I think we need to define orbital precession. According to my thinking, precession of an angular momentum vector occurs on a time
scale much longer than the rotational period of the matter causing the angular momentum. For example, Earth spins one revolution
per day, but the precession of the polar axis has a period of 26,000 years.
If my view of precession is what this question is about, then wobbles of the instantaneous orbital angular momentum vector because
of monthly wobbles of the earth-moon system out of the ecliptic plane would not constitute precession of earth's orbital axis. I am
thinking the question is whether there is long scale (millions of years) precession of Earth's orbital axis around some reference
line such as the sun's spin axis, or better, the solar system's total angular momentum vector, or better, with respect to distant
stars.
If this is the question, I am wondering if we even have ways to determine it. Currently we don't know enough about how much mass is
in the solar system (e.g. mass beyond Pluto) to know exactly where the solar system's total angular momentum points, and what
precession that vector might have with respect to the distant stars. Thus, if we felt we did observe some apparent precession of
Earth's orbital angular momentum with respect to the stars, would we know if it is Earth as opposed to the whole solar system that
is precessing with respect to the distant stars? It seems we first have to know what way the solar-system angular momentum vector
points, then ask if the Earth's orbital momentum vector is precessing about that axis on some time scale longer than a year.
Michael D. Edmiston, Ph.D.
Professor of Physics and Chemistry
Chair of Sciences
Bluffton College
Bluffton, OH 45817
(419)-358-3270
edmiston@bluffton.edu
This posting is the position of the writer, not that of SUNY-BSC, NAU or the AAPT.