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    Re: Calculated Altitudes for Lunars
    From: Herbert Prinz
    Date: 2002 Oct 24, 15:26 +0000

    Bill,
    
    You write
    
    > If you knew your longitude but only guessed GMT, then the error in
    > computed LHA of any body would be about equal to the error in GMT
    > (converting time to arc).
    
    But if I know my longitude, I do not need a lunar distance observation!!! I
    just take the altidude of any celestial body that I find in the almanac,
    and I am done. It is a totally unrealistic scenario to assume that I know
    my position, but not GMT, and take a lunar exclusively for the latter. This
    only occurs in backyard navigation, where the goal is to practice the
    distance sight itself and one needs a quick way of reducing the sight in
    order to evaluate it.
    
    In the real world (of times long gone, to be sure), how would a captain at
    sea know his longitude, but not local time? He would have to see land (or
    trust his DR 100%) while having no chronometer and no usable horizon for
    taking altitudes. How would he then work a lunar distance anyway and why
    would he bother?
    
    At any rate, GMT from lunar distance at known terrestrial position and GMT
    from lunar distance at known celestial position (i.e. latitude and time)
    are two entirely different problems that require different methods for
    their solution. It does not make sense to compare the efficiency of the
    respective algorithms. You have no choice between them.
    
    Herbert Prinz
    
    
    

       
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