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    Re: sextant precision.
    From: Frank Reed CT
    Date: 2005 Jun 18, 22:20 EDT

    George H, you wrote:
    "one such shade on my  sextant quite defeats any such attempts. It's
    the very darkest shade, a very  deep-blue one in my case, that's required
    for viewing the sun. When I look  through that shade, it's so dark that the
    only object I can see is the sun.  Without that shade, I can't safely look
    at the sun at all. So how do I  compare two measured angles, observed with
    and without that shade? What do I  look at, to do that job? Others must have
    met that same problem. Suggestions,  please."
    Yes, I know what you're talking about. What you need is  something brighter
    than the Moon and fainter than the Sun. That's a big range:  around 14
    magnitudes or a factor of 400,000 in luminosity, so lots or  possibilities... I have
    used the setting sun which is faint enough to look at  comfortably with a
    medium shade and bright enough to see through a very dense  shade --there is *some*
    altitude near the horizon where this should be possible.  I've also used
    metal rooftops that are reflecting almost direct sunlight. You  get an IC using
    the medium shade (whose shade error you've already determined  with the Moon
    perhaps) and then you get an independent IC with the dense shade.  A little
    arithmetic yields the shade error of the dense  shade.
    42.0N 87.7W, or 41.4N  72.1W.

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