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The Moon
The Moon
is an astronomical body that orbits planet Earth, being Earth's only permanent natural satellite. It is the fifth-largest natural satellite in the Solar System, and the largest among planetary satellites relative to the size of the planet that it orbits (its primary). Following Jupiter's satellite Io, the Moon
Moon
is the second-densest satellite in the Solar System
Solar System
among those whose densities are known. The Moon
The Moon
is thought to have formed about 4.51 billion years ago, not long after Earth. The most widely accepted explanation is that the Moon
Moon
formed from the debris left over after a giant impact between Earth
Earth
and a Mars-sized body called Theia. The Moon
The Moon
is in synchronous rotation with Earth, always showing the same face, with its near side marked by dark volcanic maria that fill the spaces between the bright ancient crustal highlands and the prominent impact craters. As seen from the Earth, it is the second-brightest regularly visible celestial object in Earth's sky, after the Sun. Its surface is actually dark, although compared to the night sky it appears very bright, with a reflectance just slightly higher than that of worn asphalt. Its gravitational influence produces the ocean tides, body tides, and the slight lengthening of the day. The Moon's average orbital distance at the present time is 384,402 km (238,856 mi),[10][11] or 1.28 light-seconds. This is about thirty times the diameter of Earth, with its apparent size in the sky almost the same as that of the Sun
Sun
(due to it being 400x farther and larger), resulting in the Moon
Moon
covering the Sun
Sun
nearly precisely in total solar eclipse. This matching of apparent visual size will not continue in the far future, because the Moon's distance from Earth
Earth
is slowly increasing. The Soviet Union's Luna program
Luna program
was the first to reach the Moon
Moon
with unmanned spacecraft in 1959; the United States' NASA
NASA
Apollo program achieved the only manned missions to date, beginning with the first manned lunar orbiting mission by Apollo 8
Apollo 8
in 1968, and six manned lunar landings between 1969 and 1972, with the first being Apollo 11. These missions returned lunar rocks which have been used to develop a geological understanding of the Moon's origin, internal structure, and later history. Since the Apollo 17
Apollo 17
mission in 1972, the Moon
Moon
has been visited only by unmanned spacecraft. Within human culture, both the Moon's natural prominence in the earthly sky, and its regular cycle of phases as seen from the Earth have provided cultural references and influences for human societies and cultures since time immemorial. Such cultural influences can be found in language, lunar based calendar systems, art, and mythology.

Contents

1 Name and etymology 2 Formation 3 Physical characteristics

3.1 Internal structure 3.2 Surface geology

3.2.1 Volcanic
Volcanic
features 3.2.2 Impact craters 3.2.3 Lunar swirls 3.2.4 Presence of water

3.3 Gravitational field 3.4 Magnetic field 3.5 Atmosphere

3.5.1 Dust 3.5.2 Past thicker atmosphere

3.6 Seasons

4 Relationship to Earth

4.1 Orbit 4.2 Relative size 4.3 Appearance from Earth 4.4 Tidal effects 4.5 Eclipses

5 Observation and exploration

5.1 Ancient and medieval studies 5.2 By spacecraft

5.2.1 20th century

5.2.1.1 Soviet missions 5.2.1.2 United States missions 5.2.1.3 1980s–2000

5.2.2 21st century 5.2.3 Planned commercial missions

6 Astronomy
Astronomy
from the Moon 7 Legal status 8 In culture

8.1 Mythology 8.2 Calendar 8.3 Lunacy

9 See also 10 References

10.1 Notes 10.2 Citations 10.3 Bibliography

11 Further reading 12 External links

12.1 Cartographic resources 12.2 Observation tools 12.3 General

Name and etymology

The Moon, tinted reddish, during a lunar eclipse

See also: list of lunar deities The usual English proper name for Earth's natural satellite is "the Moon", which in nonscientific texts is usually not capitalized.[12][13][14][15][16] The noun moon is derived from Old English mōna, which (like all Germanic language cognates) stems from Proto-Germanic
Proto-Germanic
*mēnô, which comes from Proto-Indo-European *mḗh₁n̥s "moon", "month", which comes from the Proto-Indo-European
Proto-Indo-European
root *meh₁- "to measure", the month being the ancient unit of time measured by the Moon.[17][18] Occasionally, the name "Luna" is used. In literature, especially science fiction, "Luna" is used to distinguish it from other moons, while in poetry, the name has been used to denote personification of our moon.[19] The modern English adjective pertaining to the Moon
Moon
is lunar, derived from the Latin
Latin
word for the Moon, luna. The adjective selenic (usually only used to refer to the chemical element selenium) is so rarely used to refer to the moon that this meaning is not recorded in most major dictionaries.[20][21][22] It is derived from the Ancient Greek
Ancient Greek
word for the Moon, σελήνη (selḗnē), from which is however also derived the prefix "seleno-", as in selenography, the study of the physical features of the Moon, as well as the element name selenium.[23][24] Both the Greek goddess Selene
Selene
and the Roman goddess Diana were alternatively called Cynthia.[25] The names Luna, Cynthia, and Selene
Selene
are reflected in terminology for lunar orbits in words such as apolune, pericynthion, and selenocentric. The name Diana comes from the Proto-Indo-European
Proto-Indo-European
*diw-yo, "heavenly", which comes from the PIE root *dyeu- "to shine," which in many derivatives means "sky, heaven, and god" and is also the origin of Latin
Latin
dies, "day".

The Moon

Near side of the Moon

Far side of the Moon

Lunar north pole

Lunar south pole

Formation Main articles: Origin of the Moon
Origin of the Moon
and Giant-impact hypothesis Several mechanisms have been proposed for the Moon's formation 4.51 billion years ago,[f] and some 60 million years after the origin of the Solar System.[26] These mechanisms included the fission of the Moon
Moon
from Earth's crust through centrifugal force[27] (which would require too great an initial spin of Earth),[28] the gravitational capture of a pre-formed Moon[29] (which would require an unfeasibly extended atmosphere of Earth
Earth
to dissipate the energy of the passing Moon),[28] and the co-formation of Earth
Earth
and the Moon
Moon
together in the primordial accretion disk (which does not explain the depletion of metals in the Moon).[28] These hypotheses also cannot account for the high angular momentum of the Earth– Moon
Moon
system.[30]

Play media

The evolution of the Moon
Moon
and a tour of the Moon

The prevailing hypothesis is that the Earth– Moon
Moon
system formed as a result of the impact of a Mars-sized body (named Theia) with the proto- Earth
Earth
(giant impact), that blasted material into orbit about the Earth
Earth
that then accreted to form the present Earth-Moon system.[31][32] The far side of the Moon
Moon
has a crust that is 30 mi (48 km) thicker than the near side of the Moon. This is thought to be due to the Moon
Moon
having been amalgamated from two different bodies. This hypothesis, although not perfect, perhaps best explains the evidence. Eighteen months prior to an October 1984 conference on lunar origins, Bill Hartmann, Roger Phillips, and Jeff Taylor challenged fellow lunar scientists: "You have eighteen months. Go back to your Apollo data, go back to your computer, do whatever you have to, but make up your mind. Don't come to our conference unless you have something to say about the Moon's birth." At the 1984 conference at Kona, Hawaii, the giant impact hypothesis emerged as the most popular.

Before the conference, there were partisans of the three "traditional" theories, plus a few people who were starting to take the giant impact seriously, and there was a huge apathetic middle who didn’t think the debate would ever be resolved. Afterward there were essentially only two groups: the giant impact camp and the agnostics.[33]

Giant impacts are thought to have been common in the early Solar System. Computer simulations of a giant impact have produced results that are consistent with the mass of the lunar core and the present angular momentum of the Earth– Moon
Moon
system. These simulations also show that most of the Moon
Moon
derived from the impactor, rather than the proto-Earth.[34] More recent simulations suggest a larger fraction of the Moon
Moon
derived from the original Earth
Earth
mass.[35][36][37][38] Studies of meteorites originating from inner Solar System
Solar System
bodies such as Mars and Vesta show that they have very different oxygen and tungsten isotopic compositions as compared to Earth, whereas Earth
Earth
and the Moon have nearly identical isotopic compositions. The isotopic equalization of the Earth- Moon
Moon
system might be explained by the post-impact mixing of the vaporized material that formed the two,[39] although this is debated.[40] The great amount of energy released in the impact event and the subsequent re-accretion of that material into the Earth- Moon
Moon
system would have melted the outer shell of Earth, forming a magma ocean.[41][42] Similarly, the newly formed Moon
Moon
would also have been affected and had its own lunar magma ocean; estimates for its depth range from about 500 km (300 miles) to its entire depth (1,737 km (1,079 miles)).[41] While the giant impact hypothesis might explain many lines of evidence, there are still some unresolved questions, most of which involve the Moon's composition.[43]

Oceanus Procellarum
Oceanus Procellarum
("Ocean of Storms")

Ancient rift valleys – rectangular structure (visible – topography – GRAIL gravity gradients)

Ancient rift valleys – context.

Ancient rift valleys – closeup (artist's concept).

In 2001, a team at the Carnegie Institute of Washington reported the most precise measurement of the isotopic signatures of lunar rocks.[44] To their surprise, the team found that the rocks from the Apollo program
Apollo program
carried an isotopic signature that was identical with rocks from Earth, and were different from almost all other bodies in the Solar System. Because most of the material that went into orbit to form the Moon
Moon
was thought to come from Theia, this observation was unexpected. In 2007, researchers from the California Institute of Technology announced that there was less than a 1% chance that Theia and Earth
Earth
had identical isotopic signatures.[45] Published in 2012, an analysis of titanium isotopes in Apollo lunar samples showed that the Moon
Moon
has the same composition as Earth,[46] which conflicts with what is expected if the Moon
Moon
formed far from Earth's orbit
Earth's orbit
or from Theia. Variations on the giant impact hypothesis may explain this data. Physical characteristics Internal structure Main article: Internal structure of the Moon

Structure of the Moon

Chemical composition of the lunar surface regolith (derived from crustal rocks)[47]

Compound Formula Composition (wt %)

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%

Total 99.9% 100.0%

The Moon
The Moon
is a differentiated body: it has a geochemically distinct crust, mantle, and core. The Moon
The Moon
has a solid iron-rich inner core with a radius possibly as small as 240 km (150 mi) and a fluid outer core primarily made of liquid iron with a radius of roughly 300 km (190 mi). Around the core is a partially molten boundary layer with a radius of about 500 km (310 mi).[48][49] 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.[50] 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.[51] 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 the crust of mostly anorthosite.[9] The Moon rock
Moon rock
samples of the flood lavas that erupted onto the surface from partial melting in the mantle confirm the mafic mantle composition, which is more iron-rich than that of Earth.[1] The crust is on average about 50 km (31 mi) thick.[1] The Moon
The Moon
is the second-densest satellite in the Solar System, after Io.[52] However, the inner core of the Moon
Moon
is small, with a radius of about 350 km (220 mi) or less,[1] around 20% of the radius of the Moon. Its composition is not well defined, 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.[53] Surface geology Main articles: Geology of the Moon
Geology of the Moon
and Moon
Moon
rocks

Topography of the Moon

The topography of the Moon
Moon
has been measured with laser altimetry and stereo image analysis.[54] Its most visible 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
Moon
and the second-largest confirmed impact crater in the Solar System.[55][56] At 13 km (8.1 mi) deep, its floor is the lowest point on the surface of the Moon.[55][57] The highest elevations of the Moon's surface are located directly to the northeast, and it has been suggested might have been thickened by the oblique formation impact of the South Pole–Aitken basin.[58] Other large impact basins, such as Imbrium, Serenitatis, Crisium, Smythii, and Orientale, also possess regionally low elevations and elevated rims.[55] 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 by the Lunar Reconnaissance Orbiter suggest that the Moon
Moon
has shrunk within the past billion years, by about 90 metres (300 ft).[59] Similar shrinkage features exist on Mercury. Volcanic
Volcanic
features Main article: Lunar mare

Lunar nearside with major maria and craters labeled

The dark and relatively featureless lunar plains, clearly seen with the naked eye, are called maria ( Latin
Latin
for "seas"; singular mare), as they were once believed to be filled with water;[60] they are now known to be vast solidified pools of ancient basaltic lava. Although similar to terrestrial basalts, lunar basalts have more iron and no minerals altered by water.[61] The majority of these lavas 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".[62]

Evidence of young lunar volcanism

Almost all maria are on the near side of the Moon, and cover 31% of the surface of the near side,[63] compared with 2% of the far side.[64] This is thought to be due to a concentration of heat-producing elements under the crust on the near side, seen on geochemical maps obtained by Lunar Prospector's gamma-ray spectrometer, which would have caused the underlying mantle to heat up, partially melt, rise to the surface and erupt.[51][65][66] Most of the Moon's mare basalts erupted during the Imbrian period, 3.0–3.5 billion years ago, although some radiometrically dated samples are as old as 4.2 billion years.[67] Until recently, the youngest eruptions, dated by crater counting, appeared to have been only 1.2 billion years ago.[68] In 2006, a study of Ina, a tiny depression in Lacus Felicitatis, found jagged, relatively dust-free features that, due to the lack of erosion by infalling debris, appeared to be only 2 million years old.[69] Moonquakes and releases of gas also indicate some continued lunar activity.[69] In 2014 NASA announced "widespread evidence of young lunar volcanism" at 70 irregular mare patches identified by the Lunar Reconnaissance Orbiter, 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 due to the greater concentration of radioactive elements.[70][71][72][73] Just prior to this, evidence has been presented for 2–10 million years younger basaltic volcanism inside Lowell crater,[74][75] Orientale basin, located in the transition zone between the near and far sides of the Moon. An initially hotter mantle and/or local enrichment of heat-producing elements in the mantle could be responsible for prolonged activities also on the far side in the Orientale basin.[76][77] The lighter-coloured regions of the Moon
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.[67][68] In contrast to Earth, no major lunar mountains are believed to have formed as a result of tectonic events.[78] 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
Earth
a few tens of millions of years after their formation.[79][80] Impact craters Further information: List of craters on the Moon

Lunar crater
Lunar crater
Daedalus on the Moon's far side

The other major geologic process that has affected the Moon's surface is impact cratering,[81] 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 alone.[82] 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 kilometres in diameter and associated with a broad apron of ejecta deposits that form a regional stratigraphic horizon.[83] 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.[83] The radiometric ages of impact-melted rocks collected during the Apollo missions
Apollo missions
cluster between 3.8 and 4.1 billion years old: this has been used to propose a Late Heavy Bombardment
Late Heavy Bombardment
of impacts.[84] Blanketed on top of the Moon's crust is a highly comminuted (broken into ever smaller particles) and impact gardened 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.[85] The regolith of older surfaces is generally thicker than for younger surfaces: it varies in thickness from 10–20 km (6.2–12.4 mi) in the highlands and 3–5 km (1.9–3.1 mi) in the maria.[86] Beneath the finely comminuted regolith layer is the megaregolith, a layer of highly fractured bedrock many kilometres thick.[87] Comparison of high-resolution images obtained by the Lunar Reconnaissance Orbiter has shown a contemporary crater-production rate significantly higher than previously estimated. A secondary cratering process caused by distal ejecta is thought to churn the top two centimetres of regolith a hundred times more quickly than previous models suggested–on a timescale of 81,000 years.[88][89]

Lunar swirls
Lunar swirls
at Reiner Gamma

Lunar swirls Main article: Lunar swirls Lunar swirls
Lunar swirls
are enigmatic features found across the Moon's surface, which are characterized by a high albedo, appearing optically immature (i.e. the optical characteristics of a relatively young regolith), and often displaying a sinuous shape. Their curvilinear shape is often accentuated by low albedo regions that wind between the bright swirls. Presence of water 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.[90][91] Computer simulations suggest that up to 14,000 km2 (5,400 sq mi) of the surface may be in permanent shadow.[92] The presence of usable quantities of water on the Moon
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.[93] In years since, signatures of water have been found to exist on the lunar surface.[94] 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.[95] In 1998, the neutron spectrometer on the Lunar Prospector
Lunar Prospector
spacecraft showed that high concentrations of hydrogen are present in the first meter of depth in the regolith near the polar regions.[96] Volcanic
Volcanic
lava beads, brought back to Earth
Earth
aboard Apollo 15, showed small amounts of water in their interior.[97] The 2008 Chandrayaan-1
Chandrayaan-1
spacecraft has since confirmed the existence of surface water ice, using the on-board Moon
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.[98] In 2009, LCROSS
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.[99][100] Another examination of the LCROSS
LCROSS
data showed the amount of detected water to be closer to 155 ± 12 kg (342 ± 26 lb).[101] In May 2011, 615–1410 ppm water in melt inclusions in lunar sample 74220 was reported,[102] the famous high-titanium "orange glass soil" of volcanic origin collected during the Apollo 17
Apollo 17
mission in 1972. The inclusions were formed during explosive eruptions on the Moon approximately 3.7 billion years ago. This concentration is comparable with that of magma in Earth's upper mantle. Although of considerable selenological interest, this announcement affords little comfort to would-be lunar colonists—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. Gravitational field Main article: Gravity of the Moon

GRAIL's gravity map of the Moon

The gravitational field of the Moon
Moon
has 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.[103][104] 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.[105] Magnetic field Main article: Magnetic field
Magnetic field
of the Moon The Moon
The Moon
has an external magnetic field of about 1–100 nanoteslas, less than one-hundredth that of Earth. It does not currently have a global dipolar magnetic field and only has crustal magnetization, probably acquired early in lunar history when a dynamo was still operating.[106][107] Alternatively, some of the remnant magnetization may be from transient magnetic fields generated during large impact events through the expansion of an impact-generated plasma cloud in the presence of an ambient magnetic field. This is supported by the apparent location of the largest crustal magnetizations near the antipodes of the giant impact basins.[108] Atmosphere Main article: Atmosphere
Atmosphere
of the Moon

Sketch by the Apollo 17
Apollo 17
astronauts. The lunar atmosphere was later studied by LADEE.[109][110]

The Moon
The Moon
has an atmosphere so tenuous as to be nearly vacuum, with a total mass of less than 10 metric tons (9.8 long tons; 11 short tons).[111] 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.[9][112] 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[113] from the solar wind; and argon-40, radon-222, and polonium-210, outgassed after their creation by radioactive decay within the crust and mantle.[114][115] 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.[114] Water vapour has been detected by Chandrayaan-1
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.[116] These gases either return into the regolith due to 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.[114] Dust A permanent asymmetric moon dust cloud exists around the Moon, created by small particles from comets. Estimates are 5 tons of comet particles strike the Moon's surface each 24 hours. The particles strike the Moon's surface ejecting moon dust above the Moon. The dust stays above the Moon
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 to 100 kilometers above the surface. The dust measurements were made by LADEE's Lunar Dust EXperiment (LDEX), between 20 and 100 kilometers above the surface, during a six-month period. LDEX detected an average of one 0.3 micrometer moon dust particle each minute. Dust particle counts peaked during the Geminid, Quadrantid, Northern Taurid, and Omicron Centaurid meteor showers, when the Earth, and Moon, pass through comet debris. The cloud is asymmetric, more dense near the boundary between the Moon's dayside and nightside.[117][118] Past thicker atmosphere In October 2017, NASA
NASA
scientists at the Marshall Space Flight Center and the Lunar and Planetary Institute
Lunar and Planetary Institute
in Houston
Houston
announced their finding, based on studies of Moon
Moon
magma samples retrieved by the Apollo missions, that the Moon
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.[119] Seasons The Moon's axial tilt with respect to the ecliptic is only 1.5424°,[120] much less than the 23.44° of Earth. Because of this, the Moon's solar illumination varies much less with season, and topographical details play a crucial role in seasonal effects.[121] From images taken by Clementine in 1994, it appears that four mountainous regions on the rim of Peary Crater at the Moon's north pole may remain illuminated for the entire lunar day, creating peaks of eternal light. No such regions exist at the south pole. Similarly, there are places that remain in permanent shadow at the bottoms of many polar craters,[92] and these "craters of eternal darkness" are extremely cold: Lunar Reconnaissance Orbiter
Lunar Reconnaissance Orbiter
measured the lowest summer temperatures in craters at the southern pole at 35 K (−238 °C; −397 °F)[122] and just 26 K (−247 °C; −413 °F) close to the winter solstice in north polar Hermite Crater. This is the coldest temperature in the Solar System
Solar System
ever measured by a spacecraft, colder even than the surface of Pluto.[121] Average temperatures of the Moon's surface are reported, but temperatures of different areas will vary greatly depending upon whether they are in sunlight or shadow.[123] Relationship to Earth Orbit Main articles: Orbit
Orbit
of the Moon
Moon
and Lunar theory

Earth– Moon
Moon
system (schematic)

DSCOVR
DSCOVR
satellite sees the Moon
Moon
passing in front of Earth

The Moon
The Moon
makes a complete orbit around Earth
Earth
with respect to the fixed stars about once every 27.3 days[g] (its sidereal period). However, because Earth
Earth
is moving in its orbit around the Sun
Sun
at the same time, it takes slightly longer for the Moon
Moon
to show the same phase to Earth, which is about 29.5 days[h] (its synodic period).[63] Unlike most satellites of other planets, the Moon
Moon
orbits closer to the ecliptic plane than to the planet's equatorial plane. The Moon's orbit is subtly perturbed by the Sun
Sun
and Earth
Earth
in many small, complex and interacting ways. For example, the plane of the Moon's orbit gradually rotates once every 18.61[124] years, which affects other aspects of lunar motion. These follow-on effects are mathematically described by Cassini's laws.[125] Relative size The Moon
The Moon
is exceptionally large relative to Earth: a quarter its diameter and 1/81 its mass.[63] It is the largest moon in the Solar System relative to the size of its planet,[i] though Charon is larger relative to the dwarf planet Pluto, at 1/9 Pluto's mass.[j][126] The Earth
Earth
and the Moon's barycentre, their common centre of mass, is located 1,700 km (1,100 mi) (about a quarter of Earth's radius) beneath Earth's surface. The Earth
Earth
revolves around the Earth- Moon
Moon
barycentre once a sidereal month, moving at 1/81 the speed of the Moon, or about 12.5 metres (41 ft) per second. This motion is superimposed on the much larger revolution of the Earth
Earth
around the Sun
Sun
at a speed of about 30 kilometres (19 mi) per second. Appearance from Earth

