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  1. #1

    Default Relating TheSkyX FOVI angle to sky PA

    This is something that has been confusing to me and may be related to my difficulty in locating guide stars on my SBIG guide chip. Bear with me, looking the TheSkyX FOVI, if it's not connected to my rotator it is always orientated north up. this is whether the object is east or the west of the meridian. My SBIG camera (with internal guide chip) is oriented north up (sky PA=0.0 more or less) when pointing east and the FOVI correctly reflects that my guide chip is located along the top (north) edge of the main chip. The problem is when looking at objects on the west side of the meridian the FOVI is still oriented guide chip North but sky PA=0.0 is now at the bottom edge (180 degree side) of the FOVI. I know this is an observing problem ACP handles with ease. My concern is when using TheSkyX to locate and orient guide stars while working with targets on the west side of the meridian.

    When I was sorting things out by running the NiteCrawler rotator script, which used a location on the west side, I observed the rotator move to the bottom of the FOVI for sky PA=0.0, it then moved to FOVI=270 degrees for sky PA=90 degrees and then to FOVI=40 degrees for sky PA=220. Bob, recall these were the angles your scripts called out. So here's my confusion: when setting up and object to image and if I'm choosing a guide star when the object is located on the screen west of the meridian do I set the sky PA of my chosen guide star to the angle on the FOVI or should I use the angle on the opposite side? That is, on the west side of the meridian, does the 180 degrees on the screen FOVI actually mean the sky PA=0.0, does 270 degrees on the screen FOVI actually mean sky PA=90 and does 220 on the screen FOVI actually mean sky PA=40? If the answers are yes to the translations (and I know they are simple enough to do in your head) is there a way to flip the FOVI (automatically?) to reflect the correct sky PA angles?

    I hope this makes sense but I've noticed some issues with guide star location when running my plans and it's possible this may be part of my problem.
    Dan Simpson
    Galisteo Observatory
    Santa Fe, NM

  2. #2
    Join Date
    Oct 2005
    Mesa, AZ


    I canít visualize what youíre doing with the night crawler program etc. Hereís a YouTube playlist with two videos that should clarify things. No matter what, you read the PA off the FOVI. This is for east or west of the meridian. The PA is the PA independent of mount geometry. After viewing these, if youíre still confused we can set up a phone call next week (on the freeway now with Stevie driving).
    -- Bob



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