Moon

A moon is a solid body that orbits a planet, dwarf planet, or other celestial body. A moon produces no light of its own; it is visible only by reflecting sunlight. The term 'natural satellite' refers to moons that occur naturally, as opposed to artificial satellites created by humans.

When 'moon' (dayax) is used alone in Somali, it typically refers to Earth's moon, the only natural satellite of Earth. Technically, every moon is held in orbit around a larger body by that body's gravitational pull, and follows an orbital path around it.

How a moon behaves

A moon and the body it orbits share a common center of mass. A moon's orbit is not circular; it is usually elliptical, elongated or compressed. When a moon orbits a large body for a long time, gravitational forces typically cause the moon to present only one side to the body it orbits—a phenomenon known as tidal locking. Earth's moon is an example: we always see the same face.

Type and origin

Scientists classify moons according to their formation process. Some formed from dust and gas present in the vicinity of each planet at the time of planetary formation. Others are small bodies whose origin lies elsewhere, captured by the gravitational pull of a planet—for example, the small moons of Mars and some of Jupiter's moons. There is also a theory that some moons formed as a result of a giant collision.

Moons of the solar system

The large gas planets—Jupiter, Saturn, Uranus, and Neptune—have many moons. Mercury and Venus have no moons. Earth has one moon; Mars has two small ones. The number of known moons increases as new instruments are used, so the counts are not fixed.