Moon

Natural satellite orbiting the Earth

This article is about Earth's natural satellite. For moons in general, see Natural satellite. For other uses, see Moon (disambiguation).

Moon ☾File:FullMoon2010.jpg

The near side of the Moon (north at top) as seen from Earth

Designations

Designation

| Earth I

Alternative names

* Luna
* Selene (poetic)
* Cynthia (poetic)

Adjectives|

* Lunar
* Selenian (poetic)
* Cynthian (poetic)
* Moonly (poetic)

Orbital characteristics
Epoch J2000
Perigee| 362600 km
(356400–370400 km)
Apogee| 405400 km
(404000–406700 km)

Semi-major axis

| 384399 km (1.28 ls, 0.00257 AU)[1]
Eccentricity| 0.0549[1]

Orbital period (sidereal)

27.321661 d
(27 d 7 h 43 min 11.5 s[1])

Orbital period (synodic)

29.530589 d
(29 d 12 h 44 min 2.9 s)

Average orbital speed

| 1.022 km/s
Inclination| 5.145° to the ecliptic[2][a]

Longitude of ascending node

Regressing by one revolution in 18.61 years

Argument of perigee

Progressing by one
revolution in 8.85 years

Satellite of| Earth[b][3]
Physical characteristics

Mean radius

| 1737.4 km
(0.2727 of Earth's)[1][4][5]

Equatorial radius

| 1738.1 km
(0.2725 of Earth's)[4]

Polar radius

| 1736.0 km
(0.2731 of Earth's)[4]
Flattening| 0.0012[4]
Circumference| 10921 km (equatorial)

Surface area

| 3.793×107 km2
(0.074 of Earth's)
Volume| 2.1958×1010 km3
(0.02 of Earth's)[4]
Mass| 7.342×1022 kg
(0.0123 of Earth's)[1][4][6]

Mean density

| 3.344 g/cm3[1][4]
0.606 × Earth

Surface gravity

| 1.622 m/s2 (0.1654 g; 5.318 ft/s2)[4]

Moment of inertia factor

| 0.3929±0.0009[7]

Escape velocity

| 2.38 km/s
(8600 km/h; 5300 mph)

Synodic rotation period

29.530589 d
(29 d 12 h 44 min 2.9 s; synodic; solar day) (spin-orbit locked)

Sidereal rotation period

| 27.321661 d (spin-orbit locked)

Equatorial rotation velocity

| 4.627 m/s

Axial tilt

* 1.5424° to ecliptic[8]
* 6.687° to orbit plane[2]
* 24° to Earth's equator [9]

North pole right ascension

* 17h 47m 26s
* 266.86°[10]

North pole declination

| 65.64°[10]
Albedo| 0.136[11]
| Surface temp. | min | mean | max

|
|
|

Equator | 100 K[12] | 250 K | 390 K[12]
85°N |  | 150 K | 230 K[13]
Surface absorbed dose rate| 13.2 μGy/h[14]
Surface equivalent dose rate| 57.0 μSv/h[14]

Apparent magnitude

* −2.5 to −12.9[c]
* −12.74 (mean full moon)[4]

Angular diameter

| 29.3 to 34.1 arcminutes[4][d]
Atmosphere[15]

Surface pressure

* 10−7 Pa (1 picobar) (day)
* 10−10 Pa (1 femtobar)
(night)[e]

Composition by volume|

* He
* Ar
* Ne
* Na
* K
* H
* Rn

The Moon is Earth's only natural satellite. Its diameter is about one-quarter the diameter of the Earth (comparable to the width of Australia).[16] The Moon is the fifth largest satellite in the Solar System. It is larger than any of the known dwarf planets and is the largest (and most massive) satellite relative to its parent planet.[f] The Moon is a planetary-mass object that formed a differentiated rocky body, making it a satellite planet under the geophysical definitions of the term.[17] It lacks any significant atmosphere, hydrosphere, or magnetic field. Its surface gravity is about one-sixth of Earth's (0.1654 g). Jupiter's moon Io is the only satellite in the Solar System known to have a higher surface gravity and density.

Orbiting Earth at an average distance of 384,400 km (238,900 mi), or about 30 times Earth's diameter, its gravitational influence very slowly lengthens Earth's day and is the main driver of Earth's tides. The Moon's orbit around Earth has a sidereal period of 27.3 days. During each synodic period of 29.5 days, the amount of visible surface illuminated by the Sun varies from none up to 100%, resulting in lunar phases that form the basis for the months of a lunar calendar. The Moon is tidally locked to Earth, which means that the length of a full rotation of the Moon on its own axis causes its same side (the near side) to always face Earth, and the somewhat longer lunar day is the same as the synodic period. However, 59% of the total lunar surface can be seen from Earth through shifts in perspective due to libration.

The most widely accepted origin explanation posits that the Moon formed 4.51 billion years ago, not long after Earth, out of the debris from a giant impact between the planet and a hypothesized Mars-sized body called Theia. It then receded to a wider orbit because of tidal interaction with the Earth. The near side of the Moon is marked by dark volcanic maria ("seas"), which fill the spaces between bright ancient crustal highlands and prominent impact craters. Most of the large impact basins and mare surfaces were in place by the end of the Imbrian period, some three billion years ago. The lunar surface is relatively non-reflective, with a reflectance just slightly brighter than that of worn asphalt. However, because it has a large angular diameter, the full moon is the brightest celestial object in the night sky. The Moon's apparent size is nearly the same as that of the Sun, allowing it to cover the Sun almost completely during a total solar eclipse.

Both the Moon's prominence in Earth's sky and its regular cycle of phases have provided cultural references and influences for human societies throughout history. Such influences can be found in language, calendar systems, art, and mythology. The first artificial object to reach the Moon was the Soviet Union's Luna 2 uncrewed spacecraft in 1959; this was followed by the first successful soft landing by Luna 9 in 1966. The only human lunar missions to date have been those of the United States' Apollo program, which landed twelve men on the surface between 1969 and 1972. These and later uncrewed missions returned lunar rocks that have been used to develop a detailed geological understanding of the Moon's origins, internal structure, and subsequent history.

## Contents

* 1 Names and etymology
* 2 Natural history
* 2.1 Lunar geologic timescale
* 2.2 Formation
* 2.3 Natural development
* 3 Physical characteristics
* 3.1 Size and mass
* 3.2 Internal structure
* 3.2.1 Magnetic field
* 3.2.2 Gravitational field
* 3.3 Surface conditions
* 3.3.1 Surface temperature
* 3.3.2 Atmosphere
* 3.3.3 Dust cloud
* 3.4 Surface features
* 3.4.1 Volcanic features
* 3.4.2 Impact craters
* 3.4.3 Lunar swirls
* 3.5 Surface composition
* 3.5.1 Regolith
* 3.5.2 Presence of water
* 4 Earth–Moon system
* 4.1 Orbit
* 4.2 Tidal effects
* 4.2.1 Tides of the Moon
* 4.2.2 Ocean tides
* 4.2.3 Influence on Earth's magnetic field
* 4.2.4 Influence on orbit and rotation
* 5 Position and appearance
* 5.1 Rotation
* 5.2 Libration
* 5.3 Movement across Earth's skies
* 5.3.1 Apparent orientation
* 5.4 Albedo and colour
* 5.4.1 Apparent colour
* 5.4.2 Cultural references
* 5.5 Phases
* 5.6 Apparent size
* 5.6.1 Moon illusion
* 5.7 Illumination and brightness
* 5.8 Eclipses
* 5.9 Transient lunar phenomena
* 6 History of exploration and human presence
* 6.1 Before spaceflight
* 6.1.1 Pre-telescopic observation (until 1609)
* 6.1.2 Telescopic exploration (1609-1959)
* 6.2 First missions to the Moon (1959–1990)
* 6.2.1 First robotic missions (Soviet lunar program 1959-1976)
* 6.2.2 First crewed missions (United States lunar program 1962-1973)
* 6.2.3 Moon Treaty and explorational absence (1976–1990)
* 6.3 Renewed exploration (1990-present)
* 6.4 Future
* 7 Human presence
* 7.1 Human impact
* 7.1.1 Pollution, contamination and sustainability
* 7.1.2 Intended remains
* 7.1.3 Infrastructure
* 7.2 Astronomy from the Moon
* 7.3 Living on the Moon
* 8 Legal status
* 8.1 Coordination
* 9 In culture and life
* 9.1 Calendar
* 9.2 Cultural representation
* 9.2.1 Modern representation
* 9.3 Lunar effect
* 10 See also
* 11 Explanatory notes
* 12 References
* 13 Further reading
* 14 External links
* 14.1 Cartographic resources
* 14.2 Observation tools
* 14.3 General

## Names and etymology[edit | edit source]

See also: Moon § Mythology and art

The usual English proper name for Earth's natural satellite is simply Moon, with a capital M.[18][19] The noun moon is derived from Old English mōna, which (like all its Germanic cognates) stems from Proto-Germanic *mēnōn,[20] which in turn comes from Proto-Indo-European *mēnsis "month"[21] (from earlier *mēnōt, genitive *mēneses) which may be related to the verb "measure" (of time).[22]

Occasionally, the name Luna /ˈluːnə/ is used in scientific writing[23] 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.[24] Cynthia /ˈsɪnθiə/ is another poetic name, though rare, for the Moon personified as a goddess,[25] while Selene /səˈliːniː/ (literally "Moon") is the Greek goddess of the Moon.

