NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Frank Reed
Date: 2026 Mar 31, 15:55 -0700
Roger E., you wrote:
"for us mere mortasls and neophytes on this journey, could you please detail how two altitudes guarantee a latitude."
I shoot an altitude of one star, let's say Sirius, and record the exact GMT/UT. Then I turn and shoot an altitude of another star, let's say Procyon, and record the exact GMT/UT. That's two sights of known objects so of course I get a fix, right? It's just two standard circles of position. Yes, there's some momentary ambiguity since two circles cross in two places, but that's not a real problem in practice, right?
So now suppose you remove on detail above. I don't have the exact GMT/UT, and more than that I don't even know the date. So now what? We still have exactly the same fix, but the longitude is indeterminate! Latitude? No problem. How do you find that latitude?? Many ways, but the easiest is just to feed in any old arbitrary date and GMT. Get your fix. Toss the longitude.
See? Easy.
Frank Reed
