A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Gary LaPook
Date: 2011 Jan 23, 16:41 -0800
|Just looking at the equation of time issue. |
The NA gives it to the second. It is added or subtracted to 12:00 to find the time of Local Apparent Noon. So you do not add it to the time of meridian passage as it has already been added to 12:00 to derive the time of meridian passage. The NA gives the time of meridian passage at the Greenwich Meridian rounded to the whole minute only but the actual time of passage of the Greenwich Meridian was actually 12:11:29 on January 22nd.
Since this is the time of noon LAT (local apparent time), the time that the sun crosses the meridian that you are actually on, you must account for the difference between your meridian and the standard meridian for your time zone to determine the zone time of noon at you meridian, LAN. The standard meridian for your time zone is 75° west so your meridian is actually 1° 21.7' further west so it takes 5 minutes and 26 seconds for the sun to move from the standard meridian to your meridian so your noon will be 5 minutes and 26 seconds later on your watch so your noon would have been 12:16:56 EST, 17:16:29 Z. But the equation of time keeps changing and it is 11 minutes 45 seconds on January 23 so you must interpolate between the two dates. The equation of time of time increased 16 seconds in 24 hours so it increased about 3 seconds in the period between noon at Greenwich and noon at you location so your noon occurred at 17:16:32 Z.
--- On Sun, 1/23/11, Frank Reed <FrankReed@HistoricalAtlas.com> wrote: