The Moon is slowly drifting away from Earth.

The Moon feels fixed because it has been the same companion in human skies for all recorded history. But fixed is not the same as unchanged. NASA JPL notes that our Moon drifts away from Earth by about 1.5 inches, or 3.8 centimeters, each year. Tidal interactions between Earth and the Moon are gradually moving it outward. The annual change is tiny, but the direction is surprising: the familiar object overhead is not locked into a permanent distance. The sky looks stable because our lives are short.

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