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Author Topic: Does the Moon Rotate?  (Read 2850 times)

Offline astr0144

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Does the Moon Rotate?
« on: September 10, 2017, 05:33:46 pm »
Does the Moon Rotate?

Have you ever noticed that the Moon always looks the same? Sure, the phase changes, but the actual features on the Moon always look the same from month to month.

Does the Moon rotate? What’s going on?

From our perspective here on Earth, the Moon always shows us the same face because it’s tidally locked to our planet. At some point in the distant past, the Moon did rotate from our perspective, but the Earth’s gravity kept pulling unevenly at the Moon, slowing its rotation. Eventually the Moon locked into place, always displaying the same side to us.

But if you looked down on the Earth-Moon system from the north celestial pole, from the perspective of Polaris, the North Star, you’d see that the Moon actually does rotate on its axis. In fact, as the Moon travels around the Earth in a counter-clockwise orbit every 27.5 days, it also completes one full rotation on its axis – also moving in a counter-clockwise direction.

If you look at a time lapse animation of the Moon moving entirely through its phases over the course of a month, you’ll notice a strange wobble, as if the Moon is rocking back and forth on its axis a bit.

This is known as libration.

https://www.youtube.com/watch?time_continue=73&v=5YXhnQcoyOw


On average, the Moon is tidally locked to the Earth’s surface. But its actual orbit is elliptical, it moves closer and then more distant from the Earth.

When the Moon is at its closest point, it’s rotation is slower than its orbital speed, so we see an additional 8 degrees on its eastern side. And then when the Moon is at the most distant point, the rotation is faster than its orbital speed, so we can see 8 degrees on the Western side.

Libration allowed astronomers to map out more of the Moon’s surface than we could if the Moon followed a circular orbit.

Until the space age, half the Moon was hidden from us, always facing away. This hemisphere of the Moon was finally first observed by the Soviet Luna 3 probe in 1959, followed by the first human eyes with Apollo 8 in 1968.

The two hemispheres of the Moon are very different.

While the near side is covered with large basaltic plains called maria, the far side is almost completely covered in craters. The reasons for this difference is still a mystery to planetary scientists, but it’s possible that a second Moon crashed into it, billions of years ago, creating the strange surface we see today.

So yes, the Moon does rotate.

But its rotation exactly matches its orbit around the Earth, which is why it looks like it never does.

https://www.universetoday.com/19699/does-the-moon-rotate/
« Last Edit: September 10, 2017, 05:35:24 pm by astr0144 »

Offline Irene

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Re: Does the Moon Rotate?
« Reply #1 on: September 11, 2017, 06:36:30 am »
Want to hear a wild theory of mine?

The moon was placed there to take the brunt of impacts from NEOs.
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Offline astr0144

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Re: Does the Moon Rotate?
« Reply #2 on: September 11, 2017, 09:06:07 am »
I happened to watch a TV Program about Tides and it showed how and why we get 2 tides a day and how the gravitaional pull of  Moon and Centrifugal forces and other factors create the tidals effects...

They then shown video images of how the moon rotated around the earth .... But I did not note if the moon was spinning on its axis... and as we always see the same face of the moon when we observe it from earth.. it is hard to understand whether it rotates (spins on its / a axis )or not..

So I am surprised as I think I understand that it does spin on its axis but over 27.5 days...

(where as our Earths rotation of its Axis spins in in one 24 hr  day)

but it ORBITS around the Earth in about the same time frame...which I thought was between 28 to 30 days as each months may vary a bit...and NOT the EXACT same time...

IF there is a Day or two in difference... I THOUGHT that we may at times see parts of the Moon that we normally would not see..
.

but somehow although I think that the back / far side of the moon is Facing Earth at certain times in the Month... that for what ever reason, maybe to do with the Position of the Sun in relation to the Earth and Moon, we cannot ever seem to see it..


but the Moon spins in such a way that we never get to see the other side..

which seems amazing !

