The orbit of the Moon around the Earth is not an easy process.

The Moon makes a complete orbit around the Earth approximately once every 28 days. This means that the Moon orbits the Earth around 13 times in a year. The complex part pops up because there are several ways to consider a complete orbit of the Moon, but the two most familiar are: the "sidereal month" being the time it takes to make a complete orbit with respect to the stars, about 27.3 days; and the "synodic month" being the time it takes to reach the same phase, about 29.5 days. These differ because in the meantime the Earth and Moon have both orbited some distance around the Sun.

"Phase" is the way to describe the relative position of any object that moves in a cyclical form. The phase of the Moon is measured in degrees, from 0(zero) to 360 (three hundred and sixty).

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