Are indicated compass directions in VPHOT WCS solved images rotated 90 degrees from true?

American Association of Variable Star Observers (AAVSO)
Mon, 05/09/2011 - 02:34

VPHOT shows field orientation in the lower right corner of WCS solved images. Two perpendicular lines point respectively E and N. The funny thing is, the orientation of the two lines is rotated 90 degrees clockwise from the compass directions given on my AAVSO chart. I produced the AAVSO chart using the online chart plotter with CCD option, non-reversed. The 90 rotation of WCS compass directions occurs in all fields (six or so) that I've uploaded to VPHOT. (I just discovered VPHOT yesterday. It's great!) I am using an SCT, with 2 mirror reflections.

The result is that what's shown as N should be W, and what's shown as E should be N.

Has anyone else noticed this behavior?

- Andy Howell (HOA)

Norwegian Astronomical Society, Variable Star Section (NAS)
Probably a bug

Hi Andy,

Yes, VPHOT seems to get the orientation arrows wrong from time to time. Probably a bug in the code that shows for certain configurations.

Can't promise when I will have it fixed, but it is on my to-do list.