NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: The Nautical Mile and the arc minute
From: Henry Halboth
Date: 2015 Jun 6, 13:44 -0400
From: Henry Halboth
Date: 2015 Jun 6, 13:44 -0400
Francis,
You are correct in that, except when observing a body on the prime vertical, an accurate Latitude is required to obtain a true Longitude by one observation utilizing the Time Sight However, the Time Sight can and was adapted to LOP navigation with results generally equivalent to the Marc St.Hilaire method, whether by the tangent or chord determination. As Capt. Sumner demonstrated, apparently by accident, regardless of the Latitude employed it, in combination with the Longitude calculated, constitutes a point on the LOP of the observer. Therefore, by plotting a line at right angles to the azimuth, the tangent method, or by recalculating another Longitude by use of a different Latitude (as Sumner did) and connecting the two positions, the chord method, a LOP is established identical to that provided by the St. Hilaire method. The argument used to be whether the chord or tangent methods provided the greater accuracy - but lets leave that for further discussion.
Henry
On Fri, Jun 5, 2015 at 5:51 PM, Francis Upchurch <NoReply_Upchurch@fer3.com> wrote:
Thanks Frank,
Wonderful exposition of what we are all about.
re the issue of old time (e.g.time sights) versus Sumner/St. Hilaire ,am I correct in thinking that you need accurate latitude to get good longitude by the old methods and that is not the case for the new methods, and hence their appartent superiority? Correct me if I have this wrong.
Francis
