Why isn't the Earth tidally-locked to the Sun?

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Alfred Wright

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Why isn't the Earth tidally-locked to the Sun?
« on: 28/09/2009 11:30:04 »
Alfred Wright asked the Naked Scientists:
   
I know that the moon orbits Earth and revolves in such a way that the man in the moon is always facing us.

Why, then, doesn't the Earth revolve in such a way that only one side is facing the sun?

What do you think?

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Offline Soul Surfer

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Why isn't the Earth tidally-locked to the Sun?
« Reply #1 on: 28/09/2009 23:32:17 »
The earth has not yet been orbiting the sun long enough for this to happen although it could in theory happen at some time in the far distant future.  However the sun will probably expand to become a red giant before then.
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Offline syhprum

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Why isn't the Earth tidally-locked to the Sun?
« Reply #2 on: 29/09/2009 20:44:52 »
It is believed that shortly after its creation the Earth rotated about 4 times as fast as it does now, the Earth/Moon system stores a great deal of rotational energy and there is very little means by which it can be dissipated.
As Soul Surfer says it is doubtful whether there is sufficient time before the swelling Sun swallows it up for tidal locking to achieved.
« Last Edit: 29/09/2009 20:48:33 by syhprum »
syhprum

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Offline Mr. Scientist

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Why isn't the Earth tidally-locked to the Sun?
« Reply #3 on: 30/09/2009 18:53:32 »
Interesting read.
http://www.youtube.com/watch?v=SZGcNx8nV8U

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Offline daveshorts

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Why isn't the Earth tidally-locked to the Sun?
« Reply #4 on: 02/10/2009 16:15:40 »
I think that mercury's rotation is tidally locked with the sun but not as you would think, it rotates exactly 1.5 times every time it orbits once. bizarrely this is a fairly stable state. I once worked out in a hand wavey kind of way that it is stable due to the eccentricity of mercury's orbit

http://cseligman.com/text/planets/mercuryrot.htm