Moon
Moon
setting in western sky over the High Desert in California

Moon
Moon
above Makarska, Croatia

See also: Lunar observation, Lunar phase, Moonlight, and Earthlight (astronomy) The Moon
The Moon
is in synchronous rotation as it orbits Earth; it rotates about its axis in about the same time it takes to orbit Earth. This results in it always keeping nearly the same face turned towards Earth. However, due to the effect of libration, about 59% of the Moon's surface can actually be seen from Earth. The side of the Moon that faces Earth
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
Earth
days. During new moon, the near side is dark.[127] The Moon
The Moon
had once 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.[128] With time, the energy of rotation of the Moon
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 much earlier NASA
NASA
Lunar Prospector
Lunar Prospector
mission, found two hydrogen-rich areas on opposite sides of the Moon, probably in the form of water ice. It is speculated that these patches were the poles of the Moon
Moon
billions of years ago, before it was tidally locked to Earth.[129] The Moon
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.[63][k] This is partly due to the brightness enhancement of the opposition surge; the Moon
Moon
at quarter phase is only one-tenth as bright, rather than half as bright, as at full moon.[130] 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
Moon
is perceived as a bright object. The edges of the full moon seem as bright as the centre, without limb darkening, due to the reflective properties of lunar soil, which retroreflects light more towards the Sun
Sun
than in other directions. The Moon
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.[131] The full Moon's angular diameter is about 0.52° (on average) in the sky, roughly the same apparent size as the Sun
Sun
(see § Eclipses). The Moon's highest altitude at culmination varies by its phase and time of year. The full moon is currently northernmost during winter. The 18.61-year nodal cycle has an influence on lunar standstill. When the ascending node of the lunar orbit is in the vernal equinox, the lunar declination can reach up to plus or minus 28° each month. This means the Moon
Moon
can pass overhead if viewed from latitudes up to 28° north or south (of the Equator), instead of only 18°. The orientation of the Moon's crescent also depends on the latitude of the viewing location; an observer in the tropics can see a smile-shaped crescent Moon.[132] The Moon
The Moon
is visible for two weeks every 27.3 days at the North and South Poles. Zooplankton
Zooplankton
in the Arctic
Arctic
use moonlight when the Sun
Sun
is below the horizon for months on end.[133]

14 November 2016 supermoon was 356,511 kilometres (221,526 mi) away[134] from the center of Earth, the closest occurrence since 26 January 1948. It will not be closer until 25 November 2034.[135]

The distance between the Moon
Moon
and Earth
Earth
varies from around 356,400 km (221,500 mi) to 406,700 km (252,700 mi) at perigee (closest) and apogee (farthest), respectively. On 14 November 2016, it was closer to Earth
Earth
when at full phase than it has been since 1948, 14% closer than its farthest position in apogee.[136] Reported as a "supermoon", this closest point coincides within an hour of a full moon, and it was 30% more luminous than when at its greatest distance due to its angular diameter being 14% greater, because

1.14

2

≈ 1.30

displaystyle scriptstyle 1.14^ 2 approx 1.30

.[137][138][139] At lower levels, the human perception of reduced brightness as a percentage is provided by the following formula:[140][141]

perceived reduction

% = 100 ×

actual reduction

%

100

displaystyle text perceived reduction %=100times 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.[142] There has been historical controversy over whether 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.[143][144] The Moon's appearance, like the Sun's, can be affected by Earth's atmosphere. Common optical effects are the 22° halo ring, formed when the Moon's light is refracted through the ice crystals of high cirrostratus clouds, and smaller coronal rings when the Moon
Moon
is seen through thin clouds.[145]

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

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

The libration of the Moon
Moon
over a single lunar month. Also visible is the slight variation in the Moon's visual size from Earth.

The gravitational attraction that masses have for one another decreases inversely with the square of the distance of those masses from each other. As a result, the slightly greater attraction that the Moon
Moon
has for the side of Earth
Earth
closest to the Moon, as compared to the part of the Earth
Earth
opposite the Moon, results in tidal forces. Tidal forces affect both the Earth's crust and oceans. The most obvious effect of tidal forces is to cause two bulges in the Earth's oceans, one on the side facing the Moon
Moon
and the other on the side opposite. This results in elevated sea levels called ocean tides.[146] As the Earth
Earth
spins 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.[146] Since the Moon
Moon
is orbiting the Earth
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. The Sun
Sun
has the same tidal effect on the Earth, but its forces of attraction are only 40% that of the Moon's; the Sun's and Moon's interplay is responsible for spring and neap tides.[146] If the Earth
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.[147] As a result, the timing of the tides at most points on the Earth
Earth
is a product of observations that are explained, incidentally, by theory. While gravitation causes acceleration and movement of the Earth's fluid oceans, gravitational coupling between the Moon
Moon
and Earth's solid body is mostly elastic and plastic. The result is a further tidal effect of the Moon
Moon
on the Earth
Earth
that causes a bulge of the solid portion of the Earth
Earth
nearest the Moon
Moon
that acts as a torque in opposition to the Earth's rotation. This "drains" angular momentum and rotational kinetic energy from Earth's spin, slowing the Earth's rotation.[146][148] That angular momentum, lost from the Earth, is transferred to the Moon
Moon
in a process (confusingly known as tidal acceleration), which lifts the Moon
Moon
into a higher orbit and results in its lower orbital speed about the Earth. Thus the distance between Earth
Earth
and Moon
Moon
is increasing, and the Earth's spin is slowing in reaction.[148] Measurements from laser reflectors left during the Apollo missions
Apollo missions
(lunar ranging experiments) have found that the Moon's distance increases by 38 mm (1.5 in) per year[149] (roughly the rate at which human fingernails grow).[150] Atomic clocks also show that Earth's day lengthens by about 15 microseconds every year,[151] slowly increasing the rate at which UTC is adjusted by leap seconds. Left to run its course, this tidal drag would continue until the spin of Earth
Earth
and the orbital period of the Moon
Moon
matched, creating mutual tidal locking between the two. As a result, the Moon
Moon
would be suspended in the sky over one meridian, as is already currently the case with Pluto
Pluto
and its moon Charon. However, the Sun
Sun
will become a red giant engulfing the Earth- Moon
Moon
system long before this occurrence.[152][153] In a like manner, the lunar surface experiences tides of around 10 cm (4 in) amplitude over 27 days, with two components: a fixed one due to Earth, because they are in synchronous rotation, and a varying component from the Sun.[148] The Earth-induced component arises from libration, a result of the Moon's orbital eccentricity (if the Moon's orbit were perfectly circular, there would only be solar tides).[148] Libration
Libration
also changes the angle from which the Moon
Moon
is seen, allowing a total of about 59% of its surface to be seen from Earth
Earth
over time.[63] The cumulative effects of stress built up by these tidal forces produces moonquakes. Moonquakes are much less common and weaker than are earthquakes, although moon quakes can last for up to an hour—a significantly longer time than terrestrial quakes—because of the absence of water to damp out the seismic vibrations. The existence of moonquakes was an unexpected discovery from seismometers placed on the Moon
Moon
by Apollo astronauts from 1969 through 1972.[154] Eclipses Main articles: Solar eclipse, Lunar eclipse, and Eclipse
Eclipse
cycle

From Earth, the Moon
Moon
and the Sun
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
Moon
appears much smaller than the Sun (right).[155]

