This article is about Earth's Moon. For moons in general see Natural satellite. For other uses see Moon (disambiguation). Moon   A moon just past full as seen from Earth's northern hemisphere Designations Adjective lunar Orbital characteristics Perigee 362570 km (0.0024 AU) (356400-370400 km) Apogee 405410 km (0.0027 AU) (404000-406700 km) Semi-major axis 384399 km (0.00257 AU)1 Eccentricity 0.05491 Orbital period 27.321582 d (27 d 7 h 43.1 min1) Synodic period 29.530589 d (29 d 12 h 44 min 2.9 s) Average orbital speed 1.022 km/s Inclination 5.145 to the ecliptic1 (between 18.29 and 28.58 to Earth's equator) Longitude of ascending node regressing by one revolution in 18.6 years Argument of perigee progressing by one revolution in 8.85 years Satellite of Earth Physical characteristics Mean radius 1737.10 km  (0.273 Earths)12 Equatorial radius 1738.14 km (0.273 Earths)2 Polar radius 1735.97 km  (0.273 Earths)2 Flattening 0.00125 Circumference 10921 km (equatorial) Surface area 3.793  107 km2  (0.074 Earths) Volume 2.1958  1010 km3  (0.020 Earths) Mass 7.3477  1022 kg  (0.0123 Earths1) Mean density 3.3464 g/cm31 Equatorial surface gravity 1.622 m/s2 (0.165 4 g) Escape velocity 2.38 km/s Sidereal rotation period 27.321582 d (synchronous) Equatorial rotation velocity 4.627 m/s Axial tilt 1.5424 (to ecliptic) 6.687 (to orbit plane) Albedo 0.1363 Surface temp.    equator    85N4 min mean max 100 K 220 K 390 K 70 K 130 K 230 K Apparent magnitude 2.5 to 12.9nb 1 12.74 (mean full Moon)2 Angular diameter 29.3 to 34.1 arcminutes2nb 2 Atmosphere5nb 3 Surface pressure 107 Pa (day) 1010 Pa (night) Composition Ar He Na K H Rn

The Moon is Earth's only natural satellitenb 46 and the fifth largest satellite in the Solar System. It is the largest natural satellite of a planet in the Solar System relative to the size of its primary a quarter the diameter of Earth and 181 its mass (Charon is proportionally larger in comparison to Pluto but Pluto has been reclassified as a dwarf planet). The Moon is the second densest satellite after Io. It is in synchronous rotation with Earth always showing the same face; the near side is marked with dark volcanic maria among the bright ancient crustal highlands and prominent impact craters. It is the brightest object in the sky after the Sun although its surface is actually very dark with a similar reflectance to coal. Its prominence in the sky and its regular cycle of phases have since ancient times made the Moon an important cultural influence on language calendars art and mythology. The Moon's gravitational influence produces the ocean tides and the minute lengthening of the day. The Moon's current orbital distance about thirty times the diameter of the Earth causes it to appear almost the same size in the sky as the Sun allowing it to cover the Sun nearly precisely in total solar eclipses.

The Moon is the only celestial body on which humans have landed. While the Soviet Union's Luna programme was the first to reach the Moon with unmanned spacecraft in 1959 the United States' NASA Apollo program achieved the only manned missions to date beginning with the first manned lunar orbiting mission by Apollo 8 in 1968 and six manned lunar landings between 1969 and 1972the first being Apollo 11. These missions returned over 380 kg of lunar rocks which have been used to develop a detailed geological understanding of the Moon's origins (it is thought to have formed some 4.5 billion years ago in a giant impact event involving Earth) the formation of its internal structure and its subsequent history.

After the Apollo 17 mission in 1972 the Moon has been visited only by unmanned spacecraft notably by the final Soviet Lunokhod rover. Since 2004 Japan China India the United States and the European Space Agency have each sent lunar orbiters. These spacecraft have contributed to confirming the discovery of lunar water ice in permanently shadowed craters at the poles and bound into the lunar regolith. Future manned missions to the Moon have been planned including government as well as privately funded efforts. The Moon remains under the Outer Space Treaty free to all nations to explore for peaceful purposes. Contents 1 Name and etymology 2 Formation 3 Physical characteristics 3.1 Internal structure 3.2 Surface geology 3.2.1 Volcanic features 3.2.2 Impact craters 3.2.3 Presence of water 3.3 Gravity and magnetic fields 3.4 Atmosphere 3.5 Seasons 4 Relationship to Earth 4.1 Orbit 4.2 Relative size 4.3 Appearance from Earth 4.4 Tidal effects 4.5 Eclipses 5 Study and exploration 5.1 Early studies 5.2 First direct exploration: 19591976 5.2.1 Soviet missions 5.2.2 United States missions 5.3 Current era: 1990present 6 Astronomy from the Moon 7 Legal status 8 In culture 9 References 10 Further reading 11 External links Name and etymology

The English proper name for Earth's natural satellite is "the Moon".78 The noun moon derives from moone (around 1380) which developed from mone (1135) which derives from Old English mna (dating from before 725) which like all Germanic language cognates ultimately stems from Proto-Germanic *mnn.9

The principal modern English adjective pertaining to the Moon is lunar derived from the Latin Luna. Another less common adjective is selenic derived from the Ancient Greek Selene () from which the prefix "seleno-" (as in selenography) is derived.10 Formation Main article: Giant impact hypothesis

Several mechanisms have been proposed for the Moon's formation 4.527 0.010 billion years agonb 5 some 3050 million years after the origin of the Solar System.11 These include the fission of the Moon from the Earth's crust through centrifugal forces12 which would require too great an initial spin of the Earth13 the gravitational capture of a pre-formed Moon14 which would require an unfeasibly extended atmosphere of the Earth to dissipate the energy of the passing Moon13 and the co-formation of the Earth and the Moon together in the primordial accretion disk which does not explain the depletion of metallic iron in the Moon.13 These hypotheses also cannot account for the high angular momentum of the EarthMoon system.15

The prevailing hypothesis today is that the EarthMoon system formed as a result of a giant impact: a Mars-sized body hit the nearly formed proto-Earth blasting material into orbit around the proto-Earth which accreted to form the Moon.16 Giant impacts are thought to have been common in the early Solar System. Computer simulations modelling a giant impact are consistent with measurements of the angular momentum of the EarthMoon system and the small size of the lunar core; they also show that most of the Moon came from the impactor not from the proto-Earth.17 However meteorites show that other inner Solar System bodies such as Mars and Vesta have very different oxygen and tungsten isotopic compositions to the Earth while the Earth and Moon have near-identical isotopic compositions. Post-impact mixing of the vaporized material between the forming Earth and Moon could have equalized their isotopic compositions18 although this is debated.19

