Does anyone recognize this precession matrix?

[solarblast]

Anyone know who was the originator of the matrix in the jpg file?

[lpetrich]

That looks like something out of Explanatory Supplement to the Astronomical Almanac, P. Kenneth Seidelmann (http://www.uscibooks.com/seid.htm) -- I remember seeing similar-looking formulas in it long ago.

In any case, that looks like it'll only be good for a few centuries around our time.

[solarblast]

Thanks. The book costs about $75, but it's possible that I might get an inter library loan from some university here in Calif.

I think the modern method is based on a 1976 paper by Lieske, et al. Expressions for Precession Quantities.

[lpetrich]

You'll likely find a copy at some well-stocked university library. I once found a copy at the UC Berkeley campus library. You can search the UC catalog online at WorldCat: University of California Libraries (http://melvyl.worldcat.org/) I did so, and indeed it was there. You may also be able to search other university libraries from your home.