NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Emergency sun declination
From: Henry Halboth
Date: 2004 May 22, 16:19 -0400
From: Henry Halboth
Date: 2004 May 22, 16:19 -0400
Determination of the Sun's declination lacking a conventional tabulation thereof, whether approximate or accurate, is really a rather simple matter. Basic input requires that an understanding that ....... The obliquity of the ecliptic = 23-26-30, or thereabouts The Sun's average daily motion in the ecliptic = 59'08" + is a measure of celestial longitude The ecliptic constitutes a great circle, as well as the hyp of a right spherical triangle Utilizing the foregoing, in the application of Napier's Rules, declination may be calculated by ... Sine declination = Sine 23-26-30 x Sine (59'08" x # days since equinox) The solution can be as accurate or approximate as circumstances may warrant. Accuracy will be increased as the following factors become known ...... Date + time of Sun's entry into Aries or Libra, which varies per year Date + time of Sun's entry into Gemini + Taurus + Cancer, etc. True daily motion established by other means. Estimation of a table of natural sines can be produced in a myriad of ways, whether graphic, interpolative, or otherwise, and seems unnecessary of very much explanation. Regardless, if you have planned well enough to wind up in a lifeboat dry and equipped with sextant + dividers + penciis + plotting sheets + protractor + whatever + space to work + seasickness remedy to keep your workspace clean, you most probably will have a set of navigational tables as well, and maybe even a pocket GPS. By the way, I am surprised that mention has not been made of the traverse table in conjunction with the graphical methods mentioned, as further proposed but Dutton + others. On Wed, 19 May 2004 18:37:20 -0300 Jim Thompsonwrites: > What about this method for emergency calcuation of declination? > > 1. Label a compass rose June 22 at 000o, Sept 23 at 090o, Dec 22 at > 180o and > March 21 at 270o. > 2. The radius on the vertical axis is the declination of the sun. A > horizontal line from any date around the circle intersects that > vertical > radius. > 3. Measure the length of the vertical axis from the center to the > intersection of the horizontal line, divide that length by the full > radius, > and multiply that ratio by 22.5o. > 4. Error is +/- 0.5o. > > Jim Thompson > jim2@jimthompson.net > www.jimthompson.net > Outgoing mail scanned by Norton Antivirus > ----------------------------------------- >