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    Re: Bowditch long term almanac
    From: Gary LaPook
    Date: 2012 May 19, 18:15 -0700
    And you can also use the shorter "long term almanac" from H.O. 249 covering 1981 to 2016 for the sun and 2006 to 2014 for Aries and for the stars by use of the P&N table which is available here
    https://sites.google.com/site/fredienoonan/other-flight-navigation-information/self-contained-long-term-celestial-navigation-system

    gl

    --- On Sat, 5/19/12, Hewitt <hhew36---.com> wrote:

    From: Hewitt <hhew36---.com>
    Subject: [NavList] Re: Bowditch long term almanac
    To: "NavList@fer3.com" <NavList@fer3.com>
    Date: Saturday, May 19, 2012, 2:22 PM

    Geoffrey -

    This is interesting.

    I used the 1972 Bowditch 4-year sun corrections for a long-term almanac I made based on the cycle 1976, 1977, 1978, 1979. Because I wanted to have the data by the hour, I simply sliced out the sun columns from the Nautical Almanac, pasted them on paper and they were photographically reproduced for Latitude & Longitude by The Noon Sight, and Celestial Navigation by Sun lines. The 1972 Bowditch GHA and Declination corrections were printed on the page following the four tables.

    I'd have to dig my copies out of storage, but my recollection is that Bowditch differed from you mainly around the equinoxes. My recollection is that the largest Bowditch correction was 0.75' in 4 years for Declination. Whereas yours are about half that. Which means Bowditch's max deviation would be 3.75' in 40 years. In the context of small-boat navigation, I'd say the minuscule 1772 Bowditch table would still be useful. I had it tucked in plain sight in the certificate window of my old Plath. When 'Abandon Ship' was called, my sextant was sure as hell going into the liferaft with me.  :-)

    Hewitt

    Sent from my iPad

    On May 19, 2012, at 12:15 AM, Geoffrey Kolbe <geoffreykolbe---.com> wrote:

    > There does seem to be a considerable difference between the 1956 epoch LTA and the 1972 epoch LTA as given in Bowditch, so it would seem that the corrections were not transplanted wholesale as I suggested.
    >
    > That still leaves the problem as to why the given 1972 epoch quadrennial corrections are so poor. I tried to determine the period of validity - or at least the period over which the corrections would have been calculated, but I could not. It was at that point that I gave up and created my own.
    >
    >
    >> oops, just came to think of a tiny problem, as all parts of the 4 year sun cycle use same correction in this almanac, I guess it would have to use some kind of middle ground for the correction to gha and declination, what would you sugest?, median? average? use correction for middle of cycle?
    >
    > I am not sure what you are saying here. Perhaps you could restate it?
    >
    > Too, I am afraid the accents in your name mean that your name is reproduced as gibberish on my computer. I would be grateful for an un-accented version of your name so I can address you personally.
    >
    > Geoffrey Kolbe
    >
    >
    >
    >
    >
    >




       
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