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From: "Robert I. Eachus" <rieachus@comcast.net>
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Subject: Re: [OT] Hints for an algorithm - avoiding O(n^2)
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Date: 2004-03-13T10:21:46-05:00
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Bj�rn Persson wrote:

> I didn't mean to say that the Sun doesn't affect the Moon. "If what J-P 
> wrote were true, the Moon would not orbit both the Sun and the Earth, as 
> it does, but only orbit the solar system's center of gravity (if we 
> ignore the rest of the universe)." Is that better?
> 
> You can't choose your words too carefully when there are Ada language 
> lawyers in the audience. :-)

I think you missed my point.  Earth's moon is unique in the solar 
system.  It is the only moon whose path around the Sun doesn't cross 
itself.  In fact, the effect of the Earth's gravity is so slight that if 
you are calculating the Moon's orbit, it is better to compute it the 
same way as other planets.  (Treat it as orbiting the sun, with 
perturbations by the gravity from other planets.  For all other moons, 
you are better off calculating them as orbiting some planet, with the 
Sun's gravitational effect as a perturbation.)

In a discussion of how to calculate the positions in a complex 
gravitational environment, that is a point worth knowing.


-- 
                                           Robert I. Eachus

"The only thing necessary for the triumph of evil is for good men to do 
nothing." --Edmund Burke