{{Further|Extraterrestrial sky#The Moon}}

File:Earth’s geocorona from the Moon.jpg illuminated creating its geocorona, visible in ultraviolet and viewed by the Far Ultraviolet Camera/Spectrograph of Apollo 16 in 1972 from the Moon's surface]]

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

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

{{Main|Lunar habitation}}

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

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.{{cite web |url=https://www.scmp.com/news/china/science/article/2182111/chinese-lunar-landers-cotton-seeds-lead-way-plant-life-germinates |title=Chinese lunar lander's cotton seeds spring to life on far side of the moon |last1=Zheng |first1=William |date=January 15, 2019 |website=South China Morning Post |access-date=November 26, 2020 |archive-date=January 16, 2019 |archive-url=https://web.archive.org/web/20190116174611/https://www.scmp.com/news/china/science/article/2182111/chinese-lunar-landers-cotton-seeds-lead-way-plant-life-germinates |url-status=live}}

{{See also|Space law|Politics of outer space|Space advocacy|Colonization of the Moon}}

Although Luna landers scattered pennants of the Soviet Union on the Moon, and U.S. flags were symbolically planted at their landing sites by the Apollo astronauts, no nation claims ownership of any part of the Moon's surface. Likewise no private ownership of parts of the Moon, or as a whole, is considered credible.

The 1967 Outer Space Treaty defines the Moon and all outer space as the "province of all mankind". It restricts the use of the Moon to peaceful purposes, explicitly banning military installations and weapons of mass destruction. A majority of countries are parties of this treaty.

The 1979 Moon Agreement was created to elaborate, and restrict the exploitation of the Moon's resources by any single nation, leaving it to a yet unspecified international regulatory regime.{{cite web |title=The Space Review: Is outer space a de jure common-pool resource? |website=The Space Review |date=October 25, 2021 |url=https://www.thespacereview.com/article/4270/1 |access-date=April 9, 2022 |archive-date=November 2, 2021 |archive-url=https://web.archive.org/web/20211102004759/https://thespacereview.com/article/4270/1 |url-status=live}} As of January 2020, it has been signed and ratified by 18 nations, none of which have human spaceflight capabilities.

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

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.{{cite web |title=Australia Between the Moon Agreement and the Artemis Accords |website=Australian Institute of International Affairs |date=June 2, 2021 |url=https://www.internationalaffairs.org.au/australianoutlook/australia-between-the-moon-agreement-and-the-artemis-accords/ |access-date=February 1, 2022 |archive-date=February 1, 2022 |archive-url=https://web.archive.org/web/20220201052259/https://www.internationalaffairs.org.au/australianoutlook/australia-between-the-moon-agreement-and-the-artemis-accords/ |url-status=live}} 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.{{cite web |title=The Space Review: The Artemis Accords: repeating the mistakes of the Age of Exploration |website=The Space Review |date=June 29, 2020 |url=https://www.thespacereview.com/article/3975/1 |access-date=February 1, 2022 |archive-date=January 25, 2022 |archive-url=https://web.archive.org/web/20220125075833/https://www.thespacereview.com/article/3975/1 |url-status=live}}{{cite web |title=The Space Treaty Institute – Dedicated to Peace and Sustainability in Outer Space. Our Mission: To give people Hope and Inspiration by helping the nations of Earth to build a Common Future |website=The Space Treaty Institute – Dedicated to Peace and Sustainability in Outer Space. Our Mission |url=http://www.spacetreaty.org/ |access-date=February 1, 2022 |archive-date=February 1, 2022 |archive-url=https://web.archive.org/web/20220201060827/http://www.spacetreaty.org/ |url-status=live}}

