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Moon

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

Moon

Full moon (Si apre in una nuova finestra) seen from Earth

Designations

Designation

Earth I

Alternative names (Si apre in una nuova finestra)

Adjectives (Si apre in una nuova finestra)

Orbital characteristics (Si apre in una nuova finestra)Epoch (Si apre in una nuova finestra) J2000 (Si apre in una nuova finestra)Perigee (Si apre in una nuova finestra)362600 km
(356400–370400 km)Apogee (Si apre in una nuova finestra)405400 km
(404000–406700 km)

Semi-major axis (Si apre in una nuova finestra)

384399 km (1.28 ls (Si apre in una nuova finestra), 0.00257 AU (Si apre in una nuova finestra))[1] (Si apre in una nuova finestra)Eccentricity (Si apre in una nuova finestra)0.0549[1] (Si apre in una nuova finestra)

Orbital period (Si apre in una nuova finestra)

27.321661 d (Si apre in una nuova finestra)
(27 d 7 h 43 min 11.5 s[1] (Si apre in una nuova finestra))

Synodic period (Si apre in una nuova finestra)

29.530589 d
(29 d 12 h 44 min 2.9 s)

Average orbital speed (Si apre in una nuova finestra)

1.022 km/s (Si apre in una nuova finestra)Inclination (Si apre in una nuova finestra)5.145° to the ecliptic (Si apre in una nuova finestra)[2] (Si apre in una nuova finestra)[a] (Si apre in una nuova finestra)

Longitude of ascending node (Si apre in una nuova finestra)

Regressing by one revolution (Si apre in una nuova finestra)in 18.61 years

Argument of perigee (Si apre in una nuova finestra)

Progressing by one
revolution in 8.85 years

Satellite of (Si apre in una nuova finestra)Earth (Si apre in una nuova finestra)[b] (Si apre in una nuova finestra)[3] (Si apre in una nuova finestra)Physical characteristics

Mean radius

1737.4 km
(0.2727 of Earth's)[1] (Si apre in una nuova finestra)[4] (Si apre in una nuova finestra)[5] (Si apre in una nuova finestra)

Equatorial (Si apre in una nuova finestra)radius

1738.1 km
(0.2725 of Earth's)[4] (Si apre in una nuova finestra)

Polar (Si apre in una nuova finestra) radius

1736.0 km
(0.2731 of Earth's)[4] (Si apre in una nuova finestra)Flattening (Si apre in una nuova finestra)0.0012[4] (Si apre in una nuova finestra)Circumference10921 km (equatorial (Si apre in una nuova finestra))

Surface area (Si apre in una nuova finestra)

3.793×107 km2
(0.074 of Earth's)Volume (Si apre in una nuova finestra)2.1958×1010 km3
(0.020 of Earth's)[4] (Si apre in una nuova finestra)Mass (Si apre in una nuova finestra)7.342×1022 kg
(0.012300 of Earth's)[1] (Si apre in una nuova finestra)[4] (Si apre in una nuova finestra)[6] (Si apre in una nuova finestra)

Mean density (Si apre in una nuova finestra)

3.344 g/cm3 (Si apre in una nuova finestra)[1] (Si apre in una nuova finestra)[4] (Si apre in una nuova finestra)
0.606 × Earth

Surface gravity (Si apre in una nuova finestra)

1.62 m/s2 (Si apre in una nuova finestra) (0.1654 g (Si apre in una nuova finestra))[4] (Si apre in una nuova finestra)

Moment of inertia factor (Si apre in una nuova finestra)

0.3929±0.0009[7] (Si apre in una nuova finestra)

Escape velocity (Si apre in una nuova finestra)

2.38 km/s
(8600 km/h; 5300 mph)

Sidereal rotation period (Si apre in una nuova finestra)

27.321661 d (synchronous (Si apre in una nuova finestra))

Equatorial rotation velocity

4.627 m/s

Axial tilt (Si apre in una nuova finestra)

North pole right ascension (Si apre in una nuova finestra)

North pole declination (Si apre in una nuova finestra)

65.64°[9] (Si apre in una nuova finestra)Albedo (Si apre in una nuova finestra)0.136[10] (Si apre in una nuova finestra)Surface temp. (Si apre in una nuova finestra)minmeanmaxEquator100 K (Si apre in una nuova finestra)250 K390 K85°N 150 K230 K[11] (Si apre in una nuova finestra)

Apparent magnitude (Si apre in una nuova finestra)

Angular diameter (Si apre in una nuova finestra)

29.3 to 34.1 arcminutes (Si apre in una nuova finestra)[4] (Si apre in una nuova finestra)[d] (Si apre in una nuova finestra)Atmosphere[12] (Si apre in una nuova finestra)

Surface pressure (Si apre in una nuova finestra)

Composition by volume (Si apre in una nuova finestra)

The Moon from Earth

The Moon is Earth (Si apre in una nuova finestra)'s only proper (Si apre in una nuova finestra) natural satellite (Si apre in una nuova finestra). At one-quarter the diameter of Earth (comparable to the width of Australia (Si apre in una nuova finestra)),[13] (Si apre in una nuova finestra) it is the largest natural satellite in the Solar System (Si apre in una nuova finestra) relative to the size of its planet, and the fifth largest satellite (Si apre in una nuova finestra) in the Solar System overall (larger than any dwarf planet (Si apre in una nuova finestra)). Orbiting Earth at an average lunar distance (Si apre in una nuova finestra) of 384,400 km (238,900 mi),[14] (Si apre in una nuova finestra) or about 30 times Earth's diameter, its gravitational influence is the main driver of Earth's tides (Si apre in una nuova finestra) and slightly lengthens (Si apre in una nuova finestra) Earth's day. The Moon is classified as a planetary-mass object (Si apre in una nuova finestra) and a differentiated (Si apre in una nuova finestra) rocky (Si apre in una nuova finestra) body, and lacks any significant atmosphere (Si apre in una nuova finestra), hydrosphere (Si apre in una nuova finestra), or magnetic field (Si apre in una nuova finestra). Its surface gravity is about one-sixth of Earth's (0.1654 g (Si apre in una nuova finestra)); Jupiter (Si apre in una nuova finestra)'s moon Io (Si apre in una nuova finestra) is the only satellite in the Solar System known to have a higher surface gravity and density.

The Moon's orbit (Si apre in una nuova finestra) around Earth has a sidereal period (Si apre in una nuova finestra) of 27.3 days, and a synodic period (Si apre in una nuova finestra) of 29.5 days. The synodic period drives its lunar phases (Si apre in una nuova finestra), which form the basis for the months of a lunar calendar (Si apre in una nuova finestra). The Moon is tidally locked (Si apre in una nuova finestra) to Earth, which means that the length of a full rotation of the Moon on its own axis (a lunar day (Si apre in una nuova finestra)) is the same as the synodic period, resulting in its same side (the near side (Si apre in una nuova finestra)) always facing Earth. That said, 59% of the total lunar surface can be seen from Earth through shifts in perspective (its libration (Si apre in una nuova finestra)).[15] (Si apre in una nuova finestra)

The near side of the Moon is marked by dark volcanic maria (Si apre in una nuova finestra) ("seas"), which fill the spaces between bright ancient crustal highlands and prominent impact craters (Si apre in una nuova finestra). The lunar surface is relatively non-reflective, with a reflectance (Si apre in una nuova finestra) just slightly brighter than that of worn asphalt (Si apre in una nuova finestra). However, because it reflects direct sunlight, is contrasted (Si apre in una nuova finestra) by the relatively dark sky (Si apre in una nuova finestra), and has a large apparent size (Si apre in una nuova finestra) when viewed from Earth, the Moon is the brightest celestial object (Si apre in una nuova finestra) in Earth's sky after the Sun (Si apre in una nuova finestra). 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 (Si apre in una nuova finestra).

The first manmade object to reach the Moon was the Soviet Union (Si apre in una nuova finestra)'s Luna 2 (Si apre in una nuova finestra) uncrewed spacecraft (Si apre in una nuova finestra) in 1959; this was followed by the first successful soft landing by Luna 9 (Si apre in una nuova finestra) in 1966. The only human lunar missions to date have been those of the United States (Si apre in una nuova finestra)' NASA Apollo program (Si apre in una nuova finestra), which conducted the first manned lunar orbiting mission with Apollo 8 (Si apre in una nuova finestra) in 1968. Beginning with Apollo 11 (Si apre in una nuova finestra), six human landings took place between 1969 and 1972. These and later uncrewed missions returned lunar rocks (Si apre in una nuova finestra) which have been used to develop a detailed geological understanding (Si apre in una nuova finestra) of the Moon's origins (Si apre in una nuova finestra), internal structure (Si apre in una nuova finestra), and subsequent history; the most widely accepted origin explanation posits that the Moon formed about 4.51 billion years ago, not long after Earth (Si apre in una nuova finestra), out of the debris from a giant impact (Si apre in una nuova finestra) between the planet and a hypothesized Mars (Si apre in una nuova finestra)-sized body called Theia (Si apre in una nuova finestra).

Both the Moon's natural prominence in the earthly sky and its regular cycle of phases (Si apre in una nuova finestra) as seen from Earth have provided cultural references and influences for human societies and cultures throughout history. Such cultural influences can be found in language, calendar systems, art, and mythology.

Contents

Name and etymology

See also: List of lunar deities (Si apre in una nuova finestra)

The Moon, tinted reddish, during a lunar eclipse (Si apre in una nuova finestra)

During the lunar phases (Si apre in una nuova finestra), only portions of the Moon can be observed from Earth (Si apre in una nuova finestra).

The usual English (Si apre in una nuova finestra) proper name for Earth's natural satellite is simply the Moon, with a capital M.[16] (Si apre in una nuova finestra)[17] (Si apre in una nuova finestra) The noun moon is derived from Old English (Si apre in una nuova finestra)mōna, which (like all its Germanic (Si apre in una nuova finestra) cognates) stems from Proto-Germanic (Si apre in una nuova finestra) *mēnōn,[18] (Si apre in una nuova finestra) which in turn comes from Proto-Indo-European (Si apre in una nuova finestra) *mēnsis"month"[19] (Si apre in una nuova finestra) (from earlier *mēnōt, genitive *mēneses) which may be related to the verb "measure" (of time).[20] (Si apre in una nuova finestra)

Occasionally, the name Luna /ˈluːnə/ (Si apre in una nuova finestra) is used in scientific writing[21] (Si apre in una nuova finestra) and especially in science fiction to distinguish the Earth's moon from others, while in poetry "Luna" has been used to denote personification of Earth's moon.[22] (Si apre in una nuova finestra) Cynthia /ˈsɪnθiə/ (Si apre in una nuova finestra) is another poetic name, though rare, for the Moon personified as a goddess,[23] (Si apre in una nuova finestra) while Selene (Si apre in una nuova finestra) /səˈliːniː/ (Si apre in una nuova finestra) (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/ (Si apre in una nuova finestra),[24] (Si apre in una nuova finestra) 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,[25] (Si apre in una nuova finestra) while its cognate selenic was originally a rare synonym[26] (Si apre in una nuova finestra) but now nearly always refers to the chemical element selenium (Si apre in una nuova finestra).[27] (Si apre in una nuova finestra) The Greek word for the Moon does however provide us with the prefix seleno-, as in selenography (Si apre in una nuova finestra), the study of the physical features of the Moon, as well as the element name selenium.[28] (Si apre in una nuova finestra)[29] (Si apre in una nuova finestra)

The Greek goddess of the wilderness and the hunt, Artemis (Si apre in una nuova finestra), equated with the Roman Diana (Si apre in una nuova finestra), one of whose symbols was the Moon and who was often regarded as the goddess of the Moon, was also called Cynthia (Si apre in una nuova finestra), from her legendary birthplace on Mount Cynthus (Si apre in una nuova finestra).[30] (Si apre in una nuova finestra) These names – Luna, Cynthia and Selene – are reflected in technical terms for lunar orbits (Si apre in una nuova finestra) such as apolune, pericynthion and selenocentric.

