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Author Topic: The Moon - why do we see only 1 face ?  (Read 4331 times)

Offline neilep

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The Moon - why do we see only 1 face ?
« on: 06/03/2004 14:34:46 »
Can someone please remind me of the facts regarding some coincedences about the moon ?...How come it spins to the exact degree that we only see one side and what's the thing I heard about the fact that it's size relative to the distance we are/it is from the sun means that it just happens to fit snuggly during solar eclipses. I know I probably haven't explained it right and that's why I'm asking, but there is a particular size/distance thing going on here isn't there ?, something like it's 50 times smaller than the earth and ....oh I don't know !!!![?]

ta very much[:X]

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« Last Edit: 07/03/2004 05:11:01 by NakedScientist »


 

Offline tweener

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Re: The Moon - why do we see only 1 face ?
« Reply #1 on: 07/03/2004 22:42:51 »
Neil,
If you can find it, I wrote a rather long post here about the moon and how it orbits the earth.  It was a couple of months ago, so it may not be archived.  If not, I'll do it again sometime.

As for why the moon rotates to keep one face toward the earth, it is due to gravitational tides.  Over the time since the formation of the earth and moon, the rotation of the moon has slowed because the gravity from the earth slightly deforms the moon.  The friction of the parts of the moon moving around absorbs the energy and slows the spin.  The final state (lowest energy) is where the moon rotates exactly once in an orbit and thus keeps one face to the earth.  I believe that some of Jupiter's moons have done the same thing.

The apparent size relative to the sun is a coincidence.  It appears almost exactly the same angular size as the sun.  I don't remember the exact size ratio to the earth, but it doesn't really matter.  The apparent size is driven by both the actual size and the distance.  The sun is many times farther away, and many times bigger and just happens to appear to be the same size.  If the moon was smaller but orbited at the same distance, it would appear smaller than the sun.

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John - The Eternal Pessimist.
 

Offline neilep

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Re: The Moon - why do we see only 1 face ?
« Reply #2 on: 07/03/2004 23:09:14 »
Thanks John, I'll try and trace your post.

As far as the coincidence is concerned, I completely agree with you that that is what it is, just a coincidence, even though it may appear quite extraordinary.

Thanks for clearing that up for me.

'Men are the same as women...just inside out !'
 

Offline chris

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Re: The Moon - why do we see only 1 face ?
« Reply #3 on: 08/03/2004 08:03:11 »
John - all of the material that you enter is preserved on this forum and you should be able to find it using the search facility at the top right (this one searches the forum specifically. - the main site search engine - http://www.thenakedscientists.com/html/search.htm - looks at everything, including the forum) They are both as good as each other, but, obviously, it helps if the titles are concise and the the topics stay on-thread (mild dig at Neil ! ;))

Chris

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Offline chris

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Re: The Moon - why do we see only 1 face ?
« Reply #4 on: 08/03/2004 08:11:37 »
Here's your post John :

http://www.thenakedscientists.com/forum/topic.asp?TOPIC_ID=582

about the moon etc. I am sure that we have had this debate even further back, but a cursory check didn't turn up anything...

Chris

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Re: The Moon - why do we see only 1 face ?
« Reply #4 on: 08/03/2004 08:11:37 »

 

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