The Moon

The Moon is an astronomical body that orbits planet Earth, and is Earth's only permanent natural satellite. It is the fifth-largest natural satellite in the Solar System, and the largest among planetary satellites relative to the size of the planet that it orbits (its primary). The Moon is after Jupiter's satellite to the second-densest satellite in the Solar System among those whose densities are known.

“Moon.” Wikipedia, Wikimedia Foundation, 1 May 2018, en.wikipedia.org/wiki/Moon.