The large amount of energy released in the giant impact event and the subsequent reaccretion of material in Earth orbit would have melted the outer shell of the Earth forming a magma ocean.2021 The newly formed Moon would also have had its own lunar magma ocean; estimates for its depth range from about 500 km to the entire radius of the Moon.20 Physical characteristics Internal structure Main article: Internal structure of the Moon Internal structure of the moon Chemical composition of the lunar surface regolith (derived from crustal rocks)22 Compound Formula Composition (wt %) Maria Highlands silica SiO2 45.4% 45.5% alumina Al2O3 14.9% 24.0% lime CaO 11.8% 15.9% iron(II) oxide FeO 14.1% 5.9% magnesia MgO 9.2% 7.5% titanium dioxide TiO2 3.9% 0.6% sodium oxide Na2O 0.6% 0.6% Total 99.9% 100.0%

The Moon is a differentiated body: it has a geochemically distinct crust mantle and core. The moon has a solid iron-rich inner core with a radius of 240 kilometers and a fluid outer core primarily made of liquid iron with a radius of roughly 300 kilometers. Around the core is a partially molten boundary layer with a radius of about 500 kilometers.23 This structure is thought to have developed through the fractional crystallization of a global magma ocean shortly after the Moon's formation 4.5 billion years ago.24 Crystallization of this magma ocean would have created a mafic mantle from the precipitation and sinking of the minerals olivine clinopyroxene and orthopyroxene; after about three-quarters of the magma ocean had crystallised lower-density plagioclase minerals could form and float into a crust on top.25 The final liquids to crystallise would have been initially sandwiched between the crust and mantle with a high abundance of incompatible and heat-producing elements.1 Consistent with this geochemical mapping from orbit shows the crust is mostly anorthosite5 and moon rock samples of the flood lavas erupted on the surface from partial melting in the mantle confirm the mafic mantle composition which is more iron rich than that of Earth.1 Geophysical techniques suggest that the crust is on average 50 km thick.1 The Moon is the second densest satellite in the Solar System after Io.26 However the inner core of the Moon is small with a radius of about 350 km or less;1 this is only 20% the size of the Moon in contrast to the 50% of most other terrestrial bodies. Its composition is not well constrained but it is probably metallic iron alloyed with a small amount of sulphur and nickel; analyses of the Moon's time-variable rotation indicate that it is at least partly molten.27 Surface geology Main articles: Geology of the Moon and Moon rocks See also: Topography of the Moon and List of features on the Moon Near side of the Moon Far side of the Moon. Note the lack of dark maria.28 Topography of the Moon. The topography of the Moon has been measured with laser altimetry and stereo image analysis.29 The most visible topographic feature is the giant far side South Pole Aitken basin some 2240 km in diameter the largest crater on the Moon and the largest known crater in the Solar System.3031 At 13 km deep its floor is the lowest elevation on the Moon.3032 The highest elevations are found just to its north-east and it has been suggested that this area might have been thickened by the oblique formation impact of South Pole Aitken.33 Other large impact basins such as Imbrium Serenitatis Crisium Smythii and Orientale also possess regionally low elevations and elevated rims.30 The lunar far side is on average about 1.9 km higher than the near side.1 Volcanic features Main article: Lunar mare The dark and relatively featureless lunar plains which can clearly be seen with the naked eye are called maria (Latin for "seas"; singular mare) since they were believed by ancient astronomers to be filled with water.34 They are now known to be vast solidified pools of ancient basaltic lava. While similar to terrestrial basalts the mare basalts have much higher abundances of iron and are completely lacking in minerals altered by water.3536 The majority of these lavas erupted or flowed into the depressions associated with impact basins. Several geologic provinces containing shield volcanoes and volcanic domes are found within the near side maria.37 Maria are found almost exclusively on the near side of the Moon covering 31% of the surface on the near side38 compared with a few scattered patches on the far side covering only 2%.39 This is thought to be due to a concentration of heat-producing elements under the crust on the near side seen on geochemical maps obtained by Lunar Prospector's gamma-ray spectrometer which would have caused the underlying mantle to heat up partially melt rise to the surface and erupt.254041 Most of the Moon's mare basalts erupted during the Imbrian period 3.03.5 billion years ago although some radiometrically dated samples are as old as 4.2 billion years42 and the youngest eruptions dated by crater counting appear to have been only 1.2 billion years ago.43 The lighter-coloured regions of the Moon are called terrae or more commonly highlands since they are higher than most maria. They have been radiometrically dated as forming 4.4 billion years ago and may represent plagioclase cumulates of the lunar magma ocean.4243 In contrast to the Earth no major lunar mountains are believed to have formed as a result of tectonic events.44 Impact craters See also: List of craters on the Moon The other major geologic process that has affected the Moon's surface is impact cratering45 with craters formed when asteroids and comets collide with the lunar surface. There are estimated to be roughly 300000 craters wider than 1 km on the Moon's near side alone.46 Some of these are named for scholars scientists artists and explorers.47 The lunar geologic timescale is based on the most prominent impact events including Nectaris Imbrium and Orientale structures characterized by multiple rings of uplifted material typically hundreds to thousands of kilometres in diameter and associated with a broad apron of ejecta deposits that form a regional stratigraphic horizon.48 The lack of an atmosphere weather and recent geological processes mean that many of these craters are well-preserved. While only a few multi-ring basins have been definitively dated they are useful for assigning relative ages. Since 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.48 The radiometric ages of impact-melted rocks collected during the Apollo missions cluster between 3.8 and 4.1 billion years old: this has been used to propose a Late Heavy Bombardment of impacts.49 Blanketed on top of the Moon's crust is a highly comminuted (broken into ever smaller particles) and impact gardened surface layer called regolith formed by impact processes. The finer regolith the lunar soil of silicon dioxide glass has a texture like snow and smell