What is a moon
The Moon 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). It is the second-densest satellite among those whose densities are known (after Jupiter's satellite Io).
The average distance of the Moon from the Earth is 384,400 km (238,900 mi), or 1.28 light-seconds