A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Robin Stuart
Date: 2018 Jan 23, 06:42 -0800
Commercial Gnomonic charts provide 2 graphical methods of determining great circle distances. At the bottom of this chart you can see Charles Lindbergh’s original construction doing just that. They also provide a nomogram (Lindbergh’s lines visible on chart) and table for determining initial great circle courses. How the nomogram works was discussed in the thread starting here and explained in detail here.
My previous post contained a typo in the second equation and should have read
Starting at a latitude, longitude L0, λ0 and traveling a distance D(°) on a course C° measured East from North the necessary formulas are:
sin L = sin L0 cos D + cos L0 sin D cos C
sin ( λ - λ0 ) = sin D sin C / cos L