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    Precision of lunars
    From: Alexandre Eremenko
    Date: 2007 Apr 15, 09:59 -0700

    What  accuracy can be really achieved with  the lunar method?
    This question was discussed several times, and now I want
    to contribute some data. Let me first cite a great authority,
    Lord Kelvin, then I will post some of my recent observations.
    
    Lord Kelvin says:
    "...to observe the moon's position accurately
    to half a minute of angle.
    This can be done, but this is about the most
    that can be done in the way of accuracy at sea."
    
    And then:
    "If he has extraordinary skill, and has bestowed an extraordinary
    care on his instrument, he may, by repeated observations,
    attain an accuracy equivalent to the determination
    of a single linar distance within a quarter of a minute of
    an angle, and so may find the ships place within seven miles
    of east and west distance; but, practically we cannot expect that the
    ships place
    will be found within less than twenty miles, by the method od Lunars
    in tropical seas
    or within ten miles in latitude 60d;
    and to be able to do even so much as this
    is an accomplishment which not even a good modern navigator,
    now that the habit of taking lunars is so much lost by the use of
    chronometers,
    can be expected to possess.
    
    (Sir William Thomson
    Popular lectures and addresses,
    London, McMillan 1891, vol. 3 Navigational affairs.
    Navigation 1-138 (Lecture delivered in the City Hall,
    Glasgow, Thursday, Nov 11, 1875. Pages 101-102 ).
    
    I also analysed Cook's maps and observations, comparing his Lunar
    determinations
    of the longitudes of known places (those that can be found on
    Terraserver.
    If someone is interested, I can post the results of this analysis.
    
    It is interesting to compare this with my own experience.
    After 3 years of practice, I was able to eliminate the systematic
    errors
    in my SNO-T Lunars, and now I post the data which on my opinion are
    consistent with what Kelvin says (in the next message).
    
    Alex.
    
    
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