How far does the moon move away from earth every year?

Question

Physics

Beckett Lowe

17 May, 22:51

How far does the moon move away from earth every year?

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Trystan Villegas · Answer 1

The moon is moving away from Earth at a rate of approximately 3.78 cm per year.

This migration of the Moon from the Earth is mainly due to the action of the Earth tides. It can be explained as follows:

- the Moon exerts a gravitational force on the Earth, which is stronger at the Equator (since the Equator is closer to the Moon), creating the tides

- However, the Earth rotates faster on its axis (one rotation every 24 hours) than the Moon (one rotation every 27 days), therefore the tidal bulge on Earth tries to pull the Moon "ahead" in its orbit. As a result, the Moon tends to sped up.

- As opposite reaction, the Earth tends to slow down in its rotation, with a loss of angular momentum. Since the angular momentum must be conserved, the radius of the orbit of the Moon becomes larger, and this explains why the Moon is moving away from the Earth.