NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: David Pike
Date: 2020 Dec 26, 11:03 -0800
Frank reed you wrote: That's the key to this. If we're using the standard definition of sunrise and sunset, the Sun has to cross an extra 50' of altitude below the horizon. How long does that take? This is a small enough angle that we can use the instantaneous derivative, which happens to be quite simple:
dh/dT = 15ʹ × cos(Lat) × sin(Azm),
I had a feeling I’d been required to study this from a different angle in the 60s and 70s when learning about the Air Almanac. That document showed the results graphically. Indeed, they’re still there on page A153 of the current almanac Air Almanac 2021 — Naval Oceanography Portal (navy.mil) although it has to be said the diagrams are now getting a bit fuzzy at differentiating hours from minutes. DaveP
