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    Re: Question on Lunars
    From: Herbert Prinz
    Date: 2004 Oct 26, 19:32 -0400

    George Huxtable wrote:
    
    > The first navigator to use lunars in a practical way at sea was Edmond
    > Halley (famous for Halley's comet),
    
    I would prefer to say "systematic" rather than "practical". Amerigo Vespucci
    claimed to have used the conjunction of Mars and Moon of 1499-08-03 to
    determine his longitude at 82 1/2 W of Cadix. On account of several flaws in
    his procedure, there has been some controversy about the authenticity of this
    claim. But there is a letter that documents the procedure, the data and the
    result. Would this not qualify him as the first navigator to make a practical
    effort, albeit an isolated one?
    
    
    > [... ]line though the horns continues sweeping through the
    > stars at constant speed.
    
    This line is not necessarily perpendicular to the ecliptic. Does Halley correct
    for this or confine himself to cases where it is?
    
    
    > Even parallax matters little
    > if a star can be chosen which passes the horn-line near the time of Moon's
    > meridian passage.
    
    If the Moon passes through the meridian you can still have considerable
    parallax in longitude. The question is whether the ecliptic is perpendicular to
    the vertical through the Moon. If this is the case alone, the parallax in
    altitude affects only the Moon's latitude and does not interfere with the
    observation of the conjunction.
    
    Herbert Prinz
    
    
    

       
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