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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.

Cheers,
Peter

   

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