Found a document with a table of values:

https://astropedia.astrogeology.usgs.gov/download/Docs/WGCCRE/WGCCRE2009reprint.pdf

The pertinent variables are alpha, delta and W. What do I do with these 
variables? Dunno for sure. This document provides a formula:

https://depositonce.tu-berlin.de/bitstream/11303/6237/4/burmeister_steffi.pdf

I /think/ I need to rotate around the z-axis by W, around the x-axis by 
(90-δ), and around the z-axis again by (90+α), in that order. Lastly, an 
additional rotation (around the x-axis?) by 23.43928 degrees must be 
done to get the body out of the ICRF frame and into the ecliptic frame.

But I still don't know the starting conditions. I.e. before applying the 
transformations, should the globe's North Pole point upward? Should the 
intersection of the Prime Meridian and Equator lie along the x-axis? 
Also, am I wrong, and should I perform the inverse matrix calculations 
instead? Either way, I have not gotten results that match what I see in 
Celestia for the same Julian Date.


Mike

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