Eclipses can only occur when the Sun, Earth, and Moon
Moon
are all in a straight line (termed "syzygy"). Solar eclipses occur at new moon, when the Moon
Moon
is between the Sun
Sun
and Earth. In contrast, lunar eclipses occur at full moon, when Earth
Earth
is between the Sun
Sun
and Moon. The apparent size of the Moon
Moon
is roughly the same as that of the Sun, with both being viewed at close to one-half a degree wide. The Sun
Sun
is much larger than the Moon
Moon
but it is the vastly greater distance that gives it the same apparent size as the much closer and much smaller Moon
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
Moon
appearing larger than the Sun) and annular (with the Moon appearing smaller than the Sun) solar eclipses.[156] In a total eclipse, the Moon
Moon
completely covers the disc of the Sun
Sun
and the solar corona becomes visible to the naked eye. Because the distance between the Moon
Moon
and Earth
Earth
is very slowly increasing over time,[146] the angular diameter of the Moon
Moon
is decreasing. Also, as it evolves toward becoming a red giant, the size of the Sun, and its apparent diameter in the sky, are slowly increasing.[l] The combination of these two changes means that hundreds of millions of years ago, the Moon
Moon
would always completely cover the Sun
Sun
on solar eclipses, and no annular eclipses were possible. Likewise, hundreds of millions of years in the future, the Moon
Moon
will no longer cover the Sun
Sun
completely, and total solar eclipses will not occur.[157] Because the Moon's orbit around Earth
Earth
is inclined by about 5.145° (5° 9') to the orbit of Earth
Earth
around the Sun, eclipses do not occur at every full and new moon. For an eclipse to occur, the Moon
Moon
must be near the intersection of the two orbital planes.[158] The periodicity and recurrence of eclipses of the Sun
Sun
by the Moon, and of the Moon
Moon
by Earth, is described by the saros, which has a period of approximately 18 years.[159] Because the Moon
Moon
is continuously blocking our view of a half-degree-wide circular area of the sky,[m][160] the related phenomenon of occultation occurs when a bright star or planet passes behind the Moon
Moon
and is occulted: hidden from view. In this way, a solar eclipse is an occultation of the Sun. Because the Moon
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.[161] Observation and exploration Ancient and medieval studies Main articles: Exploration of the Moon: Early history, Selenography, and Lunar theory

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

A study of the Moon
Moon
in Robert Hooke's Micrographia, 1665

Understanding of the Moon's cycles was an early development of astronomy: by the 5th century BC, Babylonian astronomers had recorded the 18-year Saros cycle
Saros cycle
of lunar eclipses,[162] and Indian astronomers had described the Moon's monthly elongation.[163] The Chinese astronomer Shi Shen (fl. 4th century BC) gave instructions for predicting solar and lunar eclipses.[164] Later, the physical form of the Moon
Moon
and the cause of moonlight became understood. The ancient Greek philosopher Anaxagoras
Anaxagoras
(d. 428 BC) reasoned that the Sun
Sun
and Moon
Moon
were both giant spherical rocks, and that the latter reflected the light of the former.[165][166] Although the Chinese of the Han Dynasty believed the Moon
Moon
to be energy equated to qi, their 'radiating influence' theory also recognized that the light of the Moon
Moon
was merely a reflection of the Sun, and Jing Fang (78–37 BC) noted the sphericity of the Moon.[167] In the 2nd century AD, Lucian
Lucian
wrote the novel A True Story, in which the heroes travel to the Moon
Moon
and meet its inhabitants. In 499 AD, the Indian astronomer Aryabhata mentioned in his Aryabhatiya
Aryabhatiya
that reflected sunlight is the cause of the shining of the Moon.[168] The astronomer and physicist Alhazen (965–1039) found that sunlight was not reflected from the Moon
Moon
like a mirror, but that light was emitted from every part of the Moon's sunlit surface in all directions.[169] Shen Kuo
Shen Kuo
(1031–1095) of the Song dynasty
Song dynasty
created an allegory equating the waxing and waning of the Moon
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.[170]

Galileo's sketches of the Moon
Moon
from Sidereus Nuncius

In Aristotle's (384–322 BC) description of the universe, the Moon
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.[171] However, 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.[172] In the same century, Aristarchus computed the size and distance of the Moon
Moon
from Earth, obtaining a value of about twenty times the radius of Earth
Earth
for the distance. These figures were greatly improved by Ptolemy (90–168 AD): his values of a mean distance of 59 times Earth's radius and a diameter of 0.292  Earth
Earth
diameters were close to the correct values of about 60 and 0.273 respectively.[173] Archimedes
Archimedes
(287–212 BC) designed a planetarium that could calculate the motions of the Moon
Moon
and other objects in the Solar System.[174] During the Middle Ages, before the invention of the telescope, the Moon
Moon
was increasingly recognised as a sphere, though many believed that it was "perfectly smooth".[175] In 1609, Galileo Galilei
Galileo Galilei
drew one of the first telescopic drawings of the Moon
Moon
in his book Sidereus Nuncius
Sidereus Nuncius
and noted that it was not smooth but had mountains and craters. Telescopic mapping of the Moon followed: later in the 17th century, the efforts of Giovanni Battista Riccioli and Francesco Maria Grimaldi
Francesco Maria Grimaldi
led to the system of naming of lunar features in use today. The more exact 1834–36 Mappa Selenographica of Wilhelm Beer
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
Moon
at accuracies possible in earthly geography.[176] Lunar craters, first noted by Galileo, were thought to be volcanic until the 1870s proposal of Richard Proctor that they were formed by collisions.[63] This view gained support in 1892 from the experimentation of geologist Grove Karl Gilbert, and from comparative studies from 1920 to the 1940s,[177] leading to the development of lunar stratigraphy, which by the 1950s was becoming a new and growing branch of astrogeology.[63] By spacecraft See also: Robotic exploration of the Moon, List of proposed missions to the Moon, Colonization of the Moon, and List of artificial objects on the Moon 20th century Soviet missions Main articles: Luna program
Luna program
and Lunokhod
Lunokhod
programme

Luna 2, the first human-made object to reach the surface of the Moon (left) and Soviet Moon
Moon
rover Lunokhod
Lunokhod
1

The Cold War-inspired Space Race
Space Race
between the Soviet Union
Soviet Union
and the U.S. led to an acceleration of interest in exploration of the Moon. Once launchers had the necessary capabilities, these nations sent unmanned probes on both flyby and impact/lander missions. Spacecraft from the Soviet Union's Luna program
Luna program
were the first to accomplish a number of goals: following three unnamed, failed missions in 1958,[178] the first human-made object to escape Earth's gravity and pass near the Moon
Moon
was Luna 1; 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
Moon
were made by Luna 3, all in 1959. The first spacecraft to perform a successful lunar soft landing was Luna 9
Luna 9
and the first unmanned vehicle to orbit the Moon
Moon
was Luna 10, both in 1966.[63] Rock and soil samples were brought back to Earth
Earth
by three Luna sample return missions ( Luna 16
Luna 16
in 1970, Luna 20
Luna 20
in 1972, and Luna 24
Luna 24
in 1976), which returned 0.3 kg total.[179] Two pioneering robotic rovers landed on the Moon
Moon
in 1970 and 1973 as a part of Soviet Lunokhod
Lunokhod
programme. Luna 24
Luna 24
was the last Soviet/Russian mission to the Moon. United States missions Main articles: Apollo program
Apollo program
and Moon
Moon
landing

Earthrise
Earthrise
(Apollo 8, 1968)

Moon rock
Moon rock
(Apollo 17, 1972)

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 manned military outpost on the Moon
Moon
called Project Horizon with the potential to conduct a wide range of missions from scientific research to nuclear Earth
Earth
bombardment. The study included the possibility of conducting a lunar-based nuclear test.[180][181] 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.[182][183][180] However, both these proposals were ultimately passed over as the space program was largely transferred from the military to the civilian agency NASA.[183] 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 unmanned probes to develop an understanding of the lunar surface in preparation for manned missions: the Jet Propulsion Laboratory's Ranger program
Ranger program
produced the first close-up pictures; the Lunar Orbiter program
Lunar Orbiter program
produced maps of the entire Moon; the Surveyor program
Surveyor program
landed its first spacecraft four months after Luna 9. The manned Apollo program
Apollo program
was developed in parallel; after a series of unmanned and manned tests of the Apollo spacecraft in Earth
Earth
orbit, and spurred on by a potential Soviet lunar flight, in 1968 Apollo 8
Apollo 8
made the first manned mission to lunar orbit. The subsequent landing of the first humans on the Moon
Moon
in 1969 is seen by many as the culmination of the Space Race.[184]

Neil Armstrong
Neil Armstrong
working at the lunar module

"That's one small step ..."

