A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Richard Toohey
Date: 2021 Feb 16, 06:51 -0500
David - I sent my proof a bit ago, but damn, yours is about 10 times simpler! Love it!
Except I was too slick. You have to consider direction of bending. A better argument is:
Letting clockwise be positive, starlight is bent (180-2v) - (180-2u) = Minus Theta, so Theta = 2(v-u)
For triangle ABC, (90-v) + (90+u) + Phi = 180, or Phi = v-u, so Theta = 2 Phi. Got there in the end. Sorry. DaveP