[fitsbits] Q: Determining coordinates

[David Berry]

Marten Blixt wrote:
> 
> 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?

Gaia is another solution. It is a tool with lots of built in functionality
for displaying and analysing FITS images (and some other astronomical
image formats). It can create and manipulate WCS solutions either from RA
and DECs that you type in, or it can go on-line and get them from various 
catalogues. It can also pick up a WCS from another image - you identify
some stars in the other image and it works out the RA and DECs from those
(it can automatically obtain and display a DSS image of any part of the
sky for this purpose).

See http://star-www.dur.ac.uk/~pdraper/gaia/gaia.html


David Berry

UK Starlink applications programmer.