NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Alexandre Eremenko
Date: 2019 May 22, 13:30 -0700
Frank, You wrote:
Take any pair of stars with both altitudes above 45°. Refraction compresses the angular distance between them. The correction is beautifully simple: it's one part in 3000, which is equivalent to 0.1' per 5° of angular separation, and this works for all distances, no matter their relative altitudes, no matter how they are oriented, and no worries about temperature and pressure. Atmospheric refraction decreases the apparent angles between the stars. The corrected angles are slightly larger than what we observe. This is an approximation, and the result can be wrong by as much as 0.1' but it's fast and easy and really that's an excellent approximation for our needs.
Your rule works.
A justification is attached.
Alex.
[NOTE from FER: Alex originally sent two messages. One ended up in the spam folder due to an archaic non-UTF8-compliant email product on his end. That was probably a good thing. I have combined the content of the two messages into one. Hope that works for you, Alex.]
