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    Re: Latitude by Lunar Distance
    From: Alexandre Eremenko
    Date: 2006 Oct 5, 11:29 -0400

    
    This method is essentially based on the Moon parallax.
    (Imagine that the Earth is very small. Then the
    method will not work: all lunar distances are
    the same, independently of your place on a small Earth).
    
    To estimate the accuracy, notice that the ratio
    of the distance to the Moon to the Earth radius is
    60 (very roughly). So the loss of precision due to the
    method is by the factor of 60 under the most
    favorable conditions.
    These most favorable conditions are:
    a) The Moon is near zenith, and
    b) The two directions Moon-star are perpendicular.
    
    So under these conditions, the method is less accurate
    than the usual Lunar distances by a factor of 2.
    If the Moon's altitude is 30,
    multiply by enother factor of 2.
    
    Now it is hard for me to believe that one can
    measure distances with 0.1 or even 0.2 accuracy
    permanently and reliably:-)
    Some results posted by Frank seem to show that he can,
    but it is still unclear whether he posts his best
    results of average results:-)
    
    I still have no definite opinion on this matter,
    but my analysis of observations of Cook's expedition
    seems to indicate much lower accuracy than 0.2'
    And this was done from the ground,
    by professional astronomers, possibly with the best
    sextants ever made (?)
    
    The Lunar method was advertized as having approx 1/4 of
    a degree accuracy. This I believe.
    Then the lunar-with-chronometer-but-no-horizon
    method has probably 1/2 degree accuracy or so.
    
    Alex.
    
    
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