ATM alt/az to ra/dec

[Dan Gray <grayarea@teleport.com>]

I have need of a way to convert from altitude and azimuth to right
ascension and declination.  I have found formula's for the other way
around, and am presently using them, but I need to convert from alt/az
to ra/dec, to take refraction into account, for my computer controlled
scope.

The formula's for ra/dec to alt az are:

cos Z = sin(lat) sin(dec) + cos(lat) cos(dec) cos(hr)

Z is the zenith distance and hr is the hour angle.

cos A = (sin(lat) cos (Z) - sin (dec)) / cos(lat) sin (Z)

A is the Azimuth.

These are from Microcomputer Control of Telescopes by Mark Trueblood and
Russel Genet, page 109.

I haven't had much education in trig or algebra, so any help would be
appreciatted.


By the way, Mel Bartels, I used your suggestion to calculate the 'Z2'
error, and it worked fine.  I'm still waiting for these clouds to clear
off so I can star test it!

Dan Gray