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: Douglas Denny
Date: 2009 Sep 25, 23:51 -0700
From: Douglas Denny
Date: 2009 Sep 25, 23:51 -0700
I do not believe I have missed the point. I believe you have. I am aware of the changing declination of the Sun - it is changing constantly, hence a meridian passage curve such as the one I gave is actually skewed - in theory. The question is: to what extent? Answer - very small as to be of no practical concern to practical navigators. The change in declination per DAY, as you say is only 0.8 minutes of arc - which applied as an altitude correction it is negligable in practical navigation. The differences between actual (appareent) max Altitude and true Mer passage of the Sun are so small as to be negligable if max altitude is calculated near to the apparent Mer Passage... and if not so, why does the Nautical Almanac persist in publishing the Sun's Mer Passage each day so navigators can use Max altitude? There is a vast difference between practical navigation and theoretical astronomy. That is the point which you have academically and pedantically missed. Douglas Denny. Chichester. England. Douglas Denny has missed the point. The nearness of his observation point to Greenwich has nothing to do with it. The time correction, due to changing declination, as the same the whole world over, at the same latitude and time-of-year.. His calculated time of Meridian Passage may well be correct. But he isn't observing Meridian Passage, when the Sun is due South. He is observing maximum altitude, the peak of the curve, which is subtly different. George. --~--~---------~--~----~------------~-------~--~----~ NavList message boards: www.fer3.com/arc Or post by email to: NavList@fer3.com To , email NavList-@fer3.com -~----------~----~----~----~------~----~------~--~---