The usual English adjective pertaining to the Moon is "lunar", derived from the Latin word for the Moon, lūna. The adjective selenian /səliːniən/,[26] derived from the Greek word for the Moon, σελήνη selēnē, and used to describe the Moon as a world rather than as an object in the sky, is rare,[27] while its cognate selenic was originally a rare synonym[28] but now nearly always refers to the chemical element selenium.[29] The Greek word for the Moon does however provide us with the prefix seleno-, as in selenography, the study of the physical features of the Moon, as well as the element name selenium.[30][31]

The Greek goddess of the wilderness and the hunt, Artemis, equated with the Roman Diana, one of whose symbols was the Moon and who was often regarded as the goddess of the Moon, was also called Cynthia, from her legendary birthplace on Mount Cynthus.[32] These names – Luna, Cynthia and Selene – are reflected in technical terms for lunar orbits such as apolune, pericynthion and selenocentric.

The astronomical symbol for the Moon is a crescent, ☾, for example in M☾ 'lunar mass' (also ML).

## Natural history[edit | edit source]

### Lunar geologic timescale[edit | edit source]

Main article: Lunar geologic timescale

Millions of years before present

File:The geologic map of the Moon at 1-2.5M scale.png

Geologic map of the Moon with general features are coloured in by age, except in the case of mares (in blue), KREEP (red) and other special features. Oldest to youngest: Aitkenian (pink), Nectarian (brown), Imbrian (greens/turquoise), Eratosthenian (light orange) and Copernican (yellow).

### Formation[edit | edit source]

Main articles: Origin of the Moon, Giant-impact hypothesis, and Circumplanetary disk

Isotope dating of lunar samples suggests the Moon formed around 50 million years after the origin of the Solar System.[33][34] Historically, several formation mechanisms have been proposed,[35] but none satisfactorily explains the features of the Earth–Moon system. A fission of the Moon from Earth's crust through centrifugal force[36] would require too great an initial rotation rate of Earth.[37] Gravitational capture of a pre-formed Moon[38] depends on an unfeasibly extended atmosphere of Earth to dissipate the energy of the passing Moon.[37] A co-formation of Earth and the Moon together in the primordial accretion disk does not explain the depletion of metals in the Moon.[37] None of these hypotheses can account for the high angular momentum of the Earth–Moon system.[39]

File:The Earth and the Moon photographed from Mars orbit.jpg

Earth–Moon system from Mars orbit

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 impact blasted material into orbit about the Earth and the material accreted and formed the Moon[40][41] just beyond the Earth's Roche limit of ~2.56 R🜨.[42]

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.[43] However, more recent simulations suggest a larger fraction of the Moon derived from the proto-Earth.[44][45][46][47] 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,[48] although this is debated.[49]

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.[50][51] Similarly, the newly formed Moon would have had its own lunar magma ocean; its depth is estimated from about 500 km (300 miles) to 1,737 km (1,079 miles).[50]

While the giant-impact theory explains many lines of evidence, some questions are still unresolved, most of which involve the Moon's composition.[52][example needed]Above a high resolution threshold for simulations, a study published in 2022 finds that giant impacts can immediately place a satellite with similar mass and iron content to the Moon into orbit far outside Earth's 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.[53]

### Natural development[edit | edit source]

File:Archean.png

Artist's impression of the Moon as it might have appeared in Earth's sky after the Late Heavy Bombardment around 4 billion years ago. At that time the Moon orbited Earth much closer,[54] appearing much larger.

After the Moon's formation the Moon settled in orbit around Earth much closer than today, making both bodies appear much larger in each's sky and causing on both more frequent and stronger eclipses and tidal effects.[54] Since then, due to tidal acceleration, the Moon's orbit around Earth has become significantly larger as well as longer, tidally locking the so-called lunar near side, always facing Earth with this same side.

The post formation cooled lunar surface has been shaped by large and many small impact events, retaining a broadly cratered landscape of all ages, as well as by volcanic activity, producing the prominent lunar mares. Volcanically active until 1.2 billion years ago, 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[55] and some as old as 4.2 billion years.[56] The causes for the eruption of mare basalts, particularly their uneven occurrence on mainly the near-side, like the lunar highlands on the far side, has been an unresolved issue due to differing explanations. One explanation suggests that large meteorites were hitting the Moon in its early history leaving large craters which then were filled with lava. Other explanations suggest processes of lunar volcanism.[57]

## Physical characteristics[edit | edit source]

The Moon

File:LRO WAC Nearside Mosaic.jpg

Near side of the Moon

File:Moon Farside LRO.jpg

Far side of the Moon

File:LRO WAC North Pole Mosaic (PIA14024).jpg

Lunar north pole

File:LRO WAC South Pole Mosaic.jpg

Lunar south pole

File:LROC wac643nm Moon rotation268.gif

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 adjust to its orbit.[58]

### Size and mass[edit | edit source]

Further information: List of natural satellites

File:Moons of solar system v7.jpg

Size comparison of the main moons of the Solar System with Earth to scale. Nineteen moons are large enough to be round, several having subsurface oceans and one, Titan, having a considerable atmosphere.

The Moon is by size and mass the fifth largest natural satellite of the Solar System, categorizeable as one of its planetary-mass moons, making it a satellite planet under the geophysical definitions of the term.[17] It is smaller than Mercury and considerably larger than the largest dwarf planet of the Solar System, Pluto. While the minor-planet moon Charon of the Pluto-Charon system is larger relative to Pluto,[f][59] the Moon is the largest natural satellite of the Solar System relative to their primary planets.[g]

The Moon's diameter is about 3,500 km, more than a quarter of Earth's, with the face of the Moon comparable to the width of Australia.[16] The whole surface area of the Moon is about 38 million square kilometers, slightly less than the area of the Americas (North and South America).

The Moon's mass is 1/81 of Earth's,[60] being the second densest among the planetary moons, and having the second highest surface gravity, after Io, at 0.1654 g and an escape velocity of 2.38 km/s (8600 km/h; 5300 mph).

### Internal structure[edit | edit source]

Main article: Internal structure of the Moon

The Moon is a differentiated body that was initially in hydrostatic equilibrium but has since departed from this condition.[61] 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 240 kilometres (150 mi) and a fluid outer core primarily made of liquid iron with a radius of roughly 300 kilometres (190 mi). Around the core is a partially molten boundary layer with a radius of about 500 kilometres (310 mi).[62][63] 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.[64]

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 crystallised, lower-density plagioclase minerals could form and float into a crust atop.[65] The final liquids to crystallise would have been initially sandwiched between the crust and mantle, with a high abundance of incompatible and heat-producing elements.[1] Consistent with this perspective, geochemical mapping made from orbit suggests a crust of mostly anorthosite.[15] 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.[1] The crust is on average about 50 kilometres (31 mi) thick.[1]

The Moon is the second-densest satellite in the Solar System, after Io.[66] However, the inner core of the Moon is small, with a radius of about 350 kilometres (220 mi) or less,[1] 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.[67] The pressure at the lunar core is estimated to be 5 GPa (49,000 atm).[68]

#### Magnetic field[edit | edit source]

Main article: Magnetic field of the Moon

The Moon has an external magnetic field of generally less than 0.2 nanoteslas,[69] or less than one hundred thousandth that of Earth. The Moon does not currently have a global dipolar magnetic field and only has crustal magnetization likely acquired early in its history when a dynamo was still operating.[70][71] However, early in its history, 4 billion years ago, its magnetic field strength was likely close to that of Earth today.[69] This early dynamo field apparently expired by about one billion years ago, after the lunar core had completely crystallized.[69] 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.[72]

#### Gravitational field[edit | edit source]

Main article: Gravity of the Moon

The Moon's gravitational field is not uniform, but on average, at the Moon's surface, it is 1.622 m/s2 (0.1654 g; 5.318 ft/s2)[4] strong. Therefore, the surface gravity of the Moon is about half of the surface gravity of Mars and about a sixth of Earth's.

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.[73][74] 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.[75]

### Surface conditions[edit | edit source]

The surface of the Moon, having a surface pressure of 10−10 Pa, lacks an atmosphere which can regulate the resulting extreme conditions of the surface. The surface is exposed to drastic temperature differences ranging from 140 °C to −171 °C depending on the solar irradiance. Ionizing radiation from cosmic rays, the Sun and the resulting neutron radiation[76] produce radiation levels on average of 1,369 microsieverts per day, which is about 2-3 times more than on the International Space Station at about 400 km above Earth in orbit,[77] 5-10 times more than during a trans-Atlantic flight,[78] 200 times more than on Earth's surface.[77] For further comparison radiation on a flight to Mars is about 1.84 millisieverts per day and on Mars 0.64 millisieverts per day.[79] These extreme conditions for example are considered making it unlikely for spacecrafts to harbor bacterial spores at the Moon longer than just one lunar orbit.[80]

The surface gravity of the Moon is approximately 1.625 m/s2, about a sixth or 0.166 ɡ of that on Earth's surface[4] and about half on Mars'.

