A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Sean C
Date: 2019 Jan 17, 13:53 -0800
Here are two formulae you can use to find the vertex:
cos(Latv) = cos(Lat1) ∙ sin(C)
sin(dLon) = cos(C) / sin(Latv)
"Latv" is the latitude of the vertex; "Lat1" is a latitude point along the great circle; "C" is the course you would travel along the great circle from "Lat1"; "dLon" is the difference in longitude from "Lat1" to the vertex.