Moon
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This article is about Earth's moon. For moons in general, see Natural satellite.
For other uses, see Moon (disambiguation).
Moon
The Moon as seen by an observer on Earth
Orbital characteristics
Perigee: 363,104 km
0.0024 AU
Apogee 405,696 km
0.0027 AU
Semi-major axis: 384,399 km
0.00257 AU [1]
Eccentricity: 0.0549 [1]
Orbital period: 27.321582 d
27 d 7 h 43.1 min [1]
Synodic period: 29.530588 d
29 d 12 h 44.0 min
Avg. orbital speed: 1.022 km/s
Inclination: 5.145° to ecliptic [1]
(between 18.29° and 28.58° to Earth's equator)
Longitude of ascending node: regressing,
1 revolution in 18.6 years
Argument of perigee: progressing,
1 revolution in 8.85 years
Satellite of: Earth
Physical characteristics
Mean radius: 1,737.10 km
0.273 Earths [1]
Equatorial radius: 1,738.14 km
0.273 Earths
Polar radius: 1,735.97 km
0.273 Earths
Flattening: 0.00125
Circumference: 10,921 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 Earths [1]
Mean density: 3,346.4 kg/m³ [1]
Equatorial surface gravity: 1.622 m/s²
0.1654 g
Escape velocity: 2.38 km/s
Sidereal rotation period: 27.321582 d (synchronous)
Rotation velocity at equator: 4.627 m/s
Axial tilt: 1.5424° (to ecliptic)
6.687° (to orbit plane)
Albedo: 0.12
Surface temp.:
equator
85°N [5] min mean max
100 K 220 K 390 K
70 K 130 K 230 K
Apparent magnitude: –2.5 to –12.9 [2]
–12.74 (mean full moon)[3]
Angular diameter: 29.3' — 34.1' [3][4]
Adjectives: lunar
Atmosphere [6][7]
Surface pressure: 10-7 Pa (day)
10-10 Pa (night)
The Moon (Latin: Luna) is Earth's only natural satellite, and is the fifth
largest one in the Solar System. The average centre-to-centre distance from
the Earth to the Moon is 384,403 km, which is about thirty times the diameter
of the Earth. The Moon has a diameter of 3,474 km[8]—slightly more than
a quarter that of the Earth and slightly smaller than the east–west distance
across the United States. This means that the volume of the Moon is about
2 percent that of Earth. The gravitational pull at its surface is about 17
percent of the Earth's. The Moon makes a complete orbit around the Earth every
27.3 days, and the periodic variations in the geometry of the Earth–Moon–Sun
system are responsible for the lunar phases that repeat every 29.5 days.
The Moon is the only celestial body to which humans have travelled and upon which humans have landed. The first artificial object to escape Earth's gravity and pass near the Moon was the Soviet Union's Luna 1, the first artificial 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.[8] The United States (U.S.) Apollo program achieved the only manned missions to date, resulting in six landings between 1969 and 1972. Human exploration of the Moon ceased with the conclusion of the Apollo program, although several countries have announced plans to send people or robotic spacecraft to the Moon