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

In 2021, the Declaration of the Rights of the Moon{{cite web |title=Declaration of the Rights of the Moon |date=February 11, 2021 |publisher=Australian Earth Laws Alliance |url=https://www.earthlaws.org.au/moon-declaration/ |access-date=May 10, 2021 |archive-date=April 23, 2021 |archive-url=https://web.archive.org/web/20210423050426/https://www.earthlaws.org.au/moon-declaration/ |url-status=live}} 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.{{Cite journal |last1=Tepper |first1=Eytan |last2=Whitehead |first2=Christopher |date=December 1, 2018 |title=Moon, Inc.: The New Zealand Model of Granting Legal Personality to Natural Resources Applied to Space |url=https://www.liebertpub.com/doi/abs/10.1089/space.2018.0025 |journal=New Space |volume=6 |issue=4 |pages=288–298 |doi=10.1089/space.2018.0025 |bibcode=2018NewSp...6..288T |s2cid=158616075 |issn=2168-0256 |access-date=July 30, 2022 |archive-date=June 28, 2021 |archive-url=https://web.archive.org/web/20210628015902/https://www.liebertpub.com/doi/abs/10.1089/space.2018.0025 |url-status=live}}{{cite web |last=Evans |first=Kate |title=Hear Ye! Hear Ye! A Declaration of the Rights of the Moon |website=Eos |date=July 20, 2021 |url=http://eos.org/features/hear-ye-hear-ye-a-declaration-of-the-rights-of-the-moon |access-date=April 9, 2022 |archive-date=February 6, 2022 |archive-url=https://web.archive.org/web/20220206102833/https://eos.org/features/hear-ye-hear-ye-a-declaration-of-the-rights-of-the-moon |url-status=live}}

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

In particular the establishment of an international or United Nations regulatory regime for lunar human activity has been called for by the Moon Treaty and suggested through an Implementation Agreement, but remains contentious. Current lunar programs are multilateral, with the US-led Artemis program and the China-led International Lunar Research Station. For broader international cooperation and coordination, the International Lunar Exploration Working Group (ILEWG), the Moon Village Association (MVA) and more generally the International Space Exploration Coordination Group (ISECG) has been established.

{{Further|Lunar calendar |Lunisolar calendar |Metonic cycle }}

File:Venus-de-Laussel-detail-corne.jpg (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).{{Cite book |last=Thompson, William Irwin. |url=https://www.worldcat.org/oclc/6890108 |title=The time falling bodies take to light : mythology, sexuality, and the origins of culture |date=1981 |publisher=St. Martin's Press |isbn=0-312-80510-1 |location=New York |pages=105 |oclc=6890108 |access-date=July 30, 2022 |archive-url=https://web.archive.org/web/20211003030402/https://www.worldcat.org/title/time-falling-bodies-take-to-light-mythology-sexuality-and-the-origins-of-culture/oclc/6890108 |archive-date=October 3, 2021 |url-status=live}}{{cite web |last=Boyle |first=Rebecca |date=July 9, 2019 |title=Ancient humans used the moon as a calendar in the sky |url=https://www.sciencenews.org/article/moon-time-calendar-ancient-human-art |url-status=live |archive-url=https://web.archive.org/web/20211104145754/https://www.sciencenews.org/article/moon-time-calendar-ancient-human-art |archive-date=November 4, 2021 |access-date=November 4, 2021 |website=Science News}}]]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.{{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}}{{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}} The counting of the days between the Moon's phases eventually gave rise to generalized time periods of lunar cycles as months, and possibly of its phases as weeks.{{cite book |last=Zerubavel |first=E. |title=The Seven Day Circle: The History and Meaning of the Week |publisher=University of Chicago Press |year=1989 |isbn=978-0-226-98165-9 |url=https://books.google.com/books?id=Cd5ZjRsNj4sC&pg=PA9 |access-date=February 25, 2022 |page=9 |archive-date=July 25, 2022 |archive-url=https://web.archive.org/web/20220725234921/https://books.google.com/books?id=Cd5ZjRsNj4sC&pg=PA9 |url-status=live}}

