Hi Bob,

robertjmodic@... wrote:

> I have about 300 images from the various sky surveys that
> I've downloaded as .fits files from:
>
> http://archive.stsci.edu/cgi-bin/dss_plate_finder
>
> Most of these display just fine in Guide 8. A small number of them,
> however, are skewed or rotated about the center slightly so that
> cataloged stars do not register with those in the images. I've
> examined the headers, but there are so many parameters, I'm not
> sure what to look for.

Yup, DSS FITS headers tend to have about a bazillion odd parameters.
And many DSS images are _supposed_ to be somewhat tilted, either because
the plate was taken that way or because you're near the edge of the
plate; those plates are six degrees on a side, and there are
significant projection effects over that sort of field.

Are the plates mostly in a particular area (say, near the poles)?

The position and orientation of a FITS image can be stored in at
least three ways (two "standard", one DSS-specific). Guide looks for
all of them. Maybe these files are implementing a fourth method.
Or a slightly "off" version of the other three.

Can you give me an RA/dec and the survey from which the image was
taken? I gather this happens with 'a small number of them', so I
presumably wouldn't stumble upon them at random.

-- Bill