The Moon

Near side of the Moon (Si apre in una nuova finestra)

Far side of the Moon (Si apre in una nuova finestra)

Lunar north pole (Si apre in una nuova finestra)

Lunar south pole (Si apre in una nuova finestra)

Formation

Main articles: Origin of the Moon (Si apre in una nuova finestra), Giant-impact hypothesis (Si apre in una nuova finestra), and Circumplanetary disk (Si apre in una nuova finestra)

The Moon formed 4.51 billion years ago,[f] (Si apre in una nuova finestra) or even 100 million years earlier, some 50 million years after the origin of the Solar System, as research published in 2019 suggests.[31] (Si apre in una nuova finestra) Several forming mechanisms have been proposed,[32] (Si apre in una nuova finestra) including the fission of the Moon from Earth's crust through centrifugal force (Si apre in una nuova finestra)[33] (Si apre in una nuova finestra) (which would require too great an initial rotation rate of Earth),[34] (Si apre in una nuova finestra) the gravitational capture of a pre-formed Moon[35] (Si apre in una nuova finestra) (which would require an unfeasibly extended atmosphere of Earth (Si apre in una nuova finestra) to dissipate (Si apre in una nuova finestra) the energy of the passing Moon),[34] (Si apre in una nuova finestra) and the co-formation of Earth and the Moon together in the primordial (Si apre in una nuova finestra) accretion disk (Si apre in una nuova finestra) (which does not explain the depletion of metals in the Moon).[34] (Si apre in una nuova finestra) These hypotheses also cannot account for the high angular momentum (Si apre in una nuova finestra) of the Earth–Moon system.[36] (Si apre in una nuova finestra)

The evolution of the Moon and a tour of the Moon

The prevailing theory is that the Earth–Moon system formed after a giant impact (Si apre in una nuova finestra) of a Mars (Si apre in una nuova finestra)-sized body (named Theia (Si apre in una nuova finestra)) with the proto-Earth (Si apre in una nuova finestra). The impact blasted material into Earth's orbit and then the material accreted and formed the Moon.[37] (Si apre in una nuova finestra)[38] (Si apre in una nuova finestra)

This theory 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 consensual.

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.[39] (Si apre in una nuova finestra)

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 also show that most of the Moon derived from the impactor, rather than the proto-Earth.[40] (Si apre in una nuova finestra) However, more recent simulations suggest a larger fraction of the Moon derived from the proto-Earth.[41] (Si apre in una nuova finestra)[42] (Si apre in una nuova finestra)[43] (Si apre in una nuova finestra)[44] (Si apre in una nuova finestra) Other bodies of the inner Solar System such as Mars and Vesta (Si apre in una nuova finestra) have, according to meteorites from them, very different oxygen and tungsten isotopic (Si apre in una nuova finestra) 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,[45] (Si apre in una nuova finestra) although this is debated.[46] (Si apre in una nuova finestra)

The impact released a lot of energy and then the released material re-accreted into the Earth–Moon system. This would have melted the outer shell of Earth, and thus formed a magma ocean.[47] (Si apre in una nuova finestra)[48] (Si apre in una nuova finestra) Similarly, the newly formed Moon would also have been affected and had its own lunar magma ocean (Si apre in una nuova finestra); its depth is estimated from about 500 km (300 miles) to 1,737 km (1,079 miles).[47] (Si apre in una nuova finestra)

While the giant-impact theory explains many lines of evidence, some questions are still unresolved, most of which involve the Moon's composition.[49] (Si apre in una nuova finestra)

Oceanus Procellarum (Si apre in una nuova finestra) ("Ocean of Storms")

Ancient rift valleys (Si apre in una nuova finestra) – rectangular structure (visible – topography – GRAIL gravity gradients (Si apre in una nuova finestra))

Ancient rift valleys (Si apre in una nuova finestra)– context

Ancient rift valleys (Si apre in una nuova finestra) – closeup (artist's concept)

In 2001, a team at the Carnegie Institute of Washington reported the most precise measurement of the isotopic signatures (Si apre in una nuova finestra) of lunar rocks.[50] (Si apre in una nuova finestra) The rocks from the Apollo program had the same isotopic signature as rocks from Earth, differing from almost all other bodies in the Solar System. This observation was unexpected, because most of the material that formed the Moon was thought to come from Theia (Si apre in una nuova finestra) and it was announced in 2007 that there was less than a 1% chance that Theia and Earth had identical isotopic signatures.[51] (Si apre in una nuova finestra) Other Apollo lunar samples had in 2012 the same titanium isotopes composition as Earth,[52] (Si apre in una nuova finestra) which conflicts (Si apre in una nuova finestra) with what is expected if the Moon formed far from Earth or is derived from Theia. These discrepancies may be explained by variations of the giant-impact theory.

Physical characteristics

The Moon is a very slightly scalene ellipsoid (Si apre in una nuova finestra) 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.[53] (Si apre in una nuova finestra)

Internal structure

Main article: Internal structure of the Moon (Si apre in una nuova finestra)

Lunar surface chemical composition[54] (Si apre in una nuova finestra)CompoundFormulaCompositionMariaHighlandssilica (Si apre in una nuova finestra)SiO245.4%45.5%alumina (Si apre in una nuova finestra)Al2O314.9%24.0%lime (Si apre in una nuova finestra)CaO11.8%15.9%iron(II) oxide (Si apre in una nuova finestra)FeO14.1%5.9%magnesia (Si apre in una nuova finestra)MgO9.2%7.5%titanium dioxide (Si apre in una nuova finestra)TiO23.9%0.6%sodium oxide (Si apre in una nuova finestra)Na2O0.6%0.6% 99.9%100.0%

The Moon is a differentiated (Si apre in una nuova finestra) body. It has a geochemically (Si apre in una nuova finestra) distinct crust (Si apre in una nuova finestra), mantle (Si apre in una nuova finestra), and core (Si apre in una nuova finestra). 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).[55] (Si apre in una nuova finestra)[56] (Si apre in una nuova finestra) This structure is thought to have developed through the fractional crystallization (Si apre in una nuova finestra) of a global magma ocean shortly after the Moon's formation 4.5 billion years ago.[57] (Si apre in una nuova finestra)

Crystallization of this magma ocean would have created a mafic (Si apre in una nuova finestra) mantle from the precipitation (Si apre in una nuova finestra) and sinking of the minerals olivine (Si apre in una nuova finestra), clinopyroxene (Si apre in una nuova finestra), and orthopyroxene (Si apre in una nuova finestra); after about three-quarters of the magma ocean had crystallised, lower-density plagioclase (Si apre in una nuova finestra) minerals could form and float into a crust atop.[58] (Si apre in una nuova finestra) The final liquids to crystallise would have been initially sandwiched between the crust and mantle, with a high abundance of incompatible (Si apre in una nuova finestra) and heat-producing elements.[1] (Si apre in una nuova finestra)

Consistent with this perspective, geochemical mapping made from orbit suggests the crust of mostly anorthosite (Si apre in una nuova finestra).[12] (Si apre in una nuova finestra) The Moon rock (Si apre in una nuova finestra) 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] (Si apre in una nuova finestra) The crust is on average about 50 kilometres (31 mi) thick.[1] (Si apre in una nuova finestra)

The Moon is the second-densest satellite in the Solar System, after Io (Si apre in una nuova finestra).[59] (Si apre in una nuova finestra) However, the inner core of the Moon is small, with a radius of about 350 kilometres (220 mi) or less,[1] (Si apre in una nuova finestra) 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.[60] (Si apre in una nuova finestra)

Surface geology

Main articles: Topography of the Moon (Si apre in una nuova finestra), Geology of the Moon (Si apre in una nuova finestra), Moon rock (Si apre in una nuova finestra), and List of lunar features (Si apre in una nuova finestra)

The Topographic Globe of the Moon

Geological features of the Moon (near side / north pole at left, far side / south pole at right)

Topography of the Moon

STL 3D model (Si apre in una nuova finestra) of the Moon with 10× elevation exaggeration rendered with data from the Lunar Orbiter Laser Altimeter of the Lunar Reconnaissance Orbiter (Si apre in una nuova finestra)

The topography of the Moon (Si apre in una nuova finestra) has been measured with laser altimetry (Si apre in una nuova finestra) and stereo image analysis (Si apre in una nuova finestra).[61] (Si apre in una nuova finestra) Its most visible topographic feature (Si apre in una nuova finestra) is the giant far-side South Pole–Aitken basin (Si apre in una nuova finestra), 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 (Si apre in una nuova finestra).[62] (Si apre in una nuova finestra)[63] (Si apre in una nuova finestra) At 13 km (8.1 mi) deep, its floor is the lowest point on the surface of the Moon.[62] (Si apre in una nuova finestra)[64] (Si apre in una nuova finestra) The highest elevations of the 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.[65] (Si apre in una nuova finestra) Other large impact basins such as Imbrium (Si apre in una nuova finestra), Serenitatis (Si apre in una nuova finestra), Crisium (Si apre in una nuova finestra), Smythii (Si apre in una nuova finestra), and Orientale (Si apre in una nuova finestra) also possess regionally low elevations and elevated rims.[62] (Si apre in una nuova finestra) 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] (Si apre in una nuova finestra)

The discovery of fault scarp (Si apre in una nuova finestra) cliffs by the Lunar Reconnaissance Orbiter (Si apre in una nuova finestra) suggest that the Moon has shrunk within the past billion years, by about 90 metres (300 ft).[66] (Si apre in una nuova finestra) Similar shrinkage features exist on Mercury (Si apre in una nuova finestra). A recent study of over 12000 images from the orbiter has observed that Mare Frigoris near the north pole, a vast basin assumed to be geologically dead, has been cracking and shifting. Since the Moon doesn't have tectonic plates, its tectonic activity is slow and cracks develop as it loses heat over the years.[67] (Si apre in una nuova finestra)

Volcanic features

Main article: Volcanism on the Moon (Si apre in una nuova finestra)

Lunar nearside (Si apre in una nuova finestra) with major maria (Si apre in una nuova finestra) and craters (Si apre in una nuova finestra) labeled

The dark and relatively featureless lunar plains, clearly seen with the naked eye, are called maria (Si apre in una nuova finestra) (Latin (Si apre in una nuova finestra) for "seas"; singular mare), as they were once believed to be filled with water;[68] (Si apre in una nuova finestra) they are now known to be vast solidified pools of ancient basaltic (Si apre in una nuova finestra) lava. Although similar to terrestrial basalts, lunar basalts have more iron and no minerals altered by water.[69] (Si apre in una nuova finestra) The majority of these lavas erupted or flowed into the depressions associated with impact basins (Si apre in una nuova finestra). Several geologic provinces (Si apre in una nuova finestra) containing shield volcanoes (Si apre in una nuova finestra) and volcanic domes (Si apre in una nuova finestra) are found within the near side "maria".[70] (Si apre in una nuova finestra)