like spent gunpowder.50 The regolith of older surfaces is generally thicker than for younger surfaces: it varies in thickness from 1020 m in the highlands and 35 m in the maria.51 Beneath the finely comminuted regolith layer is the megaregolith a layer of highly fractured bedrock many kilometres thick.52 Presence of water Main article: Lunar water Mosaic image of the lunar south pole as taken by Clementine: note permanent polar shadow. Liquid water cannot persist on the lunar surface. When exposed to solar radiation water quickly decomposes through a process known as photodissociation and is lost to space. However since the 1960s scientists have hypothesized that water ice may be deposited by impacting comets or possibly produced by the reaction of oxygen-rich lunar rocks and hydrogen from solar wind leaving traces of water which could possibly survive in cold permanently shadowed craters at either pole on the Moon.5354 Computer simulations suggest that up to 14000 km2 of the surface may be in permanent shadow.55 The presence of usable quantities of water on the Moon is an important factor in rendering lunar habitation as a cost-effective plan; the alternative of transporting water from Earth would be prohibitively expensive.56 In years since signatures of water have been found to exist on the lunar surface.57 In 1994 the bistatic radar experiment located on the Clementine spacecraft indicated the existence of small frozen pockets of water close to the surface. However later radar observations by Arecibo suggest these findings may rather be rocks ejected from young impact craters.58 In 1998 the neutron spectrometer located on the Lunar Prospector spacecraft indicated that high concentrations of hydrogen are present in the first meter of depth in the regolith near the polar regions.59 In 2008 an analysis of volcanic lava beads brought back to Earth aboard Apollo 15 showed small amounts of water to exist in the interior of the beads.60 The 2008 Chandrayaan-1 spacecraft has since confirmed the existence of surface water ice using the on-board Moon Mineralogy Mapper. The spectrometer observed absorption lines common to hydroxyl in reflected sunlight providing evidence of large quantities of water ice on the lunar surface. The spacecraft showed that concentrations may possibly be as high as 1000 ppm.61 In 2009 LCROSS sent a 2300 kg impactor into a permanently shadowed polar crater and detected at least 100 kg of water in a plume of ejected material.6263 Another examination of the LCROSS data showed the amount of detected water to be closer to 155-kilograms ( 12 kg).64 In May 2011 Erik Hauri et al. reported65 615-1410 ppm water in melt inclusions in lunar sample 74220 the famous high-titanium "orange glass soil" of volcanic origin collected during the Apollo 17 mission in 1972. The inclusions were formed during explosive eruptions on the moon approximately 3.7 billion years ago. This concentration is comparable with that of magma in Earth's upper mantle. While 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. Gravity and magnetic fields Main articles: Gravity of the Moon and Magnetic field of the Moon The gravitational field of the Moon has been measured through tracking the Doppler shift of radio signals emitted by orbiting spacecraft. The main lunar gravity features are mascons large positive gravitational anomalies associated with some of the giant impact basins partly caused by the dense mare basaltic lava flows that fill these basins.66 These 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.67 The Moon has an external magnetic field of the order of one to a hundred nanoteslas less than one-hundredth that of the Earth. It does not currently have a global dipolar magnetic field as would be generated by a liquid metal core geodynamo and only has crustal magnetization probably acquired early in lunar history when a geodynamo was still operating.6869 Alternatively some of the remnant magnetization may be from transient magnetic fields generated during large impact events through the expansion of an impact-generated plasma cloud in the presence of an ambient magnetic fieldthis is supported by the apparent location of the largest crustal magnetizations near the antipodes of the giant impact basins.70 Atmosphere Main article: Atmosphere of the Moon The Moon has an atmosphere so tenuous as to be nearly vacuum with a total mass of less than 10 metric tons.71 The surface pressure of this small mass is around 3  1015 atm (0.3 nPa); it varies with the lunar day. Its sources include outgassing and sputtering the release of atoms from the bombardment of lunar soil by solar wind ions.572 Elements that have been detected include sodium and potassium produced by sputtering which are also found in the atmospheres of Mercury and Io; helium-4 from the solar wind; and argon-40 radon-222 and polonium-210 outgassed after their creation by radioactive decay within the crust and mantle.7374 The absence of such neutral species (atoms or molecules) as oxygen nitrogen carbon hydrogen and magnesium which are present in the regolith is not understood.73 Water vapour has been detected by Chandrayaan-1 and found to vary with latitude with a maximum at 6070 degrees; it is possibly generated from the sublimation of water ice in the regolith.75 These gases can either return into the regolith due to the Moon's gravity or be lost to space: either through solar radiation pressure or if they are ionised by being swept away by the solar wind's magnetic field.73 Seasons The Moon's axial tilt is only 1.54 much less than the 23.44 of the Earth. Because of this the Moon's solar illumination varies much less with season and topographical details play a crucial role in seasonal effects.76 From images taken by Clementine in 1994 it appears that four mountainous regions on the rim of Peary crater at the Moon's north pole remain illuminated for the entire lunar day creating peaks of eternal light. No such regions exist at the south pole. Similarly there are places that remain in permanent shadow at the bottoms of many polar craters55 and these dark craters are extremely cold: Lunar Reconnaissance Orbiter measured the lowest summer temperatures in craters at the southern pole at 35 K (238 C)77 and just 26 K close to the winter solstice in north polar Hermite Crater. This is the coldest temperature in the Solar System ever measured by a spacecraft colder even than the surface of Pluto.76 Relationship to Earth Schematic of the Earth-Moon system (without a consistent scale) Orbit Main articles: Orbit of the Moon and Lunar theory The Moon makes a complete orbit around the Earth with respect to the fixed stars about once every 27.3 daysnb 6 (its sidereal period). However since the Earth is moving in its orbit about the Sun at the same time it takes slightly longer for the Moon to show the same phase to Earth which is about 29.5 daysnb 7 (its synodic period).38 Unlike most satellites of other planets the Moon orbits