#### Surface temperature[edit | edit source]

File:Earth-Moon.svg

Angles of inclination of the Sun-Earth-Moon system

The Moon's axial tilt with respect to the ecliptic is only 1.5427°,[8][81] much less than the 23.44° of Earth. Because of this small tilt, the Moon's solar illumination varies much less with season than on Earth and it allows for the existence of some peaks of eternal light at the Moon's north pole, at the rim of the crater Peary.

Because of the lack of atmosphere, temperatures of different areas vary particularly upon whether they are in sunlight or shadow,[82] making topographical details play a decisive role on local surface temperatures.[83] Parts of many craters, particularly the bottoms of many polar craters,[84] 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 35 K (−238 °C; −397 °F)[85] and just 26 K (−247 °C; −413 °F) 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.[83]

#### Atmosphere[edit | edit source]

Main article: Atmosphere of the Moon

File:Apollo 17 twilight ray sketch.jpg

The thin lunar atmosphere is visible on the Moon's surface at sunrise and sunset with the Lunar Horizon Glow[86] and lunar twilight rays, like Earth's crepuscular rays. This Apollo 17 sketch depicts the glow and rays[87] among the general zodiacal light[88][89].

The Moon has an atmosphere so tenuous as to be nearly vacuum, with a total mass of less than 10 tonnes (9.8 long tons; 11 short tons).[90] 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.[15][91] 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[92] from the solar wind; and argon-40, radon-222, and polonium-210, outgassed after their creation by radioactive decay within the crust and mantle.[93][94] 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.[93] 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.[95] 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.[93]

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.[96]

#### Dust cloud[edit | edit source]

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 more dense near the boundary between the Moon's dayside and nightside.[97][98]

### Surface features[edit | edit source]

Main articles: Topography of the Moon, List of lunar features, and List of quadrangles on the Moon

File:MoonTopoLOLA.png

Topography of the Moon

The topography of the Moon has been measured with laser altimetry and stereo image analysis.[99] Its most extensive topographic feature is the giant far-side South Pole–Aitken basin, some 2,240 km (1,390 mi) in diameter, the largest crater on the Moon and the second-largest confirmed impact crater in the Solar System.[100][101] At 13 km (8.1 mi) deep, its floor is the lowest point on the surface of the Moon.[100][102] The highest elevations of the Moon's surface are located directly to the northeast, which might have been thickened by the oblique formation impact of the South Pole–Aitken basin.[103] Other large impact basins such as Imbrium, Serenitatis, Crisium, Smythii, and Orientale possess regionally low elevations and elevated rims.[100] The far side of the lunar surface is on average about 1.9 km (1.2 mi) higher than that of the near side.[1]

The discovery of fault scarp cliffs suggest that the Moon has shrunk by about 90 metres (300 ft) within the past billion years.[104] 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 doesn't have tectonic plates, its tectonic activity is slow and cracks develop as it loses heat.[105]

#### Volcanic features[edit | edit source]

Main article: Volcanism on the Moon

File:Oceanus Procellarum (LRO).png

The largest mare, the main dark region of the near side, is Oceanus Procellarum, with smaller mare, such as Imbrium and Serenitatis, that sit within its ring. Left of the centerline is Procellarum proper.

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)[106] are vast solidified pools of ancient basaltic lava. Although similar to terrestrial basalts, lunar basalts have more iron and no minerals altered by water.[107] The majority of these lava deposits erupted or flowed into the depressions associated with impact basins. Several geologic provinces containing shield volcanoes and volcanic domes are found within the near side "maria".[108]

Almost all maria are on the near side of the Moon, and cover 31% of the surface of the near side[60] compared with 2% of the far side.[109] 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.[65][110][111] 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[55] and as old as 4.2 billion years.[56]

File:PIA18822-LunarGrailMission-OceanusProcellarum-Rifts-Overall-20141001.jpg

GRAIL gravity gradients have revealed past rift valleys at the rim of the cooled magma filled Oceanus Procellarum.

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.[112] Moonquakes and releases of gas indicate continued lunar activity.[112] 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.[113][114][115][116] Evidence has been found for 2–10 million years old basaltic volcanism within the crater Lowell,[117][118] 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.[119][120]

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.[56][55] In contrast to Earth, no major lunar mountains are believed to have formed as a result of tectonic events.[121]

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.[122][123] Alternatively, it may be a consequence of asymmetrical tidal heating when the Moon was much closer to the Earth.[124]

#### Impact craters[edit | edit source]

Further information: List of craters on the Moon

File:Moon-craters.jpg

Lunar crater Daedalus on the Moon's far side

A major geologic process that has affected the Moon's surface is impact cratering,[125] with craters formed when asteroids and comets collide with the lunar surface. There are estimated to be roughly 300,000 craters wider than 1 km (0.6 mi) on the Moon's near side.[126] The lunar geologic timescale is based on the most prominent impact events, including Nectaris, Imbrium, and Orientale; structures characterized by multiple rings of uplifted material, between hundreds and thousands of kilometers in diameter and associated with a broad apron of ejecta deposits that form a regional stratigraphic horizon.[127] 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.[127] 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.[128]

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.[129][130] This rate is 100 times faster than the rate computed from models based solely on direct micrometeorite impacts.[131]

#### Lunar swirls[edit | edit source]

Main article: Lunar swirls

File:Reiner Gamma.jpg

Lunar Reconnaissance Orbiter Wide Angle Camera image of the lunar swirl Reiner Gamma

Lunar swirls are enigmatic features found across the Moon's surface. They are characterized by a high albedo, appear optically immature (i.e. the optical characteristics of a relatively young regolith), and often have a sinuous shape. Their shape is often accentuated by low albedo regions that wind between the bright swirls. They are located in places with enhanced surface magnetic 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.[132]

### Surface composition[edit | edit source]

Main article: Geology of the Moon

#### Regolith[edit | edit source]

Further information: Regolith § Moon, Moon rock, and Lunar soil

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.[133] The regolith of older surfaces is generally thicker than for younger surfaces: it varies in thickness from 10–15 m (33–49 ft) in the highlands and 4–5 m (13–16 ft) in the maria.[134] Beneath the finely comminuted regolith layer is the megaregolith, a layer of highly fractured bedrock many kilometers thick.[135]

File:Composition of lunar soil.svg

Relative elemental composition of the lunar soil

Relative molecular composition of the lunar surface[136] Compound | Formula | Composition

|
|

Maria | Highlands
silica | SiO2 | 45.4% | 45.5%
alumina | Al2O3 | 14.9% | 24.0%
lime | CaO | 11.8% | 15.9%
iron(II) oxide | FeO | 14.1% | 5.9%
magnesia | MgO | 9.2% | 7.5%
titanium dioxide | TiO2 | 3.9% | 0.6%
sodium oxide | Na2O | 0.6% | 0.6%
| 99.9% | 100.0%

#### Presence of water[edit | edit source]

Main article: 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.[137][138] Computer simulations suggest that up to 14,000 km2 (5,400 sq mi) of the surface may be in permanent shadow.[84] 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.[139]

In years since, signatures of water have been found to exist on the lunar surface.[140] 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.[141] 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.[142] Volcanic lava beads, brought back to Earth aboard Apollo 15, showed small amounts of water in their interior.[143]

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.[144] Using the mapper's reflectance spectra, indirect lighting of areas in shadow confirmed water ice within 20° latitude of both poles in 2018.[145] In 2009, LCROSS sent a 2,300 kg (5,100 lb) impactor into a permanently shadowed polar crater, and detected at least 100 kg (220 lb) of water in a plume of ejected material.[146][147] Another examination of the LCROSS data showed the amount of detected water to be closer to 155 ± 12 kg (342 ± 26 lb).[148]

In May 2011, 615–1410 ppm water in melt inclusions in lunar sample 74220 was reported,[149] 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.[150][151] The data revealed the distinct reflective signatures of water-ice, as opposed to dust and other reflective substances.[152] 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.[150][152]

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).[153][154][155][156]

## Earth–Moon system[edit | edit source]

See also: Satellite system (astronomy), Other moons of Earth, and Double planet

### Orbit[edit | edit source]

Main articles: Orbit of the Moon and Lunar theory

File:Dscovrepicmoontransitfull.gif

DSCOVR satellite sees the Moon passing in front of Earth

The Earth and the Moon form the Earth-Moon satellite system with a shared center of mass, or barycentre. This barycentre stays located at all times 1,700 km (1,100 mi) (about a quarter of Earth's radius) beneath the Earth's surface, making the Moon seemingly orbit the Earth.

The orbital eccentricity, giving ovalness of the orbit, is 0.055.[1] The Lunar distance, or the semi-major axis of the geocentric lunar orbit, is approximately 400,000 km, which is a quarter of a million miles or 1.28 light-seconds, and a unit of measure in astronomy. This is not to be confused with the instantaneous Earth–Moon distance, or distance to the Moon, the momentanous distance from the center of Earth to the center of the Moon.