Problems playing this file? See media help.

Neil Armstrong
Neil Armstrong
became the first person to walk on the Moon
Moon
as the commander of the American mission Apollo 11
Apollo 11
by first setting foot on the Moon
Moon
at 02:56 UTC on 21 July 1969.[185] 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.[186][187] The Apollo missions
Apollo missions
11 to 17 (except Apollo 13, which aborted its planned lunar landing) returned 380.05 kilograms (837.87 lb) of lunar rock and soil in 2,196 separate samples.[188] The American Moon landing
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.[189][190] 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
Earth
concluded in late 1977 due to budgetary considerations,[191][192] 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 centimetres, and data from this experiment are being used to place constraints on the size of the lunar core.[193] 1980s–2000

An artificially coloured mosaic constructed from a series of 53 images taken through three spectral filters by Galileo' s imaging system as the spacecraft flew over the northern regions of the Moon
Moon
on 7 December 1992.

After the first Moon
Moon
race there were years of near quietude but starting in the 1990s, many more countries have become involved in direct exploration of the Moon. In 1990, Japan became the third country to place a spacecraft into lunar orbit with its Hiten spacecraft. The spacecraft released a smaller probe, Hagoromo, in lunar orbit, but the transmitter failed, preventing further scientific use of the mission.[194] In 1994, the U.S. sent the joint Defense Department/ NASA
NASA
spacecraft Clementine to lunar orbit. This mission obtained the first near-global topographic map of the Moon, and the first global multispectral images of the lunar surface.[195] This was followed in 1998 by the Lunar Prospector
Lunar Prospector
mission, whose instruments indicated the presence of excess hydrogen at the lunar poles, which is likely to have been caused by the presence of water ice in the upper few meters of the regolith within permanently shadowed craters.[196] India, Japan, China, the United States, and the European Space Agency each sent lunar orbiters, and especially ISRO's Chandrayaan-1
Chandrayaan-1
has contributed to confirming the discovery of lunar water ice in permanently shadowed craters at the poles and bound into the lunar regolith. The post-Apollo era has also seen two rover missions: the final Soviet Lunokhod
Lunokhod
mission in 1973, and China's ongoing Chang'e 3 mission, which deployed its Yutu rover on 14 December 2013. The Moon remains, under the Outer Space Treaty, free to all nations to explore for peaceful purposes. 21st century

Artistic representation of a future Moon
Moon
colony

The European spacecraft SMART-1, the second ion-propelled spacecraft, was in lunar orbit from 15 November 2004 until its lunar impact on 3 September 2006, and made the first detailed survey of chemical elements on the lunar surface.[197] The ambitious Chinese Lunar Exploration Program
Chinese Lunar Exploration Program
began with Chang'e 1, which successfully orbited the Moon
Moon
from 5 November 2007 until its controlled lunar impact on 1 March 2009.[198] It obtained a full image map of the Moon. Chang'e 2, beginning in October 2010, reached the Moon
Moon
more quickly, mapped the Moon
Moon
at a higher resolution over an eight-month period, then left lunar orbit for an extended stay at the Earth– Sun
Sun
L2 Lagrangian point, before finally performing a flyby of asteroid 4179 Toutatis
4179 Toutatis
on 13 December 2012, and then heading off into deep space. On 14 December 2013, Chang'e 3
Chang'e 3
landed a lunar lander onto the Moon's surface, which in turn deployed a lunar rover, named Yutu (Chinese: 玉兔; literally "Jade Rabbit"). This was the first lunar soft landing since Luna 24
Luna 24
in 1976, and the first lunar rover mission since Lunokhod
Lunokhod
2 in 1973. China intends to launch another rover mission (Chang'e 4) before 2020, followed by a sample return mission (Chang'e 5) soon after.[199] Between 4 October 2007 and 10 June 2009, the Japan Aerospace Exploration Agency's Kaguya (Selene) mission, a lunar orbiter fitted with a high-definition video camera, and two small radio-transmitter satellites, obtained lunar geophysics data and took the first high-definition movies from beyond Earth
Earth
orbit.[200][201] India's first lunar mission, Chandrayaan I, orbited from 8 November 2008 until loss of contact on 27 August 2009, creating a high resolution chemical, mineralogical and photo-geological map of the lunar surface, and confirming the presence of water molecules in lunar soil.[202] The Indian Space Research Organisation
Indian Space Research Organisation
planned to launch Chandrayaan II
Chandrayaan II
in 2013, which would have included a Russian robotic lunar rover.[203][204] However, the failure of Russia's Fobos-Grunt
Fobos-Grunt
mission has delayed this project.

Copernicus's central peaks as observed by the LRO, 2012

The Ina formation, 2009

The U.S. co-launched the Lunar Reconnaissance Orbiter
Lunar Reconnaissance Orbiter
(LRO) and the LCROSS
LCROSS
impactor and follow-up observation orbiter on 18 June 2009; LCROSS
LCROSS
completed its mission by making a planned and widely observed impact in the crater Cabeus on 9 October 2009,[205] whereas LRO is currently in operation, obtaining precise lunar altimetry and high-resolution imagery. In November 2011, the LRO passed over the large and bright Aristarchus crater. NASA
NASA
released photos of the crater on 25 December 2011.[206] Two NASA
NASA
GRAIL spacecraft began orbiting the Moon
Moon
around 1 January 2012,[207] on a mission to learn more about the Moon's internal structure. NASA's LADEE
LADEE
probe, designed to study the lunar exosphere, achieved orbit on 6 October 2013. Upcoming lunar missions include Russia's Luna-Glob: an unmanned lander with a set of seismometers, and an orbiter based on its failed Martian Fobos-Grunt
Fobos-Grunt
mission.[208][209] Privately funded lunar exploration has been promoted by the Google
Google
Lunar X Prize, announced 13 September 2007, which offers US$20 million to anyone who can land a robotic rover on the Moon
Moon
and meet other specified criteria.[210] Shackleton Energy Company is building a program to establish operations on the south pole of the Moon
Moon
to harvest water and supply their Propellant Depots.[211] NASA
NASA
began to plan to resume manned missions following the call by U.S. President George W. Bush
George W. Bush
on 14 January 2004 for a manned mission to the Moon
Moon
by 2019 and the construction of a lunar base by 2024.[212] The Constellation program
Constellation program
was funded and construction and testing begun on a manned spacecraft and launch vehicle,[213] and design studies for a lunar base.[214] However, that program has been cancelled in favor of a manned asteroid landing by 2025 and a manned Mars
Mars
orbit by 2035.[215] India
India
has also expressed its hope to send a manned mission to the Moon
Moon
by 2020.[216] On February 28, 2018, SpaceX, Vodafone, Nokia
Nokia
and Audi
Audi
announced a collaboration to install a 4G wireless communication network on the Moon, with the aim of streaming live footage on the surface to Earth.[217] Planned commercial missions In 2007, the X Prize Foundation together with Google
Google
launched the Google Lunar X Prize
Google Lunar X Prize
to encourage commercial endeavors to the Moon. A prize of $20 million will be awarded to the first private venture to get to the moon with a robotic lander by the end of March 2018, with additional prizes worth $10 million for further milestones.[218][219] As of August 2016, 16 teams are participating in the competition.[220] In August 2016, the US government granted permission to US-based start-up Moon
Moon
Express to land on the Moon.[221] This marked the first time that a private enterprise was given the right to do so. The decision is regarded as a precedent helping to define regulatory standards for deep-space commercial activity in the future, as thus far companies' operation had been restricted to being on or around Earth.[221] Astronomy
Astronomy
from the Moon

A false-color image of Earth
Earth
in ultraviolet light taken from the surface of the Moon
Moon
on the Apollo 16
Apollo 16
mission. The day-side reflects a lot of UV light from the Sun, but the night-side shows faint bands of UV emission from the aurora caused by charged particles.[222]