I am not sure what you mean Irene and can only guess ..
what NEO stands for..

I thought it meant Near Earth Orbit ...

But in terms of that relating to Impacts...

The only Impacts that I can envision at the moment is Meteor impacts that make the craters that we see.

As the Moon is only on one side of the Earth at any time..

and it was placed where it is... it could only take impacts from one part of the Solar System...

it could not absorb anything from other directions of anything threatening to hit the Earth.

I was also wondering if other Planets Moons spin on an axis and what times they take to do one 360 degree rotation. and generally how they compare in orbit spin rotation to our Moon.





Want to hear a wild theory of mine?

The moon was placed there to take the brunt of impacts from NEOs.
« Last Edit: September 11, 2017, 09:33:26 am by astr0144 »

Offline ArMaP

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Re: Does the Moon Rotate?
« Reply #3 on: September 11, 2017, 01:34:22 pm »
So I am surprised as I think I understand that it does spin on its axis but over 27.5 days...

(where as our Earths rotation of its Axis spins in in one 24 hr  day)

but it ORBITS around the Earth in about the same time frame...which I thought was between 28 to 30 days as each months may vary a bit...and NOT the EXACT same time...
The months we use are an adaptation from the original lunar months, as an year made of 12 lunar months is smaller than the solar year we use now. Also, from an Earth point of view, the Moon takes around 29.5 days to make a full rotation, as the Earth is also moving during the 27.5 days it takes for the Moon to do a full orbit.

Quote
but somehow although I think that the back / far side of the moon is Facing Earth at certain times in the Month... that for what ever reason, maybe to do with the Position of the Sun in relation to the Earth and Moon, we cannot ever seem to see it..
No, the far side of the Moon never faces the Earth. The only occasion in which we don't see the Moon is during the New Moon, but just before and just after the New Moon we can see that the little we see of the Moon is the same, so unless the Moon moved extremely fast during the New Moon it could not be showing the far side at the time we can't see it.

Quote
I am not sure what you mean Irene and can only guess ..
what NEO stands for..

I thought it meant Near Earth Orbit ...

But in terms of that relating to Impacts...
Near Earth Object, the asteroids that have orbits close to the Earth's orbit.

Quote
I was also wondering if other Planets Moons spin on an axis and what times they take to do one 360 degree rotation. and generally how they compare in orbit spin rotation to our Moon.
They do rotate, with many variations. The two Mars satellites, for example, have very different orbits, with one of them (Phobos) having such a fast orbit that it makes a full orbit in less time than a Martian day, so it rises in the West and sets in the East.

Offline astr0144

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Re: Does the Moon Rotate?
« Reply #4 on: September 11, 2017, 03:03:28 pm »
Thank for your comments on the post ArMaP.

If I get time , I need to try to think a bit more about some of your points...

I am not as yet sure that I can grasp some parts to do with ..that if the Moon does rotate (spin on its axis) over 27 to 30 days as well as it orbits around the Earth in about the same time.. with 2 to 3 days...

and the fact that we do not get to be able to see it..

I have to somehow try to visualise what happens..

One of the best ways I think is if .. there was a suitable diagram as if looking from above... looking down on the Earth and moon..

At one time I used to be able to find animations to embed in posts that ar easier to view than a video sometimes..

Ive got to try to get my head around how its rotating on its own axis ..rather slowly, over 27.5 days to rotate 360 degrees..

while at the same time , Making a circular type orbit around the Earth..

then try to understand ,why we are not seeing its other or far  side..

The Earth would have spun on its axis about  30 times in the time it took the moon to orbit around the Earth.

For some reason I am not properly visualising it in my mind easily...




