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A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Latitude and Longitude by "noon sight"
From: Henry Halboth
Date: 2005 Jun 9, 11:09 -0400
From: Henry Halboth
Date: 2005 Jun 9, 11:09 -0400
Most recent posts on this List have dealt with the time sight for Longitude and the meridian altitude for Latitude as separate entities, without consideration as to how they were, in practice, combined to obtain the noon position, actually a running fix, by simple calculation, and without the necessity for plotting. From a historical perspective, there are several methods for accomplishing this end, however, the following working, in my opinion, is the simplest to comprehend. 1. Observe for AM Longitude, intending time sight solution, and precalculate all elements other than Latitude. Hold completion of solution until LAN. 2. Maintain as accurate as possible DR from time of AM sight to LAN, and by traverse table or computer take out difference of Latitude + departure for course and distance made good over time period. From departure calculate difference of Longitude (DLo) over time period. 3. At LAN observe for Latitude by meridian altitude or, if necessary, reduction to meridian. Apply previously calculated difference of Latitude to obtain most correct Latitude at time of AM sight for Longitude. 4. Complete working up AM time sight, utilizing Latitude run back from LAN, and obtain AM Longitude. 5. Apply DLo to LAN, as calculated under 2 above, to AM Longitude - and, presto, position at LAN by running fix - no different than advancing LOP's over several hours. This is the way it was done by some well into the 1930's. There are other ways, including the Longitude Factor method per Bodwitch, but that given here is probably the easiest to understand. Actually it takes less time to do than to write about. Henry