nearer the ecliptic plane than to the planet's equatorial plane. The Moon's orbit is subtly perturbed by the Sun and Earth in many small complex and interacting ways. For example the plane of the Moon's orbital motion gradually rotates which affects other aspects of lunar motion. These follow-on effects are mathematically described by Cassini's laws.78 Earth and Moon showing their sizes and distance to scale. The yellow bar represents a beam of light traveling from Earth to Moon in 1.26 seconds. Relative size Comparative sizes of the Earth and the Moon as imaged at separation of 50 million km79 The Moon is exceptionally large relative to the Earth: a quarter the diameter of the planet and 1/81 its mass.38 It is the largest moon orbiting a planet in the solar system relative to the size of its planet (although Charon is larger relative to the dwarf planet Pluto at slightly more than 1/9 (11.6%) of Pluto's mass.)80 However the Earth and Moon are still considered a planetsatellite system rather than a double-planet system as their barycentre the common centre of mass is located 1700 km (about a quarter of the Earth's radius) beneath the surface of the Earth.81 Appearance from Earth See also: Lunar phase Earthshine and Observing the Moon The Moon is in synchronous rotation: it rotates about its axis in about the same time it takes to orbit the Earth. This results in it nearly always keeping the same face turned towards the Earth. The Moon used to rotate at a faster rate but early in its history its rotation slowed and became tidally locked in this orientation as a result of frictional effects associated with tidal deformations caused by the Earth.82 The side of the Moon that faces Earth is called the near side and the opposite side the far side. The far side is often called the "dark side" but in fact it is illuminated as often as the near side: once per lunar day during the new Moon phase we observe on Earth when the near side is dark.83 The Moon has an exceptionally low albedo giving it a similar reflectance to coal. Despite this it is the second brightest object in the sky after the Sun.38nb 8 This is partly due to the brightness enhancement of the opposition effect; at quarter phase the Moon is only one-tenth as bright rather than half as bright as at full Moon.84 Additionally colour constancy in the visual system recalibrates the relations between the colours of an object and its surroundings and since 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 centre with no limb darkening due to the reflective properties of lunar soil which reflects more light back 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 first described in the 7th century BC.85 The full Moon subtends an arc of about 0.52 (on average) in the sky roughly the same apparent size as the Sun (see eclipses). The monthly changes of angle between the direction of illumination by the Sun and viewing from Earth and the phases of the Moon that result The highest altitude of the Moon in the sky varies: while it has nearly the same limit as the Sun it alters with the lunar phase and with the season of the year with the full Moon highest during winter. The 18.6-year nodes cycle also has an influence: when the ascending node of the lunar orbit is in the vernal equinox the lunar declination can go as far as 28 each month. This means the Moon can go overhead at latitudes up to 28 from the equator instead of only 18. The orientation of the Moon's crescent also depends on the latitude of the observation site: close to the equator an observer can see a smile-shaped crescent Moon.86 The distance between the moon and the Earth varies from around 356400 km to 406700 km at the extreme perigees (closest) and apogees (farthest). On 19 March 2011 it was closer to the earth while at full phase than it has been since 1993.87 Reported as a "super moon" this closest point coincides within an hour of a full moon and it thus appeared 30 percent brighter and 14 percent larger than when at its greatest distance.888990 There has been historical controversy over whether features on the Moon's surface change over time. Today many of these claims are thought to be illusory resulting from observation under different lighting conditions poor astronomical seeing or inadequate drawings. However outgassing does occasionally occur and could be responsible for a minor percentage of the reported lunar transient phenomena. Recently it has been suggested that a roughly 3 km diameter region of the lunar surface was modified by a gas release event about a million years ago.9192 The Moon's appearance like that of the Sun can be affected by Earth's atmosphere: common effects are a 22 halo ring formed when the Moon's light is refracted through the ice crystals of high cirrostratus cloud and smaller coronal rings when the Moon is seen through thin clouds.93 Tidal effects Main articles: Tidal force Tidal acceleration Tide and Theory of tides The tides on the Earth are mostly generated by the gradient in intensity of the Moon's gravitational pull from one side of the Earth to the other the tidal forces. This forms two tidal bulges on the Earth which are most clearly seen in elevated sea level as ocean tides.94 Since the Earth spins about 27 times faster than the Moon moves around it the bulges are dragged along with the Earth's surface faster than the Moon moves rotating around the Earth once a day as it spins on its axis.94 The ocean tides are magnified by other effects: frictional coupling of water to Earth's rotation through the ocean floors the inertia of water's movement ocean basins that get shallower near land and oscillations between different ocean basins.95 The gravitational attraction of the Sun on the Earth's oceans is almost half that of the Moon and their gravitational interplay is responsible for spring and neap tides.94 The libration of the Moon over a single lunar month. Gravitational coupling between the Moon and the bulge nearest the Moon acts as a torque on the Earth's rotation draining angular momentum and rotational kinetic energy from the Earth's spin.9496 In turn angular momentum is added to the Moon's orbit accelerating it which lifts the Moon into a higher orbit with a longer period. As a result the distance between the Earth and Moon is increasing and the Earth's spin slowing down.96 Measurements from lunar ranging experiments with laser reflectors left during the Apollo missions have found that the Moon's distance to the Earth increases by 38 mm per year97 (though this is only 0.10 ppb/year of the radius of the Moon's orbit). Atomic clocks also show that the Earth's day lengthens by about 15 microseconds every year98 slowly increasing the rate at which UTC is adjusted by leap seconds. This tidal drag will continue until the spin of the Earth has slowed to match the orbital period of the Moon; however long before this could happen the Sun will have become a red giant engulfing the Earth.99100 The lunar surface also