Question about the Moon

[JamesK]

Was thinking earlier on:

You know they say the Moon's orbit time is identical to the time it takes to rotate on it's axis once- and that's why we have a "Dark" side of the Moon?

Well I was just wondering if it was exacly identical- or over millions of years the "Dark" side and the "Visable" side switch places- I mean it would only have to be out by a few seconds every 28 days, and it would cause a change over long periods of time.

And if it is exact, is that just the biggest coincidence in the the history of the solar system or is their a physical reason for it?

[GazOC]

Its not a coincidence, the Moon has been tidally locked over time so the rotation is the same length as the orbit.

[JamesK]

Now I know. Thanks!

[The Warthog]

As well, the Moon is inching away from the Earth, and the Moon is causing the Earth's rotation to slow ever so slightly (on the order of fractions of a second per century) as time goes by.

Although the Moon rotates evenly, it slows and speeds up a bit every month in its orbit, and this allows us to see a little 'round the corner' at the edges of the Moon, and also at the north and south limbs. This phenomenon is called 'libration' and is shown on Moon maps, usually with a dotted line to indicate minimum libration.

[GazOC]

The big coincidence is the moon and the sun being the same apparent size in the sky thus giving us the phenomenon of a total eclipse.

[barkis]

Here is a little Info. that explains the Earth/Moon relationship.

Some of which has already been explained in the thread.

Ron.

Interesting Facts and Figures about the Moon | Lunar Properties