# NavList:

## A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding

**HO 211 and Calculator Almanacs**

**From:**Gordon Talge

**Date:**1999 Sep 07, 11:12 PM

First HO 211: I have seen several HO 211s for sale at used book stores. They usually sell for around $3.00 to $6.00. I have also seen Ageton's later methods that contain HO 211 plus combine it with a later method of his. Second Calculator Almanacs: There seems to be several ideas for Calculator Almanacs. 1) Have polynomial approximations for the Sun, Moon, Planets etc. a la the USNO's now out of print, "Almanac for Computers". HMNAO in Britain publishes almost the same thing with their polynomials. Matter of fact, you can take the USNO's polynomials and turn them into HMNAO's. A couple of years back I wrote a program to make these polynomials from DE200/LE200 the JPL ephemeris that the Nautical Almanac is based on. 2) Another method is to use the French "VSOP87". An abreviated version is in the book, "Astronomical Alogrithms", by Jean Meeus. The full versions you can get off the net from the BDL in Paris. The HP48 Navigation Card by Sparcom uses this. The series for the Moon is lifted verbatum from Meeus' book. For the Planets, it uses a truncated VSOP87C which is the "Heliocentric Dynamical Eclipitc and Equinox of the Date in rectangular coordinates (X,Y,Z) then converted to GHA and Dec. The series are "Poisson Series" which means the terms of the series are themselves series. A real bear to evaluate without a computer or high powered calculator. For example, a reasonable series for the Earth ( Sun ) might take 43 terms for the 1st term of X, 3 terms for the 2nd term for X, and 1 term for the 3rd term for X. Duplicate this for Y. Things are a little better for Z. Maybe only 2 terms for only 1 term for Z. The precision of the retained terms can be calculated from a little formula given nu sq(n)A where nu =2 and n is the number of retained terms and A is the smallest amplitude retained. You can get all the info from "Planetary theories in rectangular and spherical variables. VSOP87 solutions" by P. Bretagnon and G. Francou. Astron. Astrophys. 202, 309-315 (1988). 3) Another method which I am thinking about working on is to use the BDL's "Connaissance des Temps". These are chebyshev series that are much faster and easier to evaluate and give the full accuracy of the VSOP87 which has thousands of terms. The down side is that the polynomials have to replaced every year. Upside, you can get them free off the net and down load them into your calculator. -- Gordon ,,, (. .) +-----------------------ooO-(_)-Ooo----------------------+ | Gordon Talge WB6YKK e-mail: gtalge{at}pe.net | | Department of Mathematics QTH: Loma Linda, CA | | Aquinas High School Lat. N 34� 03.1' | | San Bernardino, CA 92404 Long. W 117� 15.2' | | http://www.AquinasHS.net | +--------------------------------------------------------+