The words for the month in a range of different languages carry this relation between the period of the month and the Moon etymologically. The English month as well as moon, and its cognates in other Indo-European languages (e.g. the Latin {{lang|la |mensis}} and Ancient Greek {{lang|grc |μείς}} (meis) or {{lang |grc |μήν}} (mēn), meaning "month"){{cite book |author=Smith, William George |title=Dictionary of Greek and Roman Biography and Mythology: Oarses-Zygia |url=https://books.google.com/books?id=PJ0YAAAAIAAJ |access-date=March 29, 2010 |volume=3 |date=1849 |publisher=J. Walton |page=768 |archive-date=November 26, 2020 |archive-url=https://web.archive.org/web/20201126140722/https://books.google.com/books?id=PJ0YAAAAIAAJ |url-status=live}}{{cite book |author=Estienne, Henri |title=Thesaurus graecae linguae |url=https://books.google.com/books?id=0qQ_AAAAcAAJ |access-date=March 29, 2010 |volume=5 |date=1846 |publisher=Didot |page=1001 |archive-date=July 28, 2020 |archive-url=https://web.archive.org/web/20200728014911/https://books.google.com/books?id=0qQ_AAAAcAAJ |url-status=live}}{{L&S |mensis |ref}}{{LSJ |mei/s |μείς |shortref}}. stem from the Proto-Indo-European (PIE) root of moon, *méh₁nōt, derived from the PIE verbal root *meh₁-, "to measure", "indicat[ing] a functional conception of the Moon, i.e. marker of the month" (cf. the English words measure and menstrual).{{cite book |title=The Oxford Introduction to Proto-Indo-European and the Proto-Indo-European World |series=Oxford Linguistics |author1-first=J.P. |author1-last=Mallory |author2-first=D.Q. |author2-last=Adams |date=2006 |pages=98, 128, 317 |publisher=Oxford University Press |isbn=978-0-19-928791-8}}{{OEtymD |measure |}}{{OEtymD |menstrual |}} To give another example from a different language family, the Chinese language uses the same word ({{lang|zh |{{linktext|月}}}}) for moon as for month, which furthermore can be found in the symbols for the word week ({{lang|zh |{{linktext|星期}}}}).

This lunar timekeeping gave rise to the historically dominant, but varied, lunisolar calendars. The 7th-century Islamic calendar is an example of a purely lunar calendar, where months are traditionally determined by the visual sighting of the hilal, or earliest crescent moon, over the horizon.{{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}}

Of particular significance has been the occasion of full moon, highlighted and celebrated in a range of calendars and cultures, an example being the Buddhist Vesak. The full moon around the southern or 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 the Chinese lunisolar Lunar New Year.{{cite web |title=Mid-Autumn Festival Celebration |website=Confucius Institute for Scotland |date=August 30, 2022 |url=https://www.confuciusinstitute.ac.uk/events/mid-autumn-festival-activities-10-september/ |access-date=November 22, 2022 |archive-date=November 22, 2022 |archive-url=https://web.archive.org/web/20221122172612/https://www.confuciusinstitute.ac.uk/events/mid-autumn-festival-activities-10-september/ |url-status=live}}

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

{{Further|Cultural astronomy|Archaeoastronomy|Lunar deity |Selene |Luna (goddess) |Crescent |Man in the Moon }}

{{see also|Nocturne (painting)|Moon magic}}

{{multiple image

| title = Recurring lunar 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 Lamma (protective goddess).{{cite web |title=Cylinder vase |website=Collections Search – Museum of Fine Arts, Boston |date=May 20, 1987 |url=https://collections.mfa.org/objects/6027/cylinder-vase;jsessionid=F2E906D47F69B2A85DB31D259E691783 |access-date=November 11, 2021 |archive-date=November 11, 2021 |archive-url=https://web.archive.org/web/20211111060850/https://collections.mfa.org/objects/6027/cylinder-vase;jsessionid=F2E906D47F69B2A85DB31D259E691783 |url-status=live}}

| caption1 = The crescent of 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, chariot and velificatio as lunar aspect found in different cultures.

| caption2 = Crescent headgear, chariot and velificatio of Luna, 2nd–5th century

| image3 = Goddess O Ixchel.jpg

| alt3 = Rabbits are in a range of cultures identified with the Moon, from China to the Indigenous peoples of the Americas, as with the rabbit (on the left) of the Maya moon goddess (6th–9th century).

| caption3 = A Moon rabbit of the Mayan moon goddess, 6th–9th century

| image4 =

| caption4 =

}}

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

This rich history of humans viewing the Moon has been evidenced starting with depictions from 40,000 BP and in written form from the 4th millennium BCE in the earliest cases of writing. The oldest named astronomer and poet Enheduanna, Akkadian high priestess to the lunar deity Nanna/Sin and pricess, daughter of Sargon the Great ({{circa|2334}} – {{circa|2279}} BCE), tracked the Moon and wrote poems about her divine Moon.

