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    Re: Determining List by Vega DSLR Image
    From: Frank Reed
    Date: 2013 Aug 29, 10:45 -0700

    Greg, that's a nice photo, and I like the idea!

    I agree with your angular scale nearly enough. I get about 0.378 minute of arc per pixel. Averaging from a couple of stars I get a "list" (tilt of the mast east/west from the zenith) of only about 3 minutes of arc. I find it's listing towards the south or to port if I'm doing this right. I would say that this is below reasonable limits on the procedures so essentially zero.

    For ye landlubbers (like me), you can determine your latitude and longitude using this procedure with anything that is tall and "plumb" --a building or a carefully aligned pole. If you don't have anything like that convenient, you can hang a couple of long, weighted strings from somewhere high. If you take a photograph from beneath the two plumb lines but offset just a little to one side, you can connect the lines at infinity to find the zenith. Then with enough stars in the frame (like in Greg's photo of Lyra), it's just "Dec zenith equals latitude, GHA zenith equals longitude".


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