NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Time of meridian passage accuracy
From: Antoine Cou�tte
Date: 2009 Sep 26, 00:14 -0700
From: Antoine Cou�tte
Date: 2009 Sep 26, 00:14 -0700
COMPLEMENT TO POST 9938 ... last part of my post # 9938 has partially disappeared, must be an error from my side ! Here it is, as it gives better view of the full picture : What are the practical implications on position accuracy if and when Meridian transit time not equal to Culmination time ? If the vessel has a significant north/south speed component, such as in the extreme case listed here-above, then : Body declination may have changed by up to 1/15 arc minute during that time period, so it is (almost) negligible for conventional Celnav, and Vessel's latitude will have changed by 0.2 ' during that time period. You may start wanting to take it in account. The story does not end here however ! BUT ... IF you decide to derive ship's longitude from the time of meridian transit (deduced from observation of the culmination time), THEN a 25 second difference between both events (Transit time and Culmination time) has definitive practical implications on your longitude position. You SHOULD take this effect in consideration since in 25 seconds of elapsed time, the Body will have travelled some 6 arcminutes on a meridian. Therefore if you make the assumption that Transit Time equals culmination time, then in extreme cases, you might get a Observed Longitude in error by up to 6 arc minutes. Best Regards to all, Antoine Antoine M."Kermit" Couette --~--~---------~--~----~------------~-------~--~----~ NavList message boards: www.fer3.com/arc Or post by email to: NavList@fer3.com To , email NavList-@fer3.com -~----------~----~----~----~------~----~------~--~---
