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    Re: CelNav without sextants
    From: Alexandre Eremenko
    Date: 2004 Nov 2, 16:04 -0500

    Dave,
    I disagree with what you said.
    Namely, with the "logic".
    Suppose indeed that the methods I mentioned
    gave the SAME precision as the methods based
    on the use of sextant.
    The sextant-based methods will still have
    an advantage of their wider applicability.
    (The rise and set events occur only few times
    a day... occultations are rare etc. At the time
    needed for observation, the objects can be obscured
    by clouds etc.)
    
    Second, I was not talking of the same precision,
    but the same "order of magnitude".
    
    In other words. It is hard to imagine a ship
    doing an ocean crossing without a compass.
    So I DO assume there is a compass (and maps).
    So dead reckoning is available.
    Columbus experience shows that you can do very
    well with dead reckoning only.
    
    The question was whether you can improve on this.
    So "100 miles error" is something non-acceptable.
    But "10 miles error" is something very useful
    on an ocean crossing.
    
    I conjecture that one can do reasonably well (say 10 miles)
    with WATCH and ALMANACH ONLY. (Assuming there are days
    in your trip with reasonably good weather:-)
    
    In fact, my question stated as precisely as I can
    and as technically as I can is this:
    
    "To what precision can you hope to get a position line
    from timing (GMT) of a sunset/sunrise"?
    
    Alex.
    
    
    

       
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