# NavList:

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

**Re: Emergency sun declination**

**From:**Fred Hebard

**Date:**2004 May 21, 17:09 -0400

Ahha, A graphical method of computing the sine of a function. Sine is opposite over the hypotenuse. #3 =opposite, #4=hypotenuse. Then dec = 22.5*sine(days past vernal equanox), etc for other seasons. Fred On May 20, 2004, at 4:48 PM, Royer, Doug wrote: > What Jim has shown in his emergency dec. post has been taught in > lifeboat or > emergency navigation courses for sometime.It is accurate enough for > use in > these circumstances to warrant knowing how to accomplish it.It is a > straight > forward procedure.But you must have a rose or universal plotting > sheet.This > is something most likely to be had in a lifeboat or ditchbag. > Between each cardinal point there will lay roughly 90 days/points.Try > to > evenly section off in 1/3rds or less groups of days.Within the > sectioned off > group for the date in question guestimate the location for that date's > point > on the arc. > 1.Take a parrallel rule and from the horizontal axis,makeing sure it > stays > parrallel with that axis,move the rule up to the date's point on the > arc. > 2.Draw a line from that point to the vertical axis. > 3.Measure the distance from the line thus drawn to the point where the > vertical and horizontal axis's meet in the center of the rose. > 4.Measure the distance from the center of the rose to the edge of the > arc. > 5.Divide the "date measurement"(#3) by the total radius > measurement(#4)to > get the ratio of the two. > 6.Multiply that ratio by 22.50*(degree) > This will give you a working dec. of the sun enough to reduce a sight > or > series to establish some deceant idea of where you are in an emergency > situation. > Ken's meathod appears to be along the same lines,though I've never > seen it > before. > Hope this answered your question. > > > > > > > Thanks for taking the first stab Ken. I too am not sure that I > understand > what Jim but was ashamed to admit it. > > Jim, do you have a diagram to illustrate your method? > > Ken, I am going to take a stab at yours. Sounds interesting. > > Robert > >> >>> 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. >>> >>> >> I am not sure I understand what Jim is saying, but here is what I have > been >> preaching for many years. I would very much appreciate someone >> telling me >> if I am wrong, and if so, how much wrong! >> I tell people to take a piece of paper and draw horizontal lines, each >> separated by an equal amount. Label them +30, +20,+10,0,-10,-20,-30. > Draw >> a circle centered on the 0 line so that the top of the circle is on >> 23.5, >> and the bottom is on -23.5. Label the cardinal points June 21, Sept >> 23, > Dec >> 22, and March 21. Then I tell them to fill in the dates around the >> circle >> (easier said than done), and read the declination directly. >> >> I am guessing that if the Earth were in a circular orbit around the >> sun >> instead of elliptical, then my analogue would be OK. Does the >> ellipticity > of >> the orbit make this wrong? >> >> Ken Gebhart >> >> >