ArMaP
Quote
No, the far side of the Moon never faces the Earth. The only occasion in which we don't see the Moon is during the New Moon, but just before and just after the New Moon we can see that the little we see of the Moon is the same, so unless the Moon moved extremely fast during the New Moon it could not be showing the far side at the time we can't see it.
« Last Edit: September 11, 2017, 03:14:01 pm by astr0144 »

Offline ArMaP

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Re: Does the Moon Rotate?
« Reply #5 on: September 11, 2017, 03:32:49 pm »
Do this: get a chair, put it on the middle of a room, then start walking around the chair, always looking at it.

From the chair's point of view, you are always facing it, so you have a "far side", like the Moon when seen from Earth.

From the room's point of view you are walking around the chair and rotating on a vertical axis, so sometimes you are facing one wall and sometimes you have your back to the same wall.

PS: don't get dizzy. ;)

Offline astr0144

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Re: Does the Moon Rotate?
« Reply #6 on: September 11, 2017, 04:00:50 pm »
I will probably need some time to grasp what you refer to ArMaP..when my mind is free some other things on my mind at the moment..

On a very quick read and attempt to understand..

Id need to lable how the Moon or Earth relates...in your eg to the person facing the Chair..

Is the Chair relating to the Earth and person circling around the chair the moon ?  or the other way around...maybe..where you maybe on the Earth appearing to rotate around the moon..!
or is it on the moon appearing to rotate around the Earth ?  :)

Im Going a bit insane on this one ...I sometimes get mental blocks and this maybe one of them...

I initially assumed so.. but if so.... the person I think would also need to slowly rotate as they walk around the Chair..

Also if the Chair is the Earth ... it will be rotating about 30 times as One walks around the chair..

so I need to visualise that if initially I start facing the chair like the Moon Face we see..(FROM MY FRONT)., at some point my BACK  will then be facing the Earth...

But as the Earth is rotating..depending where one is one the Earth as its rotated.. ... a sometime during one days 24 hr rotation.. I should face the moon...

But whether I can see the moon, may also depend how both Earth and moon relate to the Sun..

Generally I think we see the Moon when the Sun shines on it from the opposite direction..to some degree...and maybe we see a full moon when it is 180 degrees apart..

Thats when my mind starts to over complex things...and I start to loose it.. ???

I need to be quite and calm to think this out at a suitable time..

but my mind is far too much distractd by many other things at moment..

I need to start doing some meditation !  :)


Do this: get a chair, put it on the middle of a room, then start walking around the chair, always looking at it.

From the chair's point of view, you are always facing it, so you have a "far side", like the Moon when seen from Earth.

From the room's point of view you are walking around the chair and rotating on a vertical axis, so sometimes you are facing one wall and sometimes you have your back to the same wall.

PS: don't get dizzy. ;)
« Last Edit: September 11, 2017, 04:06:56 pm by astr0144 »

Offline The Seeker

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Re: Does the Moon Rotate?
« Reply #7 on: September 11, 2017, 04:57:25 pm »
Astro, the earth rotating is irrelevant; the chair is the earth; you walking around it is the moon

one orbit of the moon around the earth takes the same amount of time as one rotation of the moon on its axis, so yes, we only see one side
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Offline ArMaP

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Re: Does the Moon Rotate?
« Reply #8 on: September 11, 2017, 05:11:07 pm »
Is the Chair relating to the Earth and person circling around the chair the moon ?
The chair is acting like the Earth, the person circling around the chair is acting like the Moon. The Moon circles around the Earth, right?

Quote
I initially assumed so.. but if so.... the person I think would also need to slowly rotate as they walk around the Chair..
That's why I said "always looking at the chair".

Quote
Also if the Chair is the Earth ... it will be rotating about 30 times as One walks around the chair..
Yes, but that's irrelevant for now.

I think your problem is that you are trying to visualize too many things at the same time. Start with just one, see if you understand it, then try the next, and, when you understand it, try both together.

Breaking a problem into smaller, easier problems is the most common way of solving problems. :)

Offline astr0144

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Re: Does the Moon Rotate?
« Reply #9 on: September 11, 2017, 06:14:51 pm »
I think its come to me now...

