A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Frank Reed
Date: 2016 Sep 1, 10:24 -0700
Tony Oz, you asked:
"how do you deal with leap years (on the calendar scale)?"
Finally, you asked:
"how do you obtain UTC from it (if you do)?"
This is impossible. There is no way to get UT from a nocturnal unless you know your longitude already (and therefore probably already know UT). The most significant use of sidereal time in modern navigation is for a Polaris correction. Sidereal time tells us the orientation of the celestial sphere relative to the observer, which lets us know where Polaris on its little circumpolar circle around the true north celestial pole. The radius of the circle is currently 40 minutes of arc, so if we ignore this correction a latitude by Polaris is rather poor. But using a nocturnal, or using a simple calculation for GHA Aries (a synonym for sidereal time, but in angular units rather than hourly units) such as is found in air almanacs and H.O. 249 etc., we can reduce that error in practice to just one or two minutes of arc.
Conanicut Island USA