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    Re: Lunar Distance in Wikipedia
    From: Fred Hebard
    Date: 2007 Aug 2, 11:27 -0400

    George,
    
    Rephrase or rewrite as you see appropriate.  The main point was was
    that the need for high precision-calculation stemmed from the
    slowness of the Moon's motion, the imprecision of its predicted
    position, and the practical limit of 30 arcsecond observation
    precision, maybe going to 10" on excellent days.  A sidelight is why
    a sextant was preferred to an octant: lunars are why octants became
    sextants (although perhaps sextants also became preferred because of
    the need for three-point determinations of distance from shore).
    
    I additionally was suggesting that the need for high precision in the
    calculations is a natural leadin to a later, unwritten section on the
    various clearing methods and some overview of what they were, such as
    Frank Reed's Taylor series-like numeric approximation method versus
    brute force methods --and didn't the approximation methods start with
    Maskelyne?-- and Bowditch's role in that, which is famous to every
    American navigator, if not to those from other countries.  This stems
    from the necessity to use five-figure log tables, which can be very
    difficult to use, especially when you are tired, etc. Finally, it can
    lead in to Bruce Stark's new brute-force method for clearing lunars
    which accomplishes the subtraction within the logs rather than taking
    antilogs and going back into logs.
    
    Another area of contention is to discuss Maskelyne versus Harrison in
    the broader picture of which method worked first for the larger
    number of mariners. Examples can come from Frank Reed's forays into
    the logs of American whaling vessels.
    
    Fred
    
    On Aug 2, 2007, at 10:10 AM, George Huxtable wrote:
    
    >
    >
    >
    > Thanks to Fred for his comments.
    >
    > He wrote-
    >
    > | Move the sentence on calculation precision to the end of this
    > | paragraph, to dovetail with the discussion of overall error.  This
    > | also sets up a discussion of the various methods of clearing, which
    > | all aimed to simplify the clearing process, hence Bowditch's
    > claim to
    > | fame.
    >
    >  I had intended to steer clear of any detail about various methods of
    > clearing, because that could be never-ending. Was I right?
    >
    > And Fred has suggested the following insertion, the sentence starting
    > "Because"-
    >
    > "...it
    > | > became a
    > | > severe test of a navigator's skill.  Because of the half-arc-
    > minute
    > | > errors in both the moon's position predicted by almanacs and in
    > the
    > | > measurement, great precision was required in the calculation of
    > | > Greenwich time.  The calculations, which were complex, called for
    > | > five-figure log tables of trig functions."
    >
    > I disagree in detail with those words, Fred. It wasn't really the
    > imprecision of the observation or prediction that gave rise to that
    > need for
    > precise calculation. More, it was due to that factor of 30, because
    > of the
    > Moon's slow motion. The precision was needed in the clearing
    > process, of
    > course.
    >
    > George.
    >
    > contact George Huxtable at george---.u-net.com
    > or at +44 1865 820222 (from UK, 01865 820222)
    > or at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.
    >
    >
    >
    > >
    
    
    
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