A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Homer Smith
Date: 2022 Sep 21, 12:06 -0700
I'm a long-time lurker, first-time poster on NavList. I have several questions stemming from when I looked up the time of the upcoming equinox (I see 01:03 UT and 01:04 UT) and noticed that it was close to the time (19:24 MDT) of sunset at my location (W111.811degrees). I figured that if I moved to a more easterly longitude I could find a meridian where the 2 events occured simultaneously, but what west longitude would that be? My limited knowledge base only allowed me to determine that it would be 5 degrees east of me (20 minutes = 5 degrees). I have a friend that helped me with the finer points of the determination (i.e. taking EOT into consideration), but I am interested in how others would approach this problem. Where would the longitude of simultaneity be on the fall equinox 4 years from now?
For the time of the equinox, I got 01:06 UT by interpolating for 0 degrees N/S lat between 01:00 and 02:00 in the NA and 01:02:42 by interpolating to find when GHA Aries and GHA Sun differed by 180 degrees (also from NA).
Another question : Why is the time of the equinox only given to the nearest whole minute. It must be known more precisely than that. How is the time of the equinox officially determined?