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    Re: Coordinates on Cook's maps
    From: George Huxtable
    Date: 2007 Apr 29, 17:47 +0100

    Alex wrote, about Cook, a week or two back-
    | I just wanted to make sure that he
    | used exactly the same published Nautical almanacs
    | (rather than some more precise data his
    | astronomers-associates could possibly provide).
    | One thing which makes me doubt is this:
    | Cook's voyages lasted more than one year.
    | The ordinary almanac is published just one year ahead,
    | even now. Then how did Cook obtain the data for
    | more than one year?
    From George-
    The first Nautical Almanac was for 1767, published the previous year. Cook
    departed on his first voyage in 1768, and carried the Almanac for that year,
    and the (hastily produced) almanac for 1769 with him. From the start of
    1770, his Almanac ran
    out. From then on, it was necessary to calculate the position of the Moon
    from scratch, according to Mayer's tables, as the few mariners who tried it
    had to do, before the Almanac existed. It was an immensely difficult
    procedure, which if it interests you is detailed in the first edition of
    Maskelyne's "British Mariner's Guide". That gave Moon ecliptic lat and long
    for noon and midnight. Then you had to do a quadratic interpolation, using
    four of those consecutive positions, to get Moon lat and long at the
    required 3-hour intervals. Then you had to do the same for the Sun (for
    Sun-Moon lunars), which was much easier. Then you had to calculate the
    great-circle distance between those positions. If there were no blunders,
    that should correspond to the lunar distance that would have been found from
    the almanac, if you had one.
    For Cook's later voyages, he was supplied
    with almanacs to cover the conceivable length it might take, as Ken has
    pointed out.
    contact George Huxtable at george@huxtable.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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