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Re: Change in lunar revolution period

Subject: Re: Change in lunar revolution period
From: "Navillus"
Date: 10 Apr 2006 13:27:08 -0700
Newsgroups: sci.astro.amateur
William Hamblen wrote:
> On 10 Apr 2006 01:27:42 -0700, "Navillus" <cwsullivan@xxxxxxxxxxx>
> wrote:
>
> >My question: Was the lunar revolution period smaller when it was closer
> >to Earth, or has it slowed it's velocity as it has retreated for no net
> >effect? If it's still moving at the same velocity as it was 200 million
> >years ago, that would mean it would have cycled the Earth faster than
> >it does now (because it would be moving around in a smaller radius),
> >probably to a period of like 25 days instead of 27 like it is now. Is
> >this true? Does anyone know the math behind this, to know exactly how
> >the period of revolution changes as the moon receeds?
>
> Apply Kepler's third law: the square of the period is proportional to
> the cube of the semimajor radius of the orbit.

I'm having trouble with this... qualitatively speaking, when the moon
was closer to the Earth, it completed each full period in less time
than it takes today, correct?


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