Evidence of young lunar volcanism (Si apre in una nuova finestra)

Almost all maria are on the near side of the Moon, and cover 31% of the surface of the near side,[71] (Si apre in una nuova finestra) compared with 2% of the far side.[72] (Si apre in una nuova finestra) This is thought to be due to a concentration of heat-producing elements (Si apre in una nuova finestra) under the crust on the near side, seen on geochemical maps obtained by Lunar Prospector (Si apre in una nuova finestra)'s gamma-ray spectrometer, which would have caused the underlying mantle to heat up, partially melt, rise to the surface and erupt.[58] (Si apre in una nuova finestra)[73] (Si apre in una nuova finestra)[74] (Si apre in una nuova finestra) Most of the Moon's mare basalts (Si apre in una nuova finestra) 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.[75] (Si apre in una nuova finestra) Until recently, the youngest eruptions, dated by crater counting (Si apre in una nuova finestra), appeared to have been only 1.2 billion years ago.[76] (Si apre in una nuova finestra) In 2006, a study of Ina (Si apre in una nuova finestra), a tiny depression in Lacus Felicitatis (Si apre in una nuova finestra), found jagged, relatively dust-free features that, because of the lack of erosion by infalling debris, appeared to be only 2 million years old.[77] (Si apre in una nuova finestra) Moonquakes (Si apre in una nuova finestra) and releases of gas also indicate some continued lunar activity.[77] (Si apre in una nuova finestra) In 2014 NASA announced "widespread evidence of young lunar volcanism" at 70 irregular mare patches (Si apre in una nuova finestra) 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 because of the greater concentration of radioactive elements.[78] (Si apre in una nuova finestra)[79] (Si apre in una nuova finestra)[80] (Si apre in una nuova finestra)[81] (Si apre in una nuova finestra) Just prior to this, evidence has been presented for 2–10 million years younger basaltic volcanism inside the crater Lowell,[82] (Si apre in una nuova finestra)[83] (Si apre in una nuova finestra) 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.[84] (Si apre in una nuova finestra)[85] (Si apre in una nuova finestra)

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 (Si apre in una nuova finestra)cumulates (Si apre in una nuova finestra) of the lunar magma ocean.[75] (Si apre in una nuova finestra)[76] (Si apre in una nuova finestra) In contrast to Earth, no major lunar mountains are believed to have formed as a result of tectonic events.[86] (Si apre in una nuova finestra)

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 their formation.[87] (Si apre in una nuova finestra)[88] (Si apre in una nuova finestra)

Impact craters

Further information: List of craters on the Moon (Si apre in una nuova finestra)

Lunar crater Daedalus (Si apre in una nuova finestra) on the Moon's far side (Si apre in una nuova finestra)

The other major geologic process that has affected the Moon's surface is impact cratering (Si apre in una nuova finestra),[89] (Si apre in una nuova finestra) 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.[90] (Si apre in una nuova finestra) The lunar geologic timescale (Si apre in una nuova finestra) is based on the most prominent impact events, including Nectaris (Si apre in una nuova finestra), Imbrium (Si apre in una nuova finestra), and Orientale (Si apre in una nuova finestra), 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 (Si apre in una nuova finestra).[91] (Si apre in una nuova finestra) 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 (Si apre in una nuova finestra) 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.[91] (Si apre in una nuova finestra) The radiometric ages of impact-melted rocks collected during the Apollo missions (Si apre in una nuova finestra) cluster between 3.8 and 4.1 billion years old: this has been used to propose a Late Heavy Bombardment (Si apre in una nuova finestra) of impacts.[92] (Si apre in una nuova finestra)

Blanketed on top of the Moon's crust is a highly comminuted (Si apre in una nuova finestra) (broken into ever smaller particles) and impact gardened (Si apre in una nuova finestra) surface layer called regolith (Si apre in una nuova finestra), formed by impact processes. The finer regolith, the lunar soil (Si apre in una nuova finestra) of silicon dioxide (Si apre in una nuova finestra) glass, has a texture resembling snow and a scent resembling spent gunpowder (Si apre in una nuova finestra).[93] (Si apre in una nuova finestra)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.[94] (Si apre in una nuova finestra) Beneath the finely comminuted regolith layer is the megaregolith, a layer of highly fractured bedrock many kilometers thick.[95] (Si apre in una nuova finestra)

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 (Si apre in una nuova finestra) is thought to churn the top two centimeters of regolith a hundred times more quickly than previous models suggested – on a timescale of 81,000 years.[96] (Si apre in una nuova finestra)[97] (Si apre in una nuova finestra)

Lunar swirls at Reiner Gamma (Si apre in una nuova finestra)

Lunar swirls

Main article: Lunar swirls (Si apre in una nuova finestra)

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 have often a sinuous shape. Their shape is often accentuated by low albedo regions that wind between the bright swirls.

Presence of water

Main article: Lunar water (Si apre in una nuova finestra)

Liquid water cannot persist on the lunar surface. When exposed to solar radiation, water quickly decomposes through a process known as photodissociation (Si apre in una nuova finestra) and is lost to space. However, since the 1960s, scientists have hypothesized that water ice may be deposited by impacting comets (Si apre in una nuova finestra) or possibly produced by the reaction of oxygen-rich lunar rocks, and hydrogen from solar wind (Si apre in una nuova finestra), leaving traces of water which could possibly persist in cold, permanently shadowed craters at either pole on the Moon.[98] (Si apre in una nuova finestra)[99] (Si apre in una nuova finestra) Computer simulations suggest that up to 14,000 km2 (5,400 sq mi) of the surface may be in permanent shadow.[100] (Si apre in una nuova finestra) The presence of usable quantities of water on the Moon is an important factor in rendering lunar habitation (Si apre in una nuova finestra) as a cost-effective plan; the alternative of transporting water from Earth would be prohibitively expensive.[101] (Si apre in una nuova finestra)

In years since, signatures of water have been found to exist on the lunar surface.[102] (Si apre in una nuova finestra) In 1994, the bistatic radar experiment (Si apre in una nuova finestra) located on the Clementine (Si apre in una nuova finestra) spacecraft, indicated the existence of small, frozen pockets of water close to the surface. However, later radar observations by Arecibo (Si apre in una nuova finestra), suggest these findings may rather be rocks ejected from young impact craters.[103] (Si apre in una nuova finestra) In 1998, the neutron spectrometer (Si apre in una nuova finestra) 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.[104] (Si apre in una nuova finestra) Volcanic lava beads, brought back to Earth aboard Apollo 15, showed small amounts of water in their interior.[105] (Si apre in una nuova finestra)

The 2008 Chandrayaan-1 (Si apre in una nuova finestra) spacecraft has since confirmed the existence of surface water ice, using the on-board Moon Mineralogy Mapper (Si apre in una nuova finestra). The spectrometer observed absorption lines common to hydroxyl (Si apre in una nuova finestra), 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 (Si apre in una nuova finestra).[106] (Si apre in una nuova finestra) Using the mapper's reflectance spectra, indirect lighting of areas in shadow confirmed water ice within 20° latitude of both poles in 2018.[107] (Si apre in una nuova finestra) In 2009, LCROSS (Si apre in una nuova finestra) sent a 2,300 kg (5,100 lb) impactor into a permanently shadowed (Si apre in una nuova finestra) polar crater, and detected at least 100 kg (220 lb) of water in a plume of ejected material.[108] (Si apre in una nuova finestra)[109] (Si apre in una nuova finestra) Another examination of the LCROSS data showed the amount of detected water to be closer to 155 ± 12 kg (342 ± 26 lb).[110] (Si apre in una nuova finestra)

In May 2011, 615–1410 ppm water in melt inclusions (Si apre in una nuova finestra) in lunar sample 74220 was reported,[111] (Si apre in una nuova finestra) the famous high-titanium "orange glass soil" of volcanic origin collected during the Apollo 17 (Si apre in una nuova finestra) 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 (Si apre in una nuova finestra). 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.

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.[112] (Si apre in una nuova finestra)[113] (Si apre in una nuova finestra) The data revealed the distinct reflective signatures of water-ice, as opposed to dust and other reflective substances.[114] (Si apre in una nuova finestra) 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.[112] (Si apre in una nuova finestra)[114] (Si apre in una nuova finestra)

In October 2020, astronomers reported detecting molecular water (Si apre in una nuova finestra) on the sunlit surface of the Moon by several independent spacecraft, including the Stratospheric Observatory for Infrared Astronomy (Si apre in una nuova finestra) (SOFIA).[115] (Si apre in una nuova finestra)[116] (Si apre in una nuova finestra)[117] (Si apre in una nuova finestra)[118] (Si apre in una nuova finestra)

Gravitational field

Main article: Gravity of the Moon (Si apre in una nuova finestra)

GRAIL (Si apre in una nuova finestra)'s gravity map of the Moon

The gravitational field (Si apre in una nuova finestra) of the Moon has been measured through tracking the Doppler shift (Si apre in una nuova finestra) of radio signals emitted by orbiting spacecraft. The main lunar gravity features are mascons (Si apre in una nuova finestra), 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.[119] (Si apre in una nuova finestra)[120] (Si apre in una nuova finestra) 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.[121] (Si apre in una nuova finestra)

Magnetic field

Main article: Magnetic field of the Moon (Si apre in una nuova finestra)

The Moon has an external magnetic field (Si apre in una nuova finestra) of generally less than 0.2 nanoteslas (Si apre in una nuova finestra),[122] (Si apre in una nuova finestra) or less than one hundred thousandth that of Earth (Si apre in una nuova finestra). The Moon does not currently have a global dipolar (Si apre in una nuova finestra) magnetic field and only has crustal magnetization likely acquired early in its history when a dynamo was still operating.[123] (Si apre in una nuova finestra)[124] (Si apre in una nuova finestra) However, early in its history, 4 billion years ago, its magnetic field strength was likely close to that of Earth today.[122] (Si apre in una nuova finestra) This early dynamo field apparently expired by about one billion years ago, after the lunar core had completely crystallized.[122] (Si apre in una nuova finestra) 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 (Si apre in una nuova finestra) of the giant impact basins.[125] (Si apre in una nuova finestra)

Atmosphere

Main article: Atmosphere of the Moon (Si apre in una nuova finestra)

Sketch by the Apollo 17 astronauts. The lunar atmosphere was later studied by LADEE (Si apre in una nuova finestra).[126] (Si apre in una nuova finestra)[127] (Si apre in una nuova finestra)

