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Still Waters

Why Doesn't the Moon Spin?

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I've been asked on a number of occasions recently why the moon always seems to show us the same face -- the lunar nearside. I'm not sure why there's the sudden interest, but it's a very good and valid question, especially as tonight (March 27) is a full moon.

Look at the moon at any time and -- aside from the constantly changing phases that are caused by changing relative positions of the Earth, the moon and sun -- it does indeed show us the same face, constantly. Perhaps surprisingly, it's 'non-rotation' (from our perspective) comes from its interaction with the Earth.

http://news.discover...cked-130327.htm

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It's a surprize to some that the moon does indeed rotate. If the Moon didn't rotate then we would actually see all sides of it!

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Because its smiling at us. :yes: The moon is moving away from us however slowly. Which is interesting as well.

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Because its not a moon at all.

It was built as an alien outpost and always faces us on the same side because its engineers want to keep an eye on us.

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This is a simple geometry - the moon rotates, but we see only one side because its self-rotating period is the same as its orbital period. Just put two balls on the table and try to simulate it yourself :)

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Given enough time and the moon will only be visale from ne side of earth. It will stil move north and south but will not move east, west.

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Posted (edited)

If the Moon didn't rotate then we would actually see all sides of it!

Huh????

That is clearly a mis-statement.

How can one see "all sides" of anything that's not rotating. Excepting space-craft, going around the moon, of course.

Edited by pallidin

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Huh????

That is clearly a mis-statement.

How can one see "all sides" of anything that's not rotating. Excepting space-craft, going around the moon, of course.

Currently the moons orbit matches its rotation. If the moon had no rotation it would always how the same face to the sun. Meaning we would see all of the moon. Each side facing the earth every two weeks give or take. By the way that is how a lunar day is.

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Posted (edited)

Currently the moons orbit matches its rotation. If the moon had no rotation it would always how the same face to the sun. Meaning we would see all of the moon. Each side facing the earth every two weeks give or take. By the way that is how a lunar day is.

Maybe it's just me, but in the last 40 years I have not seen the moon rotate even an inch. (from earth perspective)

I see the exact same moon craters as I saw 40 years ago.

Edited by pallidin

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Maybe it's just me, but in the last 40 years I have not seen the moon rotate even an inch. (from earth perspective)

I see the exact same moon craters as I saw 40 years ago.

From earth it doesn't look like it spinning. Get a bucket and spin around. Then have someone else do it while you watch, to the spinner the bucket will not seem to spin. To the watcher it will.

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From earth it doesn't look like it spinning. Get a bucket and spin around. Then have someone else do it while you watch, to the spinner the bucket will not seem to spin. To the watcher it will.

Right, BUT THE BUCKET IS NOT ROTATING on it's own.

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Right, BUT THE BUCKET IS NOT ROTATING on it's own.

Yes, it is it has to.

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Posted (edited)

If a person in, say, North Amerca, observes different craters than those, say, in South America, than this would be a different story.

But, everyone on the planet earth see's the same craters as everyone else elsewhere

Do they not?

EDIT: Show me at least 1 earth observation that a different part of the earth has observed the "dark side" of the moon.

Edited by pallidin
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If a person in, say, North Amerca, observes different craters than those, say, in South America, than this would be a different story.

But, everyone on the planet earth see's the same craters as everyone else elsewhere

Do they not?

EDIT: Show me at least 1 earth observation that a different part of the earth has observed the "dark side" of the moon.

I can't from earth. But thinking small. Besides we see about 55% of ther moon. The bucket analigy is a good one, because as with the bucket the earths gravity keeps the same side of the moon facing us.

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Posted (edited)

This is a simple geometry - the moon rotates, but we see only one side because its self-rotating period is the same as its orbital period. Just put two balls on the table and try to simulate it yourself :)

Agreed;

"The rotation of the Moon is a strange situation. It takes the same amount of time for the Moon to complete a full orbit around the Earth as it takes for it to complete one rotation on its axis. In other words, the Moon rotation time is 27.3 days, just the same as its orbital time: 27.3 days.

What this means to us here on Earth is that the Moon always presents the same face to the Earth. We only see one side of the Moon, and not the other. And if you could stand on the surface of the Moon, the Earth would appear to just hang in the sky, not moving anywhere."

http://www.universet.../moon-rotation/

Edited by jules99

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If a person in, say, North Amerca, observes different craters than those, say, in South America, than this would be a different story.

But, everyone on the planet earth see's the same craters as everyone else elsewhere

Do they not?

EDIT: Show me at least 1 earth observation that a different part of the earth has observed the "dark side" of the moon.

Read this link: http://en.wikipedia.org/wiki/Tidal_locking

It explains it better than I can.

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Maybe it's just me, but in the last 40 years I have not seen the moon rotate even an inch. (from earth perspective)

I see the exact same moon craters as I saw 40 years ago.

Mostly, but not exactly, due to an effect called libration it is actually possible to see 59% of the moons surface from the Earth, but given the difficulty you have grasping danielost's point I don't intend to muddy the waters further by describing it here.

Right, BUT THE BUCKET IS NOT ROTATING on it's own.

danielost is quite right, from a stationary view point the bucket will have rotated.

Forgive my (non-existent) artistic capabilities, but I have drawn a diagram to illustrate Daniels point. It represents the person with the bucket as viewed from above looking down.

As the person rotates from position "A" to position "B" you will notice that they are still only seeing the green side of the bucket. However from our view point it is clear to see that the bucket has actually rotated through 90 degrees.

bucketb.jpg

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Posted (edited)

Ok, Waspie, but if the moon itself rotates from the perspective of the earth, would we not eventually see all "sides" of it?

Someone here said that the the moon does rotate, but that it matches exactly the rotation of the earth, thus appearing the same.

Fine, I can go with that(I think) but how does the moon's self rotation EXACTLY match that of our planet, especially considering it's elliptical orbit around the earth.

I'm just confused as how that "lock" can occur when the moon distance changes, yet we, here on earth, see zero rotation.

EDIT: Perhaps I am wrong, and that a full rotation of the moon from the perspective of the earth, and given it's elliptical orbit(which I assume breaks the "lock", just takes maybe thousands of years to observe?

Or is it's elliptical orbit (distance differances) still within a functional "lock" with our earth regardless of time?

EDIT: For example, would the moon have presented differenty, say 100,000 years ago?

Edited by pallidin

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The moon is a hologram anyways.

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Ok, Waspie, but if the moon itself rotates from the perspective of the earth, would we not eventually see all "sides" of it?

Someone here said that the the moon does rotate, but that it matches exactly the rotation of the earth, thus appearing the same.

Fine, I can go with that(I think) but how does the moon's self rotation EXACTLY match that of our planet, especially considering it's elliptical orbit around the earth.

I'm just confused as how that "lock" can occur when the moon distance changes, yet we, here on earth, see zero rotation.

EDIT: Perhaps I am wrong, and that a full rotation of the moon from the perspective of the earth, and given it's elliptical orbit(which I assume breaks the "lock", just takes maybe thousands of years to observe?

Or is it's elliptical orbit (distance differances) still within a functional "lock" with our earth regardless of time?

EDIT: For example, would the moon have presented differenty, say 100,000 years ago?

Due to the moons orbit, it does rock back and forth. Giving us a view of about 59% of its surface. This is called liberation.

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The left eye of Horus does not spin because Khonsu would get dizzy and vomit. Always go for the obvious answer first.....

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I would pay to see the dark side of the Moon!

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I would pay to see the dark side of the Moon!

Google it. They may have photo shots of it.

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I would pay to see the dark side of the Moon!

I'll sell you a picture for 100 bucks

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