How is the Moon slowly moving away from Earth?

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near and far sides of Earth's Moon — Moon (Left) Near side of Earth's Moon, photographed by the Galileo spacecraft on its way to Jupiter. (Right) Far side of the Moon with some of the near side visible (upper right), photographed by the Apollo 16 spacecraft.

The Moon is slowly moving away from Earth due to tidal friction, a process involving the gravitational interaction between the two bodies.12

Earth’s rotation causes the tidal bulge in its seas and crust to be carried ahead of the Moon’s position. The mutual gravitational attraction between the Moon and this displaced bulge exerts a force that accelerates the Moon in its orbit. As the Moon gains energy, it moves into a higher, more distant orbit, receding from Earth at a rate of approximately three centimeters (1.2 inches) per year.2

Because the angular momentum of the Earth-Moon system must remain constant, this transfer of energy also results in the slowing of Earth’s daily rotation. Consequently, both the length of the day and the length of the month are gradually increasing over time.12