The Moon has an atmosphere (Si apre in una nuova finestra) so tenuous as to be nearly vacuum (Si apre in una nuova finestra), with a total mass of less than 10 tonnes (9.8 long tons; 11 short tons).[128] (Si apre in una nuova finestra) The surface pressure of this small mass is around 3 × 10−15 atm (Si apre in una nuova finestra) (0.3 nPa (Si apre in una nuova finestra)); it varies with the lunar day. Its sources include outgassing (Si apre in una nuova finestra) and sputtering (Si apre in una nuova finestra), a product of the bombardment of lunar soil by solar wind ions.[12] (Si apre in una nuova finestra)[129] (Si apre in una nuova finestra) Elements that have been detected include sodium (Si apre in una nuova finestra) and potassium (Si apre in una nuova finestra), produced by sputtering (also found in the atmospheres of Mercury (Si apre in una nuova finestra) and Io (Si apre in una nuova finestra)); helium-4 (Si apre in una nuova finestra) and neon (Si apre in una nuova finestra)[130] (Si apre in una nuova finestra) from the solar wind; and argon-40 (Si apre in una nuova finestra), radon-222 (Si apre in una nuova finestra), and polonium-210 (Si apre in una nuova finestra), outgassed after their creation by radioactive decay (Si apre in una nuova finestra) within the crust and mantle.[131] (Si apre in una nuova finestra)[132] (Si apre in una nuova finestra) The absence of such neutral species (atoms or molecules) as oxygen (Si apre in una nuova finestra), nitrogen (Si apre in una nuova finestra), carbon (Si apre in una nuova finestra), hydrogen (Si apre in una nuova finestra) and magnesium (Si apre in una nuova finestra), which are present in the regolith (Si apre in una nuova finestra), is not understood.[131] (Si apre in una nuova finestra) Water vapor has been detected by Chandrayaan-1 (Si apre in una nuova finestra) and found to vary with latitude, with a maximum at ~60–70 degrees; it is possibly generated from the sublimation (Si apre in una nuova finestra) of water ice in the regolith.[133] (Si apre in una nuova finestra) 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.[131] (Si apre in una nuova finestra)

Dust

A permanent asymmetric Moon dust (Si apre in una nuova finestra) cloud exists around the Moon, created by small particles from comets. Estimates are 5 tons of comet particles strike the Moon's surface every 24 hours. The particles striking the Moon's surface eject Moon dust above the Moon. 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 to 100 kilometers above the surface. The dust measurements were made by LADEE (Si apre in una nuova finestra)'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 (Si apre in una nuova finestra), Quadrantid (Si apre in una nuova finestra), Northern Taurid (Si apre in una nuova finestra), and Omicron Centaurid (Si apre in una nuova finestra) meteor showers (Si apre in una nuova finestra), 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.[134] (Si apre in una nuova finestra)[135] (Si apre in una nuova finestra)

Past thicker atmosphere

In October 2017, NASA scientists at the Marshall Space Flight Center (Si apre in una nuova finestra) and the Lunar and Planetary Institute (Si apre in una nuova finestra) in Houston (Si apre in una nuova finestra) announced their finding, based on studies of Moon magma samples retrieved by the Apollo (Si apre in una nuova finestra) missions, 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 (Si apre in una nuova finestra). The ancient lunar atmosphere was eventually stripped away by solar winds and dissipated into space.[136] (Si apre in una nuova finestra)

Seasons

The Moon's axial tilt (Si apre in una nuova finestra) with respect to the ecliptic (Si apre in una nuova finestra) is only 1.5424°,[137] (Si apre in una nuova finestra) 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.[138] (Si apre in una nuova finestra) From images taken by Clementine (Si apre in una nuova finestra) in 1994, it appears that four mountainous regions on the rim of the crater Peary (Si apre in una nuova finestra) at the Moon's north pole may remain illuminated for the entire lunar day (Si apre in una nuova finestra), creating peaks of eternal light (Si apre in una nuova finestra). No such regions exist at the south pole. Similarly, there are places that remain in permanent shadow at the bottoms of many polar craters,[100] (Si apre in una nuova finestra) and these "craters of eternal darkness (Si apre in una nuova finestra)" are extremely cold: Lunar Reconnaissance Orbiter measured the lowest summer temperatures in craters at the southern pole at 35 K (−238 °C; −397 °F)[139] (Si apre in una nuova finestra) and just 26 K (−247 °C; −413 °F) close to the winter solstice in the north polar crater Hermite (Si apre in una nuova finestra). This is the coldest temperature in the Solar System ever measured by a spacecraft, colder even than the surface of Pluto (Si apre in una nuova finestra).[138] (Si apre in una nuova finestra) 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.[140] (Si apre in una nuova finestra)

Rotation

The Moon is rotating around its own axis. This rotation is due to tidal locking (Si apre in una nuova finestra) synchronous to its orbital period (Si apre in una nuova finestra) around Earth.

The rotation period (Si apre in una nuova finestra) depends on the frame of reference. There are sidereal rotation periods (or sidereal day (Si apre in una nuova finestra), in relation to the stars), and synodic rotation periods (or synodic day (Si apre in una nuova finestra), in relation to the Sun). A lunar day (Si apre in una nuova finestra) is a synodic day.

Because of the tidal locked rotation, the sidereal and synodic rotation periods correspond to the sidereal (27.3 Earth days) and synodic (29.5 Earth days) orbital periods.[141] (Si apre in una nuova finestra)

Earth–Moon system

See also: Satellite system (astronomy) (Si apre in una nuova finestra) and Other moons of Earth (Si apre in una nuova finestra)

Lunar distance

Main article: Lunar distance (astronomy) (Si apre in una nuova finestra)

This section is an excerpt from Lunar distance (astronomy) (Si apre in una nuova finestra)[edit (Si apre in una nuova finestra)]

Lunar distance (Si apre in una nuova finestra) (LD or ), also called Earth–Moon distance, Earth–Moon characteristic distance, or distance to the Moon, is a unit of measure (Si apre in una nuova finestra) in astronomy (Si apre in una nuova finestra). It is the average distance from the center of Earth (Si apre in una nuova finestra) to the center of the Moon. More technically, it is the mean semi-major axis (Si apre in una nuova finestra) of the geocentric lunar orbit (Si apre in una nuova finestra). It may also refer to the time-averaged distance between the centers of the Earth and the Moon, or less commonly, the instantaneous Earth–Moon distance. The lunar distance is approximately 400,000 km (Si apre in una nuova finestra), which is a quarter of a million miles (Si apre in una nuova finestra) or 1.28 light-seconds (Si apre in una nuova finestra). This is roughly Earth's circumference (Si apre in una nuova finestra) times ten, its diameter (Si apre in una nuova finestra) times thirty or 1/389 of Earth's distance to the Sun (the astronomical unit (Si apre in una nuova finestra)).A lunar distance, 384402 km (Si apre in una nuova finestra), is the Moon's average distance to Earth. The actual distance varies over the course of its orbit (Si apre in una nuova finestra). The image compares the Moon's apparent size (Si apre in una nuova finestra) when it is closest (Si apre in una nuova finestra)and farthest from Earth.

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

Orbit

Main articles: Orbit of the Moon (Si apre in una nuova finestra) and Lunar theory (Si apre in una nuova finestra)

Animation of Moon's orbit around Earth from 2018 to 2027
 Moon ·   Earth (Si apre in una nuova finestra)

Earth–Moon system (schematic)

DSCOVR satellite (Si apre in una nuova finestra) sees the Moon passing in front of Earth

The Moon makes a complete orbit around Earth with respect to the fixed stars about once every 27.3 days[g] (Si apre in una nuova finestra) (its sidereal period (Si apre in una nuova finestra)). However, because Earth is moving in its orbit around the Sun at the same time, it takes slightly longer for the Moon to show the same phase (Si apre in una nuova finestra) to Earth, which is about 29.5 days[h] (Si apre in una nuova finestra) (its synodic period (Si apre in una nuova finestra)).[71] (Si apre in una nuova finestra) Unlike most satellites of other planets, the Moon orbits closer to the ecliptic plane (Si apre in una nuova finestra) than to the planet's equatorial plane (Si apre in una nuova finestra). The Moon's orbit is subtly perturbed (Si apre in una nuova finestra) by the Sun and Earth in many small, complex and interacting ways. For example, the plane of the Moon's orbit gradually rotates (Si apre in una nuova finestra) once every 18.61 years,[142] (Si apre in una nuova finestra) which affects other aspects of lunar motion. These follow-on effects are mathematically described by Cassini's laws (Si apre in una nuova finestra).[143] (Si apre in una nuova finestra)

Relative size

The Moon is an exceptionally large natural satellite relative to Earth: Its diameter is more than a quarter and its mass is 1/81 of Earth's.[71] (Si apre in una nuova finestra) It is the largest moon in the Solar System relative to the size of its planet,[i] (Si apre in una nuova finestra) though Charon (Si apre in una nuova finestra) is larger relative to the dwarf planet Pluto, at 1/9 Pluto's mass.[j] (Si apre in una nuova finestra)[144] (Si apre in una nuova finestra) The Earth and the Moon's barycentre (Si apre in una nuova finestra), their common center of mass, is located 1,700 km (1,100 mi) (about a quarter of Earth's radius) beneath the Earth's surface.

The Earth revolves around the Earth-Moon barycentre once a sidereal month, with 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 around the Sun at a speed of about 30 kilometres (19 mi) per second.

The surface area of the Moon is slightly less than the areas of North and South America (Si apre in una nuova finestra) combined.

Appearance from Earth

A full moon appears as a half moon during an eclipse moonset over the High Desert (Si apre in una nuova finestra) in California, on the morning of the Trifecta: Full moon (Si apre in una nuova finestra), Supermoon (Si apre in una nuova finestra), Lunar eclipse (Si apre in una nuova finestra), January 2018 lunar eclipse (Si apre in una nuova finestra)

See also: Lunar observation (Si apre in una nuova finestra), Lunar phase (Si apre in una nuova finestra), Moonlight (Si apre in una nuova finestra), and Earthlight (astronomy) (Si apre in una nuova finestra)

The Moon is in synchronous rotation (Si apre in una nuova finestra) as it orbits (Si apre in una nuova finestra) 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, because of the effect of libration (Si apre in una nuova finestra), about 59% of the Moon's surface can actually be seen from Earth. The side of the Moon that faces Earth is called the near side (Si apre in una nuova finestra), and the opposite the far side (Si apre in una nuova finestra). 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 new moon (Si apre in una nuova finestra), the near side is dark.[145] (Si apre in una nuova finestra)

The Moon had once rotated at a faster rate, but early in its history its rotation slowed and became tidally locked (Si apre in una nuova finestra) in this orientation as a result of frictional (Si apre in una nuova finestra) effects associated with tidal (Si apre in una nuova finestra) deformations caused by Earth.[146] (Si apre in una nuova finestra) 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 much earlier NASA Lunar Prospector (Si apre in una nuova finestra) 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.[147] (Si apre in una nuova finestra)

The Moon is prominently featured in Vincent van Gogh (Si apre in una nuova finestra)'s 1889 painting, The Starry Night (Si apre in una nuova finestra)

The Moon has an exceptionally low albedo (Si apre in una nuova finestra), giving it a reflectance (Si apre in una nuova finestra) that is slightly brighter than that of worn asphalt (Si apre in una nuova finestra). Despite this, it is the brightest object in the sky after the Sun (Si apre in una nuova finestra).[71] (Si apre in una nuova finestra)[k] (Si apre in una nuova finestra) This is due partly to the brightness enhancement of the opposition surge (Si apre in una nuova finestra); the Moon at quarter phase is only one-tenth as bright, rather than half as bright, as at full moon (Si apre in una nuova finestra).[148] (Si apre in una nuova finestra) Additionally, color constancy (Si apre in una nuova finestra) in the visual system (Si apre in una nuova finestra) 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 (Si apre in una nuova finestra), because of the reflective properties (Si apre in una nuova finestra) of lunar soil (Si apre in una nuova finestra), which retroreflects (Si apre in una nuova finestra) light more towards the Sun than in other directions. The Moon does appear larger when close to the horizon, but this is a purely psychological effect, known as the moon illusion (Si apre in una nuova finestra), first described in the 7th century BC.[149] (Si apre in una nuova finestra) The full Moon's angular diameter (Si apre in una nuova finestra) is about 0.52° (on average) in the sky, roughly the same apparent size as the Sun (see § Eclipses (Si apre in una nuova finestra)).

