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    Re: Bowditch Long Term Almanac Tables
    From: Gordon Talge
    Date: 2002 Oct 23, 15:53 -0700

    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
    
    
    
    --
                                  ,,,
                                 (. .)
    +-------------------------ooO-(_)-Ooo------------------------+
    | Gordon Talge WB6YKK               e-mail: gtalge{at}pe.net    |
    | Department of Mathematics       http://www.lbusd.k12.ca.us |
    | Wilson High School                  Long Beach, CA         |
    | (o-    Debian / GNU / Linux                                |
    | //\    The Choice of the GNU Generation                    |
    | v_/_                  .oooO                                |
    |    - E Aho Laula -     (  )   Oooo. - Wider is Better -    |
    +-------------------------\ (---(  )-------------------------+
                               \_)  ) /
                                   (_/
    
    
    

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