A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Murray Peake
Date: 2017 Nov 19, 02:28 -0800
This is the result of my effort to reproduce the star altitude charts published around 1940 for epoch Jan 1 1945. The star positions are adjusted for precession, nutation and proper motion using the NOVAS library and the plotted on a Mercator projection by plotting against a grid of meridional parts relabelled to latitude. Setting up for another latitude band requires recalculation of the number of minutes of Local Sidereal Time consistent with the difference in meridional parts for the difference in latitude.
I reworked the example in The Observer's Book on Astro-Navigation by Francis Chichester (part 3) 1941, George Allen and Unwin, London and got a result of 59 00 N, 10 14 W compared with 59 03 N , 10 17 W in Chichester. Even with limited accuracy, a fix in 2 minutes time without almanac is a good result I think.
The example doesn't allow for refraction - I read that Weems allowed for refraction at sea-level which seems odd for a method essentially only useful above cloud levels.