A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: David Pike
Date: 2019 Mar 12, 14:56 -0700
The watch time of sunrise/sunset, at a place 90° different in latitude from your own, gives the time when the Sun is due east or west of you at your own latitude. Prime Vertical, the best time to do time sights for longitude by chronometer, and reduce and simplify the wretched mathematics involved. Brian Walton
That sounds a cunning trick Brian, but I’m not sure I follow all of it.
I can draw a diagram to show that the plane of the horizon of someone at 50N would be parallel to the plane of the prime vertical of someone at the same longitude and 40S and vice versa, but I can’t see where to go from there. Please explain further. DaveP