• Section: Space /Sunday 12th October 2014


    Search β):

    * Moon *

    کره ماه

    (Wikipedia) - Moon This article is about Earth''s natural satellite. For moons in general, see Natural satellite. For other uses, see Moon (disambiguation). Moon Designations Adjectives Orbital characteristics Perigee Apogee Semi-major axis Eccentricity Orbital periodSynodic periodAverage orbital speed Inclination Longitude of ascending nodeArgument of perigeeSatellite of Physical characteristics Mean radiusEquatorial radiusPolar radius Flattening Circumference Surface area Volume Mass Mean densitySurface gravityMoment of inertia factorEscape velocitySidereal rotation periodEquatorial rotation velocityAxial tilt Albedo Apparent magnitudeAngular diameter Atmosphere Surface pressure Composition
    Full moon as seen from Earth''s northern hemisphere.
    • lunar
    • selenic
    362600 km (356400–370400 km)
    405400 km (404000–406700 km)
    384399 km  (0.00257 AU)
    27.321582 d (27 d 7 h 43.1 min)
    29.530589 d (29 d 12 h 44 min 2.9 s)
    1.022 km/s
    5.145° to the ecliptic
    regressing by one revolution in 18.6 years
    progressing by one revolution in 8.85 years
    1737.10 km  (0.273 Earths)
    1738.14 km  (0.273 Earths)
    1735.97 km  (0.273 Earths)
    10921 km  (equatorial)
    3.793×107 km2  (0.074 Earths)
    2.1958×1010 km3  (0.020 Earths)
    7.3477×1022 kg  (0.012300 Earths)
    3.3464 g/cm3 0.606 × Earth
    1.622 m/s2  (0.1654 g)
    2.38 km/s
    27.321582 d  (synchronous)
    4.627 m/s
    • 1.5424° to ecliptic
    • 6.687° to orbit plane
    Surface temp. min mean max Equator 85°N 
    100 K 220 K 390 K
    70 K 130 K 230 K
    • −2.5 to −12.9
    • −12.74  (mean full moon)
    29.3 to 34.1 arcminutes
    • 10−7 Pa  (day)
    • 10−10 Pa  (night)
    • Ar
    • He
    • Na
    • K
    • H
    • Rn

    The Moon (Latin: Luna) is the Earth''s only natural satellite. Although not the largest natural satellite in the Solar System, it is, among the satellites of major planets, the largest relative to the size of the object it orbits (its primary)  and, after Jupiter''s satellite Io, it is the second most dense satellite among those whose densities are known.

    The Moon is in synchronous rotation with Earth, always showing the same face with its near side marked by dark volcanic maria that fill between the bright ancient crustal highlands and the prominent impact craters. It is the most luminous object in the sky after the Sun. Although it appears a very bright white, its surface is actually dark, with a reflectance just slightly higher than that of worn asphalt. 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 slight lengthening of the day. The Moon''s current orbital distance is about thirty times the diameter of Earth, causing it to have an apparent size in the sky almost the same as that of the Sun. This allows the Moon to cover the Sun nearly precisely in total solar eclipse. This matching of apparent visual size is a coincidence. The Moon''s linear distance from Earth is currently increasing at a rate of 3.82±0.07 cm per year, but this rate is not constant.


    The Moon is the only celestial body other than Earth on which humans have currently set foot. 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 1972, with the first being Apollo 11. These missions returned over 380 kg of lunar rocks, which have been used to develop a geological understanding of the Moon''s origin, the formation of its internal structure, and its subsequent history.

    After the Apollo 17 mission in 1972, the Moon has been visited by only unmanned spacecraft. Of these, orbital missions have dominated: Since 2004, Japan, China, India, the United States, and the European Space Agency have each sent lunar orbiters, which have contributed to confirming the discovery of lunar water ice in permanently shadowed craters at the poles and bound into the lunar regolith. The post-Apollo era has also seen two rover missions: the final Soviet Lunokhod mission in 1973, and China''s ongoing Chang''e 3 mission, which deployed its Yutu rover on 14 December 2013.


