Moon

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

Moon
Near side of the Moon, lunar north pole at top
Designations
Alternative names
  • Luna
  • Selene (poetic)
  • Cynthia (poetic)
Symbol or
Orbital characteristics
Epoch J2000
Uncertainty parameter 0
Perigee362600 km
(356400–370400 km)
Apogee405400 km
(404000–406700 km)
384399 km  (1.28 ls; 1/389 AU; 1 LD)[1]
Mean orbit radius
384784 km[2]
(1.28 ls; 1/384 AU; 1.001 LD)
Eccentricity0.0549[1]
27.321661 d
(27 d 7 h 43 min 11.5 s[1])
29.530589 d
(29 d 12 h 44 min 2.9 s)
Average orbital speed
1.022 km/s
Inclination5.145° to the ecliptic[3][a]
Regressing by one revolution in 18.61 years
Argument of perigee
Progressing by one
revolution in 8.85 years
Satellite ofEarth[b][4]
Physical characteristics
Mean radius
1737.4 km  
(0.2727 of Earth's)[1][5][6]
Equatorial radius
1738.1 km  
(0.2725 of Earth's)[5]
Polar radius
1736.0 km  
(0.2731 of Earth's)[5]
Flattening0.0012[5]
Circumference10921 km  (equatorial)
3.793×107 km2  
(0.074 of Earth's)
Volume2.1958×1010 km3  
(0.02 of Earth's)[5]
Mass7.346×1022 kg  
(0.0123 of Earth's)[1][5][7]
Mean density
3.344 g/cm3[1][5]
0.606 × Earth
Surface gravity
1.622 m/s2 (5.32 ft/s2)[5]
0.1654 g0
Moment of inertia factor
0.3929±0.0009[8]
2.38 km/s
(8600 km/h; 5300 mph)
Synodic rotation period
29.530589 d
(29 d 12 h 44 min 2.9 s; synodic; solar day) (spin-orbit locked)
Sidereal rotation period
27.321661 d  (spin-orbit locked)
Equatorial rotation velocity
4.627 m/s
North pole right ascension
  • 17h 47m 26s
  • 266.86°[11]
North pole declination
65.64°[11]
Albedo0.136[12]
Surface temp. min mean max
Equator 100 K[13] 250 K 390 K[13]
85°N  150 K 230 K[14]
Surface absorbed dose rate13.2 μGy/h
(during lunar daytime)[15]
Surface equivalent dose rate57.0 μSv/h
(during lunar daytime)[15]
0.2[16]
Angular diameter
29.3 to 34.1 arcminutes[5][d]
Atmosphere[17]
Surface pressure
  • 10−7 Pa (1 picobar)  (day)
  • 10−10 Pa (1 femtobar)   
    (night)[e]
Composition by volume

The Moon is Earth's only natural satellite. It orbits around Earth at an average distance of 384,399 kilometres (238,854 mi),[f] about 30 times Earth's diameter, and completes an orbit (lunar month) every 29.5 days. This is the same length it takes the Moon to complete a rotation (lunar day). The rotation period is synchronized with the orbital period by Earth's gravity forcing the Moon to face Earth always with the same side, making it tidally locked. The Moon's gravity causes tidal forces on Earth, which are the main driver of Earth's tides.

In geophysical terms, the Moon is a planetary-mass object or satellite planet. Its mass is 1.2% that of the Earth, and its diameter is 3,474 km (2,159 mi), roughly one-quarter of Earth's (about as wide as the contiguous United States). Within the Solar System, it is larger and more massive than any known dwarf planet, and the fifth-largest and fifth-most massive moon, as well as the largest and most massive in relation to its parent planet.[18] Its surface gravity is about one-sixth of Earth's, about half that of Mars, and the second-highest among all moons in the Solar System after Jupiter's moon Io. The body of the Moon is differentiated and terrestrial, with only a minuscule hydrosphere, atmosphere, and magnetic field. The lunar surface is covered in regolith dust, which mainly consists of the fine material ejected from the lunar crust by impact events. The lunar crust is marked by impact craters, with some younger ones featuring bright ray-like streaks. The Moon was volcanically active until 1.2 billion years ago, surfacing lava mostly on the thinner near side of the Moon, filling ancient craters, which through cooling formed the today prominently visible dark plains of basalt called maria ('seas'). The Moon formed out of material from Earth, ejected by a giant impact into Earth of a hypothesized Mars-sized body named Theia 4.51 billion years ago, not long after Earth's formation.

From a distance, the day and night phases of the lunar day are visible as the lunar phases, and when the Moon passes through Earth's shadow a lunar eclipse is observable. The Moon's apparent size in Earth's sky is about the same as that of the Sun, which causes it to cover the Sun completely during a total solar eclipse. The Moon is the brightest celestial object in Earth's night sky because of its large apparent size, while the reflectance (albedo) of its surface is comparable to that of asphalt. About 59% of the surface of the Moon is visible from Earth owing to the different angles at which the Moon can appear in Earth's sky (libration), making parts of the far side of the Moon visible.