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

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

The particular arrangement of the crescent with a star known as the star and crescent (☪️) goes back to the Bronze Age, representing either the Sun and Moon, or the Moon and the planet Venus, in combination. It came to represent the selene goddess Artemis, and via the patronage of Hecate, which as triple deity under the epithet trimorphos/trivia included aspects of Artemis/Diana, came to be used as a symbol of Byzantium, with Virgin Mary (Queen of Heaven) later taking her place, becoming depicted in Marian veneration on a crescent and adorned with stars. Since then the heraldric use of the star and crescent proliferated, Byzantium's symbolism possibly influencing the development of the Ottoman flag, specifically the combination of the Turkish crescent with a star,"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 and becoming a popular symbol for Islam (as the hilal of the Islamic calendar) and for a range of nations.{{cite encyclopedia |last=Kadoi |first=Yuka |title=Crescent (symbol of Islam) |encyclopedia=Encyclopedia of Islam Online |date=October 1, 2014 |url=https://referenceworks.brillonline.com/entries/encyclopaedia-of-islam-3/crescent-symbol-of-islam-COM_25588?s.num=27&s.start=20}}

The features of the Moon, the contrasting brighter highlands and darker maria, have been seen by different cultures forming abstract shapes. Such shapes are among others the Man in the Moon (e.g. Coyolxāuhqui) or the Moon Rabbit (e.g. the Chinese Tu'er Ye or in Indigenous American mythologies the aspect of the Mayan Moon goddess, from which possibly Awilix is derived, or of Metztli/Tēcciztēcatl).

Occasionally some lunar deities have been also depicted driving a chariot across the sky, such as the Hindu Chandra/Soma, the Greek Artemis, which is associated with Selene, or Luna, Selene's ancient Roman equivalent.

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

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

{{See also|Moon in science fiction|List of appearances of the Moon in fiction}}

{{Multiple images

| align = right

| total_width = 410

| image1 = Van Gogh - Starry Night - Google Art Project.jpg

| image2 = Melies_color_Voyage_dans_la_lune.jpg

| caption1 = The Moon is prominently featured in Vincent van Gogh's 1889 painting The Starry Night.

| caption2 = An iconic image of the Man in the Moon from the first science-fiction film set in space, A Trip to the Moon (1902, Georges Méliès), inspired by a history of literature about going to the Moon.

}}

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

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

In 2021 20 July, the date of the first crewed Moon landing, became the annual International Moon Day.{{cite web |author= United Nations |title=International Moon Day |publisher=United Nations |date=July 20, 2021 |url=https://www.un.org/en/observances/moon-day |access-date=November 8, 2023 |archive-date=June 27, 2023 |archive-url=https://web.archive.org/web/20230627042218/https://www.un.org/en/observances/moon-day |url-status=live}}

{{Main|Lunar effect}}

The lunar effect is a purported unproven correlation between specific stages of the roughly 29.5-day lunar cycle and behavior and physiological changes in living beings on Earth, including humans. The Moon has long been associated with insanity and irrationality; the words lunacy and lunatic are derived from the Latin name for the Moon, Luna. Philosophers Aristotle and Pliny the Elder argued that the full moon induced insanity in susceptible individuals, believing that the brain, which is mostly water, must be affected by the Moon and its power over the tides, but the Moon's gravity is too slight to affect any single person. 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.

