Years ago, before the dominance of the internet, I bought S&Ts Sky Catalogue 2000.0, vol 1 and 2. In volume 1 in the introduction, pages xiii and xiv, they give the the formulas for rigorous precession. It uses Newcomb's expressions for some constants. With Newcomb's expressions and the other formulas given, I can calculate what the RA and DEC was for Polaris, for example, way back to 1755 to almost exact accuracy to what was observed by J Bradley. I searched the internet for precession correction formulas but could not find any, perhaps because I have dial up and so I cannot take the time to do a real thorough search. Then I remembered the Catalogue I just mentioned had the formulas. I wrote my program and it works very nice. However, I did run into one problem others may have encountered if they attempted to program the same S&T precession formulas. The Newcomb expressions have all the coefficient values in seconds, but they need to be in degrees. I divided each coefficient value by 3600 to make the conversion. When I did this, I reproduced exactly the book example, the one going back to year 1755. This was confusing because the quick and dirty method they had given in an in a preceding page worked with coefficients in seconds and trig values in degrees. Stan -- See message header for info on list archives or unsubscribing, and please send personal replies to the author, not the list.