The Moon is Earth's only natural satellite and the fifth-largest satellite in the Solar System. It is a rocky body with a surface gravity that is about one-sixth of Earth's gravity. The Moon orbits Earth at an average distance of about 384,400 kilometers (238,855 miles) and is tidally locked to Earth, meaning that the same side of the Moon always faces Earth. The Moon's presence stabilizes Earth's axial tilt and influences ocean tides. The Moon's surface is marked by impact craters, volcanic features, and highlands. The Moon is also known as Luna in Latin, and its name in Hebrew is יָרֵחַ (Yareakh). In other languages, the Moon is called La Lune in French, Der Mond in German, and La Luna in Spanish and Italian. The study of the Moon is known as selenology, from the Greek word for the Moon, Selene.