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Re: The Online Nautical Almanac- beware!
From: Ken Muldrew
Date: 2004 Jul 5, 10:21 -0600
From: Ken Muldrew
Date: 2004 Jul 5, 10:21 -0600
On 4 Jul 2004 at 21:36, George Huxtable wrote: > I know that Ken Muldrew has been investigating David Thompson and other > travellers in Canada around this period, and one of his postings > specifically refers to data from the Online Nautical Almanac for October > 1800. This is close in time to the moment when the Almanac goes haywire so > Ken needs to take care that none of the data he uses (or has used) relates > to that period before 28 Feb 1800. Thanks for the warning, George. I haven't had time to pursue any further investigation of the fur trader's navigation in recent weeks but I do intend to follow it up soon. Bruce Stark was kind enough to send me photocopies of the nautical almanac for the period that I was looking at so I will be able to use the same data that Thompson used when I get back to some analysis. I briefly compared the values that Thompson recorded with the values from the almanac and they all agreed except for the moon. To interpolate the values for the moon's motion I used the polynomial given in the 1804 almanac that is online at the Mystic Seaport site, but my interpolation differed from what Thompson wrote down by about a minute in right ascension and about 3 minutes in declination. Perhaps the coefficients printed in the 1800 almanac were slightly different or maybe I made a mistake in following the instructions given in the almanac. Of course these values are only used to calculate altitudes and therefore aren't critical in the lunar distance calculation, but I wanted to recapitulate Thompson's data so that I could be confident in the rest of the calculation. Ken Muldrew