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    Re: Digital Camera Celestial Navigation
    From: Paul Hirose
    Date: 2008 Jul 09, 09:10 -0700

    Marcel Tschudin wrote:
    > Paul wrote:
    > "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[sec
    > arc]".
    > I couldn't figure out how you obtained this value. Looking at it
    > geometrically by linear interpolation: about 0.5 deg refraction at the
    > horizon and 0 refraction in zenith direction results in a much larger
    > value. Looking at it using differential refraction shouldn't result in
    > a more or less constant value (0.27"). I would appreciate if you could
    > explain the cause of the effect in more detail.
    Your values are the vertical refraction. My message was about the
    decrease in *horizontal* semidiameter due to refraction.
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