A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Frank Reed
Date: 2017 Dec 19, 14:13 -0800
"The results were as shown in the photos below. The n-s error was 0.5nm and the e-w error was 1.4nm. "
Very nice! Did you try, or have you heard of, my trick for getting the exact time for the central line? Plot your sights on thin graph paper or even a transparency and then fold it in half, loosely at first. Hold it up to a light. The sights before noon and the sight after should overlap as narrowly as possible on one half-parabola. You slide the folded paper back and forth until they line up and then you make a hard fold. The crease now represents the axis of symmetry. Unfold and you can then read off the GMT. This is the best way I have found to do this manually --without a least squares fit in a spreadsheet or similar app, that is. Note: at sea almost always, and on land when not near the solstices (not a worry at this time of year), you have to correct this symmetry axis time for relative motion between the observer and the Sun. This is easy: either a simple table or a short calculation. But if we neglect this it can throw off the longitude by many miles.