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Re: Bowditch Long Term Almanac Tables
From: Gordon Talge
Date: 2002 Oct 23, 15:53 -0700
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@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 - | +-------------------------\ (---( )-------------------------+ \_) ) / (_/