# NavList:

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

**Almanac for Computers**

**From:**Gordon Talge

**Date:**1996 Aug 28, 04:09 EDT

Since I found out that the "Almanac for Computers" is no longer available from the USNO since 1991, I decided to try and duplicate some of their results. I would like a little bit of feed back on my efforts. Power Series for the Sun Dates : Sep. 1 to Oct. 1 1996 A = 16.0 W = 1 Sun Sun S.D. GHA Dec. Term 0 6301.3640 2.2319 0.2652 1 5761.4229 -6.1853 0.0012 2 0.0052 -0.0954 0.0001 3 -0.0506 0.0697 0.0000 4 -0.0067 0.0045 0.0000 5 -0.0023 -0.0063 0.0000 sums 12062.7325 -3.9809 0.2665 They way to use these series is first convert UT into decimal then t = d + 24 /UT, where d is the day of the month. Next, get x where x in between -1 and +1. ie [-1,+1] using the formula x = ( (t - W ) / A ) -1, use x as the argument to evaluate the polynomial. f(x) = a0 + a1*x + a2 * x^2 + a3 * x^3 + a4 * x^4 + a5 *x^5 . This can be better evaluated as f(x) = a0 + x*(a1+x*(a2+x*(a3+x*(a4+x*a5)))). Once the GHA, Dec. or S.D. is obtained, remove any multiples of 360 degrees and convert to degrees and mins. or in the case of the S.D. mins, round off to the nearest .1 min Example: GHA for Sept 18th 7h 28m 19s UT 7h 28m 19s = 7.471944444 hours or 7.471944444 / 24 = 0.311331019 parts of a day. Since d= 18 we have for t, t= 18.311331019 days x = (( 18.311331019 - 1 )/ 16 ) -1 or x = 0.081958189 This is what we use for the argument of the polynomial. Evaluating the GHA polynomial at 0.081958189 we get GHA = 6773.559794 . Removing multiples of 360 degrees we get 293.5597932d or ** 293d 33.6 mins ** So the GHA for Sept 18th 7h 28m 19s is 293d 33.6min By the 1996 Air Almanac I get for Sept 18th 7h 20mins 291d 28.8 min The correction for 8min 19s is 2d 4.8min so the ** GHA is 293d 33.6 min ** Using the same argument for the Dec. Series I get 1.7244 or ** N 1d 43.5 ** (Note: N is + and S is - ) The Air Almanac give N 1d 43.6 for 7h 20min and N 1d 43.4 for 7h 30min Since 28min 19sec is between 20 and 30mins and is closer to 30 but still less and the dec is going down, N 1d 43.5 seems resonable. I don't know what the Nautical Almanac says with it's d correction. I have tried to fit the polynomial to give the proper value with an error of not more then 0.1 min The series is ONLY valid for Sept 1996, NOT before and NOT after. The sums at the bottom are NOT used in calculations, they are used to check that you entered the coefficients correctly. What I did was use a programable calculator to evaluate the polynomial by loading in the coefficients into the storage registers and then running it through. The reference ephemeris used is JPL's DE200 which is the background basis for the Astronomial Almanac and Nautical Almanacs. -- Gordon ------------------------------------------------------------------------ This mail list is managed by the majordomo program. To unsubscribe from this list, send the following message to majordomo{at}XXX.XXX: unsubscribe navigation For help, send the following message to majordomo{at}XXX.XXX: help Do NOT send administrative requests to navigation{at}XXX.XXX -ben ------------------------------------------------------------------------