[fitsbits] Q: Determining coordinates

[Marten Blixt]

This should be an ordinary task for astronomers, that said, it
implies that I'm not an astronomer.

However, in the past I've taken some CCD shots of the 
night sky (to capture the northern lights) and now I need to 
overlay a coordinate grid on them.
In my FoV (~13 deg) I've identified a few stars (thanks xephem!) so that
I know the *exact* ra and dec for them, what I need to do then is
to fit a coordinate grid to them.
I guess that this is a pretty ordinary task for an astronomer, but 
I'm getting stuck in nomenclature and .....

I've found this starast.pro program (IDL Astronomy User's Library) that seems 
to do exactly that, but I'm unsure on what it really does (don't know what
the Coordinate Description matrix contains, and I'm a total newbie when
it comes to FITS).

Is it common to assume rectangular coordinates inside the narrow FoV often
used among astronomers?

Does anyone know of routines that calculates the coordinatne grid from a 
known set of stars inside the image? Or have tips/tricks that could 
point me in the right direction?

Help is greatly appreciated,
	Marten Blixt