Back Monan hwyrft ANG مدار القمر Arabic Арбіта Месяца Byelorussian Òrbita de la Lluna Catalan Mondbahn German Τροχιά της Σελήνης Greek Órbita de la Luna Spanish Ilargiaren orbita Basque مدار ماه Persian Orbite de la Lune French

Orbit of the Moon

For the orbit of an object around the Moon, see Lunar orbit.
Orbit of the Moon
Diagram of the Moon's orbit with respect to the Earth. Angles are correct and relative sizes are to scale, but distances are not to scale.
Semi-major axis[a]384,748 km (239,071 miles)[1]
Mean distance[b]385,000 km (239,000 miles)[2]
Inverse sine parallax[c]384,400 km (238,900 miles)
Perigee363,228.9 km (225,700.0 miles), avg.
(356400–370400 km)
Apogee405,400 km (251,900 miles), avg.
(404000–406700 km)
Mean eccentricity0.0549006
(0.026–0.077)[3]
Mean obliquity6.687°[5]
Mean inclination
of orbit to ecliptic5.15° (4.99–5.30)[3]
of lunar equator to ecliptic1.543°
Period of
orbit around Earth (sidereal)27.322 days
orbit around Earth (synodic)29.530 days
precession of nodes18.5996 years
precession of line of apsides8.8504 years

The Moon orbits Earth in the prograde direction and completes one revolution relative to the Vernal Equinox and the stars in about 27.32 days (a tropical month and sidereal month) and one revolution relative to the Sun in about 29.53 days (a synodic month). Earth and the Moon orbit about their barycentre (common centre of mass), which lies about 4,670 km (2,900 miles) from Earth's centre (about 73% of its radius), forming a satellite system called the Earth–Moon system. On average, the distance to the Moon is about 384,400 km (238,900 mi) from Earth's centre, which corresponds to about 60 Earth radii or 1.282 light-seconds.

With a mean orbital velocity around the barycentre between the Earth and the Moon, of 1.022 km/s (0.635 miles/s, 2,286 miles/h),[6] the Moon covers a distance approximately its diameter, or about half a degree on the celestial sphere, each hour. The Moon differs from most regular satellites of other planets in that its orbit is closer to the ecliptic plane instead of its primary's (in this case, Earth's) equatorial plane. The Moon's orbital plane is inclined by about 5.1° with respect to the ecliptic plane, whereas Earth's equatorial plane is tilted by about 23° with respect to the ecliptic plane.

  1. ^ Cite error: The named reference box-semi was invoked but never defined (see the help page).
  2. ^ Cite error: The named reference box-distance was invoked but never defined (see the help page).
  3. ^ a b c Cite error: The named reference box-orbit was invoked but never defined (see the help page).
  4. ^ Seidelmann, P. Kenneth, ed. (1992), Explanatory Supplement to the Astronomical Almanac, University Science Books, pp. 696, 701, ISBN 0-935702-68-7
  5. ^ Cite error: The named reference Lang2011 was invoked but never defined (see the help page).
  6. ^ "Moon Fact Sheet". NASA. Retrieved 2014-01-08.


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