Weird funky precession question - sci.astro.amateur

Mensaje del debate Weird funky precession question
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From: Quadibloc <jsav...@ecn.ab.ca>
Newsgroups: sci.astro.amateur
Subject: Re: Weird funky precession question
Date: Fri, 3 Jul 2009 04:40:44 -0700 (PDT)
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On Jul 1, 10:31=A0pm, Dave Typinski <m=F6b...@trapezium.net> wrote:
> Assuming an astronomical object is a member of a two-body system and
> has a spin axis and an orbital plane, can the object's spin axis
> precess around an axis /other/ than the normal to its orbital plane?
>
> Doesn't seem likely, not with only two bodies.
>
> Okay, add a few more bodies.
>
> Take the Moon, for example. =A0Its spin axis precesses about the normal
> to its orbital plane. =A0
>
> Why couldn't its spin axis also precess around the normal to the
> ecliptic?
>
> Or does it, but to a very much smaller degree?
>
> Is that what nutation is? =A0A smaller and faster precession around some
> other axis superposed on a somewhat larger and slower "main"
> precession?

To find out what precession can do, this Wikipedia article seems like
a good one...

http://en.wikipedia.org/wiki/Precession

Since nutation, described on another Wikipedia article, is largely
tied to the advance of the Moon's nodes, no doubt it is a response to
the Moon's gravity even as ordinary precession is a response to the
Sun's. It's probably simpler to combine the torques and get the
resultant precession than to add precessions, though.

John Savard