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

[Steve Allen]

In article <4mt60p$1pn at pecos.msfc.nasa.gov>,
Peter Bunclark  <psb at ast.cam.ac.uk> wrote:
>Tim DeBenedictis wrote:
>> 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...[deletia - mod.]

>Read :
><A HREF="http://fits.cv.nrao.edu/documents/documents.html" >FITS
>Documents</A>

This reply may give the impression that there is a definitive answer
to the question.  There is not.

There are no adopted standards specifying the keyword name or format
of RA and Dec in a FITS header.  There exists decimal degrees, decimal
hours, and hexadecimal strings in hours and degrees.  The given RA and
Dec may be expressed in a catalog reference frame or as notably
inaccurate telescope encoder readings.

Similarly there is no adopted standard specifying the keyword name or
format of observation time in a FITS header.  Again, existing practice
varies rather widely as do the accuracies of the clocks used to obtain
the time.

There is a draft document at
http://fits.cv.nrao.edu/documents/wcs/wcs.html
whose adoption should solve this problem, but its recommendations
are not generally found in any existing FITS headers.

--
Steve Allen          UCO/Lick Observatory       Santa Cruz, CA 95064
sla at ucolick.org      Voice: +1 408 459 3046     FAX: +1 408 454 9863
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