NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Slocum's lunars
From: Steven Wepster
Date: 2003 Dec 23, 16:47 +0100
From: Steven Wepster
Date: 2003 Dec 23, 16:47 +0100
Hi all, Concerning the errors that Slocum would have discovered, let me add this. An article appeared in the 'Navigation' journal (Vol. 44 no. 1, 1997) in which the author (S.Y. van der Werff) discusses lunar distances and particularly the lunar distance observation of Joshua Slocum on june 16, 1896, shortly before his landfall on Nukahiva. He comes up with a completely different kind of error that Slocum discovered and corrected. Van der Werff notes that the Nautical Alamanc uses the astronomical date convention, i.e., a new day begins at noon, not at midnight. The layout of the lunar distance tables is such that one can not be mistaken by 12 hours, but not so the right ascension and declination tables. Van der Werff's suggestion is that Slocum accidentally took the RA/Dec values for a time 12 hours off (12 h too late, actually). Slocum's 'discovery', then, was that the tables were 12 hours off. If that was indeed the error that Slocum made, I conclude that he was _very_ unfamiliar with the time convention in the almanac. He would have had no earlier occasion to stumble over this difference of 12 hours, or at least no such occasion had occured in the voyage with 'Spray' and for quite some time before. It would imply that usually he took from the almanac only data that were forgiving of such an error: declinations, but no right ascensions. I would conclude that, on the large, Slocum's only means of astronomical navigation was by meridian altitudes. Does this appear as a likely scenario to list members? Steven. PS I will be away until after christmas. ----------------------------------------------------------- Steven Wepster wepster@math.uu.nl tel +31 30 253 1531 Mathematisch Instituut +31 61 251 4380 Universiteit Utrecht PO Box 80.010 3508 TA Utrecht The Netherlands ===========================================================