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    Re: lunar distance analysis.
    From: Frank Reed CT
    Date: 2006 Dec 29, 20:51 -0800

    Hi George, you wrote:
    "Nevertheless, his observation arrived at a cleared lunar distance that
    
    differed by 1.8' from the predicted value. What surprised my was that
    the lunar calculator then deduced a longitude error of 52.6', roughly
    30 times greater; just the sort of number one would expect if the
    skew-angle of the observation had been small.
    So I wondered whether a skew-angle between the sight direction and the
    Moon's travel is taken into account at all, when assessing longitude
    error. "
    
    No. It's come up before on the list, and a few minutes of
    experimentation would verify the fact. That "longitude error" is
    strictly 30x the error in the observed distance, and that's all it is.
    It's just letting the user know the approximate longitude error (within
    10% in most cases). Most people who shoot lunars today want to know one
    number first and foremost: how far off was my observation? That's the
    1.8 arcminute error in the observation you described. This, by the way,
    is pretty darn awful, but with instruments that are either not
    well-adjusted or simply have significant arc error, it's not uncommon.
    
    I have considered various enhancements for those tools on my web site,
    including an exact longitude error, but every time I look at the work
    involved, I end up shelving the project. There is very little interest
    today in "nautical astronomy" or "traditional marine navigation"
    (celestial navigation is already losing its meaning as a phrase), let
    alone navigation by lunar distances. It's only a small exaggeration to
    say that it's "just us".
    
    -FER
    www.HistoricalAtlas.com/lunars
    (please try not to store or reference the underlying address with
    "clockwk.com"! That one may disappear any day which is why I always
    include the "historicalatlas.com" reference in my signature)
    
    
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