A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Greg Rudzinski
Date: 2014 Sep 19, 07:21 -0700
To approximate the length of nautical and civil twilight solve for the time difference between a precalculated Hc 12° / Hc 6°/ Hc 0° for your given latitude and declination. The Nautical Almanac takes into account refraction and semidiameter so numbers won't quite match when comparing.