Those keywords presumably give the coordinate of the center of the
wide-field photographic plate, which could be degrees away from the center
of the small image that you retrieved. The approximate coordinates of the
center of your image appear to be given by the OBJCTRA and OBJCTDEC
keywords. The exact coordinates of any pixel in the image can be calculated
from a complicated polynomial expression whose coefficients are given by the
PPnn, AMDXn, and AMDYn header keywords, but a much simplier way to get the
coordinates is to display the image using a program such as 'ds9' that does
the calculation for you.

Bill Pence

K. L. Tah wrote:
Hi,
I've just retrieved a fits file from
http://archive.stsci.edu/cgi-bin/dss_form
and would like to know the coordinates which the center pixel of this
image corresponds to.
I notice that there are comments "Plate center RA" and "plate
center DEC" next to keywords PLTRAH,PLTRAM,PLTRAS etc. but for the most
part, these seem not to correspond to the center of the actual fits image
since they are ~ few minutes different from
the epoch 2000 coordinates and the star of interest lies fairly close to
the center (~ tens of pixels from center). Can someone explain this to me?
Thanks,
KL
--
__________________________________________________ __________________
Dr. William Pence
NASA/GSFC Code 662 HEASARC +1-301-286-4599 (voice)
Greenbelt MD 20771 +1-301-286-1684 (fax)