The Moon is Earth’s sole natural satellite and nearest large celestial body. It is a spherical rocky body, probably with a small metallic core, revolving around Earth in a slightly eccentric orbit at a mean distance of about 384,000 km (238,600 miles). Its equatorial radius is 1,738 km (1,080 miles). Because of the Moon’s small size and mass, its surface gravity is only about one-sixth of Earth’s.