A natural satellite is a non-man-made object that orbits a planet or other body larger than itself. It is commonly referred to as a moon (not capitalized). The term natural satellite may also refer to a planet orbiting a star, as is the case with the eight or nine planets orbiting the Sun. There are 240 known moons within the Solar system, including 80 orbiting minor planets (not the bodies in the asteroid belt) and over 150 orbiting the planets. 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. Mercury and Venus have no moons at all; Earth has one large moon ("the Moon" or "Luna"); Mars has two tiny moons; and Pluto has five satellites, including a large companion called Charon. Pluto-Charon and some of the asteroid systems are sometimes considered to be double planets.

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