experiences tides of amplitude 10 cm over 27 days with two components: a fixed one due to the Earth as they are in synchronous rotation and a varying component from the Sun.96 The Earth-induced component arises from libration a result of the Moon's orbital eccentricity; if the Moon's orbit were perfectly circular there would only be solar tides.96 Libration also changes the angle from which the Moon is seen allowing about 59% of its surface to be seen from the Earth (but only half at any instant).38 The cumulative effects of stress built up by these tidal forces produces moonquakes. Moonquakes are much less common and weaker than earthquakes although they can last for up to an hour a significantly longer time than terrestrial earthquakes because of the absence of water to damp out the seismic vibrations. The existence of moonquakes was an unexpected discovery from seismometers placed on the Moon by Apollo astronauts from 1969 through 1972.101 Eclipses Main articles: Solar eclipse Lunar eclipse and Eclipse cycle The 1999 solar eclipse The Moon passing in front of the Sun from the STEREO-B spacecraft.102 From the Earth the Moon and Sun appear the same size. From a satellite in an Earth-trailing orbit the Moon may appear smaller than the Sun. Eclipses can only occur when the Sun Earth and Moon are all in a straight line (termed "syzygy"). Solar eclipses occur near a new Moon when the Moon is between the Sun and Earth. In contrast lunar eclipses occur near a full Moon when the 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 precise vastly greater distance that coincidentally gives it the same apparent size as the much closer and much smaller Moon from the perspective of the Earth. The variations in apparent size due to the non-circular orbits are nearly the same as well though occurring in different cycles. This makes possible both total (with the Moon appearing larger than the Sun) and annular (with the Moon appearing smaller than the Sun) solar eclipses.103 In a total eclipse the Moon completely covers the disc of the Sun and the solar corona becomes visible to the naked eye. Since the distance between the Moon and the Earth is very slowly increasing over time94 the angular diameter of the Moon is decreasing. This 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 about 600 million years from now (if the angular diameter of the Sun does not change) the Moon will no longer cover the Sun completely and only annular eclipses will occur.104 Because the Moon's orbit around the Earth is inclined by about 5 to the orbit of the Earth around the Sun eclipses do not occur at every full and new Moon. For an eclipse to occur the Moon must be near the intersection of the two orbital planes.104 The periodicity and recurrence of eclipses of the Sun by the Moon and of the Moon by the Earth is described by the saros cycle which has a period of approximately 18 years.105 As the Moon is continuously blocking our view of a half-degree-wide circular area of the skynb 9106 the related phenomenon of occultation occurs when a bright star or planet passes behind the Moon and is occulted: hidden from view. In this way a solar eclipse is an occultation of the Sun. Because the Moon is comparatively close to the Earth occultations of individual stars are not visible everywhere on the planet nor at the same time. Because of the precession of the lunar orbit each year different stars are occulted.107 Study and exploration See also: Robotic exploration of the Moon List of current and future lunar missions Colonization of the Moon and List of man-made objects on the Moon Map of the Moon by Johannes Hevelius from his Selenographia (1647) the first map to include the libration zones. Early studies Main articles: Exploration of the Moon: Early history Selenography and Lunar theory Understanding of the Moon's cycles was an early development of astronomy: by the 5th century BC Babylonian astronomers had recorded the 18-year Saros cycle of lunar eclipses108 and Indian astronomers had described the Moons monthly elongation.109 The Chinese astronomer Shi Shen (fl. 4th century BC) gave instructions for predicting solar and lunar eclipses.110 Later the physical form of the Moon and the cause of moonlight became understood. The ancient Greek philosopher Anaxagoras (d. 428 BC) reasoned that the Sun and Moon were both giant spherical rocks and that the latter reflected the light of the former.111112 Although the Chinese of the Han Dynasty believed the Moon to be energy equated to qi their 'radiating influence' theory also recognized that the light of the Moon was merely a reflection of the Sun and Jing Fang (7837 BC) noted the sphericity of the Moon.113 In 499 AD the Indian astronomer Aryabhata mentioned in his Aryabhatiya that reflected sunlight is the cause of the shining of the Moon.114 The astronomer and physicist Alhazen (9651039) found that sunlight was not reflected from the Moon like a mirror but that light was emitted from every part of the Moon's sunlit surface in all directions.115 Shen Kuo (10311095) of the Song Dynasty created an allegory equating the waxing and waning of the Moon to a round ball of reflective silver that when doused with white powder and viewed from the side would appear to be a crescent.116 In Aristotle's (384322 BC) description of the universe the Moon marked the boundary between the spheres of the mutable elements (earth water air and fire) and the imperishable stars of aether an influential philosophy that would dominate for centuries.117 However in the 2nd century BC Seleucus of Seleucia correctly theorized that tides were due to the attraction of the Moon and that their height depends on the Moon's position relative to the Sun.118 In the same century Aristarchus computed the size and distance of the Moon from Earth obtaining a value of about twenty times the Earth radius for the distance. These figures were greatly improved by Ptolemy (90168 AD): his values of a mean distance of 59 times the Earth's radius and a diameter of 0.292 Earth diameters were close to the correct values of about 60 and 0.273 respectively.119 Archimedes (287212 BC) invented a planetarium calculating motions of the Moon and the known planets.120 During the Middle Ages before the invention of the telescope the Moon was increasingly recognised as a sphere though many believed that it was "perfectly smooth".121 In 1609 Galileo Galilei drew one of the first telescopic drawings of the Moon in his book Sidereus Nuncius and noted that it was not smooth but had mountains and craters. Telescopic mapping of the Moon followed: later in the 17th century the efforts of Giovanni Battista Riccioli and Francesco Maria Grimaldi led to the system of naming of lunar features in use today. The more exact 1834-6 Mappa Selenographica of Wilhelm Beer and Johann Heinrich Mdler and their associated 1837 book Der Mond the first trigonometrically accurate study of lunar features included the heights of more than a thousand