The Moon makes a complete orbit around Earth with respect to the fixed stars, its sidereal period, about once every 27.3 days,[h]. However, because the Earth-Moon system moves at the same time in its orbit around the Sun, it takes slightly longer, 29.5 days;[i],[60] to return at 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.[157]

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.[158]

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 years,[159] which affects other aspects of lunar motion. These follow-on effects are mathematically described by Cassini's laws.[160]

File:Moon distance range to scale.svg

Minimum, mean and maximum distances of the Moon from Earth with its angular diameter as seen from Earth's surface, to scale.

### Tidal effects[edit | edit source]

Main articles: Tidal force, Tidal acceleration, Tide, and Theory of tides

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 of closest to each other, resulting in tidal forces. Ocean tides are the most widely experienced result of this, but tidal forces considerably affect also other mechanics of Earth, as well as the Moon and their system.

#### Tides of the Moon[edit | edit source]

The lunar solid crust experiences tides of around 10 cm (4 in) 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.[161] 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).[161]

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.[162]

#### Ocean tides[edit | edit source]

Main article: Tide

The most commonly known effect of tidal forces are elevated sea levels called ocean tides.[163] 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.[163]

The tides are two bulges in the Earth's oceans, one on the side facing the Moon and the other on the side opposite. As the Earth rotates on its axis, one of the ocean bulges (high tide) is held in place "under" the Moon, while another such tide is opposite. As a result, there are two high tides, and two low tides in about 24 hours.[163] 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[164]

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.

#### Influence on Earth's magnetic field[edit | edit source]

According to recent research, scientists suggest that the Moon's influence on the Earth may contribute to maintaining Earth's magnetic field.[165]

#### Influence on orbit and rotation[edit | edit source]

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.[163][161] 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.[161] Measurements from laser reflectors left during the Apollo missions (lunar ranging experiments) have found that the Moon's distance increases by 38 mm (1.5 in) per year (roughly the rate at which human fingernails grow).[166][167][168] Atomic clocks show that Earth's day lengthens by about 17 microseconds every year,[169][170][171] slowly increasing the rate at which UTC is adjusted by leap seconds.

This tidal drag makes the rotation of 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 already the case with the Moon. Eventually, after 50 billion years,[172] also the Earth would be made to always face the Moon with the same side. This would complete the mutual tidal locking of Earth and the Moon, matching the length of Earth's day to the then also significantly increased lunar month and the Moon's day, and suspending the Moon over one meridian (comparable to the Pluto-Charon system). However, the Sun will become a red giant engulfing the Earth-Moon system long before the latter occurs.[173][174]

##  Position and appearance[edit | edit source]

See also: Lunar observation

### Rotation[edit | edit source]

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

Comparison between the Moon on the left, rotating tidally locked (correct), and with the Moon on the right, without rotation (incorrect).

The tidally locked synchronous rotation of the Moon as it orbits the Earth results in it always keeping nearly the same face turned towards the planet. The side of the Moon that faces Earth is called the near side, and the opposite the 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.[175]

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.[176] 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.[177]

### Libration[edit | edit source]

File:Lunar libration with phase Oct 2007 (continuous loop).gif

Libration, the slight variation in the Moon's apparent size and viewing angle over a single lunar month as viewed from Earth's north.

Despite the Moon's tidal locking the effect of libration makes about 59% of the Moon's surface visible from Earth.[158][60]

### Movement across Earth's skies[edit | edit source]

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.

The Moon's highest altitude at culmination varies by its phase and time of year. The full moon is highest in the sky during winter (for each hemisphere). The Moon is above the horizon for two weeks every tropical month (about 27.3 days) at the North and South Poles. Zooplankton in the Arctic use moonlight when the Sun is below the horizon for months on end.[178]

#### Apparent orientation[edit | edit source]

See also: Wet moon

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 is seen upside down compared to the view in the southern hemisphere.[179]

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.[180]

### Albedo and colour[edit | edit source]

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.[60][j] 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.[181] 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.[182]

#### Apparent colour[edit | edit source]

File:Two Lunar Phases.jpg

The changing apparent colour of the Moon, filtered by Earth's atmosphere.

Viewed from Earth the air filters the reflected light, at times giving it a red colour depending on the angle of the Moon in the sky and thickness of the atmosphere, or a blue tinge depending on the particles in the air,[182] as in cases of volcanic particles.[183]

#### Cultural references[edit | edit source]

The terms blood moon and blue moon do not necessarily refer to circumstances of red or blue moonlight, but are rather particular cultural references such as particular full moons of a year.

### Phases[edit | edit source]

Main article: Lunar phase

The Moon is always illuminated the same amount by the Sun, but the illuminated area of the visible sphere (degree of illumination) is given by  ( 1 − cos ⁡ e ) / 2 = sin 2 ⁡ ( e / 2 ) {\displaystyle (1-\cos e)/2=\sin ^{2}(e/2)} , where  e {\displaystyle e} is the elongation (i.e., the angle between Moon, the observer on Earth, and the Sun).

The monthly changes in the angle between the direction of sunlight and view from Earth, and the phases of the Moon that result, as viewed from the Northern Hemisphere. The Earth–Moon distance is not to scale.

The monthly changes in the angle between the direction of sunlight and view from Earth, and the phases of the Moon that result, as viewed from the Northern Hemisphere. The Earth–Moon distance is not to scale.

### Apparent size[edit | edit source]

File:Comparison angular diameter solar system.svg

Comparison of angular diameter of the Moon compared to other celestial objects (to get a true representation of this image view it at a size of 5 cm wide on your monitor and at 5.15 m distance).

The Moon's angular diameter is about 0.52° (on average) in the sky, roughly the same apparent size as the Sun (see § Eclipses).

The distance between the Moon and Earth varies from around 356,400 km (221,500 mi) to 406,700 km (252,700 mi) at perigee (closest) and apogee (farthest), respectively, making the Moon's apparent size fluctuate.

#### Moon illusion[edit | edit source]

The Moon does appear larger when close to the horizon, but this is a purely psychological effect, known as the Moon illusion, first described in the 7th century BC.[184]

### Illumination and brightness[edit | edit source]

See also: Moonlight and Halo (optical phenomenon)

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

File:Day moon (16669185823).jpg

Day moon, the moon is visible during daylight almost every day.[185]

On 14 November 2016, the Moon was at full phase closer to Earth than it had been since 1948. It was 14% closer and larger than its farthest position in apogee.[186] This closest point coincided within an hour of a full moon, and it was 30% more luminous than when at its greatest distance because of its increased apparent diameter, which made it a particularly notable example of a "supermoon".[187][188][189]

At lower levels, the human perception of reduced brightness as a percentage is provided by the following formula:[190][191]

perceived reduction % = 100 × actual reduction % 100 {\displaystyle {\text{perceived reduction}}\%=100\times {\sqrt {{\text{actual reduction}}\% \over 100}}}

When the actual reduction is 1.00 / 1.30, or about 0.770, the perceived reduction is about 0.877, or 1.00 / 1.14. This gives a maximum perceived increase of 14% between apogee and perigee moons of the same phase.[192]

### Eclipses[edit | edit source]

Main articles: Solar eclipse, Lunar eclipse, and Eclipse cycle

File:Full Eclipse of the Moon as seen in from Irvine, CA, USA (52075715442) (cropped).jpg

The Moon, tinted reddish, during a lunar eclipse

File:Solar eclipse 1999 4 NR.jpg

File:STEREO-B solar eclipse.jpg

From Earth, the Moon and the Sun appear the same size, as seen in the 1999 solar eclipse (left), whereas from the STEREO-B spacecraft in an Earth-trailing orbit, the Moon appears much smaller than the Sun (right).[193]

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.[194] 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,[163] 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.[k] 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.[195]

Because 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.[196] 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.[197]

Because the Moon continuously blocks the view of a half-degree-wide circular area of the sky,[l][198] 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.[199]

### Transient lunar phenomena[edit | edit source]

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 3 km (1.9 mi) diameter region of the lunar surface was modified by a gas release event about a million years ago.[200][201]

##  History of exploration and human presence[edit | edit source]

Main articles: Exploration of the Moon, List of spacecraft that orbited the Moon, List of missions to the Moon, and List of lunar probes

See also: Timeline of Solar System exploration

### Before spaceflight[edit | edit source]

Main article: Exploration of the Moon: Before spaceflight

#### Pre-telescopic observation (until 1609)[edit | edit source]

It is believed by some that 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.[202] One of the earliest-discovered possible depictions of the Moon is a 5000-year-old rock carving Orthostat 47 at Knowth, Ireland.[203][204]

The ancient Greek philosopher Anaxagoras (d. 428 BC) reasoned that the Sun and Moon were both giant spherical rocks, and that the latter reflected the light of the former.[205][206]: 227 Elsewhere in the 5th century BC to 4th century BC, Babylonian astronomers had recorded the 18-year Saros cycle of lunar eclipses,[207] and Indian astronomers had described the Moon's monthly elongation.[208] The Chinese astronomer Shi Shen (fl. 4th century BC) gave instructions for predicting solar and lunar eclipses.[206]: 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.[209] Archimedes (287–212 BC) designed a planetarium that could calculate the motions of the Moon and other objects in the Solar System.[210] In the 2nd century BC, Seleucus of Seleucia correctly theorized that tides were due to the attraction of the Moon, and that their height depends on the Moon's position relative to the Sun.[211] 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.

