Re: Reason for Procession of the Equinox?
From: Brian Tung (brian_at_isi.edu)
Date: 12/02/04
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Date: Thu, 2 Dec 2004 18:59:26 +0000 (UTC)
Dr John Stockton wrote:
> The eccentricity of an (elliptical) orbit is a pure number.
I'm well aware of that. Nonetheless, the distance 10,000 km (approximate)
represents the eccentricity. Of course, the eccentricity value itself
is the ratio of that number to the semi-major axis.
> Both Moon & Earth orbit their common centre of gravity, with minor
> corrections due to other parts of the Universe. If the separation is
> 400,000 km, and the ratio of masses 1:79 (almost, but not quite,
> correct), then the centre of the Earth is 5000 km away from the centre
> of gravity (the Earth's radius is nearly 6400 km, for those still using
> the Imperial System of units).
>
> I doubt the significance of 10,000 km, except as the diameter of the
> Earth's monthly orbit.
The 10,000 km is approximately the distance between the Earth's center
and the center of the elliptical orbit of the Moon (not the center of
gravity of the Earth-Moon system). These were the two points in question
in the post I responded to. Of course, that distance varies somewhat
over the course of time.
Brian Tung <brian@isi.edu>
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