A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Ron Jones
Date: 2017 Sep 6, 09:55 -0700
In prepration for teaching my Navigation class this fall, I thought the addition of a Sumner Line of Position worksheet to my Celestial Navigator workbook would be a good addition. (See attached)
Given an observed altitude of the Sun (Ho) and the following information:
■ Estimated DR Longitude and the Assumed Latitudes for points A, B & C
■ Date and Mean Time at Greenwich when an observation of the Sun was made
■ From the Nautical Almanac obtain Declination of the Sun, time of Sun's meridian passage at Greenwich and the Equation of Time
This worksheet provides the calculations needed to define the estimated Longitudes associated with the assumed Latitudes of points A, B & C using the method derived by Capt. Thomas H. Sumner.
Points A, B & C define a Line of Position (LOP) from which the observed altitude of the Sun (Ho) would have the same value if taken at the same instant of time from any point along the LOP.
The assumed Latitude for Point B is your DR Latitude. Points A & C representing latitudes that span your best guess for the probable error in your DR Latitude.
The Sumner LOP from Ediz Hook PDF shows the results from a sight taken @ Ediz Hook last year.
For additional information see "Finding A Ship's Position At Sea" by Capt. Thomas H. Sumner 1843