The moon is an astronomical body that orbits planet earth,being Earth's only permanent natural satelite.It is the fifth largest natural satelite in the solar system,and the largest among planetary satelites relative to the of the planet that it orbits (its primary).Following Jupitars satelite Io,the moon is second densest satelite among those whose densities are known.
The mean radius of the Moon is 1737.1km.And polar radius is 1738.1km.
The Moon is thought to have formed about 4.51 billion years ago,not long after earth.The most widely accepted explanation is that the Moon formed from the debris left over after a giant impact between Earth and a mars sized body called Theia.
Collected from #Wikipedia