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    Re: Bowditch long term almanac
    From: Hewitt Schlereth
    Date: 2012 May 19, 14:22 -0700

    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.  :-)
    Sent from my iPad
    On May 19, 2012, at 12:15 AM, Geoffrey Kolbe  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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