From: Ronn Blankenship <ronn DOT blankenship AT worldnet DOT att DOT net>
Newsgroups: nctu.club.astronomy,relcom.fido.su.astronomy,sl AT psycode DOT com,comp.os.msdos.djgpp,gac.physics.astronomy
Subject: Re: Orbits, planets, PLEASE HELP!
Date: Sun, 22 Mar 1998 01:20:48 -0600
Organization: Ever try to herd cats?
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George Pinckney wrote:

> Jack Ostroff wrote:
>
> >
> >
> > However, don't give up hope.  Accurate equations for these things
> have
> > not been discovered for more than two bodies.  (Look for references
> on
> > the "three body problem" for more history, which should also provide
>
> > leads on computational methods.)
> >
> > Good luck.
> >
> > Jack (jack_h_ostroff AT groton DOT pfizer DOT com)
> >  (the legal message below, if present, is automatically added by my
> >   corporate firewall.  There is nothing confidential in this
> message,
> >   which can be redistributed freely.)
>
>   This brings to mind questions I've had for a long time.
> At what level in physics is orbital dynamics taught?  Is it a case
> that the math for the two body problem
> is pretty straightforward, and is easily referenced when needed?
>

Depending on the school, either at the advanced undergraduate or even
the graduate school level.  The main reason for waiting is that you need
to take freshman calculus, DE, etc., first.  Also, of course, execpt for
a few schools, astronomy courses for those wanting to become astronomers
are generally delayed until graduate school, and future astronomers are
encouraged to get a good background in physics (major) and math (minor
or 2nd major) as undergraduates.

> Regarding the three body problem, I think us amateurs don't appreciate
> the complexities here.  We see
> tables for planetary positions and think they are "cast in stone."
> How far out in time do these tables
> remain relatively accurate??  When calculations are made, are
> estimates made as to how accurate they are,
> as in "accurate to within x seconds / year.
>

See the notes on the subject in the "Astronomical Almanac", also perhaps
the "Explanatory Supplement to the Astronomical Almanac".   Tables given
in general-purpose texts often do leave out a lot of the details and
caveats.

> In what reading I've done it seems the underlying assumption is that
> the three body problem will never be
> solved - that we will never discover math that accurately describes a
> >2 system.  Any thoughts?

 Well, no one has yet figured out a way to attack the system of
differential equations that the general 3-body problem (or general
n-body problem) leads to.  And people have been working on it for
centuries.

-- Ronn! :)

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