mountains and introduced the study of the Moon at accuracies possible in earthly geography.122 Lunar craters first noted by Galileo were thought to be volcanic until the 1870s proposal of Richard Proctor that they were formed by collisions.38 This view gained support in 1892 from the experimentation of geologist Grove Karl Gilbert and from comparative studies from 1920 to the 1940s123 leading to the development of lunar stratigraphy which by the 1950s was becoming a new and growing branch of astrogeology.38 First direct exploration: 19591976 Soviet missions Main articles: Luna program and Lunokhod programme Lunokhod 1 (lit. moonwalker) the first successful space rover. The Cold War-inspired Space Race between the Soviet Union and the U.S. led to an acceleration of interest in exploration of the Moon. Once launchers had the necessary capabilities these nations sent unmanned probes on both flyby and impact/lander missions. Spacecraft from the Soviet Union's Luna program were the first to accomplish a number of goals: following three unnamed failed missions in 1958124 the first man-made object to escape Earth's gravity and pass near the Moon was Luna 1; the first man-made object to impact the lunar surface was Luna 2 and the first photographs of the normally occluded far side of the Moon were made by Luna 3 all in 1959. The first spacecraft to perform a successful lunar soft landing was Luna 9 and the first unmanned vehicle to orbit the Moon was Luna 10 both in 1966.38 Rock and soil samples were brought back to Earth by three Luna sample return missions (Luna 16 20 and 24) which returned 0.3 kg total.125 Two pioneering robotic rovers landed on the Moon in 1970 and 1973 as a part of Soviet Lunokhod programme. United States missions Main articles: Apollo program and Moon landing Earth as viewed from the Moon during the Apollo 8 mission Christmas Eve 1968. Africa is at the sunset terminator both Americas are under cloud and Antarctica is at the left end of the terminator. Astronaut Buzz Aldrin photographed by Neil Armstrong during the first Moon landing on 20 July 1969 American lunar exploration began with robotic missions aimed at developing understanding of the lunar surface for an eventual manned landing: the Jet Propulsion Laboratory's Surveyor program landed its first spacecraft four months after Luna 9. NASA's manned Apollo program was developed in parallel; after a series of unmanned and manned tests of the Apollo spacecraft in Earth orbit and spurred on by a potential Soviet lunar flight in 1968 Apollo 8 made the first crewed 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.126 Neil Armstrong became the first person to walk on the Moon as the commander of the American mission Apollo 11 by first setting foot on the Moon at 02:56 UTC on 21 July 1969.127 The Apollo missions 11 to 17 (except Apollo 13 which aborted its planned lunar landing) returned 382 kg of lunar rock and soil in 2196 separate samples.128 The American Moon landing and return was enabled by considerable technological advances in the early 1960s in domains such as ablation chemistry software engineering and atmospheric re-entry technology and by highly competent management of the enormous technical undertaking.129130 Scientific instrument packages were installed on the lunar surface during all the Apollo missions. Long-lived instrument stations including heat flow probes seismometers and magnetometers were installed at the Apollo 12 14 15 16 and 17 landing sites. Direct transmission of data to Earth concluded in late 1977 due to budgetary considerations131132 but as the stations' lunar laser ranging corner-cube retroreflector arrays are passive instruments they are still being used. Ranging to the stations is routinely performed from earth-based stations with an accuracy of a few centimetres and data from this experiment are being used to place constraints on the size of the lunar core.133 Current era: 1990present Post-Apollo and Luna many more countries have become involved in direct exploration of the Moon. In 1990 Japan became the third country to place a spacecraft into lunar orbit with its Hiten spacecraft. The spacecraft released a smaller probe Hagoromo in lunar orbit but the transmitter failed preventing further scientific use of the mission.134 In 1994 the U.S. sent the joint Defense Department/NASA spacecraft Clementine to lunar orbit. This mission obtained the first near-global topographic map of the Moon and the first global multispectral images of the lunar surface.135 This was followed in 1998 by the Lunar Prospector mission whose instruments indicated the presence of excess hydrogen at the lunar poles which is likely to have been caused by the presence of water ice in the upper few meters of the regolith within permanently shadowed craters.136 The European spacecraft SMART-1 the second ion-propelled spacecraft was in lunar orbit from 15 November 2004 until its lunar impact on 3 September 2006 and made the first detailed survey of chemical elements on the lunar surface.137 China has expressed ambitious plans for exploring the Moon and successfully orbited its first spacecraft Chang'e-1 from 5 November 2007 until its controlled lunar impact on 1 March 2008.138 In its sixteen-month mission it obtained a full image map of the Moon. Between 4 October 2007 and 10 June 2009 the Japan Aerospace Exploration Agency's Kaguya (Selene) mission a lunar orbiter fitted with a high-definition video camera and two small radio-transmitter satellites obtained lunar geophysics data and took the first high-definition movies from beyond Earth orbit.139140 India's first lunar mission Chandrayaan I orbited from 8 November 2008 until loss of contact on 27 August 2009 creating a high resolution chemical mineralogical and photo-geological map of the lunar surface and confirming the presence of water molecules in lunar soil.141 The Indian Space Research Organisation plans to launch Chandrayaan II in 2013 which is slated to include a Russian robotic lunar rover.142143 The U.S. co-launched the Lunar Reconnaissance Orbiter (LRO) and the LCROSS impactor and follow-up observation orbiter on 18 June 2009; LCROSS completed its mission by making a planned and widely observed impact in the crater Cabeus on 9 October 2009144 while LRO is currently in operation obtaining precise lunar altimetry and high-resolution imagery. Other upcoming lunar missions include Russia's Luna-Glob: an unmanned lander set of seismometers and an orbiter based on its Martian Phobos-Grunt mission which is slated to launch in 2012.145146 Privately funded lunar exploration has been promoted by the Google Lunar X Prize 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.147 NASA began to plan to resume manned missions following the call by U.S. President George W. Bush on 14 January 2004 for a manned mission to the Moon by 2019 and the construction of a lunar base by 2024.148 The Constellation program was funded and construction and testing