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: George Huxtable
Date: 2009 Sep 25, 21:23 +0100
From: George Huxtable
Date: 2009 Sep 25, 21:23 +0100
Throughout his posting [9923], Douglas Denny appears to presume that Meridian Passage of the Sun occurs at the same moment as the maximum altitude of the Sun, at the peak of the curve of altitude with time. But it doesn't, except at the solstices, because of the Sun's changing declination. On the 29th April, the Sun's declination is increasing (Northward) by about 0.8 arc-minutes per hour. By a bit of rough guesswork, that's enough to delay the moment of peak altitude, to be somewhere between 1 and 2 minutes later than Meridian Passage. Which will throw out his assessments by that amount. To set up a precise North-South line, it's a factor that must be allowed for. For star observations, there's no such problem, as the declination stays constant. George. contact George Huxtable, at george@hux.me.uk or at +44 1865 820222 (from UK, 01865 820222) or at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK. --~--~---------~--~----~------------~-------~--~----~ NavList message boards: www.fer3.com/arc Or post by email to: NavList@fer3.com To , email NavList-@fer3.com -~----------~----~----~----~------~----~------~--~---
