Re: Seeking identification of stars in photo

Date: Wed Jul 20 2011 - 01:28:07 UTC

  • Next message: George Roberts: "Re: Seeking identification of stars in photo"

    George Roberts, you wrote:
    "One more thing I just noticed.  The movement of the stars in the photo is nicely lined up with the expected rotation around the south pole as you would expect if you did a picture with a tripod instead of a motorized mount."
    Yes, definitely. Good catch. And the fit with the stars of Pyxis is even better if you carefully exclude any star-like marks which are not trailed. That one bright "star" that doesn't fit has a slightly elongated shape but it does not match the shape of the trailed images of delta and gamma Pyxidis. Presumably this extra star was just a bit of dust on an old negative. The trails also are consistent with a typical exposure for this sort of image. The difference in right ascension between delta and gamma Pyxidis is about five minutes. The length of the trail of either of those stars in the image is about one-tenth of the distance between them. So the length of the exposure is about 30 seconds (a rough estimate, of course). Capturing stars down to about sixth magnitude is very reasonable for typical film equipment of the era and a 30-second exposure. 
    Note also that these stars would have been about fifty degrees high nearly due east in morning twilight from southwestern Australia at that time of year --an easy viewing direction and a good place to see a bright satellite. The object then would have been moving at roughly a 30 degree angle with respect to the horizon (from upper left to lower right or vice versa). In fact, if you orient the image so that the "crease" is vertical and towards the left, the frame would be nearly horizontal with respect to the observer's horizon. That seems like a good sign since it's consistent with a camera on a tripod.
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