begun on a manned spacecraft and launch vehicle149 and design studies for a lunar base.150 However that program has been cancelled in favour of a manned asteroid landing by 2025 and a manned Mars orbit by 2035.151 India has also expressed its hope to send a manned mission to the Moon by 2020.152 Astronomy from the Moon For many years the Moon has been recognized as an excellent site for telescopes.153 It is relatively nearby; astronomical seeing is not a concern; certain craters near the poles are permanently dark and cold and thus especially useful for infrared telescopes; and radio telescopes on the far side would be shielded from the radio chatter of Earth.154 The lunar soil although it poses a problem for any moving parts of telescopes can be mixed with carbon nanotubes and epoxies in the construction of mirrors up to 50 meters in diameter.155 A lunar zenith telescope can be made cheaply with ionic liquid.156 Legal status Main article: Space law Although Luna landers scattered pennants of the Soviet Union on the Moon and U.S. flags were symbolically planted at their landing sites by the Apollo astronauts no nation currently claims ownership of any part of the Moon's surface.157 Russia and the U.S. are party to the 1967 Outer Space Treaty158 which defines the Moon and all outer space as the "province of all mankind".157 This treaty also restricts the use of the Moon to peaceful purposes explicitly banning military installations and weapons of mass destruction.159 The 1979 Moon Agreement was created to restrict the exploitation of the Moon's resources by any single nation but it has not been signed by any of the space-faring nations.160 While several individuals have made claims to the Moon in whole or in part none of these are considered credible.161162163 In culture See also: Moon in fiction Lunar calendar Metonic cycle Lunar deity Lunar effect and Blue moon The gods Mni (left) and Sl (right) the personified Moon and Sun in Norse mythology as depicted in an illustration by Lorenz Frlich (1895) The Moon's regular phases make it a very convenient timepiece and the periods of its waxing and waning form the basis of many of the oldest calendars. Tally sticks notched bones dating as far back as 2030000 years ago are believed by some to mark the phases of the Moon.164165166 The 30-day month is an approximation of the lunar cycle. The English noun month and its cognates in other Germanic languages stem from Proto-Germanic *mnth- which is connected to the above mentioned Proto-Germanic *mnn indicating the usage of a lunar calendar among the Germanic peoples (Germanic calendar) prior to the adoption of a solar calendar.167 The same Indo-European root as moon led via Latin to measure and menstrual words which echo the Moon's importance to many ancient cultures in measuring time (see Latin mensis and Ancient Greek (mnas) meaning "month").168169 A crescent Moon and a star are a common symbol of Islam appearing in numerous flags including those of Turkey and Pakistan. The Moon has been the subject of many works of art and literature and the inspiration for countless others. It is a motif in the visual arts the performing arts poetry prose and music. A 5000-year-old rock carving at Knowth Ireland may represent the Moon which would be the earliest depiction discovered.170 The contrast between the brighter highlands and darker maria create the patterns seen by different cultures as the Man in the Moon the rabbit and the buffalo among others. In many prehistoric and ancient cultures the Moon was personified as a deity or other supernatural phenomenon and astrological views of the Moon continue to be propagated today. The Moon has a long association with insanity and irrationality; the words lunacy and loony are derived from the Latin name for the Moon Luna. Philosophers such as Aristotle and Pliny the Elder argued that the full Moon induced insanity in susceptible individuals believing that the brain which is mostly water must be affected by the Moon and its power over the tides but the Moon's gravity is too slight to affect any single person.171 Even today people insist that admissions to psychiatric hospitals traffic accidents homicides or suicides increase during a full Moon although there is no scientific evidence to support such claims.171 References Notes The maximum value is given based on scaling of the brightness from the value of 12.74 given for an equator to Moon-centre distance of 378 000 km in the NASA factsheet reference to the minimum Earth-Moon distance given there after the latter is corrected for the Earth's equatorial radius of 6 378 km giving 350 600 km. The minimum value (for a distant new Moon) is based on a similar scaling using the maximum Earth-Moon distance of 407 000 km (given in the factsheet) and by calculating the brightness of the earthshine onto such a new Moon. The brightness of the earthshine is Earth albedo (Earth radius / Radius of Moon's orbit)2  relative to the direct solar illumination that occurs for a full Moon. (Earth albedo 0.367; Earth radius (polar radius  equatorial radius) 6 367 km.) The range of angular size values given are based on simple scaling of the following values given in the fact sheet reference: at an Earth-equator to Moon-centre distance of 378 000 km the angular size is 1896 arcseconds. The same fact sheet gives extreme Earth-Moon distances of 407 000 km and 357 000 km. For the maximum angular size the minimum distance has to be corrected for the Earth's equatorial radius of 6 378 km giving 350 600 km. Lucey et al. (2006) give 107 particles cm3 by day and 105 particles cm3 by night. Along with equatorial surface temperatures of 390 K by day and 100 K by night the ideal gas law yields the pressures given in the infobox (rounded to the nearest order of magnitude; 107 Pa by day and 1010 Pa by night. There are a number of near-Earth asteroids including 3753 Cruithne that are co-orbital with Earth: their orbits bring them close to Earth for periods of time but then alter in the long term (Morais et al 2002). These are quasi-satellites and not true moons. For more information see Other moons of Earth. This age is calculated from isotope dating of lunar rocks. More accurately the Moon's mean sidereal period (fixed star to fixed star) is 27.321661 days (27d 07h 43m 11.5s) and its mean tropical orbital period (from equinox to equinox) is 27.321582 days (27d 07h 43m 04.7s) (Explanatory Supplement to the Astronomical Ephemeris 1961 at p.107). More accurately the Moon's mean synodic period (between mean solar conjunctions) is 29.530589 days (29d 12h 44m 02.9s) (Explanatory Supplement to the Astronomical Ephemeris 1961 at p.107). The Sun's apparent magnitude is 26.7 and the full Moon's apparent magnitude is 12.7. On average the Moon covers an area of 0.21078 square degrees on the night sky. Footnotes a b c d e f g h i j k l Wieczorek M.; et al. (2006). "The constitution and structure of the lunar interior". Reviews in Mineralogy and Geochemistry 60 (1): 221364. doi:10.2138/rmg.2006.60.3.  