The Moon's highest altitude (Si apre in una nuova finestra) at culmination (Si apre in una nuova finestra) varies by its phase (Si apre in una nuova finestra) and time of year. The full moon is highest in the sky during winter (for each hemisphere). The orientation of the Moon's crescent (Si apre in una nuova finestra) also depends on the latitude of the viewing location; an observer in the tropics (Si apre in una nuova finestra) can see a smile-shaped crescent (Si apre in una nuova finestra)Moon.[150] (Si apre in una nuova finestra) The Moon is visible for two weeks every 27.3 days at the North (Si apre in una nuova finestra) and South Poles (Si apre in una nuova finestra). Zooplankton (Si apre in una nuova finestra) in the Arctic (Si apre in una nuova finestra) use moonlight (Si apre in una nuova finestra) when the Sun is below the horizon (Si apre in una nuova finestra) for months on end.[151] (Si apre in una nuova finestra)

14 November 2016 supermoon (Si apre in una nuova finestra) was 356,511 kilometres (221,526 mi) away[152] (Si apre in una nuova finestra) from the center of Earth, the closest occurrence since 26 January 1948. It will not be closer until 25 November 2034.[153] (Si apre in una nuova finestra)

The distance between the Moon and Earth (Si apre in una nuova finestra) varies from around 356,400 km (221,500 mi) to 406,700 km (252,700 mi) at perigee (Si apre in una nuova finestra) (closest) and apogee (farthest), respectively. On 14 November 2016, it was closer to Earth when at full phase than it has been since 1948, 14% closer than its farthest position in apogee.[154] (Si apre in una nuova finestra) Reported as a "supermoon (Si apre in una nuova finestra)", this closest point coincided within an hour of a full moon, and it was 30% more luminous than when at its greatest distance because its angular diameter is 14% greater and .[155] (Si apre in una nuova finestra)[156] (Si apre in una nuova finestra)[157] (Si apre in una nuova finestra) At lower levels, the human perception of reduced brightness as a percentage is provided by the following formula:[158] (Si apre in una nuova finestra)[159] (Si apre in una nuova finestra)

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.[160] (Si apre in una nuova finestra)

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 (Si apre in una nuova finestra), or inadequate drawings. However, outgassing (Si apre in una nuova finestra) does occasionally occur and could be responsible for a minor percentage of the reported lunar transient phenomena (Si apre in una nuova finestra). 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.[161] (Si apre in una nuova finestra)[162] (Si apre in una nuova finestra)

The Moon's appearance, like the Sun's, can be affected by Earth's atmosphere (Si apre in una nuova finestra). Common optical effects are the 22° halo ring (Si apre in una nuova finestra), formed when the Moon's light is refracted through the ice crystals (Si apre in una nuova finestra) of high cirrostratus (Si apre in una nuova finestra) clouds, and smaller coronal rings (Si apre in una nuova finestra) when the Moon is seen through thin clouds.[163] (Si apre in una nuova finestra)

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

The illuminated area of the visible sphere (degree of illumination) is given by , where is the elongation (Si apre in una nuova finestra) (i.e., the angle between Moon, the observer (on Earth) and the Sun).

Tidal effects

Main articles: Tidal force (Si apre in una nuova finestra), Tidal acceleration (Si apre in una nuova finestra), Tide (Si apre in una nuova finestra), and Theory of tides (Si apre in una nuova finestra)

The libration (Si apre in una nuova finestra) of the 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 has for the side of Earth closest to the Moon, as compared to the part of the Earth opposite the Moon, results in tidal forces (Si apre in una nuova finestra). 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 and the other on the side opposite. This results in elevated sea levels called ocean tides (Si apre in una nuova finestra).[164] (Si apre in una nuova finestra) 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.[164] (Si apre in una nuova finestra) 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. The 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 (Si apre in una nuova finestra).[164] (Si apre in una nuova finestra) 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 (Si apre in una nuova finestra) of water's movement, ocean basins that grow shallower near land, the sloshing of water between different ocean basins.[165] (Si apre in una nuova finestra) 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.

While gravitation causes acceleration and movement of the Earth's fluid oceans, gravitational coupling between the Moon and Earth's solid body is mostly elastic and plastic. The result is a further tidal effect of the Moon on the Earth that causes a bulge of the solid portion of the Earth nearest the Moon that acts as a torque (Si apre in una nuova finestra) in opposition to the Earth's rotation. This "drains" angular momentum (Si apre in una nuova finestra) and rotational kinetic energy (Si apre in una nuova finestra) from Earth's rotation, slowing the Earth's rotation.[164] (Si apre in una nuova finestra)[166] (Si apre in una nuova finestra) That angular momentum, lost from the Earth, is transferred to the Moon in a process (confusingly known as tidal acceleration (Si apre in una nuova finestra)), which lifts the Moon into a higher orbit and results in its lower orbital speed about the Earth. Thus the distance between Earth and Moon is increasing (Si apre in una nuova finestra), and the Earth's rotation is slowing in reaction.[166] (Si apre in una nuova finestra) Measurements from laser reflectors left during the Apollo missions (lunar ranging experiments (Si apre in una nuova finestra)) have found that the Moon's distance increases by 38 mm (1.5 in) per year[167] (Si apre in una nuova finestra) (roughly the rate at which human fingernails grow).[168] (Si apre in una nuova finestra) Atomic clocks (Si apre in una nuova finestra)also show that Earth's day lengthens by about 15 microseconds (Si apre in una nuova finestra) every year,[169] (Si apre in una nuova finestra) slowly increasing the rate at which UTC (Si apre in una nuova finestra) is adjusted by leap seconds (Si apre in una nuova finestra). Left to run its course, this tidal drag would continue until the rotation of Earth and the orbital period of the Moon matched, creating mutual tidal locking between the two. As a result, the Moon would be suspended in the sky over one meridian, as is already currently the case with Pluto and its moon Charon. However, the Sun will become a red giant (Si apre in una nuova finestra) engulfing the Earth-Moon system long before this occurrence.[170] (Si apre in una nuova finestra)[171] (Si apre in una nuova finestra) If it were to happen, the rotation of the earth would continue to slow down because of the tides caused by the sun. With the day longer than the month, the moon would move slowly from west to east in the sky. The tides caused by the moon would then cause the opposite effect from before, and the moon would get closer to the earth. Eventually it would come within the Roche limit (Si apre in una nuova finestra) and be broken up into a ring (Si apre in una nuova finestra).

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 (Si apre in una nuova finestra), and a varying component from the Sun.[166] (Si apre in una nuova finestra) The Earth-induced component arises from libration (Si apre in una nuova finestra), a result of the Moon's orbital eccentricity (if the Moon's orbit were perfectly circular, there would only be solar tides).[166] (Si apre in una nuova finestra) Libration also changes the angle from which the Moon is seen, allowing a total of about 59% of its surface to be seen from Earth over time.[71] (Si apre in una nuova finestra) The cumulative effects of stress built up by these tidal forces produces moonquakes (Si apre in una nuova finestra). 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 the absence of water to damp out the seismic vibrations. The existence of moonquakes was an unexpected discovery from seismometers (Si apre in una nuova finestra) placed on the Moon by Apollo (Si apre in una nuova finestra) astronauts (Si apre in una nuova finestra) from 1969 through 1972.[172] (Si apre in una nuova finestra)

According to recent research, scientists suggest that the Moon's influence on the Earth may contribute to maintaining Earth's magnetic field (Si apre in una nuova finestra).[173] (Si apre in una nuova finestra)

Eclipses

Main articles: Solar eclipse (Si apre in una nuova finestra), Lunar eclipse (Si apre in una nuova finestra), and Eclipse cycle (Si apre in una nuova finestra)

From Earth, the Moon and the Sun appear the same size, as seen in the 1999 solar eclipse (Si apre in una nuova finestra) (left), whereas from the STEREO-B (Si apre in una nuova finestra) spacecraft in an Earth-trailing orbit, the Moon appears much smaller than the Sun (right).[174] (Si apre in una nuova finestra)

Eclipses only occur when the Sun, Earth, and Moon are all in a straight line (termed "syzygy (Si apre in una nuova finestra)"). Solar eclipses (Si apre in una nuova finestra) occur at new moon (Si apre in una nuova finestra), when the Moon is between the Sun and Earth. In contrast, lunar eclipses (Si apre in una nuova finestra) 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 (Si apre in una nuova finestra) (with the Moon appearing larger than the Sun) and annular (Si apre in una nuova finestra) (with the Moon appearing smaller than the Sun) solar eclipses.[175] (Si apre in una nuova finestra) In a total eclipse, the Moon completely covers the disc of the Sun and the solar corona (Si apre in una nuova finestra) becomes visible to the naked eye (Si apre in una nuova finestra). Because the distance between the Moon and Earth is very slowly increasing over time,[164] (Si apre in una nuova finestra) the angular diameter of the Moon is decreasing. Also, as it evolves toward becoming a red giant (Si apre in una nuova finestra), the size of the Sun, and its apparent diameter in the sky, are slowly increasing.[l] (Si apre in una nuova finestra)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.[176] (Si apre in una nuova finestra)

Because the Moon's orbit around Earth is inclined by about 5.145° (5° 9') to the orbit of Earth around the Sun (Si apre in una nuova finestra), 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.[177] (Si apre in una nuova finestra) The periodicity and recurrence of eclipses of the Sun by the Moon, and of the Moon by Earth, is described by the saros (Si apre in una nuova finestra), which has a period of approximately 18 years.[178] (Si apre in una nuova finestra)

Because the Moon continuously blocks the view of a half-degree-wide circular area of the sky,[m] (Si apre in una nuova finestra)[179] (Si apre in una nuova finestra) the related phenomenon of occultation (Si apre in una nuova finestra) 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 (Si apre in una nuova finestra) of the lunar orbit, each year different stars are occulted.[180] (Si apre in una nuova finestra)

Observation and exploration

Main articles: Exploration of the Moon (Si apre in una nuova finestra), List of spacecraft that orbited the Moon (Si apre in una nuova finestra), List of missions to the Moon (Si apre in una nuova finestra), and List of lunar probes (Si apre in una nuova finestra)

See also: Timeline of Solar System exploration (Si apre in una nuova finestra)

Before spaceflight

Main article: Exploration of the Moon: Before spaceflight (Si apre in una nuova finestra)

Map of the Moon by Johannes Hevelius (Si apre in una nuova finestra) from his Selenographia (Si apre in una nuova finestra) (1647), the first map to include the libration (Si apre in una nuova finestra)zones

A study of the Moon in Robert Hooke's (Si apre in una nuova finestra) Micrographia (Si apre in una nuova finestra), 1665

One of the earliest-discovered possible depictions of the Moon is a 5000-year-old rock carving Orthostat 47 (Si apre in una nuova finestra) at Knowth (Si apre in una nuova finestra), Ireland.[181] (Si apre in una nuova finestra)[182] (Si apre in una nuova finestra)

