Natural satellite

A natural satellite is a non-man-made object that orbits a planet or other body larger than itself. They are often called moons. The term natural satellite may also refer to a planet orbiting a star, as is the case with planets orbiting the Sun and even the Sun itself as it orbits the galactic center of the Milky Way. There are 240 known moons within the Solar system, including 162 orbiting the planets , 4 orbiting dwarf planets, and dozens more orbiting small solar system bodies. Other stars and their planets also have natural satellites.

The large gas giants have extensive systems of moons, including half a dozen comparable in size to Earth's moon. Of the inner planets, Mercury and Venus have no moons at all; Earth has one large moon ; and Mars has two tiny moons, Phobos and Deimos. Among the dwarf planets, Ceres has no moons, Eris has one, Dysnomia, and Pluto has three known satellites, Nix, Hydra, and a large companion called Charon. Charon is also unusual in that it does not orbit Pluto, but rather both bodies orbit a barycenter in empty space, making Pluto-Charon a binary system.

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