A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Robin Stuart
Date: 2021 Jun 29, 07:19 -0700
Regarding my measurement of the zenith-ε Scorpii-Antares angle you commented: "Interesting choice".
Ideally a camera produces a gnomonic projection of the sky. As it is not conformal I'm not really entitled to measure angles in this way but hoped that by choosing a vertex near the center line of the image symmetry might prevent things from getting too far out of whack. ε Scorpii is the first star in the tail of section of the scorpion and a line drawn between it and Antares is a reasonable indicator for the overall orientation.
You also pointed out "if we knew that the sky in the image had been aligned with the correct altitude and also aligned with the apparent horizon parallel to the true horizon. It's distinct from the original question."
There are wisps of terrestrial clouds visible at lower right showing that the image is correctly oriented and, I think, that the altitudes are not way off. Also there's a lot of sky in this image. Some of it has to be low!