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    Re: Lunar Distances with Alex's SNO-T
    From: Frank Reed CT
    Date: 2006 Nov 5, 19:22 EST
    You wrote:
    "I have seen "adjustments" to NA values of up to 0.1 min to minimize
    maximum error when using the given interpolation tables, but where
    might the 0.3 min differences that Frank mentions be?"
     
    Just as one example, there's the Sun altitude corrections. One column covers October to March, the other covers April to September. Because of this organization, there is an artificial jump in the altitude correction of 0.3 minutes of arc going from March 31st to April 1st and September 30th to October 1st. This is no problem for standard line of position navigation.
     
    Also, according to section 24, "Main data" in the Explanation in the Nautical Almanac, "the largest error that can occur in the GHA or Dec of any body other than the Sun or Moon is less than 0.2'; it may reach 0.25' for the GHA of the Sun and 0.3' for that of the Moon." I don't know why that is, but I'll take their word for it. This is why you can't really trust the almanac data 100% of the time when doing lunars (I should add that most of the time, the accuracy is good enough). But no problem-- anything tabulated in the Nautical Almanac can be calculated at higher accuracy from scratch.
    -FER
    42.0N 87.7W, or 41.4N 72.1W.
    www.HistoricalAtlas.com/lunars

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