If the moon always faces the earth does this mean it is rotating around the earths axis .?

Question

I bet my son the moon was rotating around the earths axis and he said it rotated around it`s own axis.
As this bet involves a not unsubstantial amount of money ( 1 million pounds) i wondered if I had fallen into a basic semantics trap. ie had I mistaken `moving` for rotation?
or are we both correct ?

Answer 1

You lose.

Rotation implies that it turns around an internal axis, which it does.

Revolution means traveling around another body, which it also does.

But since you used the word "rotating", the crux of the argument is the location of the axis. In my opinion, you lose. Better see if you can buy your bet back from him with an ice cream cone, or a new bike, or a car, depending on how old he is.

Answer 2

The Moon orbits around the Earth once a month. It also rotates on its own axis once a month. This means the Moon keeps the same side pointing at Earth all the time, but it does NOT always keep the same side pointing the same direction in space, for example pointing at the constellation Ares.

A simple demonstration with 3 people will help. One person is the Earth and stands in the middle of the room. Another person is a star in space and stands to one side of the room. A 3rd person is the Moon and walks around the first person, always looking directly at that person he or she is walking around. The person at the side of the room will sometimes see the face and sometimes the back of the head of the person walking around, while the person being walked around will always see the face of the person walking around him or her.

Answer 3

The Moon is in synchronous rotation, meaning that it keeps nearly the same face turned towards the Earth at all times. Early in the Moon's history, its rotation slowed and became locked in this configuration as a result of frictional effects associated with tidal deformations caused by the Earth. Long ago when the Moon spun much faster, the Moon's tidal bulge preceded the Earth-Moon line because the Moon couldn't "snap back" its bulges quickly enough to keep its bulges in line with Earth. The rotation swept the bulge beyond the Earth-Moon line. This out-of-line bulge caused a torque, slowing the Moon spin, like a wrench tightening a nut. When the Moon's spin slowed enough to match its orbital rate, then the bulge always faced Earth, the bulge was in line with Earth, and the torque disappeared. That's why the Moon rotates at the same rate as it orbits and we always see the same side of the Moon.

Answer 4

The reason only one side of the moon always faces Earth is because the moon rotates on its OWN axis at about 10 mph while at the same time it's orbiting around Earth at 2,286 mph. These two velocities combined with the distance between Earth and the moon keeps only one lunar side facing Earth.

Answer 5

The moon is rotating about its OWN axis.

Try this experiment with your son.

Let him stand in the middle of the room. He is the earth.

You are the moon. walk around him in such a way that you are always facing him.

Notice that you are actually rotating relative to the room: as you orbit your son, you will face all four walls in turn. Hence, you are spinning on your axis in addition to orbiting around your son.

If you did NOT rotate, and you always faced the same wall, then your son would be looking at your back for part of your orbit. (If he cranes his head over his shoulder.) But we never see the back side of the moon.

The moon is rotating at just the right rate that it keeps turning its familiar side towards the earth as it orbits around us. That is the effect of gravitational forces acting over billions of years: the earth has tugged on the moon to "lock" it into this rotational speed.

Answer 6

The Moon rotates around its own axis. Its rotation period happens to be the same as its revolution period around the Earth, so it more or less keeps the same face towards Earth all the time. This isn't just coincidence, but is the result of tidal locking, and is found with the satellites of other planets as well.

Ask your son to send half the proceeds to me.

Answer 7

it has its own axis and it does rotate. but it has a 1:1 rotation. basically that means that for every one time it orbits the earth it rotates one time. so the same side always faces us.

you are both correct basically. the moon revolves around the earth (and therefor also its axis) and it also rotates around its own.

Answer 8

No. The moon spins along its own axis. Its orbital rate matches Earths so it appears like the moon doesn't move.

Answer 9

Sorry, but you loose.

If it rotated around the earth's axis it you always take the same trajectory through the sky. But as you know, depending on the time of year it may be higher or lower in the sky.

I think he got you.

Cheers.