Moon

The Moon as seen from Earth. This is a nearly full moon
Designations
Alternative names	Luna
Adjectives	lunar, selenic
Orbital characteristics
Perigee	363,104 km  (0.002 4 AU)
Apogee	405,696 km  (0.002 7 AU)
Semi-major axis	384,399 km  (0.002 57 AU)
Eccentricity	0.054 9
Orbital period	27.321 582 d  (27 d 7 h 43.1 min)
Synodic period	29.530 589 d  (29 d 12 h 44 min 2.9 s)
Average orbital speed	1.022 km/s
Inclination	5.145° to the ecliptic (between 18.29° and 28.58° to Earth's equator)
Longitude of ascending node	regressing by one revolution in 18.6 years
Argument of perigee	progressing by one revolution in 8.85 years
Satellite of	Earth
Physical characteristics
Mean radius	1,737.10 km  (0.273 Earths)
Flattening	0.001 25
Circumference	10,921 km (equatorial)
Surface area	3.793 × 107 km²  (0.074 Earths)
Volume	2.195 8 × 1010 km³  (0.020 Earths)
Mass	7.347 7 × 1022 kg  (0.012 3 Earths)
Mean density	3,346.4 kg/m³
Surface gravity	1.622 m/s² (0.165 4 g)
Escape velocity	2.38 km/s
Sidereal rotation period	27.321 582 d (synchronous)
Equatorial rotation velocity	4.627 m/s
Axial tilt	1.542 4° (to ecliptic) 6.687° (to orbit plane)
Albedo	0.12
Surface temp. min mean max equator 100 K 220 K 85°N 70 K 130 K 230 K
Apparent magnitude	−2.5 to −12.9 −12.74 (mean full moon)
Angular diameter	29.3 to 34.1 arcminutes
Surface pressure	2.25  × 10-12torr

The Moon is Earth's only natural satellite. We usually see it in the night sky but also during the day. Some other planets also have moons or natural satellites.

Our moon is about one-fourth of the width of the Earth. Because it is far away it looks small, about half a degree wide. The gravity on the moon is one-sixth of the Earth's gravity. It means that something will be one-sixth as heavy on the Moon than on Earth. The Moon is a rocky and dusty place. It moves slowly away from the Earth at a rate of 3.8 cm per year, due to the effect of tidal dissipation.