For many years, the Moon
Moon
has been recognized as an excellent site for telescopes.[223] 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.[224] 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.[225] A lunar zenith telescope can be made cheaply with an ionic liquid.[226] In April 1972, the Apollo 16
Apollo 16
mission recorded various astronomical photos and spectra in ultraviolet with the Far Ultraviolet Camera/Spectrograph.[227] Legal status Main article: Space law Although Luna landers scattered pennants of the Soviet Union
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.[228] Russia and the U.S. are party to the 1967 Outer Space Treaty,[229] which defines the Moon
Moon
and all outer space as the "province of all mankind".[228] This treaty also restricts the use of the Moon
Moon
to peaceful purposes, explicitly banning military installations and weapons of mass destruction.[230] The 1979 Moon Agreement was created to restrict the exploitation of the Moon's resources by any single nation, but as of November 2016, it has been signed and ratified by only 18 nations, none of which engages in self-launched human space exploration or has plans to do so.[231] Although several individuals have made claims to the Moon
Moon
in whole or in part, none of these are considered credible.[232][233][234] In culture

Luna, the Moon, from a 1550 edition of Guido Bonatti's Liber astronomiae

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

Sun
Sun
and Moon
Moon
with faces (1493 woodcut)

A 5,000-year-old rock carving at Knowth, Ireland, may represent the Moon, which would be the earliest depiction discovered.[235] The contrast between the brighter highlands and the darker maria creates the patterns seen by different cultures as the Man in the Moon, the rabbit and the buffalo, among others. In many prehistoric and ancient cultures, the Moon
Moon
was personified as a deity or other supernatural phenomenon, and astrological views of the Moon
Moon
continue to be propagated today. In Proto-Indo-European
Proto-Indo-European
religion, the moon was personified as the male god *Meh1not.[236] The ancient Sumerians believed that the moon was the god Nanna,[237][238] who was the father of Inanna, the goddess of the planet Venus,[237][238] and Utu, the god of the sun.[237][238] Nanna was later known as Sîn,[238][237] and was particularly associated with magic and sorcery.[237] In Greco-Roman mythology, the Sun
Sun
and the Moon
Moon
are represented as male and female, respectively (Helios/Sol and Selene/Luna);[236] this is a development unique to the eastern Mediterranean[236] and traces of an earlier male moon god in the Greek tradition are preserved in the figure of Menelaus.[236] In Mesopotamian iconography, the crescent was the primary symbol of Nanna-Sîn.[238] In ancient Greek art, the Moon
Moon
goddess Selene
Selene
was represented wearing a crescent on her headgear in an arrangement reminiscent of horns.[239][240] The star and crescent arrangement also goes back to the Bronze Age, representing either the Sun
Sun
and Moon, or the Moon
Moon
and planet Venus, in combination. It came to represent the goddess Artemis
Artemis
or Hecate, and via the patronage of Hecate
Hecate
came to be used as a symbol of Byzantium. An iconographic tradition of representing Sun
Sun
and Moon
Moon
with faces developed in the late medieval period. The splitting of the moon (Arabic: انشقاق القمر‎) is a miracle attributed to Muhammad.[241] Calendar Further information: Lunar calendar, Lunisolar calendar, Metonic cycle, Blue moon, and Movable feast The Moon's regular phases make it a very convenient timepiece, and the periods of its waxing and waning form the basis of many of the oldest calendars. 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.[242][243][244] The ~30-day month is an approximation of the lunar cycle. The English noun month and its cognates in other Germanic languages stem from Proto-Germanic
Proto-Germanic
*mǣnṓth-, which is connected to the above-mentioned Proto-Germanic
Proto-Germanic
*mǣnōn, indicating the usage of a lunar calendar among the Germanic peoples
Germanic peoples
(Germanic calendar) prior to the adoption of a solar calendar.[245] The PIE root of moon, *méh1nōt, derives 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),[246][247][248] and echoing the Moon's importance to many ancient cultures in measuring time (see Latin
Latin
mensis and Ancient Greek
Ancient Greek
μείς (meis) or μήν (mēn), meaning "month").[249][250][251][252] Most historical calendars are lunisolar. The 7th-century Islamic calendar
Islamic calendar
is an exceptional example of a purely lunar calendar. Months are traditionally determined by the visual sighting of the hilal, or earliest crescent moon, over the horizon.[253]

"Moonrise", 1884, picture by Stanisław Masłowski
Stanisław Masłowski
(National Museum, Kraków, Gallery of Sukiennice Museum)

Lunacy Further information: Lunar effect The Moon
The Moon
has long been associated with insanity and irrationality; the words lunacy and lunatic (popular shortening loony) are derived from the Latin
Latin
name for the Moon, Luna. Philosophers Aristotle
Aristotle
and Pliny the Elder argued that the full moon induced insanity in susceptible individuals, believing that the brain, which is mostly water, must be affected by the Moon
Moon
and its power over the tides, but the Moon's gravity is too slight to affect any single person.[254] 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.[254][255][256][257][258] See also

Solar System
Solar System
portal Moon
Moon
portal Astronomy
Astronomy
portal

List of lunar features Former classification of planets Other moons of Earth 2006 RH120 List of natural satellites Tourism on the Moon Timeline of the far future

References Notes

^ Between 18.29° and 28.58° to Earth's equator.[1] ^ There are a number of near- Earth
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. ^ 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
NASA
factsheet reference to the minimum Earth– Moon
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
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
Earth
albedo × ( Earth
Earth
radius / Radius
Radius
of Moon's orbit)2 ] relative to the direct solar illumination that occurs for a full moon. ( Earth
Earth
albedo = 0.367; Earth
Earth
radius = (polar radius × equatorial radius)½ = 6 367 km.) ^ 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
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. ^ 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. ^ This age is calculated from isotope dating of lunar zircons. ^ 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). ^ 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). ^ 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. ^ With 27% the diameter and 60% the density of Earth, the Moon
Moon
has 1.23% of the mass of Earth. The moon Charon is larger relative to its primary Pluto, but Pluto
Pluto
is now considered to be a dwarf planet. ^ The Sun's apparent magnitude is −26.7, while the full moon's apparent magnitude is −12.7. ^ See graph in Sun#Life phases. At present, the diameter of the Sun
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
Moon
is decreasing as it recedes from Earth. ^ On average, the Moon
Moon
covers an area of 0.21078 square degrees on the night sky.

