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Subject: Re: Bowditch Long Term Almanac Tables
From: Gordon Talge (gtalge@XXX.XXX)
Date: Wed Oct 23 2002 - 18:53:28 EDT
Dan Allen wrote:
>
> One of the nice features of the Bowditch volumes from 1958 until 1984
> is Appendix H:
>
> Long Term Almanac
>
> It made carrying along a Bowditch (or two from 1975 until 1984)
> self-contained: it
> had the theory and the tables needed to do "lifeboat" navigation. Now
> of course
> this useful table has been removed with no replacement in later
> editions. How sad.
> (These editions also had H.O. 211 as Table 35, "The Ageton Method",
> also now deleted.)
>
> The Appendix had two pages for the Sun's GHA and Dec for 10 different
> dates per month,
> for each month of the year. There are corrections based upon year so
> that the maximum
> error for altitude would not exceed 2.0' of arc. It also has
> information for 38
> navigational stars in a compact little table with promised errors of
> less than 1.3'
> of arc, as well as a table of the GHA of Aries, along with 2 auxiliary
> tables. The
> whole thing with explanation takes up about 5 pages. Very neat.
>
> Question: does anyone know the source of this table? Is it just
> Newcomb's formulas
> put into a table? (Newcomb's formulas were the basis of the Nautical
> Almanac before
> computers and DE405.)
>
> Question #2: could we come up with a newer, better, more compact long
> term almanac
> ourselves? Just a thought.
>
> Dan
Dan,
In vol 3 of Pub NO 249 ( The old HO 249 ) "Sight Reduction Tables for
Air Navigation" there is a very good "Sun Table" starting on page 342.
The theory is that "what goes around, comes around every 4 years" sorta,
with the appropriate corrections. The table is for 1981 to 2016. so
it has 14 more years.
The stars are pretty regular too. The moon is way to "weird" for a
simple
long term table.
A few years ago, using DE200/LE200 and Chebyshev Polynomial
approximations
I was able to duplicate the polynomials in the now defunct "Almanac for
Computers" for the Sun, Moon, and Planets. This information in a some
what
different form is still available in offical form from the British,
last time I checked.
-- Gordon
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| Gordon Talge WB6YKK e-mail: gtalge@XXX.XXX |
| Department of Mathematics http://www.lbusd.k12.ca.us |
| Wilson High School Long Beach, CA |
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