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    Re: An interesting question
    From: Peter Monta
    Date: 2013 Oct 11, 23:00 -0700

    Lu Abel writes:
    > moon directly aft of my stern.   So I whipped out my sextant and used the
    > waters as an AH.  Reduced my sight and was disappointed to come out about 20
    > miles from my KP.
    That's interesting---was the image rippling at all?  It's harder to
    explain a 20-arcminute offset if the image was visually almost still
    or rippling just a tiny bit.
    That brings up the question: how good are "flat calm" liquid surfaces
    from an image-stability point of view?  They must range from shielded
    AH on land (subarcminute at the very worst, maybe subarcsecond for all
    I know, or at least diffraction-limited by the eye or scope, not the
    AH aperture itself) to slightly ruffled seas in which the Sun or Moon
    looks like a smear when averaged over many seconds.  But even that
    smear has some useful information.  I wonder to what extent it would
    average down if a navigator were forced to take many sights like this
    in an emergency situation.

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