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    Re: Irradiation
    From: Bill B
    Date: 2004 Nov 28, 16:29 -0500

    > They mention "low altitudes, btw". What does the irradiation
    > phenomenon have to do with low altitudes?
    In low altitude Sun sights, the lower limb is affected to a "substantially"
    greater degree by refraction than the upper limb.  My best guess relates to
    the art, rather than science, of cel nav.  In cases of low Sun altitude,
    some practitioners seem willing to trade off the possible affects of
    irradiation against what they perceive to be a greater risk of error from
    refraction at low altitudes by using the lower limb.
    I suspect that even if one could quantify the affect of the scope and its
    optics, contrast ratio between the sun and sky, sea and sky, body altitude
    etc., it still comes down to how each individual's sensors and brain parses
    the input.  That seems, from what I have read, to be the fuzzy variable that
    makes it impossible to quantify irradiation for the masses.
    Good luck on nailing it down ;-)

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