    • 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 Gravitational field
      • 3.4 Magnetic field
      • 3.5 Atmosphere
      • 3.6 Seasons
    • 4 Relationship to Earth
      • 4.1 Orbit
      • 4.2 Relative size
      • 4.3 Appearance from Earth
      • 4.4 Tidal effects
      • 4.5 Eclipses
    • 5 Study and exploration
      • 5.1 Early studies
      • 5.2 First direct exploration: 1959–1976
        • 5.2.1 Soviet missions
        • 5.2.2 United States missions
      • 5.3 Current era: 1990–present
    • 6 Astronomy from the Moon
    • 7 Legal status
    • 8 In culture
    • 9 See also
    • 10 References
      • 10.1 Notes
      • 10.2 Citations
      • 10.3 Bibliography
    • 11 Further reading
    • 12 External links
      • 12.1 Cartographic resources
      • 12.2 Observation tools
      • 12.3 General

    Name and etymology



    Formation Main articles: Origin of the Moon and Giant impact hypothesisPlay mediaThe evolution of the Moon and a tour of the Moon.

    Several mechanisms have been proposed for the Moon''s formation 4.527 ± 0.010 billion years ago, some 30–50 million years after the origin of the Solar System. Recent research presented by Rick Carlson indicates a slightly younger age of between 4.40 and 4.45 billion years. These mechanisms included the fission of the Moon from Earth''s crust through centrifugal force (which would require too great an initial spin of Earth), the gravitational capture of a pre-formed Moon (which would require an unfeasibly extended atmosphere of Earth to dissipate the energy of the passing Moon), and the co-formation of Earth and the Moon together in the primordial accretion disk (which does not explain the depletion of metallic iron in the Moon). These hypotheses also cannot account for the high angular momentum of the Earth–Moon system.


    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."



    Despite its accuracy in explaining many lines of evidence, there are still some difficulties that are not fully explained by the giant impact hypothesis, most of them involving the Moon''s composition.

    Moon – Oceanus Procellarum ("Ocean of Storms")
    Ancient rift valleys – rectangular structure (visible – topography – GRAIL gravity gradients) (October 1, 2014).Ancient rift valleys – context.Ancient rift valleys – closeup (artist''s concept).


    Physical characteristics Internal structure Main article: Internal structure of the MoonStructure of the Moon Chemical composition of the lunar surface regolith (derived from crustal rocks) Compound Formula Composition (wt %) Maria Highlands Total 99.9% 100.0%
    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%



    Surface geology Main articles: Geology of the Moon and Moon rocks See also: Topography of the Moon and List of features on the MoonNear side of the MoonFar side of the Moon. Note the almost complete lack of dark maria.Topography of the MoonLunar north poleLunar south pole

    The topography of the Moon has been measured with laser altimetry and stereo image analysis. The most visible topographic feature is the giant far-side South Pole–Aitken basin, some 2,240 km in diameter, the largest crater on the Moon and the largest known crater in the Solar System. At 13 km deep, its floor is the lowest point on the surface of the Moon. The highest elevations on the surface of the Moon are located directly to the northeast, and it has been suggested that this area might have been thickened by the oblique formation impact of the South Pole–Aitken basin. Other large impact basins, such as Imbrium, Serenitatis, Crisium, Smythii, and Orientale, also possess regionally low elevations and elevated rims. The lunar far side is on average about 1.9 km higher than the near side.

    Volcanic features Main article: Lunar mareLunar nearside with major maria and craters labeled


    Maria are found almost exclusively on the near side of the Moon, covering 31% of the surface on the near side, compared with a few scattered patches on the far side covering only 2%. 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. Most of the Moon''s mare basalts erupted during the Imbrian period, 3.0–3.5 billion years ago, although some radiometrically dated samples are as old as 4.2 billion years, and the youngest eruptions, dated by crater counting, appear to have been only 1.2 billion years ago.



    Impact craters See also: List of craters on the MoonLunar crater Daedalus on the Moon''s far side



    Presence of water Main article: Lunar water




    In May 2011, Erik Hauri et al. reported 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. Although of considerable selenological interest, Hauri''s announcement affords little comfort to would-be lunar colonists—the sample originated many kilometers below the surface, and the inclusions are so difficult to access that it took 39 years to find them with a state-of-the-art ion microprobe instrument.

    Gravitational field Main article: Gravity of the Moon


    Magnetic field Main article: Magnetic field of the Moon


    AtmosphereAt sunrise and sunset many Apollo crews saw glows and light rays.Main article: Atmosphere of the Moon



    The Moon''s axial tilt with respect to the ecliptic is only 1.5424°, 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. From images taken by Clementine in 1994, it appears that four mountainous regions on the rim of Peary crater at the Moon''s north pole may remain illuminated for the entire lunar day, creating peaks of eternal light. No such regions exist at the south pole. Similarly, there are places that remain in permanent shadow at the bottoms of many polar craters, 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) 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.

