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    Re: Sextant Positions versus Map Datums?
    From: Rodney Myrvaagnes
    Date: 2002 Jan 17, 9:48 PM

    On Thu, 17 Jan 2002 13:22:32 -0800, Hal Mueller wrote:
    
    >
    >Sextant positions are referenced to the surface of this ellipsoid,
    >not to a sphere.
    
    Sextant positions measure from gravity vertical, to the extent they measure 
    from anything. That is inherent in a water surface. To the
    extent that gravity remains normal to the astronomers' ellipsoid, your statement makes sense.
    
    However, even assuming that perfection, how would anyone using a sextant 
    distinguish that vertical from the vertical of a sphere? An
    observatory can establish its celestial coordinates with a lot of measurements 
    over time. A sextant doesn't have that luxury.
    
    And, gravity has lots of local variation.
    
    How does the WGS84 ellipsoid compare with the astronomers one?
    
    Rodney Myrvaagnes                   J36 Gjo/a
    
    "Religious wisdom is to wisdom as military music is to music."
    
    "What contemptible scoundrel stole the cork from my lunch?"  --  W. C Fields
    

       
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