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>Guy Schwartz asked-
>
>An interesting questions posed on a local bay area sailing group.
>

And George Huxtable answered


>But you do can MUCH better than that by choosing an appropriate year, just
>four years previous. That puts it into the corresponding point in the
>calendar's cycle of leap-years. Then, without making any corrections, the
>Sun and star predictions will be within an arc-minute or so, and therefore
>perfectly usable for almost any practical purpose at sea. You can choose 8
>years previous, or 12, and the results will be nearly as good. Indeed, once
>you have collected a set of four such consecutive almanacs, you may never
>have to buy another for the rest of your navigating lifetime, depending on
>how picky you are. Same is true of sunrise and sunset times.
>
>Some early almanacs were sold that way, giving Sun declination for four
>years ahead, so then you could go on reusing them. Really useful to the
>navigator, but not a good business proposition to the seller. But then, they
>would spice them up with nonsensical astrological predictions.

A shameless plug here for my own "Long Term Almanac 2000 - 2050" for the
sun and selected stars, which does just that. And it is still in print, the
second edition has just been published by Starpath Publications in Seattle.
The daily values of the GHA and declination for the sun, along with the GHA
of Aries, are given for the years 2000 to 2003 (included). Quadrennial
corrections are given which allow the GHA and declination of the sun, and
the GHA of Aries, to be calculated for any year up to 2050, at which point
the error from using a single term linear quadrennial correction rapidly
escalates.

Potentially, better accuracy would be obtained by using a more recent NA.
For example, using the NA for 2006 and the quadrennial corrections from my
LTA would probably give numbers that were still accurate to around 0.1" or
so (the NAs quoted accuracy) for 2010 and 2014

It does not have any "nonsensical astrological predictions", but it does
have the NAO sight reduction tables in the back, which also feature in the
Nautical Almanac, the use of which will be familiar to Power Squadron
graduates.

And yes, there has in the past been a reluctance by some sellers of
Nautical Almanacs to stock this book for exactly the reason George mentioned.

Geoffrey Kolbe


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