Moon

''This is about the only moon of earth. For the objects orbiting planets in general, see Moons''

It is also known as Luna is the only moon of Earth with a diameter of around 3475 km. Its ratio in size to the planet it is orbiting (Earth) is the biggest in the solar system (the moon is big compared to earth), not including Pluto and Charon. It is very very very slowly moving away from earth.

Formation
The moon formed at the start of the solar system just after Earth has formed when another planet Theia had a same orbit as Earth and crashed into Earth blasting a lot of dust from both Earth and Theia into space, which later forms the moon.