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    Re: Digital Camera Celestial Navigation
    From: Frank Reed
    Date: 2008 Jul 07, 16:49 -0400

    Paul Hirose, you wrote:
    "After some debugging, I realized there was nothing wrong with my code.
    Refraction reduces the semidiameter in every direction. When the left and
    right limbs refract up, they move on great circles which converge at the
    zenith. With a body of 16' semidiameter, and sea level refraction,this
    decreases the semidiameter about .27". I tested this at several altitudes
    from 10 degrees to 80, and it didn't vary more than .01"."
    What happens when you place the Sun at a true altitude of -30' so that
    refraction is just enough to lift it above zero degrees observed altitude?
    By the logic of great circles converging at the zenith, which sounds
    reasonable to me, shouldn't refraction then slightly increase the diameter
    of the Sun in this case (the diameter measured parallel to the horizon, that
    is)? I've never worked it out myself. I'm just asking.
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