Next message: Peter Fogg: "Re: A noon sight conundrum"
<So if you were feeling particularly mean, you could keep four years of
almanacs, and use them again and again, at four-year intervals (for Sun
predictions only, not Moon or planets). This would be sufficiently accurate
that I doubt if a navigator would notice the accumulating error over 20
years.>
If your "mean" translates into the Yankee "tightwad", then in fact one can simply buy a perpetual almanac, of the abbreviated type found in the back of Hewitt Schlereth's books on navigation and others. They include 4 sets of data, plus the recurring years (198x, 199x, 199y, etc.) for which eash particular set should be used, plus one offset correction to be added to each set for each four-year cycle. Considering the physical amount of space they can avoid consuming, these permanent almanacs were logical for small craft. I say "were" because of course with modern electronics in the past 15 years, there are even smaller ways to carry better data.
The change to the Gregorian Calendar (the conventional western AD calendar) reflects, what, something like a ten-day shift that Pope Gregory decreed in order to make the paper calendar line up with an astronomical one (a sun calendar) that he'd noticed was that far out of alignment after what, 1300-odd? years.