    Relationship to EarthSchematic 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 Earth with respect to the fixed stars about once every 27.3 days (its sidereal period). 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 to Earth, which is about 29.5 days (its synodic period). Unlike most satellites of other planets, the Moon orbits closer to the ecliptic plane than to the planet''s equatorial plane. The Moon''s orbit is subtly perturbed by the Sun and Earth in many small, complex and interacting ways. For example, the plane of the Moon''s orbital motion gradually rotates, which affects other aspects of lunar motion. These follow-on effects are mathematically described by Cassini''s laws.

    Earth and Moon, showing their sizes and distance to scale. The yellow bar represents a pulse of light traveling from Earth to Moon (approx. 400,000 km or 250,000 mi) in 1.26 seconds.Relative size

    The Moon is exceptionally large relative to Earth: a quarter the diameter of the planet and 1/81 its mass. It is the largest moon in the Solar System relative to the size of its planet, though Charon is larger relative to the dwarf planet Pluto, at 1/9 Pluto''s mass.

    However, Earth and the Moon are still considered a planet–satellite system, rather than a double-planet system, because their barycentre, the common centre of mass, is located 1,700 km (about a quarter of Earth''s radius) beneath Earth''s surface.

    Appearance from EarthMoon setting in western sky over High Desert (California)See also: Lunar phase, Earthshine and Observing the Moon





    The highest altitude of the Moon in the sky varies: although 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.

    The distance between the Moon and Earth varies from around 356,400 km to 406,700 km at the extreme perigees (closest) and apogees (farthest). On 19 March 2011, it was closer to Earth when at full phase than it has been since 1993, 14% closer than its farthest position in apogee. Reported as a "super moon", this closest point coincides within an hour of a full moon, and it was 30% more luminous than when at its greatest distance due to its angular diameter being 14% greater, because . At lower levels, the human perception of reduced brightness as a percentage is provided by the following formula:


    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. 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.

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

    The tides on Earth are mostly generated by the gradient in intensity of the Moon''s gravitational pull from one side of Earth to the other, the tidal forces. This forms two tidal bulges on Earth, which are most clearly seen in elevated sea level as ocean tides. Because Earth spins about 27 times faster than the Moon moves around it, the bulges are dragged along with Earth''s surface faster than the Moon moves, rotating around Earth once a day as it spins on its axis. 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. The gravitational attraction of the Sun on Earth''s oceans is almost half that of the Moon, and their gravitational interplay is responsible for spring and neap tides.

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

    Gravitational coupling between the Moon and the bulge nearest the Moon acts as a torque on Earth''s rotation, draining angular momentum and rotational kinetic energy from Earth''s spin. 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 Earth and Moon is increasing, and Earth''s spin slowing down. Measurements from lunar ranging experiments with laser reflectors left during the Apollo missions have found that the Moon''s distance to Earth increases by 38 mm per year (though this is only 0.10 ppb/year of the radius of the Moon''s orbit). Atomic clocks also show that Earth''s day lengthens by about 15 microseconds every year, slowly increasing the rate at which UTC is adjusted by leap seconds. Left to run its course, this tidal drag would continue until the spin of Earth and the orbital period of the Moon matched, creating mutual tidal locking between the two, as is already currently the case with Pluto and its moon Charon. However, the Sun will become a red giant long before that, engulfing Earth.


    Eclipses Main articles: Solar eclipse, Lunar eclipse and Eclipse cycleThe 1999 solar eclipseThe Moon passing in front of the Sun, from the STEREO-B spacecraft.From 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.




    Study and exploration See also: Robotic exploration of the Moon, List of proposed missions to the Moon, Colonization of the Moon and List of man-made objects on the MoonMap 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


    In Aristotle''s (384–322 BC) description of the universe, the Moon marked the boundary between the spheres of the mutable elements (earth, water, air and fire), and the imperishable stars of aether, an influential philosophy that would dominate for centuries. 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. In the same century, Aristarchus computed the size and distance of the Moon from Earth, obtaining a value of about twenty times the radius of Earth for the distance. These figures were greatly improved by Ptolemy (90–168 AD): his values of a mean distance of 59 times Earth''s radius and a diameter of 0.292 Earth diameters were close to the correct values of about 60 and 0.273 respectively. Archimedes (287–212 BC) designed a planetarium that could calculate the motions of the Moon and other objects in the Solar System.


    First direct exploration: 1959–1976 Soviet missionsSoviet moonroverMain articles: Luna program and Lunokhod programme

    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 1958, 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.


