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Author Topic: Why the Moon is moving away from Earth?  (Read 3968 times)

Offline waytogo

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Why the Moon is moving away from Earth?
« on: 21/11/2012 11:01:56 »
Hi,

Any scientific explanation about that? I still have not find anything...  tnx
« Last Edit: 21/11/2012 11:37:55 by waytogo »


 

Offline RD

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Re: Why the Moon is moving away from Earth?
« Reply #1 on: 21/11/2012 14:09:55 »
Tidal braking by the moon slows down Earth's rotation about it's axis, (days are slowly getting longer), conservation of angular momentum transfers Earth's lost (rotational) energy to the moon causing it to travel faster in it's orbit around Earth, a faster orbital speed means is a bigger orbit : the moon slowly moves away from the Earth ... http://en.wikipedia.org/wiki/Tidal_acceleration
« Last Edit: 21/11/2012 14:11:26 by RD »
 

Offline waytogo

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Re: Why the Moon is moving away from Earth?
« Reply #2 on: 21/11/2012 14:20:03 »
Hi RD, tnx for reply but wikipedia has not references at all concerning the 'explanation' about it.

However do you know if is it an accepted theory? if its true, do you know when it was released?
« Last Edit: 21/11/2012 14:23:31 by waytogo »
 

Offline RD

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Re: Why the Moon is moving away from Earth?
« Reply #3 on: 21/11/2012 14:27:00 »
There is evidence for tidal acceleration throughout the solar system ... http://en.wikipedia.org/wiki/Tidal_locking#List_of_known_tidally_locked_bodies

A historical perspective here ... http://articles.adsabs.harvard.edu/full/2003A%26G....44b..22S
« Last Edit: 21/11/2012 14:37:19 by RD »
 

Offline waytogo

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Re: Why the Moon is moving away from Earth?
« Reply #4 on: 21/11/2012 15:49:20 »
.... conservation of angular momentum transfers Earth's lost (rotational) energy to the moon causing it to travel faster in it's orbit around Earth, a faster orbital speed means is a bigger orbit : the moon slowly moves away from the Earth ... http://en.wikipedia.org/wiki/Tidal_acceleration

Anyway, even in wikipedia, what you have wrote (purple text), is not reported as an explanation/fact (it's just your own interpretation) and other links you provided, didn't help very much...
« Last Edit: 21/11/2012 16:02:00 by waytogo »
 

Offline Bill S

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Re: Why the Moon is moving away from Earth?
« Reply #5 on: 21/11/2012 17:50:00 »
If it aint in Wiki, it aint true!!! :P

RD, I'm trying to get my head round the idea that the tidal effect would cause the moon to speed up.  How is the energy transferred from Earth to moon?
 

Offline Bill S

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Re: Why the Moon is moving away from Earth?
« Reply #6 on: 21/11/2012 18:02:03 »
I think I’ve answered the bit about transfer of energy:

http://www.bbc.co.uk/news/science-environment-12311119

The bit that gives me pause for thought is:

“But the energy gained as the Moon is pushed higher is balanced by a reduction in the energy of its motion - so an acceleration provided by the Earth's tides is actually slowing the Moon down.”
 

Offline CliffordK

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Re: Why the Moon is moving away from Earth?
« Reply #7 on: 21/11/2012 19:49:48 »
RD, I'm trying to get my head round the idea that the tidal effect would cause the moon to speed up.  How is the energy transferred from Earth to moon?
I think it actually slows the moon down.
The further from the central body, the orbital velocity decreases, and the orbital period increases.

However, it still requires an energy transfer to achieve a higher orbit. 

The moon is beyond the geostationary/geosynchronous orbit, and thus the moon orbits slower than the earth rotates.  It would be different below the geosynchronous orbit.
The earth rotates at 1 rotation a day.
The moon orbits at 1 orbit a month.

I'm not sure about the tidal energy transfer.  If the side of the earth facing the moon has a greater mass than other parts of the planet (tides), then the system would tend to be "sticky" in that direction, and thus they would tend to try to synchronize the speed, except that the more energy transfer to the moon, the slower it goes.
 

Offline RD

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Re: Why the Moon is moving away from Earth?
« Reply #8 on: 22/11/2012 02:57:20 »
Quote from: NASA
Ocean tides are caused by the gravitational pull of the Moon (and, to a lesser extent, the Sun). The resulting tidal bulge in Earth's oceans is dragged ahead of the Moon in its orbit due to the daily rotation of Earth. As a consequence, the ocean mass offset from the Earth-Moon line exerts a pull on the Moon and accelerates it in its orbit. Conversely, the Moon's gravitational tug on this mass exerts a torque that decelerates the rotation of Earth. The length of the day gradually increases as energy is transferred from Earth to the Moon, causing the lunar orbit and period of revolution about Earth to increase.
http://eclipse.gsfc.nasa.gov/SEcat5/secular.html
« Last Edit: 22/11/2012 03:00:25 by RD »
 

Offline yor_on

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Re: Why the Moon is moving away from Earth?
« Reply #9 on: 29/11/2012 18:05:45 »
Wow, that one was one of the shortest explanations I've seen, still making sense RD :)
 

Offline RD

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Re: Why the Moon is moving away from Earth?
« Reply #10 on: 29/11/2012 18:59:12 »
...  still making sense RD :)

Don't be so sure, I think I've got the bit about the orbital velocity increasing wrong.
The total energy (potential + kinetic) of the moon increases, but it's orbital velocity slows when the radius of the orbit increases ...



https://en.wikipedia.org/wiki/Orbital_speed#Mean_orbital_speed


The closer the orbiting body the faster its orbital speed ...


https://en.wikipedia.org/wiki/Kepler%27s_laws_of_planetary_motion

[ It's the inverse square law which is complicating matters ]
« Last Edit: 29/11/2012 19:15:52 by RD »
 

Offline yor_on

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Re: Why the Moon is moving away from Earth?
« Reply #11 on: 30/11/2012 09:52:57 »
Hmm "The length of the day gradually increases as energy is transferred from Earth to the Moon, causing the lunar orbit and period of revolution about Earth to increase." I read that as when the earth 'transfer' energy to the moon it accelerates but as its orbit increase you will from earth find it to 'slow down' as it will be further away, in the same manner as you if looking on a high flying aeroplane find it to move slower over the sky as compared to it being at a lower altitude. As it 'speeds up' (gain energy)  relative Earth its orbit must increase as I think of it, to assume that it can go to a 'higher orbit' by losing energy doesn't make sense to me?

But I will read up on it :)
 

Offline waytogo

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Re: Why the Moon is moving away from Earth?
« Reply #12 on: 30/01/2013 09:10:02 »
Oh, I forgot this one when I created this thread:

Why that information about the moon leaving the Earth its not in the school books?


 

Offline Ophiolite

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Re: Why the Moon is moving away from Earth?
« Reply #13 on: 30/01/2013 12:23:34 »
Oh, I forgot this one when I created this thread:

Why that information about the moon leaving the Earth its not in the school books?
Why should it be? You cannot put all knowledge in schoolbooks, or in university text books. Most things have to be left out. Moreover, i wouldn't be surprised if that particular piece of info was in some school text books somewhere.
 

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Re: Why the Moon is moving away from Earth?
« Reply #13 on: 30/01/2013 12:23:34 »

 

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