A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: David C
Date: 2020 Jan 26, 22:33 -0800
The following is rough and ready so it may containe errors......
I took a sight when the sun was approximately due west using an AH. The purpose was to obtain long (to within a degree or two) for an assumed position.
From which IE = 4.5' on and sun's SD =16.8'
Observation was 0456 26/1/2020 H = 60° 40'
Less IE = 60° 35.5'
H/2 = 30° 18'
Less SD and refraction 30° - 16 - 1 = 30° 01'
From Inmans (1932) the dec is 19°S.
Also from Inmans te EOT = -12 min = 3°
Approx GHA is 5 X 15 + 180° - EOT = 75° + 180° - 3° =252° (check: 252° from almanac)
cos Z = sin t cos d sec h where Z is the azimuth angle. Because the sun is approximately due west I will use Z=90.
Hence sin t = cos (30) / cos(19)
and t = 66°
long E = t - GHA = 186°
Hence my assumed long should be in the range 184° (from previous noon method) to 186°. A round number of degrees will make use of 214 or 229 easier.
Lokking at the globe the longitude line passes through the land mass of the South islad of New Zealand. I will select 43°S as the assumed AP. Thus from not knowing where in the world I was, apart from being on terra firma, not having an up to date almanac and using approximations now know that 43S 174°E is a sensible AP.
My next step will be to work a sight by the intercept method. I will then probably cheat and us google earth to measure the AP to GPS distance. If it equals the intercept will have succeeded.