Moon is an astronomical body that orbits planet Earth, and is Earth’s only permanent natural satellite. It is the fifth-largest natural satellite in the Solar System, and the largest among planetary satellites relative to the size of the planet that it orbits (its primary). The Moon is after Jupiter‘s satellite Io the second-densest satellite in the Solar System among those whose densities are known.

Moon Moon symbol
FullMoon2010.jpg

Full moon as seen from North America in Earth’s Northern Hemisphere
Designations
Adjectives
Orbital characteristics
Perigee 362600 km
(356400–370400 km)
Apogee 405400 km
(404000–406700 km)
384399 km  (0.00257 AU)[1]
Eccentricity 0.0549[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)
1.022 km/s
Inclination 5.145° to the ecliptic[2][a]
Regressing by one revolution in 18.61 years
Progressing by one revolution in 8.85 years
Satellite of Earth[b][3]
Physical characteristics
Mean radius
1737.1 km  (0.273 of Earth’s)[1][4][5]
Equatorial radius
1738.1 km  (0.273 of Earth’s)[4]
Polar radius
1736.0 km  (0.273 of Earth’s)[4]
Flattening 0.0012[4]
Circumference 10921 km  (equatorial)
3.793×107 km2  (0.074 of Earth’s)
Volume 2.1958×1010 km3  (0.020 of Earth’s)[4]
Mass 7.342×1022 kg  (0.012300of Earth’s)[1][4]
Mean density
3.344 g/cm3[1][4]
0.606 × Earth
1.62 m/s2  (0.1654 g)[4]
0.3929±0.0009[6]
2.38 km/s
27.321661 d  (synchronous)
Equatorial rotation velocity
4.627 m/s
Albedo 0.136[7]
Surface temp. min mean max
Equator 100 K 220 K 390 K
85°N 150 K 230 K[8]
29.3 to 34.1 arcminutes[4][d]
Atmosphere[9]
Surface pressure
  • 10−7 Pa (1 picobar)  (day)
  • 10−10 Pa (1 femtobar)   (night)[e]
Composition by volume

The Moon is thought to have formed about 4.51 billion years ago, not long after Earth. The most widely accepted explanation is that the Moon formed from the debris left over after a giant impact between Earth and a Mars-sized body called Theia.

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