NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: AP terminology, WAS: 2-Body Fix -- take three
From: John Karl
Date: 2009 Nov 13, 12:33 -0800
From: John Karl
Date: 2009 Nov 13, 12:33 -0800
No one has addressed my question of why the St Hilaire method calculates an altitude at a location our ship is NOT at, when we've just measured the altitude where our ship IS at. (For politically correct reasons, I'm not using the name of this location.) Now lets go back to Sumner's 1837 calculation, where he picked three different longitudes and calculated three points on the circular LOP. This calculation is exact, and the equation for each point is the same as the one of the two necessary in the St Hilaire method (thus each Sumner point is half the work of a St Hilaire reduction). And he could calculate as many exact points as he wished. So I'll put my question yet another way: Why is the St Hilaire method superior to Sumner's and consequently the only one used today?? I claim that the answer to this question has been made confusing because of the conventional name (names?) used for the location of the St Hilaire altitude calculation. As evidence of this confusion I note that some authors write that we need to assume some point because the distance between the GP and the LOP is too great to plot, that there's insufficient information to plot the LOP, or that iterations are required to get exact points on the LOP. The Sumner calculation demonstrates that none of this is correct. JK --~--~---------~--~----~------------~-------~--~----~ NavList message boards: www.fer3.com/arc Or post by email to: NavList@fer3.com To , email NavList+@fer3.com -~----------~----~----~----~------~----~------~--~---