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    Re: Irradiation
    From: Bill B
    Date: 2004 Nov 28, 21:35 -0500

    > on. Now I guess that I am doing the right thing but for the
    > wrong reason. Although this leaves me with a question now, can I shoot the
    > stares with a horizon illuminated only by the moon?
    Bruce Bauer (The Sextant Handbook) suggests, if I am reading him correctly,
    that if you are badly in need of a fix, make the observation over the
    suspect moonlighted horizon with the darkest shade feasible.  (I believe he
    is addressing the moon as the observed body as he later goes on to talk
    about stars.)
    Then set the sextant at its current index correction to make the reflected
    horizon level with the true horizon.
    Then remove the shade(s) and aim at the moonlit horizon excluding the moon
    from the field of view.  View the side areas where the reflected moonlight
    trails off into obscurity.  There may be a "jump" up in the level of the
    moonlit horizon due to irradiation.  Examine the the edge of the elevated
    horizon vs. the lower horizon with the lightest possible shade, and adjust
    the micrometer drum until the elevated and true horizon are level.  Use this
    difference as an adjustment factor.
    Finally, compare both the original and adjusted (reduced?) versions and
    compare to your DR, and make an educated guess.
    In the case of stars, it is about the same deal.  Bauer suggest checking the
    horizon with 7 X 50 wide-view binoculars to look for a possible horizon jump
    due to irradiation.
    Hope that helps,

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