Moon orbit and rotation speed. (For a boffin)

[Marbles]

Why does the moon rotate at exactly the correct speed to only ever show one face to earth.

[27-steps]

It's funny marbles, I once tried working this out, but i found it impossible!, But i too would like to know.

[Nibble]

I tried to get a simple answer for you, but the best I can do is here..... Don't get too carried away though! http://www.grantchronicles.com/astro29.htm

[Marbles]

glad it's not just me!!

[Craftypig]

Long ago when the Moon spun much faster, the Moon's tidal bulge preceded the Earth-Moon line because the Moon couldn't "snap back" its bulges quickly enough to keep its bulges in line with Earth, says James Hilton, Astronomer, U.S. Naval Observatory. The rotation swept the bulge beyond the Earth-Moon line. This out-of-line bulge caused a torque, slowing the Moon spin, like a wrench tightening a nut. When the Moon's spin slowed enough to match its orbital rate, then the bulge always faced Earth, the bulge was in line with Earth, and the torque disappeared. That's why the Moon rotates at the same rate as it orbits and we always see the same side of the Moon.

[Marbles]

Thank you Nibble..looked it up and partly understood...now my brain hurts!!

[EDDIE51]

The Moon is 'tidally locked ' to the Earth in the same way that Mercury is tidally locked to the Sun
http://en.wikipedia.org/wiki/Tidal_locking
The Earth /Moon system is actually one system and it rotates around the common centre of gravity. s the Earth is so much more massive than Earth the centre of gravity is inside the Earth.
Earth / Moon should really be regarded as a double planet as they are so close in size. Such systems always revolve around the common centre of gravity.

[Nibble]

No problem, marbles, I gave up when my brain started leaving through my left ear.... :-)

[EDDIE51]

Another link here.
http://www.digipro.com/Trials/moon.html

[Old_Geezer]

The answer is because it had a long time to get it right.
Now, how did it know to move out to just the right distance so it can cover the sun during the eclipse ?

[jomifl]

Well it didn't OG, we cunningly evolved so that we would be able to appreciate the phenomenom at just the moment in the development of the solar system when it happened. I wonder what we missed?

[Clanad]

Best estimates place the tidal locking of the Moon to the Earth at around 3.85 to 4.1 BYA (billions of years ago)... seems, then, we missed that event...

[beso]

EDDIE // Earth / Moon should really be regarded as a double planet as they are so close in size. Such systems always revolve around the common centre of gravity. //

That is incorrect.

All systems orbit around a common centre of gravity. That is why orbits are elliptical when referenced to one of the objects.

A double planetary system is defined by the common COG being outside of the bodies. A moon is when the common COG is inside the larger body.

The COG of the Earth/Moon system is about 1700km below the surface of the Earth. Consequently the Moon is definitely a moon and it is incorrect to refer to the system as a double planet.

[Old_Geezer]

But that would mean we are in a special time at a special place jomifl, and we can't have that. No, this is obviously a sign of almighty God setting everything just right for us.

[Peter Pedant]

yup that is what Brian Coz said on tel last night
and the long phrase he said was - conservation of angular momentum

[just chipping in my two penny worth]