Although the Chinese of the Han Dynasty believed the Moon to be energy equated to qi, their 'radiating influence' theory recognized that the light of the Moon was merely a reflection of the Sun, and Jing Fang (78–37 BC) noted the sphericity of the Moon.[206]: 413–414 Ptolemy (90–168 AD) greatly improved on the numbers of Aristarchus, calculating the values of a mean distance of 59 times Earth's radius and a diameter of 0.292 Earth diameters were close to the correct values of about 60 and 0.273 respectively.[212] In the 2nd century AD, Lucian wrote the novel A True Story, in which the heroes travel to the Moon and meet its inhabitants. In 499 AD, the Indian astronomer Aryabhata mentioned in his Aryabhatiya that reflected sunlight is the cause of the shining of the Moon.[213] The astronomer and physicist Alhazen (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.[214] 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.[206]: 415–416

During the Middle Ages, before the invention of the telescope, the Moon was increasingly recognised as a sphere, though many believed that it was "perfectly smooth".[215]

#### Telescopic exploration (1609-1959)[edit | edit source]

File:Galileo's sketches of the moon.png

Galileo's sketches of the Moon from the ground-breaking Sidereus Nuncius, publishing among other findings the first descriptions of the Moons topography.

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

File:Moon by Johannes hevelius 1645.PNG

Map of the Moon by Johannes Hevelius from his Selenographia (1647), the first map to include the libration zones

Telescopic mapping of the Moon followed: later in the 17th century, the efforts of Giovanni Battista Riccioli and Francesco Maria Grimaldi led to the system of naming of lunar features in use today. The more exact 1834–1836 Mappa Selenographica of Wilhelm Beer and Johann Heinrich Mädler, and their associated 1837 book 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.[216] Lunar craters, first noted by Galileo, were thought to be volcanic until the 1870s proposal of Richard Proctor that they were formed by collisions.[60] This view gained support in 1892 from the experimentation of geologist Grove Karl Gilbert, and from comparative studies from 1920 to the 1940s,[217] leading to the development of lunar stratigraphy, which by the 1950s was becoming a new and growing branch of astrogeology.[60]

### First missions to the Moon (1959–1990)[edit | edit source]

See also: Space Race and 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 spacecrafts into space. The Cold War fueled a closely followed development of the 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.

#### First robotic missions (Soviet lunar program 1959-1976)[edit | edit source]

Main articles: Luna program and Lunokhod programme

File:Luna 3 moon.jpg

First view in history of the far side of the Moon, taken by Luna 3, 7 October 1959

Spacecraft from the Soviet Union's Luna program were the first to accomplish a number of goals: following three unnamed, failed missions in 1958,[218] the first human-made object to escape Earth's gravity and pass near the Moon was Luna 1 in 1959; the first human-made object to impact the lunar surface was Luna 2, and the first photographs of the normally occluded far side of the Moon were made by Luna 3, all in 1959.

File:First Photo from the Surface of the Moon.jpg

The first image from the lunar surface, photographed by Luna 9 in 1966.

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.[60] Rock and soil samples were brought back to Earth by three Luna sample return missions (Luna 16 in 1970, Luna 20 in 1972, and Luna 24 in 1976), which returned 0.3 kg total.[219] Luna 17 deployed on the Moon the first remote controlled rover on an extraterrestrial surface, Lunokhod 1, in 1970.

File:FP2A3576 (23497689198).jpg

A replica of Lunokhod 1, which reached the Moon becoming the first remote controlled rover on an extraterrestrial surface (1970)

#### First crewed missions (United States lunar program 1962-1973)[edit | edit source]

Main articles: Apollo program and Moon landing

During the late 1950s at the height of the Cold War, the United States Army conducted a classified feasibility study that proposed the construction of a staffed military outpost on the Moon called Project Horizon with the potential to conduct a wide range of missions from scientific research to nuclear Earth bombardment. The study included the possibility of conducting a lunar-based nuclear test.[220][221] The Air Force, which at the time was in competition with the Army for a leading role in the space program, developed its own similar plan called Lunex.[222][223][220] However, both these proposals were ultimately passed over as the space program was largely transferred from the military to the civilian agency NASA.[223]

File:NASA-Apollo8-Dec24-Earthrise.jpg

Earthrise, the first colour 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.

Following President John F. Kennedy's 1961 commitment to a manned 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 produced the first close-up pictures; the Lunar Orbiter program produced maps of the entire Moon; the Surveyor program landed its first spacecraft four months after Luna 9. 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 subsequent landing of the first humans on the Moon in 1969 is seen by many as the culmination of the Space Race.[224]

File:As11-40-5886, uncropped.jpg

Neil Armstrong, the first human on the Moon, working at the Lunar Module Eagle, a first lunar base, during Apollo 11 (1969), the first Moon landing

File:Gnome-mime-sound-openclipart.svg

"That's one small step ..."

File:Phrase de Neil Armstrong.oga

* * *

Problems playing this file? See media help.

Neil Armstrong became the first person to walk on the Moon as the commander of the American mission Apollo 11 by first setting foot on the Moon at 02:56 UTC on 21 July 1969.[225] 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.[226][227] The Apollo missions 11 to 17 (except Apollo 13, which aborted its planned lunar landing) removed 380.05 kilograms (837.87 lb) of lunar rock and soil in 2,196 separate samples.[228]

File:Lunar basalt 70017.jpg

One of the first moon rocks (Lunar basalt 70017, Apollo 17, 1972), which were collected during the Apollo missions.

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,[229][230] but as the stations' lunar laser ranging corner-cube retroreflector arrays are passive instruments, they are still being used. Ranging to the stations is routinely performed from Earth-based stations with an accuracy of a few centimeters, and data from this experiment are being used to place constraints on the size of the lunar core.[231]

The American Moon landing and return was enabled by considerable technological advances in the early 1960s, in domains such as ablation chemistry, software engineering, and atmospheric re-entry technology, and by highly competent management of the enormous technical undertaking.[232][233]

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.

#### Moon Treaty and explorational absence (1976–1990)[edit | edit source]

A near lunar quietude followed the 24th and last Luna as well as Soviet mission to the Moon in 1976 until 1990, 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).

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

### Renewed exploration (1990-present)[edit | edit source]

In 1990 Hiten-Hagoromo,[234] 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.[235] 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.[236]

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.[237] The Chinese Lunar Exploration Program began with Chang'e 1 between 2007 and 2009,[238] obtaining a full image map of the Moon. India reached the Moon in 2008 for the first time with its Chandrayaan-1, creating a high-resolution chemical, mineralogical and photo-geological map of the lunar surface, and confirming the presence of water molecules in lunar soil.[239]

File:Chandrayaan1 Spacecraft Discovery Moon Water.jpg

NASA's Moon Mineralogy Mapper equipment on India's Chandrayaan-1 for the first time discovered in 2008 water-rich minerals (light blue), shown in blue around a small crater from which it was ejected.

The U.S. launched the Lunar Reconnaissance Orbiter (LRO) and the LCROSS impactor on 18 June 2009. LCROSS completed its mission by making a planned and widely observed impact in the crater Cabeus on 9 October 2009,[240] 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 (Chinese: 玉兔; literally "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.

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.[241]

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.[242]

With the signing of the U.S.-led Artemis Accords in 2020, the Artemis program aims to return in the astronauts to the Moon in the 2020s.[243] 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.[244][245][246] The U.S. developed plans for returning to the Moon beginning in 2004,[247] which resulted in several programs. The Artemis program has advanced the farthest, and includes plans to send the first woman to the Moon[248] as well as build an international lunar space station called Lunar Gateway.

### Future[edit | edit source]

See also: List of proposed missions to the Moon

Upcoming lunar missions include Artemis 1 and Russia's first lunar mission, Luna-Glob: an uncrewed lander with a set of seismometers, and an orbiter based on its failed Martian Fobos-Grunt mission.[249]

China has announced in 2021 the plan to develop and construct with Russia an International Lunar Research Station towards and into the 2030s. India in 2006 had among others expressed its hope to send people to the Moon by 2020.[250]

## Human presence[edit | edit source]

See also: Human presence in space

File:Moon landing sites.svg

Map of all soft landing sites on the near side of the Moon.

