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    Re: The Online Nautical Almanac- beware!
    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
    
    
    

       
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