Std. date/time/RA/Dec FITS keywords?

[Tim DeBenedictis]

Greetings all-

I am writing some astrometry software which needs to run with a variety 
of different FITS-format images.  It would be nice to use the R.A., Dec., 
date, and time information stored in the images' FITS headers, but 
unfortunately there does not seem to be any standard FITS keywords which 
provide this information.

I read the defining FITS paper, which describes the DATE-OBS keyword; 
however, there is no corresponding TIME-OBS keyword, and one-day time 
resolution is not sufficient.

I also read about the CRVAL, CRPIX, CRDEL, and CROT keywords, which sem 
to specify the coordinates, rotation, and image scale.  However, as far 
as I can tell, no one actually seems to use these in practice!  I've 
worked with a variety of images from institutions like Kitt Peak, Lowell 
Observatory, as well as amateur images from SBIG cameras.  The only thing 
I've seen is keywords like RA and DEC which then list an R.A. and Dec. in 
hours/minutes/seconds as an ASCII string.

Is there any standard way of handling these things?  What is the 
"correct" way to do it?  Please send e-mail, as I am not able to check 
responses to all the groups I've posted this to.

-Tim DeBenedictis
timmyd at netcom.com