Understanding of the Moon's cycles was an early development of astronomy: by the 5th century BC, Babylonian astronomers (Si apre in una nuova finestra) had recorded the 18-year Saros cycle (Si apre in una nuova finestra) of lunar eclipses (Si apre in una nuova finestra),[183] (Si apre in una nuova finestra) and Indian astronomers (Si apre in una nuova finestra) had described the Moon's monthly elongation.[184] (Si apre in una nuova finestra) The Chinese astronomer (Si apre in una nuova finestra) Shi Shen (Si apre in una nuova finestra)(fl. 4th century BC) gave instructions for predicting solar and lunar eclipses.[185] (Si apre in una nuova finestra)(p411) Later, the physical form of the Moon and the cause of moonlight (Si apre in una nuova finestra)became understood. The ancient Greek (Si apre in una nuova finestra) philosopher Anaxagoras (Si apre in una nuova finestra) (d. 428 BC) reasoned that the Sun and Moon were both giant spherical rocks, and that the latter reflected the light of the former.[186] (Si apre in una nuova finestra)[185] (Si apre in una nuova finestra)(p227) Although the Chinese of the Han Dynasty (Si apre in una nuova finestra) believed the Moon to be energy equated to qi (Si apre in una nuova finestra), their 'radiating influence' theory also recognized that the light of the Moon was merely a reflection of the Sun, and Jing Fang (Si apre in una nuova finestra) (78–37 BC) noted the sphericity of the Moon.[185] (Si apre in una nuova finestra)(pp413–414) In the 2nd century AD, Lucian (Si apre in una nuova finestra) wrote the novel A True Story (Si apre in una nuova finestra), in which the heroes travel to the Moon and meet its inhabitants. In 499 AD, the Indian astronomer Aryabhata (Si apre in una nuova finestra) mentioned in his Aryabhatiya (Si apre in una nuova finestra) that reflected sunlight is the cause of the shining of the Moon.[187] (Si apre in una nuova finestra) The astronomer and physicist Alhazen (Si apre in una nuova finestra) (965–1039) found that sunlight (Si apre in una nuova finestra) 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.[188] (Si apre in una nuova finestra) Shen Kuo (Si apre in una nuova finestra) (1031–1095) of the Song dynasty (Si apre in una nuova finestra) 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.[185] (Si apre in una nuova finestra)(pp415–416)

Galileo (Si apre in una nuova finestra)'s sketches of the Moon from Sidereus Nuncius (Si apre in una nuova finestra)

In Aristotle (Si apre in una nuova finestra)'s (384–322 BC) description of the universe (Si apre in una nuova finestra), the Moon marked the boundary between the spheres of the mutable elements (earth, water, air and fire), and the imperishable stars of aether (Si apre in una nuova finestra), an influential philosophy (Si apre in una nuova finestra) that would dominate for centuries.[189] (Si apre in una nuova finestra) However, in the 2nd century BC, Seleucus of Seleucia (Si apre in una nuova finestra) correctly theorized that tides (Si apre in una nuova finestra) were due to the attraction of the Moon, and that their height depends on the Moon's position relative to the Sun (Si apre in una nuova finestra).[190] (Si apre in una nuova finestra) In the same century, Aristarchus (Si apre in una nuova finestra) computed the size and distance (Si apre in una nuova finestra) of the Moon from Earth, obtaining a value of about twenty times the radius of Earth (Si apre in una nuova finestra) for the distance. These figures were greatly improved by Ptolemy (Si apre in una nuova finestra) (90–168 AD): his 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.[191] (Si apre in una nuova finestra) Archimedes (Si apre in una nuova finestra) (287–212 BC) designed a planetarium that could calculate the motions of the Moon and other objects in the Solar System.[192] (Si apre in una nuova finestra)

During the Middle Ages (Si apre in una nuova finestra), before the invention of the telescope, the Moon was increasingly recognised as a sphere, though many believed that it was "perfectly smooth".[193] (Si apre in una nuova finestra)

In 1609, Galileo Galilei (Si apre in una nuova finestra) drew one of the first telescopic drawings of the Moon in his book Sidereus Nuncius (Si apre in una nuova finestra) and noted that it was not smooth but had mountains and craters. Thomas Harriot (Si apre in una nuova finestra) had made, but not published such drawings a few months earlier. Telescopic mapping of the Moon followed: later in the 17th century, the efforts of Giovanni Battista Riccioli (Si apre in una nuova finestra) and Francesco Maria Grimaldi (Si apre in una nuova finestra) led to the system of naming of lunar features in use today. The more exact 1834–36 Mappa Selenographica of Wilhelm Beer (Si apre in una nuova finestra) and Johann Heinrich Mädler (Si apre in una nuova finestra), and their associated 1837 book Der Mond, the first trigonometrically (Si apre in una nuova finestra) 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.[194] (Si apre in una nuova finestra) Lunar craters, first noted by Galileo, were thought to be volcanic (Si apre in una nuova finestra) until the 1870s proposal of Richard Proctor (Si apre in una nuova finestra)that they were formed by collisions.[71] (Si apre in una nuova finestra) This view gained support in 1892 from the experimentation of geologist Grove Karl Gilbert (Si apre in una nuova finestra), and from comparative studies from 1920 to the 1940s,[195] (Si apre in una nuova finestra) leading to the development of lunar stratigraphy (Si apre in una nuova finestra), which by the 1950s was becoming a new and growing branch of astrogeology (Si apre in una nuova finestra).[71] (Si apre in una nuova finestra)

1959–1970s

See also: Space Race (Si apre in una nuova finestra) and Moon landing (Si apre in una nuova finestra)

Between the first human arrival with the robotic Soviet (Si apre in una nuova finestra) Luna program (Si apre in una nuova finestra) in 1958, to the 1970s with the last Missions of the crewed U.S. (Si apre in una nuova finestra) Apollo landings (Si apre in una nuova finestra) and last Luna mission in 1976, the Cold War (Si apre in una nuova finestra)-inspired Space Race (Si apre in una nuova finestra) between the Soviet Union and the U.S. led to an acceleration of interest in exploration of the Moon (Si apre in una nuova finestra). Once launchers had the necessary capabilities, these nations sent uncrewed probes on both flyby and impact/lander missions.

Soviet missions

Main articles: Luna program (Si apre in una nuova finestra) and Lunokhod programme (Si apre in una nuova finestra)

First view in history of the far side of the Moon, taken by Luna 3 (Si apre in una nuova finestra), 7 October 1959

A model of Soviet Moon rover Lunokhod 1 (Si apre in una nuova finestra)

Spacecraft from the Soviet Union's Luna program (Si apre in una nuova finestra) were the first to accomplish a number of goals: following three unnamed, failed missions in 1958,[196] (Si apre in una nuova finestra) the first human-made object to escape Earth's gravity and pass near the Moon was Luna 1 (Si apre in una nuova finestra); the first human-made object to impact the lunar surface was Luna 2 (Si apre in una nuova finestra), and the first photographs of the normally occluded far side of the Moon were made by Luna 3 (Si apre in una nuova finestra), all in 1959.

Stamp with a drawing of the first soft landed probe Luna 9 (Si apre in una nuova finestra), next to the first view of the lunar surface photographed by the probe

The first spacecraft to perform a successful lunar soft landing (Si apre in una nuova finestra) was Luna 9 (Si apre in una nuova finestra) and the first uncrewed vehicle to orbit the Moon was Luna 10 (Si apre in una nuova finestra), both in 1966.[71] (Si apre in una nuova finestra)Rock and soil samples (Si apre in una nuova finestra) were brought back to Earth by three Luna sample return missions (Si apre in una nuova finestra) (Luna 16 (Si apre in una nuova finestra) in 1970, Luna 20 (Si apre in una nuova finestra) in 1972, and Luna 24 (Si apre in una nuova finestra) in 1976), which returned 0.3 kg total.[197] (Si apre in una nuova finestra) Two pioneering robotic rovers (Si apre in una nuova finestra) landed on the Moon in 1970 and 1973 as a part of Soviet Lunokhod programme (Si apre in una nuova finestra).

Luna 24 was the last Soviet mission to the Moon.

United States missions

Main articles: Apollo program (Si apre in una nuova finestra) and Moon landing (Si apre in una nuova finestra)

Earthrise (Si apre in una nuova finestra) (Apollo 8 (Si apre in una nuova finestra), 1968, taken by William Anders (Si apre in una nuova finestra))

Moon rock (Si apre in una nuova finestra) (Apollo 17 (Si apre in una nuova finestra), 1972)

During the late 1950s at the height of the Cold War, the United States Army conducted a classified feasibility study (Si apre in una nuova finestra) that proposed the construction of a staffed military outpost on the Moon called Project Horizon (Si apre in una nuova finestra) 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.[198] (Si apre in una nuova finestra)[199] (Si apre in una nuova finestra) 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 (Si apre in una nuova finestra).[200] (Si apre in una nuova finestra)[201] (Si apre in una nuova finestra)[198] (Si apre in una nuova finestra) However, both these proposals were ultimately passed over as the space program was largely transferred from the military to the civilian agency NASA.[201] (Si apre in una nuova finestra)

Following President John F. Kennedy (Si apre in una nuova finestra)'s 1961 commitment to a human 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 (Si apre in una nuova finestra)'s Ranger program (Si apre in una nuova finestra) produced the first close-up pictures; the Lunar Orbiter program (Si apre in una nuova finestra) produced maps of the entire Moon; the Surveyor program (Si apre in una nuova finestra)landed its first spacecraft (Si apre in una nuova finestra) 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 (Si apre in una nuova finestra), in 1968 Apollo 8 (Si apre in una nuova finestra) 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.[202] (Si apre in una nuova finestra)

Neil Armstrong (Si apre in una nuova finestra) working at the Lunar Module Eagle (Si apre in una nuova finestra) during Apollo 11 (Si apre in una nuova finestra) (1969)

"That's one small step ..." (Si apre in una nuova finestra)

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Neil Armstrong (Si apre in una nuova finestra) became the first person to walk on the Moon as the commander of the American mission Apollo 11 (Si apre in una nuova finestra) by first setting foot on the Moon at 02:56 UTC on 21 July 1969.[203] (Si apre in una nuova finestra) An estimated 500 million people worldwide watched the transmission by the Apollo TV camera (Si apre in una nuova finestra), the largest television audience for a live broadcast at that time.[204] (Si apre in una nuova finestra)[205] (Si apre in una nuova finestra) The Apollo missions 11 to 17 (except Apollo 13 (Si apre in una nuova finestra), which aborted its planned lunar landing) removed 380.05 kilograms (837.87 lb) of lunar rock and soil in 2,196 separate samples.[206] (Si apre in una nuova finestra) The American Moon landing (Si apre in una nuova finestra) and return was enabled by considerable technological advances in the early 1960s, in domains such as ablation (Si apre in una nuova finestra) chemistry, software engineering (Si apre in una nuova finestra), and atmospheric re-entry (Si apre in una nuova finestra) technology, and by highly competent management of the enormous technical undertaking.[207] (Si apre in una nuova finestra)[208] (Si apre in una nuova finestra)

Scientific instrument packages were installed on the lunar surface during all the Apollo landings. Long-lived instrument stations (Si apre in una nuova finestra), including heat flow probes, seismometers (Si apre in una nuova finestra), and magnetometers (Si apre in una nuova finestra), were installed at the Apollo 12 (Si apre in una nuova finestra), 14 (Si apre in una nuova finestra), 15 (Si apre in una nuova finestra), 16 (Si apre in una nuova finestra), and 17 (Si apre in una nuova finestra) landing sites. Direct transmission of data to Earth concluded in late 1977 because of budgetary considerations,[209] (Si apre in una nuova finestra)[210] (Si apre in una nuova finestra)but as the stations' lunar laser ranging (Si apre in una nuova finestra) 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.[211] (Si apre in una nuova finestra)

1970s – present

An artificially (Si apre in una nuova finestra) colored mosaic constructed from a series of 53 images taken through three spectral filters (Si apre in una nuova finestra) by Galileo' s imaging system as the spacecraft flew over the northern regions of the Moon on 7 December 1992.

