NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Almanac data in 1855 (British vs American)
From: Frank Reed CT
Date: 2005 May 16, 23:25 EDT
From: Frank Reed CT
Date: 2005 May 16, 23:25 EDT
George H you wrote: "It seems that the British almanac had become unduly complacent, and had just kept on churning out lunar distance predictions that were no better than those that had been supplied to Cook by Maskelyne, 90 years earlier, in spite of the advances in astronomy that had taken place in the meantime." There's a little more to it than that. The tables for the Moon were improved several times from 1767 up through 1808 or so. By that date the lunar distance tables were very good with errors typically as small as 6 to 12 seconds of arc. But after that, they stopped improving and began a slow decline. The British Nautical Almanac calculators continued to use tables (Burckhardt's, I think) prepared way back in 1808 decades later. The predictions of the tables became steadily worse (I haven't investigated yet whether this decrease in accuracy was happening linearly with time or perhaps quadratically). This must have contributed to some extent to the declining use of lunars... but perhaps it was also a result of that decline. And: "Chauvenet is emphatic, in 1868, about the importance of this matter for US Navy vessels." He's emphatic, but he was a bit of a voice in the wilderness. It would be interesting to know how many US Navy navigators ever got around to shooting lunars and reducing them via Chauvenet's method. By this date it seems that lunars had already become what they are again today --a good challenge and a test of a skilled navigator. -FER 42.0N 87.7W, or 41.4N 72.1W. www.HistoricalAtlas.com/lunars