April 1972. Apollo 16 astronauts filmed themselves driving the Lunar Roving Vehicle. When you look up at the moon tonight, you'll be seeing where this video was filmed, 384,000km away.

Indeed, this is also known as:

TIDAL LOCKING.


Essentially, it means that the moon is rotating, at just the PERFECT speed, so that it keeps showing the same face towards Earth.

Now, you are probably wondering:

"Wow! What are the odds that the moon would be accidentally rotating at just the right speed, so that it keeps the same face aimed towards the Earth at all times??!!"


Well, in physics there is a reason for that.

Initially, that was not always the case with the moon, and in really ancient times upon Earth, you would be able to see the moon rotating, and showing it's different faces/sides towards the Earth.


But... as it turns out, the mass on the surface of the moon, and in the interior is NOT evenly distributed.

The moon is "lumpy".

This means that one of the moon's faces has more mass, or more "heavy stuff".

This also means that each time the moon did one rotation in ancient times, the Earth's gravity would pull and "grab" that lumpier, more massive side of the moon more tightly, slowing it's spin slightly.


Over the course of millions, and billions of years, with Earth's gravity pulling, or "grabbing" at that extra lumpy mass, on one particular side, it slowed the moon's spin so much, that finally Earth's gravity won:

it now had a permanent hold on that slightly more lumpy, more massive part of the moon, so that side is always facing the Earth.


In fact, the same thing is happening between the Earth and sun.

Because the Earth is "lumpy" and not perfect, eventually, given enough time, one side of the Earth will become permanently "grabbed" and tidally locked to the sun, so that the Earth's "daily" rotation will become so slow, that the same side of Earth will face the sun, ALWAYS.


But... then again, because the Earth is so far from the sun, I believe that the amount of time it would take for the Earth to become tidally locked would be longer than the time our solar system has left, to exist, if I am not mistaken...

And of course, if a body is geologically active, it can shift around it's mass, so I wonder if it might be able to become "unstuck" and liberate itself from tidal locking? Not sure.


FINAL NOTE:

Under this concept of "tidal locking"...

If the moon was an ABSOLUTELY PERFECT SPHERE, with all mass inside the moon, and on the surface, distributed PERFECTLY-EQUALLY, then we would indeed be able to still see the moon spinning, and showing different faces to Earth, and it would not become tidal locked due to spherical imperfections in such a case.

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