NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Emergency sun declination
From: Doug Royer
Date: 2004 May 21, 16:18 -0700
From: Doug Royer
Date: 2004 May 21, 16:18 -0700
You betcha.It's 23.5* though as Frank pointed out. Here's what I got in a few minutes useing a rose and the "graphic" method: The date's(05-21)number of inches on the vertical axis = 3.3 in. The vertical radius length = 3.81 in. 3.3/3.81 = 0.86614 23.50 x 0.86614 = 20.3543* = 20* 21.3' dec. = 20* 21.3'N 05-21-04 1601zt sun dec = 20*24.1'N Not to bad for 3 minutes from start to finish.That includes marking the rose.Good enough for an emergency. Let's try the below: 61 days since the equinox. 05-21 - 03-20 sin(61) = 0.8746 23.5 x 0.8746 = 20.5531 = 20* 33.2' dec = 20* 33.2'N In the ballpark. Good enough to use if one had no idea otherwise. 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 > 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)