Next message: George Huxtable: "Re: Bubble Horizon Altitude Corrections"
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
