satellite
Moon
Tidally locked, so one hemisphere has never been seen from the ground, and receding about 3.8 cm a year. It is a quarter of Earth in diameter, which makes the pair very nearly a double planet, and by pure coincidence it covers the disc of the Sun almost exactly.
Position
Computed on . For a continuously updating figure, open the live simulation.
About Moon
The Moon is a quarter of Earth’s diameter, an extreme ratio for a satellite, and the pair is sometimes described as a double planet. Tidal locking means the same hemisphere always faces us. The coincidence that makes total solar eclipses possible — the Moon and the Sun subtending almost exactly the same angle — is temporary: the Moon recedes about 3.8 cm a year, and in a few hundred million years total eclipses will stop happening.
Physical data
- Diameter
- 3,475 km
- Mass
- 0.0123 earths
- Surface gravity
- 1.62 m/s2
- Sidereal month
- 27.32 d
- Synodic month
- 29.53 d
- Rotation
- synchronous
- Mean distance
- 384,400 km
- Orbit inclination
- 5.15 deg
- Mean temperature
- -20 C
Positions from VSOP87 and an ELP-derived lunar theory, accurate to within one arcminute. Physical constants are published values and are not computed here.