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    Re: No sextant, no watch, no almanach, nothing
    From: Alexandre Eremenko
    Date: 2004 Nov 7, 22:07 -0500

    On Sun, 7 Nov 2004, Fred Hebard wrote:
    
    > Regarding longitude, the Micronesians were very aware of various
    > features of the sea at different locations,
    > such as the Sargassos Sea
    > (yes, I realize that is in the Atlantic,
    > I am using it as an example of
    > a feature in a supposedly featureless place).
    
    But this is not CelNav, observing various features.
    Cel Nav involves observing something in the sky, correct?
    
    Until now I thought that there are only 3 different methods
    for obtaining longitude (even very approximately)
    by observing the sky.
    1. Using a chronometer (or some other mean to find the time
    at some known longitude).
    2. Using Jupiter satellites (which requires a telescope
    and some sort of "almanac knowledge" about their eclipse times.
    3. By observing the Moon. (This can be distances or occultations
    or eclipses). Whatever you use related to the Moon,
    this requires an almanac or some substitute of it.
    To obtain longitude even very approximately, even to 10 degrees,
    you have to know something related to the Moon much more
    precisely, to a small fraction of a degree. Given the complexity
    of Moon motion, how can you do this without an almanac?
    
    This makes Frank's puzzle very puzzling, indeed.
    It depends, of course on what does he mean by "navigating by CelNav".
    Maybe he means something which does not involve
    determination of longitude.
    
    Like the many methods based on stars only, described in this
    discussion.
    
    Alex.
    
    
    

       
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