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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.
>
>
>  --
>  NavList message boards: www.navlist.net
>  Or post by email to: NavList@navlist.net
>  To , email NavList+@navlist.net
>

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