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Moon appears to be facing its same side to earth throughout its orbit around earth.

This is said to be because of tidal locking , i.e. the moon rotates at the same rate as it revolves around the earth.

But how close does it rotation and revolution periods match? Are they 100% equal? It could be rotating say a millionth of a degree each year with respect to earth

Is it possible that there is a slight difference and in a million years we'll see a different side of the moon

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  • $\begingroup$ The terms you are using in the question seem to be "simplified" compared with the real situation. Since the moon's orbit is not a perfect circle, and it is perturbed by the sun's gravity, it doesn't have exactly the "same side" facing the earth at all times. Also, the ocean tides on earth are slowly removing kinetic energy from the moon, and its "orbit" is really a spiral, increasing in radius by about 38mm per year, and its orbital period is slowly increasing. So the question as you asked it doesn't really have a simple "yes/no" answer. $\endgroup$
    – alephzero
    Commented Aug 21, 2016 at 0:29
  • $\begingroup$ Well my question simply is will we ever see a different face of the moon from earth in say a next billion years $\endgroup$
    – user1062760
    Commented Aug 21, 2016 at 17:00

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Is it possible that there is a slight difference and in a million years we'll see a different side of the moon

No.

Tidal locking is a process that drains energy from the rotation of the moon. The moon's shape is distorted by the gravitational attraction. This means to draw the moon out of a tidally locked state would require it to move into a configuration that is more energetic - I don't think there is a source for the additional energy required.

It is as if the moon had rolled to the bottom of a valley. Now that it is at rest there, it would require a lot of energy to roll it back up the hillside.

Also, if the moon has been tidally locked for billions of years, a million years seems too short an interval of time for anything interesting to happen.

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