The Moon has been an important source of inspiration and knowledge in human history, having been crucial to cosmography, mythology, religion, art, time keeping, natural science and spaceflight. The first human-made objects to fly to an extraterrestrial body were sent to the Moon, starting in 1959 with the flyby of the Soviet Union's Luna 1 probe and the intentional impact of Luna 2. In 1966, the first soft landing (by Luna 9) and orbital insertion (by Luna 10) followed. Humans arrived for the first time at the Moon, or any extraterrestrial body, in orbit on December 24, 1968, with Apollo 8 of the United States, and on the surface at Mare Tranquillitatis on July 20, 1969, with the lander Eagle of Apollo 11. By 1972, six Apollo missions had landed twelve humans on the Moon and stayed up to three days. Renewed robotic exploration of the Moon, in particular to confirm the presence of water on the Moon, has fueled plans to return humans to the Moon, starting with the Artemis program in the late 2020s.

  1. ^ a b c d e f g Cite error: The named reference W06 was invoked but never defined (see the help page).
  2. ^ a b "Moon Fact Sheet". NASA National Space Science Data Center. NASA. January 11, 2024. Retrieved August 6, 2025.
  3. ^ a b Cite error: The named reference Lang2011 was invoked but never defined (see the help page).
  4. ^ Cite error: The named reference Morais2002 was invoked but never defined (see the help page).
  5. ^ a b c d e f g h i j Cite error: The named reference NSSDC was invoked but never defined (see the help page).
  6. ^ Smith, David E.; Zuber, Maria T.; Neumann, Gregory A.; Lemoine, Frank G. (January 1, 1997). "Topography of the Moon from the Clementine lidar". Journal of Geophysical Research. 102 (E1): 1601. Bibcode:1997JGR...102.1591S. doi:10.1029/96JE02940. hdl:2060/19980018849. ISSN 0148-0227. S2CID 17475023.
  7. ^ Terry, Paul (2013). Top 10 of Everything. Octopus Publishing Group Ltd. p. 226. ISBN 978-0-600-62887-3.
  8. ^ Cite error: The named reference Williams1996 was invoked but never defined (see the help page).
  9. ^ Cite error: The named reference SolarViews was invoked but never defined (see the help page).
  10. ^ Makemson, Maud W. (1971). "Determination of selenographic positions". The Moon. 2 (3): 293–308. Bibcode:1971Moon....2..293M. doi:10.1007/BF00561882. S2CID 119603394.
  11. ^ a b Archinal, Brent A.; A'Hearn, Michael F.; Bowell, Edward G.; Conrad, Albert R.; Consolmagno, Guy J.; Courtin, Régis; Fukushima, Toshio; Hestroffer, Daniel; Hilton, James L.; Krasinsky, George A.; Neumann, Gregory A.; Oberst, Jürgen; Seidelmann, P. Kenneth; Stooke, Philip J.; Tholen, David J.; Thomas, Paul C.; Williams, Iwan P. (2010). "Report of the IAU Working Group on Cartographic Coordinates and Rotational Elements: 2009" (PDF). Celestial Mechanics and Dynamical Astronomy. 109 (2): 101–135. Bibcode:2011CeMDA.109..101A. doi:10.1007/s10569-010-9320-4. S2CID 189842666. Archived from the original (PDF) on March 4, 2016. Retrieved September 24, 2018. also available "via usgs.gov" (PDF). Archived (PDF) from the original on April 27, 2019. Retrieved September 26, 2018.
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  13. ^ a b Bugby, D. C.; Farmer, J. T.; O'Connor, B. F.; Wirzburger, M. J.; C. J. Stouffer, E. D. Abel (January 2010). Two-Phase Thermal Switching System for a Small, Extended Duration Lunar Surface Science Platform. AIP Conference Proceedings. Vol. 1208. pp. 76–83. Bibcode:2010AIPC.1208...76B. doi:10.1063/1.3326291. hdl:2060/20100009810.
  14. ^ Cite error: The named reference Vasavada1999 was invoked but never defined (see the help page).
  15. ^ a b Zhang S, Wimmer-Schweingruber RF, Yu J, Wang C, Fu Q, Zou Y, et al. (2020). "First measurements of the radiation dose on the lunar surface". Science Advances. 6 (39) eaaz1334. Bibcode:2020SciA....6.1334Z. doi:10.1126/sciadv.aaz1334. PMC 7518862. PMID 32978156. We measured an average total absorbed dose rate in silicon of 13.2 ± 1 μGy/hour ... LND measured an average dose equivalent of 1369 μSv/day on the surface of the Moon
  16. ^ "Encyclopedia – the brightest bodies". IMCCE. Archived from the original on March 21, 2023. Retrieved June 1, 2023.
  17. ^ Cite error: The named reference L06 was invoked but never defined (see the help page).
  18. ^ Cite error: The named reference Metzger2021 was invoked but never defined (see the help page).


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