• List of natural satellites
• Selenography (geography of the Moon)
• Timekeeping on the Moon

{{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 378 000 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 6 378 km, giving 350 600 km. The minimum value (for a distant new moon) is based on a similar scaling using the maximum Earth–Moon distance of 407 000 km (given in the factsheet) and by calculating the brightness of the earthshine onto such a new moon. The brightness of the earthshine is {{nowrap|[ Earth albedo ×}} {{nowrap|(Earth radius /}} Radius of Moon's orbit)² ] relative to the direct solar illumination that occurs for a full moon. ({{nowrap |Earth albedo {{=}} 0.367}}; {{nowrap |Earth radius {{=}} (polar}} radius × equatorial {{nowrap |radius)^½ {{=}} 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 378 000 km, the angular size is 1896 arcseconds. The same fact sheet gives extreme Earth–Moon distances of 407 000 km and 357 000 km. For the maximum angular size, the minimum distance has to be corrected for Earth's equatorial radius of 6 378 km, giving 350 600 km.

}}

{{Efn|name=pressure explanation

|Lucey et al. (2006) give {{nowrap |10⁷ particles cm⁻³}} by day and {{nowrap |10⁵ particles cm⁻³}} by night. Along with equatorial surface temperatures of 390 K by day and 100 K by night, the ideal gas law yields the pressures given in the infobox (rounded to the nearest order of magnitude): 10⁻⁷ Pa by day and 10⁻¹⁰ Pa by night.

}}

{{Efn |name=near-Earth asteroids

|There are a number of near-Earth asteroids, including 3753 Cruithne, that are co-orbital with Earth: their orbits bring them close to Earth for periods of time but then alter in the long term (Morais et al, 2002). These are quasi-satellites – they are not moons as they do not orbit Earth. For more information, see Other moons of Earth.

}}

{{Efn|name=Moon vs. Charon

|With 27% the diameter and 60% the density of Earth, the Moon has 1.23% of the mass of Earth. The moon Charon is larger relative to its primary Pluto, but Earth and the Moon are different since Pluto is considered a dwarf planet and not a planet, unlike Earth.

}}

{{Efn |name=orbpd

|More accurately, the Moon's mean sidereal period (fixed star to fixed star) is 27.321661 days {{nowrap |(27 d 07 h 43 min 11.5 s)}}, and its mean tropical orbital period (from equinox to equinox) is 27.321582 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 days {{nowrap |(29 d 12 h 44 min 02.9 s)}} (Explanatory Supplement to the Astronomical Ephemeris, 1961, at p.107).

}}

{{Efn |name=brightness

|The Sun's apparent magnitude is −26.7, while the full moon's apparent magnitude is −12.7.

}}

{{Efn|name=area

|On average, the Moon covers an area of {{nowrap |0.21078 square degrees}} on the night sky.

}}

{{Efn |name=size changes

|See graph in Sun#Life phases. At present, the diameter of the Sun is increasing at a rate of about five percent per billion years. This is very similar to the rate at which the apparent angular diameter of the Moon is decreasing as it recedes from Earth.

}}

}}

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{{cite book |last=Lang |first=Kenneth R. |year=2011 |url=https://books.google.com/books?id=S4xDhVCxAQIC&pg=PA184 |title=The Cambridge Guide to the Solar System |archive-url=https://web.archive.org/web/20160101071141/https://books.google.com/books?id=S4xDhVCxAQIC&pg=PA184 |archive-date=January 1, 2016 |edition=2nd |publisher=Cambridge University Press |isbn=978-1139494175}}

{{cite web |last=Williams |first=David R. |title=Moon Fact Sheet |publisher=NASA/National Space Science Data Center |url=http://nssdc.gsfc.nasa.gov/planetary/factsheet/moonfact.html |date=February 2, 2006 |access-date=December 31, 2008 |url-status=live |archive-url=https://web.archive.org/web/20100323165650/http://nssdc.gsfc.nasa.gov/planetary/factsheet/moonfact.html |archive-date=March 23, 2010}}

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{{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}}

{{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}}

{{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}}

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

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

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

}}

{{Refbegin}}

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

{{Refend}}

{{Sister project links |Moon |voy=Moon}}

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

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

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