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    Re: Plastic sextants. was: GPS shortcomings.
    From: George Huxtable
    Date: 2005 Jun 10, 00:14 +0100

    Dave Weilacher asked-
    
    >A retired US Navy Commander friend who was reponsible for navigation
    >aboard ship on one of his assignments is of the opinion that the horizon
    >is always suspect near shore.  The argument is that the differences in
    >temperature between land and sea screws up the horizon that you see.
    >
    >Could this account for the discrepancy between every ones expectations and
    >his measured results?
    
    =================
    
    Dave makes a fair point, but as I see it, it would apply only to
    observations where a significant fraction of the length of the sight-path
    to the horizon is over the land (or sandy shore, or drying reefs,
    whatever). Otherwise, the surface temperature, even in shallow water, would
    not differ all that much from the open sea, except in some very-odd
    environments.
    
    Certainly, observations made from a beach should be made from reasonably
    close to the waterline, not from hundreds of yards back.
    
    As Henry pointed out, it's the horizon that causes most of the inaccuracy
    in altitude measurements. "Bugaboo" was the word he used; I hope I have its
    meaning right...
    
    George.
    
    
    
    ================================================================
    contact George Huxtable by email at george---.u-net.com, by phone at
    01865 820222 (from outside UK, +44 1865 820222), or by mail at 1 Sandy
    Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.
    ================================================================
    
    
    

       
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