The Moon is 3500 km in diameter. The Earth, by comparison, is 12 800 km wide, and has a mass 81 times as great. This means that pro rata the Earth has the largest satellite of any of the planets, and strictly the Earth and Moon may be considered to be a binary planet.

The Moon orbits the Earth - or more accurately the Earth and Moon revolve around a common barycentre - at a centre-to-centre distance of 384,000 km. The Sun, some 150,000,000 km away, is 1,400,000 km across. It is an almost unbelievable coincidence that from the surface of the Earth, the Sun and the Moon appear more or less exactly the same size - around 32 arc minutes. It is this fact which allows us to see the Sunís corona during a solar eclipse. No other combination of bodies anywhere in the Solar System give rise to this phenomenon.

Inconstant Moon