### Human impact[edit | edit source]

See also: List of artificial objects on the Moon, Moon landing, and Space archaeology

#### Pollution, contamination and sustainability[edit | edit source]

See also: Planetary protection § Category V, Space pollution, and Space sustainability

While the Moon has the lowest planetary protection target-categorization, its degradation as a pristine body and scientific place has been discussed[251] and particularly understood regarding keeping the Shielded Zone of the Moon (SZM) on the far side, of value for astronomy from the Moon, free from any radio spectrum pollution, as well as conserving the special and scientifically interesting nature of the Moon, in face of prospecting commercial and national projects to claim and exploit the Moon.[252] 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.[253] 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.[254]

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.[252]

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.[255][256] As such lunar waste management has been raised as an issue which future lunar missions, particularly on the surface, need to tackle.[257][258]

File:ALSEP AS17-134-20500.jpg

Remains of human activity, Apollo 17's Lunar Surface Experiments Package.[259]

#### Intended remains[edit | edit source]

Further information: Space art § Art in space

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.[259]

#### Infrastructure[edit | edit source]

Main articles: Moonbase and List of active Solar System probes § Moon

See also: Space infrastructure, Lunar habitation, Tourism on the Moon, and Lunar resources § Mining

File:Apollo 11 Lunar Laser Ranging Experiment.jpg

A photo of the reflector of the Lunar Laser Ranging Experiment of Apollo 11, still in use.

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.[260] 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 longterm human presence on the Moon, with the Lunar Gateway as the currently most advanced project as part of the Artemis program.

### Astronomy from the Moon[edit | edit source]

Further information: Extraterrestrial sky § The Moon

For many years, the Moon has been recognized as an excellent site for telescopes.[261] It is relatively nearby; astronomical seeing is not a concern; certain craters near the poles are permanently dark and cold, and thus especially useful for infrared telescopes; and radio telescopes on the far side would be shielded from the radio chatter of Earth.[262] 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.[263] A lunar zenith telescope can be made cheaply with an ionic liquid.[264]

In April 1972, the Apollo 16 mission recorded various astronomical photos and spectra in ultraviolet with the Far Ultraviolet Camera/Spectrograph.[265]

The Moon has been also a sight of Earth observation, particularly culturally as in the imagery called Earthrise.

### Living on the Moon[edit | edit source]

Main article: Lunar habitation

The only instances of humans living on the Moon have taken place in an Apollo Lunar Module (for example, during the Apollo 17 mission) for several days at a time.[266] One challenge to astronauts during their stay on the surface is that lunar dust sticks to their suits and is carried into their quarters. Astronauts could taste and smell the dust, calling it the "Apollo aroma".[267] This fine lunar dust can cause health issues.[267]

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.[268]

## Legal status[edit | edit source]

See also: Space law, Politics of outer space, Space advocacy, and 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.[269] Likewise no private ownership of parts of the Moon, or as a whole, is considered credible.[270][271][272]

The 1967 Outer Space Treaty defines the Moon and all outer space as the "province of all mankind".[269] It restricts the use of the Moon to peaceful purposes, explicitly banning military installations and weapons of mass destruction.[273] A majority of countries are parties of this treaty.[274] 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.[275] As of January 2020, it has been signed and ratified by 18 nations,[276] 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 an 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."[277][278]

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.[245] 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, allowing it to be more widely accepted.[244][246]

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[279] and interest groups have argued for making such sites World Heritage Sites[280] and zones of scientific value protected zones, all of which add to the legal availability and territorialization of the Moon.[252]

In 2021 the Declaration of the Rights of the Moon[281] 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.[282][283]

### Coordination[edit | edit source]

In light of future development on the Moon some international and multi-space agency organizations have been created:

* International Lunar Exploration Working Group (ILEWG)
* Moon Village Association (MVA)
* International Space Exploration Coordination Group (ISECG)

## In culture and life[edit | edit source]

File:Venus-de-Laussel-detail-corne.jpg

The Venus of Laussel (c. 25,000 BP) holding a crescent shaped horn, the 13 notches on the horn may symbolize the number of days from menstruation to ovulation, or of menstrual cycles or moons per year.[284][285]

### Calendar[edit | edit source]

Further information: Lunar calendar, Lunisolar calendar, Metonic cycle, Blue moon, Black moon, and Movable feast

Since pre-historic times people have taken note of the Moon's phases, its waxing and waning, 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.[202][286][287] The counting of the days between the Moon's phases gave eventually rise to generalized time periods of the full lunar cycle as months, and possibly of its phases as weeks.[288]

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 mensis and Ancient Greek μείς (meis) or μήν (mēn), meaning "month")[289][290][291][292] 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).[293][294][295] To give another example from a different language family, the Chinese language uses the same word (月) for moon as well as for month, which furthermore can be found in the symbols for the word week (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.[296]

File:Mooncake 3-4, lotus seed paste.jpg

A Mooncake, given to people at the Harvest Moon Festival, the second most important celebration of the Chinese Lunar Calendar, after Chinese New Year.

Of particular significance has been for a range of cultures and calendars the occasion of the Full Moon, to use or celebrate, particularly around the autumnal equinox, the so-called Harvest Moon.

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

### Cultural representation[edit | edit source]

Further information: Lunar deity, Selene, Luna (goddess), Crescent, and Man in the Moon

See also: Nocturne (painting) and Moon magic

Lunar deities

File:Sumerian Cylinder Seal of King Ur-Nammu.jpg

File:Patera di Parabiago - MI - Museo archeologico - Diana - Luna - 25-7-2003 - Foto Giovanni Dall'Orto - 25-7-2003.jpg

File:Goddess O Ixchel.jpg

From top: examples of lunar deities featuring around the world recurring aspects, like the crescent (Nanna/Sîn, c. 2100 BC), crescent headgear and chariot (Luna, 2nd–5th century), as well as the Moon rabbit (Mayan moon goddess, 6th–9th century).[297]

Since prehistoric and ancient times humans have depicted and interpreted the Moon, particularly for astrology and religion, as lunar deity.

File:Moon symbol (planetary color).svg

For the representation of the Moon, especially its lunar phases, the crescent symbol (🌙) has been particularly used by many cultures. In writing systems such as Chinese the crescent has developed into the symbol 月, the word for Moon, and in ancient Egyptian it was the symbol 𓇹, which is spelled like the ancient Egyptian lunar deity Iah, meaning Moon.[298]

Iconographically the crescent was used in Mesopotamia as the primary symbol of Nanna/Sîn,[299] the ancient Sumerian lunar deity,[300][299] who was the father of Innana/Ishtar, the goddess of the planet Venus (symbolized as the eight pointed Star of Ishtar),[300][299] and Utu/Shamash, the god of the Sun (symbolized as a disc, optionally with eight rays),[300][299] all three often depicted next to each other. Nanna was later known as Sîn,[299][300] and was particularly associated with magic and sorcery.[300]

The crescent was further used as an element of lunar deities wearing headgears or crowns in an arrangement reminiscent of horns, as in the case of the ancient Greek Selene[301][302] or the ancient Egyptian Khonsu. Selene is associated with Artemis and paralleled by the Roman Luna, which both are occasionally depicted driving a chariot, like the Hindu lunar deity Chandra. The different or sharing aspects of deities within pantheons has been observed in many cultures, especially by later or contemporary culture, particularly forming triple deities. The Moon in Roman mythology for example has been associated with Juno and Diana, while Luna being identified as their byname and as part of a triplet (diva triformis) with Diana and Proserpina, Hecate being identified as their binding manifestation as trimorphos.

The star and crescent (☪️) arrangement goes back to the Bronze Age, representing either the Sun and Moon, or the Moon and planet Venus, in combination. It came to represent the goddess Artemis or Hecate, and via the patronage of Hecate came to be used as a symbol of Byzantium, possibly influencing the development of the Ottoman flag, specifically the combination of the Turkish crescent with a star.[303] Since then the heraldric use of the star and crescent proliferated becoming a popular symbol for Islam (as the hilal of the Islamic calendar) and for a range of nations.[304]

In Roman Catholic Marian veneration, the Virgin Mary (Queen of Heaven) has been depicted since the late middle ages on a crescent and adorned with stars. In Islam Muhammad is particularly attributed with the Moon through the so-called splitting of the Moon (Arabic: انشقاق القمر) miracle.[305]

The contrast between the brighter highlands and the darker maria have been seen by different cultures forming abstract shapes, which are among others the Man in the Moon or the Moon Rabbit (e.g. the Chinese Tu'er Ye or in Indigenous American mythologies, as with the aspect of the Mayan Moon goddess).[297]

In Western alchemy silver is associated with the Moon, and gold with the Sun.[306]

#### Modern representation[edit | edit source]

See also: Moon in science fiction and List of appearances of the Moon in fiction

The perception of the Moon in modern times has been informed by telescope enabled modern astronomy and later by spaceflight 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[307] and speculative fiction such as science-fiction dealing with the Moon.[308][309]

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,[252] as in the 1970 poem "Whitey on the Moon". In this light the Moon's nature has been invoked,[281] particularly for lunar conservation[256] and as a common.[310][275][283]

A song titled "Moon Anthem" by Abhay Kumar, paralleling the proposals for an Earth Anthem, was released 2019 on the occasion of India's lunar probe Chandrayaan-2.[311][312]

File:Van Gogh - Starry Night - Google Art Project.jpg

File:Melies color Voyage dans la lune.jpg

The Moon is prominently featured in Vincent van Gogh's 1889 painting, The Starry Night (left). An iconic image of the Man in the Moon from the first science-fiction film set in space, A Trip to the Moon (1902), inspired by a history of literature about going to the Moon (right).