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and Other Celestial Bodies". United Nations Office for Outer Space Affairs. Archived from the original on 9 August 2010. Retrieved 28 March 2010.  ^ "The treaties control space-related activities of States. What about non-governmental entities active in outer space, like companies and even individuals?". United Nations Office for Outer Space Affairs. Archived from the original on 21 April 2010. Retrieved 28 March 2010.  ^ "Statement by the Board of Directors of the IISL On Claims to Property Rights Regarding The Moon
The Moon
and Other Celestial Bodies (2004)" (PDF). International Institute of Space Law. 2004. Archived (PDF) from the original on 22 December 2009. Retrieved 28 March 2010.  ^ "Further Statement by the Board of Directors of the IISL On Claims to Lunar Property Rights (2009)" (PDF). International Institute of Space Law. 22 March 2009. Archived (PDF) from the original on 22 December 2009. Retrieved 28 March 2010.  ^ "Carved and Drawn Prehistoric Maps of the Cosmos". Space Today. 2006. Archived from the original on 15 March 2012. Retrieved 12 April 2007.  ^ a b c d Dexter, Miriam Robbins (1984). " Proto-Indo-European
Proto-Indo-European
Sun Maidens and Gods of the Moon". Mankind Quarterly. 25 (1 & 2): 137–144.  ^ a b c d e Nemet-Nejat, Karen Rhea (1998), Daily Life in Ancient Mesopotamia, Daily Life, Greenwood, p. 203, ISBN 978-0313294976  ^ a b c d e Black, Jeremy; Green, Anthony (1992). Gods, Demons and Symbols of Ancient Mesopotamia: An Illustrated Dictionary. The British Museum Press. p. 135. ISBN 0-7141-1705-6.  ^ Zschietzschmann, W. (2006). Hellas and Rome: The Classical World in Pictures. Whitefish, Montana: Kessinger Publishing. p. 23. ISBN 9781428655447.  ^ Cohen, Beth (2006). "Outline as a Special
Special
Technique in Black- and Red-figure Vase-painting". The Colors of Clay: Special
Special
Techniques in Athenian Vases. Los Angeles, California: Getty Publications. pp. 178–179. ISBN 9780892369423.  ^ "Muhammad." Encyclopædia Britannica. 2007. Encyclopædia Britannica Online, p.13 ^ Marshack, Alexander (1991), The Roots of Civilization, Colonial Hill, Mount Kisco, NY. ^ Brooks, A. S. and Smith, C. C. (1987): "Ishango revisited: new age determinations and cultural interpretations", The African Archaeological Review, 5 : 65–78. ^ Duncan, David Ewing (1998). The Calendar. Fourth Estate Ltd. pp. 10–11. ISBN 978-1-85702-721-1.  ^ For etymology, see Barnhart, Robert K. (1995). The Barnhart Concise Dictionary of Etymology. Harper Collins. p. 487. ISBN 978-0-06-270084-1. . For the lunar calendar of the Germanic peoples, see Birley, A. R. (Trans.) (1999). Agricola and Germany. Oxford World's Classics. USA: Oxford University Press. p. 108. ISBN 978-0-19-283300-6.  ^ Mallory, J. P.; Adams, D. Q. (2006). The Oxford Introduction to Proto-Indo-European
Proto-Indo-European
and the Proto-Indo-European
Proto-Indo-European
World. Oxford Linguistics. Oxford University Press. pp. 98, 128, 317. ISBN 978-0-19-928791-8.  ^ Harper, Douglas. "measure". Online Etymology Dictionary.  ^ Harper, Douglas. "menstrual". Online Etymology Dictionary.  ^ Smith, William George (1849). Dictionary of Greek and Roman Biography and Mythology: Oarses-Zygia. 3. J. Walton. p. 768. Retrieved 29 March 2010.  ^ Estienne, Henri (1846). Thesaurus graecae linguae. 5. Didot. p. 1001. Retrieved 29 March 2010.  ^ mensis. Charlton T. Lewis and Charles Short. A Latin
Latin
Dictionary on Perseus Project. ^ μείς in Liddell and Scott. ^ "Islamic Calendars based on the Calculated First Visibility of the Lunar Crescent". University of Utrecht. Archived from the original on 11 January 2014. Retrieved 11 January 2014.  ^ a b Lilienfeld, Scott O.; Arkowitz, Hal (2009). "Lunacy and the Full Moon". Scientific American. Archived from the original on 16 October 2009. Retrieved 13 April 2010.  ^ Rotton, James; Kelly, I. W. (1985). "Much ado about the full moon: A meta-analysis of lunar-lunacy research". Psychological Bulletin. 97 (2): 286–306. doi:10.1037/0033-2909.97.2.286.  ^ Martens, R.; Kelly, I. W.; Saklofske, D. H. (1988). "Lunar Phase and Birthrate: A 50-year Critical Review". Psychological Reports. 63 (3): 923–934. doi:10.2466/pr0.1988.63.3.923.  ^ Kelly, Ivan; Rotton, James; Culver, Roger (1986), " The Moon
The Moon
Was Full and Nothing Happened: A Review of Studies on the Moon
Moon
and Human Behavior", Skeptical Inquirer, 10 (2): 129–43 . Reprinted in The Hundredth Monkey - and other paradigms of the paranormal, edited by Kendrick Frazier, Prometheus Books. Revised and updated in The Outer Edge: Classic Investigations of the Paranormal, edited by Joe Nickell, Barry Karr, and Tom Genoni, 1996, CSICOP. ^ Foster, Russell G.; Roenneberg, Till (2008). "Human Responses to the Geophysical Daily, Annual and Lunar Cycles". Current Biology. 18 (17): R784–R794. doi:10.1016/j.cub.2008.07.003. PMID 18786384. 

Bibliography

Needham, Joseph (1986). Science and Civilization in China, Volume
Volume
III: Mathematics and the Sciences of the Heavens and Earth. Taipei: Caves Books. ISBN 978-0-521-05801-8. 

Further reading

"Revisiting the Moon". New York Times. Retrieved 8 September 2014.  The Moon. Discovery 2008. BBC World Service. Bussey, B.; Spudis, P.D. (2004). The Clementine Atlas of the Moon. Cambridge University Press. ISBN 0-521-81528-2.  Cain, Fraser. "Where does the Moon
Moon
Come From?". Universe
Universe
Today. Retrieved 1 April 2008.  (podcast and transcript) Jolliff, B. (2006). Wieczorek, M.; Shearer, C.; Neal, C., eds. "New views of the Moon". Reviews in Mineralogy and Geochemistry. Chantilly, Virginia: Mineralogy Society of America. 60 (1): 721. Bibcode:2006RvMG...60D...5J. doi:10.2138/rmg.2006.60.0. ISBN 0-939950-72-3. Retrieved 12 April 2007.  Jones, E.M. (2006). "Apollo Lunar Surface Journal". NASA. Retrieved 12 April 2007.  "Exploring the Moon". Lunar and Planetary Institute. Retrieved 12 April 2007.  Mackenzie, Dana (2003). The Big Splat, or How Our Moon
Moon
Came to Be. Hoboken, New Jersey: John Wiley & Sons. ISBN 0-471-15057-6.  Moore, P. (2001). On the Moon. Tucson, Arizona: Sterling Publishing Co. ISBN 0-304-35469-4.  " Moon
Moon
Articles". Planetary Science Research Discoveries. Hawai'i Institute of Geophysics
Geophysics
and Planetology.  Spudis, P. D. (1996). The Once and Future Moon. Smithsonian Institution Press. ISBN 1-56098-634-4.  Taylor, S.R. (1992). Solar system evolution. Cambridge University Press. p. 307. ISBN 0-521-37212-7.  Teague, K. (2006). "The Project Apollo Archive". Retrieved 12 April 2007.  Wilhelms, D.E. (1987). "Geologic History of the Moon". U.S. Geological Survey Professional paper. 1348. Retrieved 12 April 2007.  Wilhelms, D.E. (1993). To a Rocky Moon: A Geologist's History of Lunar Exploration. Tucson, Arizona: University of Arizona Press. ISBN 0-8165-1065-2. Retrieved 10 March 2009. 

External links

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Definitions from Wiktionary Media from Wikimedia Commons News from Wikinews Quotations from Wikiquote Texts from Wikisource Textbooks from Wikibooks Travel guide from Wikivoyage Learning resources from Wikiversity

NASA
NASA
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Cartographic resources

The Moon
The Moon
on Google
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. Retrieved 12 April 2007.  3D zoomable globes:

" Google
Google
Moon". Google. 2007. Retrieved 12 April 2007.  "Moon". World Wind Central. NASA. 2007. Retrieved 12 April 2007. 

Aeschliman, R. "Lunar Maps". Planetary Cartography and Graphics. Retrieved 12 April 2007.  Maps and panoramas at Apollo landing sites Japan Aerospace Exploration Agency
Japan Aerospace Exploration Agency
(JAXA) Kaguya (Selene) images Large image of the Moon's north pole area

Observation tools

"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
Moon
Watch". 2005. Retrieved 24 May 2009.  See when the next new crescent moon is visible for any location.

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