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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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