It takes the Moon 27.3 days to complete a full orbit around the Earth, but the p

Question

It takes the Moon 27.3 days to complete a full orbit around the Earth, but the period between successive full moons is 29.5 days. Why is this?

A

Because the rotation of the Moon is synchronized with its period of revolution, it ends up being about two days behind for the full Moon phase to show.

B

This is because of the retrograde revolution of the Moon.

C

During one full orbit of the Moon, the Earth has completed part of its orbit around the Sun, so the Moon has to travel a little farther in order to get on the opposite side of the Earth (opposite from the Sun).

D

This is because our calendars are based on the Sun (1 year) and the rotation of the Earth (1 day): our months are based on 1/12th of a year, not on the Moon completing an orbit.

E

This is because of the retrograde rotation of the Moon.

A

Because the rotation of the Moon is synchronized with its period of revolution, it ends up being about two days behind for the full Moon phase to show.

Explanation / Answer

The difference between  sidereal(27.3 days) and synodic(29.5 days) lunar months is because

Option C

During one full orbit of the Moon, the Earth has completed part of its orbit around the Sun, so the Moon has to travel a little farther in order to get on the opposite side of the Earth (opposite from the Sun).

During one full orbit of the Moon, the Earth has completed part of its orbit around the Sun, so the Moon has to travel a little farther in order to get on the opposite side of the Earth (opposite from the Sun).

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