NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Out of Date Almanac
From: Hewitt Schlereth
Date: 2009 Dec 8, 19:31 -0400
From: Hewitt Schlereth
Date: 2009 Dec 8, 19:31 -0400
I'm afraid I didn't understand the graph. But this subject has long
interested me and I got curious. So, I went to the Bowditch long-term
almanac, base year 1972 - a leap year. Comparing 0000 UT March 22,
1972, to 0000 UT March 22, 2008 I came up with:
Sun Dec 3-22-1972
0� 35.2' N
Corr for 36 years (9 4-year cycles) 9 X +0.53' + 4.8'
Dec 3-22-2008 by Bowditch
0� 40.0' N
Dec 3-22-2008 by Nautical Almanac
0� 41.6' N
Looking at the NA for 3-22-1996
0� 39.4' N
The difference between the 2008 NA and Bowditch is 1.6'. Between 1996
and 2008 NA' is 2.2'. In this instance at least, you'd do better with
the 36-year-old Bowditch than the 12-year-old Nautical Almanac, unless
you corrected the '96 NA..
Using the '72 Bowditch +0.53' on the '96 NA for 3 cycles 0� 41.0' N
Geoffrey Kolbe's +0.69' for two cycles on his base of 40.1': 0� 41.4' N
Net of everything, Kolbe looks very good.
Hewitt
On 12/8/09, Apache Runner wrote:
>
>
> I did the exercise of the simplest thing - solar declination by using a
> sinusoidal approximation. I then looked up two years of declination data
> and plotted the deviation from that - you can get down to perhaps a tenth or
> a couple of tenths of a degree by a mnemonic memorization on top of the
> sinusoidal approx. Definitely one of those life-rafty things.
>
> Attached is a quick description and a couple of plots.
>
>
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