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The Moon
The Moon is the natural satellite of the Earth. It orbits the Earth but no-one built it or launched it into space. Gravitational forces between the Moon and the Earth keep the Moon in orbit. The Moon is not a luminous object, so it does not make its own light. Instead, it reflects light from the Sun which, like the other stars, is a luminous object.
A satellite has to travel at the correct speed to stay in orbit at a particular distance from a planet. It takes the Moon 28 days to make a complete orbit of the Earth. As it orbits, we see different amounts of the Moon, so we see different phases of the Moon.
Remember that we can only see the part of the Moon that reflects the Sun's light. How much of that we can see depends upon the position of the Moon in its orbit.
The phases of the Moon, seen from the Earth
A common mistake is to think that the phases of the Moon happen because the Earth gets in the way, and casts a shadow. However, if this does happen, we get an eclipse of the Moon:
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