A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Frank Reed
Date: 2019 Mar 24, 06:05 -0700
Dave, you wrote:
"Might that be because the Sun’s not a point source? How long does it take to push 32' of Sun across the Equator? 50 seconds??"
No, it's not that... It's a definitional issue: what exactly is meant by the equinox?
As for time to move the whole solar disk across the equator, that's just about 32 hours. It's useful to remember that the north/south speed of the Sun for some weeks around the equinoxes is very close to one knot.
Today, while I am teaching celestial navigation at Mystic Seaport in Connecticut, and we're shooting the Sun at noon from a nearby shore point, the subSun point (Sun's GP) where the Sun is at the zenith will be passing just north of the small town of Miraflores deep in the southern tropical forest of Colombia. It's an "island" in the middle of nowhere, and it's a place with a unique problem: an economy built on poltical revolution, private militia taxation (a.k.a, extortion and protection), and huge quantities of coca base. Its rough-built airport is served by a Colombian airline... which flies DC-3s even today.
Tomorrow, the subSun point will pass about 24 nautical miles north from Miraflores...