a b c d e Williams Dr. David R. (2 February 2006). "Moon Fact Sheet". NASA (National Space Science Data Center). http://nssdc.gsfc.nasa.gov/planetary/factsheet/moonfact.html. Retrieved 31 December 2008.  Matthews Grant (2008). "Celestial body irradiance determination from an underfilled satellite radiometer: application to albedo and thermal emission measurements of the Moon using CERES". Applied Optics 47 (27): 498193. 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ISBN 978-0-19-283300-6.  Smith William George (1849). Dictionary of Greek and Roman Biography and Mythology: Oarses-Zygia. 3. J. Walton. p. 768. http://books.google.com/idPJ0YAAAAIAAJ&dqDictionary%20of%20Greek%20and%20Roman%20Biography%20and%20Mythology&pgPA768#vonepage&q. Retrieved 29 March 2010.  Estienne Henri (1846). Thesaurus graecae linguae. 5. Didot. p. 1001. http://books.google.com/id0qQAAAAcAAJ&dq%CE%BC%CE%AE%CE%BD%CE%B1%CF%82%20%CE%BC%CE%AE%CE%BD%CE%B7&pgRA1-PA581#vonepage&q. Retrieved 29 March 2010.  "Carved and Drawn Prehistoric Maps of the Cosmos". Space Today Online. 2006. http://www.spacetoday.org/SolSys/Earth/OldStarCharts.html. Retrieved 12 April 2007.  a b Lilienfeld Scott O.; Arkowitz Hal (2009). "Lunacy and the Full Moon". Scientific American. http://www.scientificamerican.com/article.cfmidlunacy-and-the-full-moon. Retrieved 13 April 2010.  Bibliography Needham Joseph (1986). Science and Civilization in China. 3 Mathematics and the Sciences of the Heavens and Earth. Taipei: Caves Books. ISBN 0-521-05801-5.  Further reading Bussey B.; Spudis P.D. (2004). The Clementine Atlas of the Moon. Cambridge University Press. ISBN 0-521-81528-2.  Jolliff B.; Wieczorek M.; Shearer C.; Neal C. (eds.) (2006). "New views of the Moon". Rev. Mineral. Geochem. (Chantilly Virginia: Min. Soc. Amer.) 60 (1): 721. doi:10.2138/rmg.2006.60.0. ISBN 0939950723. http://www.minsocam.org/msa/RIM/Rim60.html. Retrieved 12 April 2007.  Mackenzie Dana (2003). The Big Splat or How Our Moon Came to Be. Hoboken New Jersey: John Wiley & Sons Inc. ISBN 0-471-15057-6.  Moore P. (2001). On the Moon. Tucson Arizona: Sterling Publishing Co.. ISBN 0-304-35469-4.  Spudis P.D. (1996). The Once and Future Moon. Smithsonian Institution Press. ISBN 1-56098-634-4.  Taylor S.R. (1992). Solar system evolution. Cambridge Univ. Press. pp. 307. ISBN 0-521-37212-7.  Wilhelms D.E. (1987). "Geologic History of the Moon". U.S. Geological Survey Professional paper 1348. http://ser.sese.asu.edu/GHM/. Retrieved 12 April 2007.  Wilhelms D.E. (1993). To a Rocky Moon: A Geologist's History of Lunar Exploration. Tucson Arizona: University of Arizona Press. ISBN 0-8165-1065-2. http://www.lpi.usra.edu/publications/books/rockyMoon/. Retrieved 10 March 2009.  External links Find more about Moon on Wikipedia's sister projects: Definitions from Wiktionary Images and media from Commons Learning resources from Wikiversity News stories from Wikinews Quotations from Wikiquote Source texts from Wikisource Textbooks from Wikibooks Solar System portal Moon portal Further reading "Exploring the Moon". Lunar and Planetary Institute. http://www.lpi.usra.edu/expmoon/. Retrieved 12 April 2007.  "Moon Articles". Planetary Science Research Discoveries. http://www.psrd.hawaii.edu/Archive/Archive-Moon.html.  Jones E.M. (2006). "Apollo Lunar Surface Journal". NASA. http://www.hq.nasa.gov/office/pao/History/alsj/. Retrieved 12 April 2007.  Teague K. (2006). "The Project Apollo Archive". http://www.apolloarchive.com/apolloarchive.html. Retrieved 12 April 2007.  Cain Fraser. "Where does the Moon Come From". Universe Today. http://www.astronomycast.com/astronomy/episode-17-where-does-the-moon-come-from/. Retrieved 1 April 2008.  (podcast and transcript) The Moon BBC World Service Discovery 2008 Cartographic resources "Lunar Atlases". Lunar and Planetary Institute. http://www.lpi.usra.edu/resources/lunaratlases/. Retrieved 12 April 2007.  Gazetteer of Planetary Nomenclature (USGS) List of feature names. "Clementine Lunar Image Browser". U.S. Navy. 15 October 2003. http://www.cmf.nrl.navy.mil/clementine/clib/. Retrieved 12 April 2007.  3d zoomable globes: "Google Moon". Google. 2007. http://moon.google.com. Retrieved 12 April 2007.  "Moon". World Wind Central. NASA. 2007. http://www.worldwindcentral.com/wiki/Moon. Retrieved 12 April 2007.  Aeschliman R. "Lunar Maps". Planetary Cartography and Graphics. http://ralphaeschliman.com/id26.htm. Retrieved 12 April 2007.  Maps and panoramas at Apollo landing sites Japan Aerospace Exploration Agency (JAXA) Kaguya (Selene) images Observation tools "NASA's SKYCALSky Events Calendar". NASA Eclipse Home Page. http://sunearth.gsfc.nasa.gov/eclipse/SKYCAL/SKYCAL.html. Retrieved 27 August 2007.  "Find moonrise moonset and moonphase for a location". 2008. http://www.timeanddate.com/worldclock/moonrise.html. Retrieved 18 February 2008.  "HMNAO's Moon Watch". 2005. http://www.crescentmoonwatch.org/nextnewmoon.htm. Retrieved 24 May 2009.  See when the next new crescent moon is visible for any location. v d eThe Moon Physical features Internal structure  Gravity field  Topography  Magnetic field  Atmosphere   Ion tail  Moonlight Orbit Orbit of the Moon  Phases  Solar eclipse  Lunar eclipse  Tide Lunar surface Selenography  Near side  Far side  Lunar mare  Craters  South Pole Aitken basin  Shackleton crater  Water  Soil  Peak of eternal light  Space weathering  Transient lunar phenomenon Lunar science Geology (timescale)  Giant impact hypothesis  Moon rocks  Lunar meteorites  KREEP  ALSEP  Lunar laser ranging  Late Heavy Bombardment   Observing the Moon Exploration Exploration of the Moon  Apollo program  Robotic exploration  Future missions  Lunar colonization  Moon Landing hoax accusations Other topics Calendar  Month  The Moon in art and literature  The Moon in mythology  Moon illusion  Lunar effect  Craters named after people  Man in the Moon See also Solar System  Natural satellite v d eNatural satellites of the Solar System Planetary satellites Terrestrial  Martian  Jovian  Saturnian  Uranian  Neptunian Other satellite systems Asteroid satellites  Plutonian  Eridian  Haumean Largest satellites Ganymede  Titan  Callisto  Io  Moon  Europa  Triton Titania  Rhea  Oberon  Iapetus  Charon  Umbriel  Ariel  Dione  Tethys   Enceladus  Miranda  Proteus  Mimas Inner satellites  Trojans  Irregulars  List  Timeline of discovery  Naming v d eThe Solar System The Sun Mercury Venus Earth Mars Ceres Jupiter Saturn Uranus Neptune Pluto Haumea Makemake Eris Moons (Terrestrial Martian Jovian Saturnian Uranian Neptunian Plutonian Haumean Eridian) Rings (Jovian Saturnian Uranian Neptunian) Meteoroids Minor planets (Asteroids (Main belt) Centaurs TNOs (Kuiper belt Scattered disc) ) Comets (Oort cloud) Related articles: astronomical object star planet dwarf planet small body and planetary system See also the Solar System's list of objects sorted by size the list of minor planets or the Solar System Portal