### Lunar effect[edit | edit source]

Main article: 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.[313] 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.[313][314][315][316][317]

## See also[edit | edit source]

* List of natural satellites

## Explanatory notes[edit | edit source]

1. ^ Between 18.29° and 28.58° to Earth's equator.[1]
2. ^ 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.
3. ^ 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 [ Earth albedo × (Earth radius / Radius of Moon's orbit)2 ] relative to the direct solar illumination that occurs for a full moon. (Earth albedo = 0.367; Earth radius = (polar radius × equatorial radius)½ = 6 367 km.)
4. ^ 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.
5. ^ Lucey et al. (2006) give 107 particles cm−3 by day and 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.
6. ^ a b 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.
7. ^ 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.
8. ^ More accurately, the Moon's mean sidereal period (fixed star to fixed star) is 27.321661 days (27 d 07 h 43 min 11.5 s), and its mean tropical orbital period (from equinox to equinox) is 27.321582 days (27 d 07 h 43 min 04.7 s) (Explanatory Supplement to the Astronomical Ephemeris, 1961, at p.107).
9. ^ More accurately, the Moon's mean synodic period (between mean solar conjunctions) is 29.530589 days (29 d 12 h 44 min 02.9 s) (Explanatory Supplement to the Astronomical Ephemeris, 1961, at p.107).
10. ^ The Sun's apparent magnitude is −26.7, while the full moon's apparent magnitude is −12.7.
11. ^ 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.
12. ^ On average, the Moon covers an area of 0.21078 square degrees on the night sky.

## References[edit | edit source]

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## Further reading[edit | edit source]

* Angier, Natalie (7 September 2014). "The Moon Comes Around Again". The New York Times. Archived from the original on 8 September 2014. Retrieved 8 September 2014.
* "The Moon". Discovery 2008. BBC World Service. Archived from the original on 2011-03-11. Retrieved 2021-05-09.
* Bussey, B.; Spudis, P.D. (2004). The Clementine Atlas of the Moon. Cambridge University Press. ISBN 978-0-521-81528-4.
* Cain, Fraser. "Where does the Moon Come From?". Universe Today. Archived from the original on 2021-05-10. Retrieved 2021-05-09. (podcast and transcript)
* Jolliff, B. (2006). Wieczorek, M.; Shearer, C.; Neal, C. (eds.). New views of the Moon. Reviews in Mineralogy and Geochemistry. Vol. 60\. Chantilly, Virginia: Mineralogy Society of America. p. 721\. Bibcode:2006RvMG...60D...5J. doi:10.2138/rmg.2006.60.0. ISBN 978-0-939950-72-0. Archived from the original on 27 June 2007. Retrieved 12 April 2007.
* Jones, E. M. (2006). "Apollo Lunar Surface Journal". NASA. Archived from the original on 2021-05-08. Retrieved 2021-05-09.
* "Exploring the Moon". Lunar and Planetary Institute. Archived from the original on 2021-05-10. Retrieved 2021-05-09.
* Mackenzie, Dana (2003). The Big Splat, or How Our Moon Came to Be. Hoboken, NJ: John Wiley & Sons. ISBN 978-0-471-15057-2. Archived from the original on 17 June 2020. Retrieved 11 June 2019.
* Moore, P. (2001). On the Moon. Tucson, Arizona: Sterling Publishing Co. ISBN 978-0-304-35469-6.
* "Moon Articles". Planetary Science Research Discoveries. Hawai'i Institute of Geophysics and Planetology. Archived from the original on 17 November 2015. Retrieved 18 November 2006.
* Spudis, P.D. (1996). The Once and Future Moon. Smithsonian Institution Press. ISBN 978-1-56098-634-8. Archived from the original on 17 June 2020. Retrieved 11 June 2019.
* Taylor, S.R. (1992). Solar system evolution. Cambridge University Press. p. 307. ISBN 978-0-521-37212-1.
* Teague, K. (2006). "The Project Apollo Archive". Archived from the original on 4 April 2007. Retrieved 12 April 2007.
* Wilhelms, D.E. (1987). "Geologic History of the Moon". U.S. Geological Survey Professional Paper. Professional Paper. 1348. doi:10.3133/pp1348. Archived from the original on 23 February 2019. Retrieved 12 April 2007.
* Wilhelms, D.E. (1993). To a Rocky Moon: A Geologist's History of Lunar Exploration. Tucson: University of Arizona Press. ISBN 978-0-8165-1065-8. Archived from the original on 17 June 2020. Retrieved 10 March 2009.

## External links[edit | edit source]

Justapedia supports:

* Definitions from Wiktionary
* File:Commons-logo.svgMedia from Commons
* File:Wikiquote-logo.svgQuotations from Wikiquote
* File:Wikivoyage-Logo-v3-icon.svgTravel information from Wikivoyage

* NASA images and videos about the Moon
* Albums of images and high-resolution overflight videos by Seán Doran, based on LROC data, on Flickr and YouTube
* Video (04:56) – The Moon in 4K (NASA, April 2018) on YouTube
* Video (04:47) – The Moon in 3D (NASA, July 2018) on YouTube

### Cartographic resources[edit | edit source]

* Unified Geologic Map of the Moon – United States Geological Survey
* Moon Trek – An integrated map browser of datasets and maps for the Moon
* The Moon on Google Maps, a 3-D rendition of the Moon akin to Google Earth
* "Consolidated Lunar Atlas". Lunar and Planetary Institute. Retrieved 26 February 2012.
* Gazetteer of Planetary Nomenclature (USGS) List of feature names.
* "Clementine Lunar Image Browser". U.S. Navy. 15 October 2003. Archived from the original on 7 April 2007. Retrieved 12 April 2007.
* 3D zoomable globes:
* "Google Moon". 2007. Retrieved 12 April 2007.
* "Moon". World Wind Central. NASA. 2007. Retrieved 12 April 2007.
* Aeschliman, R. "Lunar Maps". Planetary Cartography and Graphics. Archived from the original on 29 May 2015. Retrieved 12 April 2007. Maps and panoramas at Apollo landing sites
* Japan Aerospace Exploration Agency (JAXA) Kaguya (Selene) images
* Lunar Earthside chart (4497 x 3150px)
* Large image of the Moon's north pole area Archived 23 August 2016 at the Wayback Machine
* Large image of Moon's south pole area (1000x1000px)[permanent dead link]

### Observation tools[edit | edit source]

* "NASA's SKYCAL – Sky Events Calendar". NASA. Archived from the original on 20 August 2007. Retrieved 27 August 2007.
* "Find moonrise, moonset and moonphase for a location". 2008. Retrieved 18 February 2008.
* "HMNAO's Moon Watch". 2005. Archived from the original on 4 February 2009. Retrieved 24 May 2009. See when the next new crescent moon is visible for any location.

### General[edit | edit source]

* Lunar shelter (building a lunar base with 3D printing)

* v
* t
* e

The Moon

Outline

Physical
properties|

* Internal structure
* Topography
* Atmosphere
* Gravity field
* Hill sphere
* Magnetic field
* Sodium tail
* Moonlight
* Earthshine

A full moon

Orbit|

* Lunar distance
* Orbital elements
* Distance
* Perigee and apogee
* Libration
* Nodes
* Nodal period
* Precession
* Syzygy
* New moon
* Full moon
* Eclipses
* Lunar eclipse
* Total penumbral lunar eclipse
* Tetrad
* Solar eclipse
* Solar eclipses on the Moon
* Eclipse cycle
* Supermoon
* Tide
* Tidal force
* Tidal locking
* Tidal acceleration
* Tidal range
* Lunar station

Surface and
features|

* Selenography
* Terminator
* Hemispheres
* Near side
* Far side
* Poles
* North pole
* South pole
* Face
* Maria
* List
* Mountains
* Peak of eternal light
* Valleys
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* Domes
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* Lava tubes
* Craters
* List
* Ray systems
* Permanently shadowed craters
* South Pole–Aitken basin
* Soil
* swirls
* Rilles
* Wrinkle ridges
* Rocks
* Lunar basalt 70017
* Changesite–(Y)
* Water
* Space weathering
* Micrometeorite
* Sputtering
* Quakes
* Transient lunar phenomenon
* Selenographic coordinate system

Science|

* Observation
* Libration
* Lunar theory
* Origin
* Giant-impact hypothesis
* Theia
* Lunar magma ocean
* Geology
* Timescale
* Late Heavy Bombardment
* Lunar meteorites
* KREEP
* Experiments
* Lunar laser ranging
* ALSEP
* Lunar sample displays
* Apollo 11
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* Lunar seismology

Exploration|

* Missions
* Apollo program
* Explorers
* Probes
* Landing
* Colonization
* Moonbase
* Tourism
* Lunar resources

Time-telling
and navigation|

* Lunar calendar
* Lunisolar calendar
* Month
* Lunar month
* Nodal period
* Fortnight
* Sennight
* Lunar station
* Lunar distance

Phases and
names|

* New
* Full
* Names
* Crescent
* Super and micro
* Blood
* Blue
* Black
* Dark
* Wet
* Tetrad

