Moon

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Earth's Moon
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Earth's Moon

A moon is a large, usually ball shaped object that goes around (orbits) a planet. The Earth has only one moon. Some other planets have many moons, and some have none. When people write just "the moon", they are usually talking about the moon of the Earth. Some people refer to it as Luna, the Latin word for it.

Anything that goes around a planet is called a satellite. Moons are natural satellites. People also use rockets to send machines into orbit around the Earth. These machines are called artificial (man-made) satellites.

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[edit] Earth's Moon

Moons do not make their own light. We can see the Earth's moon because it acts like a mirror, and reflects the light of the Sun. The same half of the moon faces toward Earth at all times, no matter where it moves. But different parts of the moon are lit up by the Sun, so it looks different at different times of the month. This change as seen from Earth is called the phases of the moon, or lunar phases.

A moon's cycle is the time the moon takes to change from looking very bright and round to looking very small and thin, and then back to bright and round again. In the case of the Earth's moon, this is about four weeks. It does this about 13 times in one year. The moon's cycle is about 28 days, a bit shorter than a calendar month.

Neil Armstrong was the first person to walk on the Moon. He did this in July, 1969.

[edit] Orbits

The orbit of a moon or other satellite is affected by two forces: gravity, and the centripetal force. For example, the Earth's moon is kept in orbit by the gravitational pull from the Earth.

[edit] Planets that have moons

Planets in our Solar System that have moon(s):

[edit] Dwarf planets that have moons

[edit] Planets that do not have moons

Planets in our Solar System that do not have moons:

The Solar System
Image:Eight Planets.png
Star: The Sun
Planets: MercuryVenusEarthMarsJupiterSaturnUranusNeptune
Dwarf planets: CeresPlutoEris
Small solar system body: Asteroid beltCometsMeteorsKuiper beltScattered disc – Oort cloud
Other: Moon