After the Moon race the focus of astronautic exploration shifted in the 1970s with probes like Pioneer 10 (Si apre in una nuova finestra) and the Voyager program (Si apre in una nuova finestra) towards the outer solar system (Si apre in una nuova finestra). Years of near lunar quietude followed, only broken by a beginning internationalization of space and the Moon through for example the negotiation of the Moon treaty (Si apre in una nuova finestra).

Since 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 (Si apre in una nuova finestra) spacecraft. The spacecraft released a smaller probe, Hagoromo, in lunar orbit, but the transmitter failed, preventing further scientific use of the mission.[212] (Si apre in una nuova finestra) In 1994, the U.S. sent the joint Defense Department/NASA spacecraft Clementine (Si apre in una nuova finestra) to lunar orbit. This mission obtained the first near-global topographic map of the Moon, and the first global multispectral (Si apre in una nuova finestra) images of the lunar surface.[213] (Si apre in una nuova finestra) This was followed in 1998 by the Lunar Prospector (Si apre in una nuova finestra) 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.[214] (Si apre in una nuova finestra)

As viewed by Chandrayaan-1 (Si apre in una nuova finestra)'s NASA Moon Mineralogy Mapper equipment, on the right, the first time discovered water-rich minerals (light blue), shown around a small crater from which it was ejected.

The European spacecraft SMART-1 (Si apre in una nuova finestra), the second ion-propelled (Si apre in una nuova finestra) 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.[215] (Si apre in una nuova finestra)

The ambitious Chinese Lunar Exploration Program (Si apre in una nuova finestra) began with Chang'e 1 (Si apre in una nuova finestra), which successfully orbited the Moon from 5 November 2007 until its controlled lunar impact on 1 March 2009.[216] (Si apre in una nuova finestra) It obtained a full image map of the Moon.  Chang'e 2 (Si apre in una nuova finestra), beginning in October 2010, reached the Moon more quickly, mapped the Moon at a higher resolution over an eight-month period, then left lunar orbit for an extended stay at the Earth–Sun L2 Lagrangian point (Si apre in una nuova finestra), before finally performing a flyby of asteroid 4179 Toutatis (Si apre in una nuova finestra) on 13 December 2012, and then heading off into deep space. On 14 December 2013, Chang'e 3 (Si apre in una nuova finestra) landed a lunar lander (Si apre in una nuova finestra) onto the Moon's surface, which in turn deployed a lunar rover (Si apre in una nuova finestra), named Yutu (Si apre in una nuova finestra) (Chinese: 玉兔; literally "Jade Rabbit"). This was the first lunar soft landing (Si apre in una nuova finestra) since Luna 24 (Si apre in una nuova finestra) in 1976, and the first lunar rover mission since Lunokhod 2 (Si apre in una nuova finestra) in 1973. Another rover mission (Chang'e 4 (Si apre in una nuova finestra)) was launched in 2019, becoming the first ever spacecraft to land on the Moon's far side. China intends to following this up with a sample return mission (Si apre in una nuova finestra) (Chang'e 5 (Si apre in una nuova finestra)) in 2020.[217] (Si apre in una nuova finestra)

Between 4 October 2007 and 10 June 2009, the Japan Aerospace Exploration Agency (Si apre in una nuova finestra)'s Kaguya (Si apre in una nuova finestra) (Selene) mission, a lunar orbiter fitted with a high-definition video (Si apre in una nuova finestra) camera, and two small radio-transmitter satellites, obtained lunar geophysics data and took the first high-definition movies from beyond Earth orbit.[218] (Si apre in una nuova finestra)[219] (Si apre in una nuova finestra) India's first lunar mission, Chandrayaan-1 (Si apre in una nuova finestra), 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 (Si apre in una nuova finestra).[220] (Si apre in una nuova finestra) The Indian Space Research Organisation (Si apre in una nuova finestra) planned to launch Chandrayaan-2 (Si apre in una nuova finestra) in 2013, which would have included a Russian robotic lunar rover.[221] (Si apre in una nuova finestra)[222] (Si apre in una nuova finestra) However, the failure of Russia's Fobos-Grunt (Si apre in una nuova finestra) mission has delayed this project, and was launched on 22 July 2019. The lander Vikram attempted to land on the lunar south pole region (Si apre in una nuova finestra) on 6 September, but lost the signal in 2.1 km (1.3 mi). What happened after that is unknown.

Copernicus (Si apre in una nuova finestra)'s central peaks as observed by the LRO (Si apre in una nuova finestra), 2012

The Ina (Si apre in una nuova finestra) formation, 2009

The U.S. co-launched the Lunar Reconnaissance Orbiter (LRO) and the LCROSS (Si apre in una nuova finestra) impactor and follow-up observation orbiter on 18 June 2009; LCROSScompleted its mission by making a planned and widely observed impact in the crater Cabeus (Si apre in una nuova finestra) on 9 October 2009,[223] (Si apre in una nuova finestra) whereas LRO is currently in operation, obtaining precise lunar altimetry (Si apre in una nuova finestra) and high-resolution imagery. In November 2011, the LRO passed over the large and bright crater Aristarchus (Si apre in una nuova finestra). NASA released photos of the crater on 25 December 2011.[224] (Si apre in una nuova finestra)

Two NASA GRAIL (Si apre in una nuova finestra) spacecraft began orbiting the Moon around 1 January 2012,[225] (Si apre in una nuova finestra) on a mission to learn more about the Moon's internal structure. NASA's LADEE (Si apre in una nuova finestra) probe, designed to study the lunar exosphere (Si apre in una nuova finestra), achieved orbit on 6 October 2013.

Future

See also: List of proposed missions to the Moon (Si apre in una nuova finestra)

Upcoming lunar missions include Russia's Luna-Glob (Si apre in una nuova finestra): an uncrewed lander with a set of seismometers, and an orbiter based on its failed Martian Fobos-Grunt (Si apre in una nuova finestra) mission.[226] (Si apre in una nuova finestra) Privately funded lunar exploration has been promoted by the Google Lunar X Prize (Si apre in una nuova finestra), announced 13 September 2007, which offers US$20 million to anyone who can land a robotic rover on the Moon and meet other specified criteria.[227] (Si apre in una nuova finestra) Shackleton Energy Company (Si apre in una nuova finestra) is building a program to establish operations on the south pole of the Moon to harvest water and supply their Propellant Depots (Si apre in una nuova finestra).[228] (Si apre in una nuova finestra)

NASA began to plan to resume human missions (Si apre in una nuova finestra) following the call by U.S. President George W. Bush (Si apre in una nuova finestra) on 14 January 2004 for a human mission to the Moon by 2019 and the construction of a lunar base by 2024.[229] (Si apre in una nuova finestra) The Constellation program (Si apre in una nuova finestra) was funded and construction and testing begun on a crewed spacecraft (Si apre in una nuova finestra) and launch vehicle (Si apre in una nuova finestra),[230] (Si apre in una nuova finestra) and design studies for a lunar base.[231] (Si apre in una nuova finestra) However, that program has been canceled in favor of a human asteroid landing by 2025 and a human Mars orbit by 2035.[232] (Si apre in una nuova finestra) India (Si apre in una nuova finestra) has also expressed its hope to send people to the Moon by 2020.[233] (Si apre in una nuova finestra)

On 28 February 2018, SpaceX (Si apre in una nuova finestra), Vodafone (Si apre in una nuova finestra), Nokia (Si apre in una nuova finestra) and Audi (Si apre in una nuova finestra) announced a collaboration to install a 4G (Si apre in una nuova finestra) wireless communication network on the Moon, with the aim of streaming live footage on the surface to Earth.[234] (Si apre in una nuova finestra)

Recent reports also indicate NASA's intent to send a woman astronaut to the Moon in their planned mid-2020s mission.[235] (Si apre in una nuova finestra)

Planned commercial missions

In 2007, the X Prize Foundation together with Google (Si apre in una nuova finestra) launched the Google Lunar X Prize (Si apre in una nuova finestra) to encourage commercial endeavors to the Moon. A prize of $20 million was to 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.[236] (Si apre in una nuova finestra)[237] (Si apre in una nuova finestra) As of August 2016, 16 teams were reportedly participating in the competition.[238] (Si apre in una nuova finestra) In January 2018 the foundation announced that the prize would go unclaimed as none of the finalist teams would be able to make a launch attempt by the deadline.[239] (Si apre in una nuova finestra)

In August 2016, the US government granted permission to US-based start-up Moon Express to land on the Moon.[240] (Si apre in una nuova finestra) 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.[240] (Si apre in una nuova finestra)

On 29 November 2018 NASA announced that nine commercial companies would compete to win a contract to send small payloads to the Moon in what is known as Commercial Lunar Payload Services (Si apre in una nuova finestra). According to NASA administrator Jim Bridenstine (Si apre in una nuova finestra), "We are building a domestic American capability to get back and forth to the surface of the moon.".[241] (Si apre in una nuova finestra)

Human presence

See also: Human presence in space (Si apre in una nuova finestra)

Human impact

See also: List of artificial objects on the Moon (Si apre in una nuova finestra), Space art § Art in space (Si apre in una nuova finestra), and Planetary protection § Category V (Si apre in una nuova finestra)

Remains of human activity, Apollo 17's Lunar Surface Experiments Package (Si apre in una nuova finestra)

Beside the traces of human activity on the Moon, there have been some intended permanent installations like the Moon Museum (Si apre in una nuova finestra) art piece, Apollo 11 goodwill messages (Si apre in una nuova finestra), Lunar plaque (Si apre in una nuova finestra), the Fallen Astronaut (Si apre in una nuova finestra) memorial, and other artifacts.

Fallen Astronaut (Si apre in una nuova finestra)

Infrastructure

Main article: Moonbase (Si apre in una nuova finestra)

See also: Space infrastructure (Si apre in una nuova finestra), Tourism on the Moon (Si apre in una nuova finestra), and Colonization of the Moon (Si apre in una nuova finestra)

A photo of the still in use reflector of the Lunar Laser Ranging Experiment (Si apre in una nuova finestra) of Apollo 11 (Si apre in una nuova finestra).

Longterm missions continuing to be active are some orbiters such as the 2009 launched Lunar Reconnaissance Orbiter (Si apre in una nuova finestra) surveiling the Moon for future missions, as well as some Landers such as the 2013 launched Chang'e 3 (Si apre in una nuova finestra) with its Lunar Ultraviolet Telescope still operational.[242] (Si apre in una nuova finestra)

There are several missions by different agencies and companies planned (Si apre in una nuova finestra) to establish a longterm human presence on the Moon, with the Lunar Gateway (Si apre in una nuova finestra) as the currently most advanced project as part of the Artemis program (Si apre in una nuova finestra).