As the Moon is ORBITING around the Earth...

Its rotation (on its Axis)

In my attempted diagram below....bit like a Compass.
which compares to the position of the moon around the Earth

with the Larger circle being the Earth or the Chair and the 4 smallers circles being the moon at 90 degrees , 180, 270, and back to 360 degrees positions around the orbit..

similar to N, E, S, W

If we were on the start at the South ... the lower circle.

where the FRONT FACE of the Moon is Facing Earth.

Assuming that its goes one direction or the other..clockwise or anticlockwise..

and this is like what I call a plan view...looking down at the North Pole of the Earth and Moon.

As the Moon ORBITS 90 degrees...around the Earth...
which took say 1/4 of the time...of an average month..
so. thats about 7 days../ 1 week.

ITS AXIS has also turned JUST by 90 degrees...

BUT its position in ref to the orbit... has now moved from where it was initially..

so initially from Earth... we may have seen it as if the Moon was below in the diagram...(some may say South)

The when the Moon has orbited 90 degrees say in a Anticlockwise direction...it is appearing to the East or right in the diagram.  and as the Moons axis has revolved also slowly by 90 degrees...in 7 days... its FRONT FACE is still still Facing Earth..

BUT The Moons position is actually now in a different position in space and is at 90 degrees in the diagram to the Earth..

The thing being its slowly revolving on its axis ..(spinning) just enough at the same rate as it orbits to maintain its Front Face being facing Earth.

SO in One Orbit around the Earth... sees it having done one full rotation on its Axis..

and when or if it was to Rotate say in a Anticlockwise direction..
(Cant as yet think which way it  orbits for real at the moment)
I dont know why I have choose anticlockwise..maybe I should have done this eg in the opposite direction.

but for this eg..

then if it got the the East position  or right of the Circle..
Its Front Face would now  point to the West. or Left...
but still towards the Earth.


Im unable to add in circular arrows in the diagram below..

I could only do so if I was able to create a diagram and upload it..

Ive no doubt gone the long way about it, But I think thats How I can grasp it..

IF the Moon did NOT rotate on its Axis....

Then as it orbited... the Front face of the Moon would face North....as it got to the East (or right side)Position in the diagram... and we would see part or maybe quarter  of the rear side of the moon..

then as its Orbit got to the 180 degrees (North ) or higher postion.. from the Initial South (Lower) Position  ... WE would actually see the Far side of the Moon...

That where my confusion was !


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Astro, the earth rotating is irrelevant; the chair is the earth; you walking around it is the moon

one orbit of the moon around the earth takes the same amount of time as one rotation of the moon on its axis, so yes, we only see one side



The chair is acting like the Earth, the person circling around the chair is acting like the Moon. The Moon circles around the Earth, right?
That's why I said "always looking at the chair".
Yes, but that's irrelevant for now.

I think your problem is that you are trying to visualize too many things at the same time. Start with just one, see if you understand it, then try the next, and, when you understand it, try both together.

Breaking a problem into smaller, easier problems is the most common way of solving problems. :)
« Last Edit: September 11, 2017, 06:31:41 pm by astr0144 »

Offline ArMaP

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Re: Does the Moon Rotate?
« Reply #10 on: September 12, 2017, 05:45:24 am »
I think its come to me now...
I think you got it now. :)

Offline The Seeker

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Re: Does the Moon Rotate?
« Reply #11 on: September 12, 2017, 06:48:17 am »


Look closely: See clearly: Think deeply; and Choose wisely...
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Offline astr0144

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Re: Does the Moon Rotate?
« Reply #12 on: September 12, 2017, 08:47:35 am »
I would hope so now that Seeker has posted that ideal video..

Thats what I had been trying to look for earlier on..

Many thanks for posting and explanations.  8)

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ArMaP...I think you got it now. :)

 


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