Daily phenomena|

* Moonrise
* Meridian passage
* Moonset

Related|

* Lunar deities
* Lunar effect
* Moon illusion
* Pareidolia
* Man in the Moon
* Moon rabbit
* Craters named after people
* Artificial objects on the Moon
* Memorials on the Moon
* Moon in science fiction
* list
* Apollo era
* futuristic exploration
* Moon landing conspiracy theories
* Moon Treaty
* "Moon is made of green cheese"
* Natural satellite
* Double planet
* Lilith (hypothetical second moon)
* Splitting of the Moon

* Category Category
* Commons
* Project WikiProject

* v
* t
* e

Earth

Continents|

* Africa
* Antarctica
* Asia
* Australia
* Europe
* North America
* South America

File:The Blue Marble (remastered).jpg

Oceans|

* Arctic Ocean
* Atlantic Ocean
* Indian Ocean
* Pacific Ocean
* Southern Ocean
* Oceanography

Geology|

* Age of Earth
* Geology
* Earth science
* Erosion
* Extremes on Earth
* Future
* Geological history
* time scale
* Geologic record
* Geophysics
* Gravity
* History of Earth
* Magnetic field
* Plate tectonics
* Structure

Atmosphere|

* Atmosphere of Earth
* Prebiotic atmosphere
* Troposphere
* Stratosphere
* Mesosphere
* Thermosphere
* Exosphere
* Weather

Climate|

* Climate system
* Energy balance
* Climate change
* Climate variability and change
* Climatology
* Paleoclimatology

Environment|

* Biome
* Biosphere
* Biogeochemical cycles
* Ecology
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* Human impact on the environment
* Evolutionary history of life
* Nature

Cartography|

* Digital mapping
* Satellite imagery
* Virtual globe
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Culture and society|

* List of sovereign states
* dependent territories
* In culture
* Earth Day
* Flag
* Symbol
* World economy
* Etymology
* World history
* Time zones
* World

Planetary science|

* Earth's orbit
* Evolution of the Solar System
* Geology of solar terrestrial planets
* Location in the Universe
* The Moon
* Solar System

* Category Category
* Commons
* Outline
* '
* '
* '
* '

* v
* t
* e

Natural satellites of the Solar System

Planetary
satellites of|

* Earth
* Mars
* Jupiter
* Saturn
* Uranus
* Neptune

File:Jupiter family.jpg
File:PIA19856-PlutoCharon-NewHorizons-Color-20150714.jpg
File:243 ida crop.jpg

Dwarf planet
satellites of|

* Orcus
* Pluto
* Haumea
* Quaoar
* Makemake
* Gonggong
* Eris

Minor-planet
moons|

* Near-Earth:
* Florence
* Didymos (Dimorphos)
* Moshup (Squannit)
* 1994 CC
* 2001 SN263

* Main belt:
* Kalliope (Linus)
* Euphrosyne
* Daphne (Peneius)
* Eugenia (Petit-Prince)
* Sylvia (Romulus * Remus)
* Minerva (Aegis * Gorgoneion)
* Camilla
* Elektra
* Kleopatra (Alexhelios * Cleoselene)
* Ida (Dactyl)
* Roxane (Olympias)
* Pulcova
* Balam

* Jupiter trojans:
* Patroclus (Menoetius)
* Hektor (Skamandrios)
* Eurybates (Queta)

* TNOs:
* Lempo (Hiisi * Paha)
* 2002 UX25
* Sila–Nunam
* Salacia (Actaea)
* Varda (Ilmarë)
* Gǃkúnǁʼhòmdímà (Gǃòʼé ǃHú)
* 2013 FY27

Ranked
by size|

* Planetary-mass moon
* Ganymede
* largest: 5268 km / 0.413 Earths
* Titan
* Callisto
* Io
* Moon
* Europa
* Triton
* Titania
* Rhea
* Oberon
* Iapetus
* Charon
* Umbriel
* Ariel
* Dione
* Tethys
* Dysnomia
* Enceladus
* Miranda
* Vanth
* Proteus
* Mimas
* Ilmarë
* Nereid
* Hiʻiaka
* Actaea
* Hyperion
* Phoebe
* ...

* Discovery timeline
* Inner moons
* Irregular moons
* List
* Planetary-mass moons
* Naming
* Subsatellite
* Regular moons
* Trojan moons

* v
* t
* e

Solar System

Error: Image is invalid or non-existent.

* Sun
* Mercury
* Venus
* Earth
* Mars
* Ceres
* Jupiter
* Saturn
* Uranus
* Neptune
* Orcus
* Pluto
* Haumea
* Quaoar
* Makemake
* Gonggong
* Eris
* Sedna

| Planets and
dwarfs|

* Terrestrials
* Mercury
* Venus
* Earth
* Mars
* Giants
* Gas
* Jupiter
* Saturn
* Ice
* Uranus
* Neptune
* Dwarfs
* Ceres
* Orcus
* Pluto
* Haumea
* Quaoar
* Makemake
* Gonggong
* Eris
* Sedna

|

Moons|

* Earth
* Moon
* other near-Earth objects
* Mars
* Phobos
* Deimos
* Jupiter
* Ganymede
* Callisto
* Io
* Europa
* all 80
* Saturn
* Titan
* Rhea
* Iapetus
* Dione
* Tethys
* Enceladus
* Mimas
* Hyperion
* Phoebe
* all 83
* Uranus
* Titania
* Oberon
* Umbriel
* Ariel
* Miranda
* all 27
* Neptune
* Triton
* Proteus
* Nereid
* all 14
* Orcus
* Vanth
* Pluto
* Charon
* Nix
* Hydra
* Kerberos
* Styx
* Haumea
* Hiʻiaka
* Namaka
* Quaoar
* Weywot
* Makemake
* S/2015 (136472) 1
* Gonggong
* Xiangliu
* Eris
* Dysnomia

Rings|

* Jovian
* Saturnian (Rhean)
* Charikloan
* Chironean
* Uranian
* Neptunian
* Haumean

Small
Solar
System
bodies|

* Comets
* Damocloids
* Meteoroids
* Minor planets
* names and meanings
* moons
* Planetesimal
* Planetary orbit-crossing minor planets
* Mercury
* Venus
* Earth
* Mars
* Jupiter
* Saturn
* Uranus
* Neptune
* Trojans
* Venus
* Earth
* Mars
* Jupiter
* Trojan camp
* Greek camp
* Saturn Moons
* Uranus
* Neptune
* Near-Earth objects
* Asteroid belt
* Asteroids
* Ceres
* Vesta
* Pallas
* Hygiea
* active
* first 1000
* families
* PHA
* exceptional
* Kirkwood gap
* Cis-Neptunian objects
* Centaurs
* Neptune trojans
* Trans-Neptunian objects
* Kuiper belt
* Cubewanos
* Plutinos
* Detached objects
* Sednoids
* Scattered disc
* Oort cloud
* Hills cloud

| Hypothetical
objects|

* Fifth giant
* Nemesis
* Phaeton
* Planet Nine
* Planet V
* Planet X
* Subsatellites
* Theia
* Tyche
* Vulcan
* Vulcanoids

|

Exploration
(outline)|

* Discovery
* astronomy
* historical models
* timeline
* Space probes
* timeline
* list
* Human spaceflight
* space stations
* list
* programs
* Mercury
* Venus
* Moon
* mining
* Mars
* Ceres
* Asteroids
* mining
* Comets
* Jupiter
* Saturn
* Uranus
* Neptune
* Pluto
* Deep space
* Colonization

Formation
and
evolution|

* Accretion
* Accretion disk
* Excretion disk
* Circumplanetary disk
* Circumstellar disc
* Circumstellar envelope
* Coatlicue
* Cosmic dust
* Debris disk
* Detached object
* EXCEDE
* Exozodiacal dust
* Extraterrestrial materials
* Sample curation
* Sample-return mission
* Frost/Ice/Snow line
* Giant-impact hypothesis
* Gravitational collapse
* Hills cloud
* Hill sphere
* Interplanetary dust cloud
* Interplanetary medium/space
* Interstellar cloud
* Interstellar medium
* Interstellar space
* Kuiper belt
* Kuiper cliff
* Molecular cloud
* Nebular hypothesis
* Oort cloud
* Outer space
* Planet
* Disrupted
* Migration
* System
* Planetesimal
* Formation
* Merging stars
* Protoplanetary disk
* Ring system
* Roche limit
* vs. Hill sphere
* Rubble pile
* Scattered disc
* Star formation

Lists|

* Comets
* Possible dwarf planets
* Gravitationally rounded objects
* Minor planets
* Natural satellites
* Solar System models
* Solar System objects
* by size
* by discovery date
* Interstellar and circumstellar molecules

* Outline of the Solar System
*   *   *

Solar System → Local Interstellar Cloud → Local Bubble → Gould Belt → Orion Arm → Milky Way → Milky Way subgroup → Local Group → Local Sheet → Virgo Supercluster → Laniakea Supercluster → KBC Void → Observable universe → Universe
Each arrow (→) may be read as "within" or "part of".
*[d.]: died
*[c.]: circa
*[v]: View this template
*[t]: Discuss this template
*[e]: Edit this template