The radius of the Moon is 1.74×10^6m. Moon is the only natural satellite of the Earth. It is the fifth largest satellite in the Solar System. The Moon's orbit around Earth has a sidereal period of 27.3 days and a synodic period of 29.5 days. It has a geochemically distinct crust, mantle and core. The Moon has a solid iron-rich inner core with a radius possibly as small as 240km and a fluid outer core primarily made of liquid iron with radius of roughly 300km.