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    Re: Dip
    From: Frank Reed CT
    Date: 2004 Dec 1, 00:42 EST
    Alex E wrote:
    "their main
    conclusions seem to imply that the refraction
    near the horizon (and thus the dip) is uncertain
    to more than 1/2 of a degree."
    Picture the Sun sitting on the horizon while you're standing on the deck of a boat. Follow the lightrays back to the visible horizon and back to the limb of the Sun. The lightray from the horizon you're seeing only has a short trip of a few miles and it passes through only small changes in air density (under average conditions). The lightray from the Sun's limb has the same path for the last couple of miles but before that it has travelled all the way down through the atmosphere (well beyond your visible horizon) and passed through a big gradient in atmospheric density. That much longer trip yields lots or refraction and also plenty of uncertainty in the net refraction.
    Frank R
    [ ] Mystic, Connecticut
    [X] Chicago, Illinois
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