[fitsbits] Plate Center on POSS2 Plates

[Steve Allen]

On Wed 2004-07-28T12:49:49 -0700, K. L. Tah hath writ:
> 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?

Aside from documentation in the published papers one thing to try
would be to get the image viewer named "ds9" from
http://hea-www.harvard.edu/saord/ds9/
This should provide world coordinates for any pixel in an image.

The underlying software which accomplishes the coordinate
interpretation is also available
http://tdc-www.harvard.edu/software/wcstools/

--
Steve Allen          UCO/Lick Observatory       Santa Cruz, CA 95064
sla at ucolick.org      Voice: +1 831 459 3046     http://www.ucolick.org/~sla
PGP: 1024/E46978C5   F6 78 D1 10 62 94 8F 2E    49 89 0E FE 26 B4 14 93