Concept art of the Lunar Gateway (Si apre in una nuova finestra) of the Artemis program (Si apre in una nuova finestra) in 2024 serving as a communication hub, science laboratory, short-term habitation and holding area for rovers in lunar orbit (Si apre in una nuova finestra).[243] (Si apre in una nuova finestra)

Astronomy from the Moon

A false-color image of Earth (Si apre in una nuova finestra) in ultraviolet light (Si apre in una nuova finestra) taken from the surface of the Moon on the Apollo 16 (Si apre in una nuova finestra) mission. The day-side reflects a large amount of UV light from the Sun, but the night-side shows faint bands of UV emission from the aurora (Si apre in una nuova finestra) caused by charged particles.[244] (Si apre in una nuova finestra)

For many years, the Moon has been recognized as an excellent site for telescopes.[245] (Si apre in una nuova finestra) It is relatively nearby; astronomical seeing (Si apre in una nuova finestra) is not a concern; certain craters near the poles are permanently dark and cold, and thus especially useful for infrared telescopes (Si apre in una nuova finestra); and radio telescopes (Si apre in una nuova finestra) on the far side would be shielded from the radio chatter of Earth.[246] (Si apre in una nuova finestra) The lunar soil (Si apre in una nuova finestra), although it poses a problem for any moving parts of telescopes (Si apre in una nuova finestra), can be mixed with carbon nanotubes (Si apre in una nuova finestra) and epoxies (Si apre in una nuova finestra) and employed in the construction of mirrors up to 50 meters in diameter.[247] (Si apre in una nuova finestra) A lunar zenith telescope (Si apre in una nuova finestra) can be made cheaply with an ionic liquid (Si apre in una nuova finestra).[248] (Si apre in una nuova finestra)

In April 1972, the Apollo 16 (Si apre in una nuova finestra) mission recorded various astronomical photos and spectra in ultraviolet with the Far Ultraviolet Camera/Spectrograph (Si apre in una nuova finestra).[249] (Si apre in una nuova finestra)

Living on the Moon

Humans have stayed for days on the Moon, such as during Apollo 17.[250] (Si apre in una nuova finestra) One particular challenge for astronauts' daily life during their stay on the surface is the lunar dust (Si apre in una nuova finestra) sticking to their suits and being carried into their quarters. Subsequently, the dust was tasted and smelled by the astronauts, calling it the "Apollo aroma".[251] (Si apre in una nuova finestra) This contamination poses a danger since the fine lunar dust can cause health issues (Si apre in una nuova finestra).[251] (Si apre in una nuova finestra)

In 2019 at least one plant seed sprouted in an experiment, carried along with other small life from Earth on the Chang'e 4 lander (Si apre in una nuova finestra) in its Lunar Micro Ecosystem.[252] (Si apre in una nuova finestra)

Legal status

Main article: Space law (Si apre in una nuova finestra)

Although Luna (Si apre in una nuova finestra) landers scattered pennants of the Soviet Union (Si apre in una nuova finestra) on the Moon, and U.S. flags (Si apre in una nuova finestra) were symbolically planted at their landing sites by the Apollo astronauts (Si apre in una nuova finestra), no nation claims ownership of any part of the Moon's surface.[253] (Si apre in una nuova finestra) Russia, China, India, and the U.S. are party to the 1967 Outer Space Treaty (Si apre in una nuova finestra),[254] (Si apre in una nuova finestra) which defines the Moon and all outer space as the "province of all mankind (Si apre in una nuova finestra)".[253] (Si apre in una nuova finestra) This treaty also restricts the use of the Moon to peaceful purposes, explicitly banning military installations and weapons of mass destruction (Si apre in una nuova finestra).[255] (Si apre in una nuova finestra) The 1979 Moon Agreement (Si apre in una nuova finestra) was created to restrict the exploitation of the Moon's resources (Si apre in una nuova finestra) by any single nation, but as of January 2020, it has been signed and ratified by only 18 nations,[256] (Si apre in una nuova finestra) none of which engages in self-launched human space exploration (Si apre in una nuova finestra). Although several individuals have made claims to the Moon (Si apre in una nuova finestra) in whole or in part, none of these are considered credible.[257] (Si apre in una nuova finestra)[258] (Si apre in una nuova finestra)[259] (Si apre in una nuova finestra)

In 2020, U.S. President Donald Trump (Si apre in una nuova finestra) signed an executive order called "Encouraging International Support for the Recovery and Use of Space Resources". The order emphasizes 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."[260] (Si apre in una nuova finestra)[261] (Si apre in una nuova finestra)

The Declaration of the Rights of the Moon (Si apre in una nuova finestra) was created by a group of independent researchers in 2021, drawing on precedents in the Rights of Nature (Si apre in una nuova finestra) movement and the concept of legal personality for non-human entities in space[262] (Si apre in una nuova finestra).

In culture

Luna, the Moon, from a 1550 edition of Guido Bonatti (Si apre in una nuova finestra)'s Liber astronomiae

See also: Moon in fiction (Si apre in una nuova finestra) and Tourism on the Moon (Si apre in una nuova finestra)

Mythology

Further information: Lunar deity (Si apre in una nuova finestra), Selene (Si apre in una nuova finestra), Luna (goddess) (Si apre in una nuova finestra), Man in the Moon (Si apre in una nuova finestra), and Crescent (Si apre in una nuova finestra)

Statue of Chandraprabha (Si apre in una nuova finestra) (meaning "as charming as the moon"), the eighth Tirthankara (Si apre in una nuova finestra) in Jainism (Si apre in una nuova finestra), with the symbol of a crescent (Si apre in una nuova finestra) moon below it

Sun and Moon with faces (1493 woodcut)

The contrast between the brighter highlands and the darker maria creates the patterns seen by different cultures as the Man in the Moon (Si apre in una nuova finestra), the rabbit (Si apre in una nuova finestra)and the buffalo, among others. In many prehistoric and ancient cultures, the Moon was personified as a deity (Si apre in una nuova finestra) or other supernatural (Si apre in una nuova finestra) phenomenon, and astrological views of the Moon (Si apre in una nuova finestra) continue to be propagated today.

In Proto-Indo-European religion (Si apre in una nuova finestra), the Moon was personified as the male god *Meh1not (Si apre in una nuova finestra).[263] (Si apre in una nuova finestra) The ancient Sumerians (Si apre in una nuova finestra) believed that the Moon was the god Nanna (Si apre in una nuova finestra),[264] (Si apre in una nuova finestra)[265] (Si apre in una nuova finestra) who was the father of Inanna (Si apre in una nuova finestra), the goddess of the planet Venus (Si apre in una nuova finestra),[264] (Si apre in una nuova finestra)[265] (Si apre in una nuova finestra) and Utu (Si apre in una nuova finestra), the god of the sun.[264] (Si apre in una nuova finestra)[265] (Si apre in una nuova finestra) Nanna was later known as Sîn,[265] (Si apre in una nuova finestra)[264] (Si apre in una nuova finestra) and was particularly associated with magic and sorcery.[264] (Si apre in una nuova finestra) In Greco-Roman mythology (Si apre in una nuova finestra), the Sun and the Moon are represented as male and female, respectively (Helios/Sol (Si apre in una nuova finestra) and Selene/Luna (Si apre in una nuova finestra));[263] (Si apre in una nuova finestra) this is a development unique to the eastern Mediterranean[263] (Si apre in una nuova finestra) and traces of an earlier male moon god in the Greek tradition are preserved in the figure of Menelaus (Si apre in una nuova finestra).[263] (Si apre in una nuova finestra)

In Mesopotamian iconography, the crescent (Si apre in una nuova finestra) was the primary symbol of Nanna-Sîn.[265] (Si apre in una nuova finestra) In ancient Greek art (Si apre in una nuova finestra), the Moon goddess Selene (Si apre in una nuova finestra) was represented wearing a crescent on her headgear in an arrangement reminiscent of horns.[266] (Si apre in una nuova finestra)[267] (Si apre in una nuova finestra) The star and crescent (Si apre in una nuova finestra) arrangement also 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 (Si apre in una nuova finestra) or Hecate (Si apre in una nuova finestra), and via the patronage of Hecate came to be used as a symbol of Byzantium (Si apre in una nuova finestra).

An iconographic tradition of representing Sun and Moon with faces developed in the late medieval period.

The splitting of the moon (Si apre in una nuova finestra) (Arabic (Si apre in una nuova finestra): انشقاق القمر‎) is a miracle attributed to Muhammad (Si apre in una nuova finestra).[268] (Si apre in una nuova finestra) A song titled 'Moon Anthem' was released on the occasion of landing of India's Chandrayan-II on the Moon.[269] (Si apre in una nuova finestra)

Calendar

Further information: Lunar calendar (Si apre in una nuova finestra), Lunisolar calendar (Si apre in una nuova finestra), Metonic cycle (Si apre in una nuova finestra), Blue moon (Si apre in una nuova finestra), and Movable feast (Si apre in una nuova finestra)

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 (Si apre in una nuova finestra), notched bones dating as far back as 20–30,000 years ago, are believed by some to mark the phases of the Moon.[270] (Si apre in una nuova finestra)[271] (Si apre in una nuova finestra)[272] (Si apre in una nuova finestra) The ~30-day month is an approximation of the lunar cycle (Si apre in una nuova finestra). The English noun month and its cognates in other Germanic languages stem from Proto-Germanic *mǣnṓth-, which is connected to the above-mentioned Proto-Germanic *mǣnōn, indicating the usage of a lunar calendar (Si apre in una nuova finestra) among the Germanic peoples (Si apre in una nuova finestra) (Germanic calendar (Si apre in una nuova finestra)) prior to the adoption of a solar calendar (Si apre in una nuova finestra).[273] (Si apre in una nuova finestra) The PIE root (Si apre in una nuova finestra) 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. (Si apre in una nuova finestra) the English words measure and menstrual),[274] (Si apre in una nuova finestra)[275] (Si apre in una nuova finestra)[276] (Si apre in una nuova finestra) and echoing the Moon's importance to many ancient cultures in measuring time (see Latin (Si apre in una nuova finestra) mensis and Ancient Greek (Si apre in una nuova finestra) μείς (meis) or μήν (mēn), meaning "month").[277] (Si apre in una nuova finestra)[278] (Si apre in una nuova finestra)[279] (Si apre in una nuova finestra)[280] (Si apre in una nuova finestra)Most historical calendars are lunisolar (Si apre in una nuova finestra). The 7th-century Islamic calendar (Si apre in una nuova finestra) is an exceptional example of a purely lunar calendar (Si apre in una nuova finestra). Months are traditionally determined by the visual sighting of the hilal, or earliest crescent moon, over the horizon.[281] (Si apre in una nuova finestra)

Moonrise, 1884, painting by Stanisław Masłowski (Si apre in una nuova finestra) (National Museum, Kraków (Si apre in una nuova finestra), Gallery of Sukiennice Museum (Si apre in una nuova finestra))

Lunar effect

Main article: Lunar effect (Si apre in una nuova finestra)

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 particularly associated with insanity and irrationality; the words lunacy and lunatic (Si apre in una nuova finestra) (popular shortening loony) are derived from the Latin name for the Moon, Luna. Philosophers Aristotle (Si apre in una nuova finestra) and Pliny the Elder (Si apre in una nuova finestra) 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.[282] (Si apre in una nuova finestra) Even today, people who believe in a lunar effect (Si apre in una nuova finestra) claim that admissions to psychiatric hospitals, traffic accidents, homicides or suicides increase during a full moon, but dozens of studies invalidate these claims.[282] (Si apre in una nuova finestra)[283] (Si apre in una nuova finestra)[284] (Si apre in una nuova finestra)[285] (Si apre in una nuova finestra)[286] (Si apre in una nuova finestra)

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