A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: David Pike
Date: 2021 Apr 12, 00:56 -0700
Geoffrey Kolbe you wrote: David Pike said "
We're of to ///backyards.calculates.dates or thereabouts shortly where there’s little light pollution but no signal, so just a quick reply before going ex-communicado. My answer was to the original question as I read it, i.e. would the Sun’s relative bearing remain constant.
A Sun compass is a fine navigational aid in areas of low horizontal magnetism or uncertain variation, or as a compass check at any time. We flicked the azimuth ring lock from ‘azimuth’ to ‘heading’ at mid-time to get a heading check every time we took an astro observation. In the Varsity, we set up the astro compass in the astrodome to take occasional checks, but it’s horses for courses. I don’t think using a Sun compass is the best solution for the situation in the question even if you'd made a little azimuth table before beforehand and could guarantee Sun on the compass at all times.
As for time between one degree tweaks, please check my calculation that time between tweaks = 60/(15-(Vgcos(trk-270)/coslat))minutes where Vg = groundspeed. As an occasional heading check, we simply took the ten minute GHA Sun from the Air Almanac; subtracted longitude west; and made sure we took the check on the ten minute time. DaveP