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    Re: The flat earth notion
    From: Herbert Prinz
    Date: 2003 Nov 5, 03:58 -0500

    Peter Fogg asked:
    
    > Any chance of a little more explanation about what this (eg 'flagpole
    > paradigm')  is all about?
    
    Many texts on the Marcq St.-Hilaire method  "explain" the intercept with the
    help of the following analogy: The vertical angle at which you see a flagpole
    increases as you approach it and decreases as you gain distance from it.
    Similarly, the observed altitude of a celestial body increases when you approach
    its GP and decreases when you move away from it.
    
    The books I mentioned in my previous message fail to make clear that these are
    two entirely different problems: The first one is one of plane trigonometry;
    indeed it applies to a flat earth only. The second one is a trivial consequence
    of the fact that the altitude is the complement of the zenith distance and
    therefore grows when the latter shrinks, and vice versa. I will never understand
    the didactic purpose of "explaining" a triviality by means of a slightly more
    complex and unrelated situation.
    
    I remember once seeing an article in a popular sailing magazine about obtaining
    a position line from a sunset. The author got himself all confused over the
    question whether his intercept was towards or away as Hc and Ho were both
    negative. The analogy with the flagpole collapses in this case.
    
    Herbert Prinz
    
    
    

       
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