| Title: | SAILING |
| Notice: | Please read Note 2.* before participating in this conference |
| Moderator: | UNIFIX::BERENS |
| Created: | Wed Jul 01 1992 |
| Last Modified: | Mon Jun 02 1997 |
| Last Successful Update: | Fri Jun 06 1997 |
| Number of topics: | 2299 |
| Total number of notes: | 20724 |
I'm in the process of developing a 'Celestial Navigation' application for the Apple Macintosh (and maybe ported to the VAX). The application (so far) is equation driven (vs. table driven). As a first pass, I approximated the equations for the sun's declination and equation of time. I thought that these would be the easiest to find exact equations for later. There not! What I am looking for is the EXACT equation for the sun's declination and equation of time. I.E. d = f(calendar day, time)... Thanks, Gary H...
| T.R | Title | User | Personal Name | Date | Lines |
|---|---|---|---|---|---|
| 555.1 | only approximation possible | PULSAR::BERENS | Alan Berens | Wed May 13 1987 15:53 | 10 |
How "exact" do you want to be? The motion of the earth around the sun, which in turn determines the sun's GHA and declination, is affected by the location and mass of every physical body in the solar system. Obviously, the effect of some bodies is very small. The equations of motion are, as I recall, rather complex and require substantial computation to solve with the accuracy of the Nautical Almanac. (I saw these equations for the first and last time in a third or fourth year college physics course in classical mechanics. The equations served as an introduction to perturbation theory.) | |||||
| 555.2 | Try Bowditch | CSSE::GARDINER | Thu May 14 1987 20:43 | 10 | |
Most of the equations you would need are contained in Volume 2 of
Bowditch. For Equation of Time you would most likely have to average
the variation. The Almanac gives Equation of time for each 3 day
period. It usually varies + or - 1 second every 3 days, sometimes
more sometimes less.
Good Luck.
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| 555.3 | HERES ONE, AND A LEAD ON THE OTHER | MTBLUE::OSTERMANN_KE | Mon Jun 01 1987 17:04 | 22 | |
THE EQUATION FOR THE DECLINATION IS,
X = 23.45 * SIN(360((284+N)/365))
WHERE N IS THE DAY OF THE YEAR. THE VALUE OF X FROM THIS EQUATION
WILL BE CORRECT WITHIN +0.37 DEGREES (WITH MAX POSITIVE DEVIATION
ON MAY 1) AND -1.70 DEGREES (WITH MAX NEGIATION ON OCTOBER 9). THIS
IS FROM ENRICO COFFARI,"THE SUN AND THE CELESTIAL VAULT," ACADEMIC
PRESS, NEY YORK, 1977.
I DON'T HAVE THE EQUATION OF TIME, BUT YOU SHOULD BE ABLE TO FIND
IT IN;
L.O. LAMM,"A NEW ANALYTICAL EXPRESSION FOR THE EQUATION OF TIME,"
SOLAR ENERGY, VOL. 26, NO. 5, P.465,1981.
HOPE THIS HELPS, KO.
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