A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Robin Stuart
Date: 2022 Feb 7, 14:56 -0800
There have been some significant developments since our paper on the Endurance's location was published. We were contacted by David Mearns of Blue Water Recoveries Limited in the UK who pointed out that expedition physicist Reginald James had worked with A.D. Crommelin of the Greenwich Observatory to correct the lunar positions given in the Nautical Almanac (NA) using observational data. The point here is that the accuracy to which positions were quoted in the NA does not reflect the accuracy to which they could actually be computed. The Moon's NA position was used in the reduction of occultations that the expedition used to rate their chronometers and hence find longitude while trapped in the Weddell Sea ice during the southern winter of 1915.
The conclusion was that the chronometers were running roughly 20 seconds faster than originally determined which pushes longitudes to the east. We reanalyzed the occultation timings using modern models of the the Moon's motion and accurate star positions from the Hipparcos catalog. Although we find agreement with the general size of Crommelin's adjustments, our results produce a better detailed fit to the observations and give a larger value for the chronometer rate (CR). This obviously has implications for the location of the wreck of Endurance. Previously it had been concluded that Worsley appeared to show a tendency to underestimate how slow his working chronometer was running. This would push the true positions to the west of those given in the log. This new adjustment works in the opposite direction with the net effect that it now seems most likely the wreck lies to the east.
Of course there are always uncertainties and assumptions need to be made. In the attached paper we examine a number of possible scenarios and give the conclusions from each. We provide sufficiently detailed numerical data that alternative scenarios can be studied by anyone who wishes to do so.