Re: the moons size coincidence?


"Mark McIntyre" <markmcintyre@xxxxxxxxxxx> wrote in message
news:fai232tv8c61f9efe21lmmk1281vq9iaj1@xxxxxxxxxx
On 3 Apr 2006 05:03:04 -0700, in uk.sci.astronomy , "Weatherlawyer"
<Weatherlawyer@xxxxxxxxxxx> wrote:


Robbie Mayhem wrote:

Ah, but the moon does spin. The period of its rotation is equal to its
orbital period, that is why the same side of the moon faces us.

And the coincidence in there escapes you?

In fact, the Earth's moon DOESNT quite keep the same face towards us.
Look up Libration and watch the limbs carefully.

But anyway its not coincidence, its a local minimum in the energy
configuration of two bodies. As the Moon rotates, its rocks are
deformed by the gravity of the earth. This absorbs energy. Eventually,
the energy loss caused the rotation to slow. Once the orbital speed
and rotational speed 'matched' the rocks stopped being distorted, no
more energy was lost, and a stable state was reached.

The same is happening to the Earth by the way, and to many other moons
in the solar system.
Mark McIntyre
--

It occurred to me long ago that the Moon's existence might well keep the
Earth more stable than it otherwise would be. To cut a long story short,
rather than a coincidence, if it were not approximately so, we might not be
here. A bit like a whale happily thinking how amazingly coincidental it is
that this big ocean is here for him to swim about in. If you see what I
mean<g>.


.

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