[AZ-Observing] Precession
- From: Howard Anderson <handy13@xxxxxxxxxxxxxx>
- To: az-observing@xxxxxxxxxxxxx
- Date: Sat, 16 Aug 2014 13:24:15 -0700
Hi,
I have written C++ code to do precession. It works and
agrees with other systems out on the internet. It uses the
math from Jean Meeus' "Astronomical Algorithms."
Since precession of the Earth has a period of about 60,000 years,
I thought for a final check I should put in RA and Dec and
precess with a value of 62,000 years.
Since I am a mathematician with a strong physics background,
I expected to get new coordinates similar to the old ones.
Shockingly they are WAY off.
Well not too shockingly perhaps because years ago
I discovered that physicists use lots of truncated series and
throw lots of stuff away. (E.g., in a statistical mechanics course
I took, I was asked to derive the Boltzmann Transport Equation
from scratch. When I finished, the equation contained a Jacobian
matrix. When I questioned my professor, he looked and said "Oh,
those are second-order partials. Just throw them away!"
Actually, they have meaning in a crystal-lattice diffusion process.)
So the question is does anyone know of a rigorous derivation of
astronomical precession that would give repeatable results for
multiples of 60,000 years? I thought Euler provided everything
necessary, 260 years ago, to solve this stuff with precision. :-)
And I realize that other effects would mess up the "true" precision
of the result over centuries but I would feel better if I thought we
at least tried to start from something repeatable...
Thanks,
Howard
http://www.astroshow.com
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