    United States missions Main articles: Apollo program, Moon landing and Project HorizonEarth as viewed from Lunar orbit 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.Neil Armstrong and a U.S. flag



    According to national security documents declassified in July 2014, the United States government had planned in the 1960s to construct a manned military outpost on the moon, which would have been home to a bombing system targeted at earthbound rivals. Part of Project Horizon, the plans also included conducting a lunar-based nuclear test, whose primary purpose would have been to demonstrate American military power to the world. However, the project was ultimately called off by Air Force leaders, who deemed it too perilous.

    Current era: 1990–present



    China has pursued an ambitious program of lunar exploration, beginning with Chang''e 1, which successfully orbited the Moon from 5 November 2007 until its controlled lunar impact on 1 March 2009. In its sixteen-month mission, it obtained a full image map of the Moon. China followed up this success with Chang''e 2 beginning in October 2010, which reached the Moon over twice as fast as Chang''e 1, mapped the Moon at a higher resolution over an eight month period, then left lunar orbit in favor of an extended stay at the Earth–Sun L2 Lagrangian point, before finally performing a flyby of asteroid 4179 Toutatis on 13 December 2012, and then heading off into deep space. On 14 December 2013, Chang''e 3 improved upon its orbital mission predecessors by landing a lunar lander onto the Moon''s surface, which in turn deployed a lunar rover, named Yutu (Chinese: 玉兔; literally "Jade Rabbit"). In so doing, Chang''e 3 made the first lunar soft landing since Luna 24 in 1976, and the first lunar rover mission since Lunokhod 2 in 1973. China intends to launch another rover mission (Chang''e 4) in 2015, followed by a sample return mission (Chang''e 5) in 2017.

    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. 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. The Indian Space Research Organisation planned to launch Chandrayaan II in 2013, which would have included a Russian robotic lunar rover. However, the failure of Russia''s Fobos-Grunt mission has delayed this project. 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 2009, whereas LRO is currently in operation, obtaining precise lunar altimetry and high-resolution imagery. In November 2011, the LRO passed over the Aristarchus crater, which spans 40 kilometres and sinks more than 3.5 kilometres deep. The crater is one of the most visible ones from Earth. "The Aristarchus plateau is one of the most geologically diverse places on the Moon: a mysterious raised flat plateau, a giant rille carved by enormous outpourings of lava, fields of explosive volcanic ash, and all surrounded by massive flood basalts", said Mark Robinson, principal investigator of the Lunar Reconnaissance Orbiter Camera at Arizona State University. NASA released photos of the crater on 25 December 2011.

    Two NASA GRAIL spacecraft begin orbiting the Moon around 1 January 2012, on a mission to learn more about the Moon''s internal structure. NASA''s LADEE probe, designed to study the lunar exosphere, achieved orbit on 6 October 2013.



    Astronomy from the Moon



    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. Russia and the U.S. are party to the 1967 Outer Space Treaty, which defines the Moon and all outer space as the "province of all mankind". This treaty also restricts the use of the Moon to peaceful purposes, explicitly banning military installations and weapons of mass destruction. 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. Although several individuals have made claims to the Moon in whole or in part, none of these are considered credible.

    In culture Further information: Moon in fiction, Lunar calendar, Metonic cycle, Lunar deity, Lunar effect and Blue moonLuna, the Moon, from a 1550 edition of Guido Bonatti''s Liber astronomiae.


    A crescent Moon and "star" (here the planet Venus) are a common symbol of Islam, appearing in flags like:  (Turkey),  (Algeria) and  (Pakistan).




    Tags:1968, 2015, Africa, Algeria, American, Arabic, Aristotle, Arizona, Astronomy, Beer, Bush, California, Carnegie, Cassini, China, Chinese, Christmas, Cold War, Computer, Dynasty, Earth, Equator, George W. Bush, Google, Greek, Hawaii, India, Ireland, Islam, Islamic, Japan, Jet, Jupiter, Legal, Mars, Martian, Middle Ages, Moon, Muslim, NASA, Ottoman, Ottoman Empire, Pakistan, Pluto, Post, President, Ptolemy, Russia, Russian, Satellite, Seleucia, Soviet, Soviet Union, Sun, Turkey, US, United States, Venus, Washington, Wikipedia, Wilhelm

    Add definition or comments on Moon

    Your Name / Alias:
    Definition / Comments
    neutral points of view
    Source / SEO Backlink:
    Anti-Spam Check
    Enter text above
    Upon approval, your definition will be listed under: Moon