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    Re: Lunar distance accuracy
    From: Frank Reed
    Date: 2007 Oct 23, 21:20 -0400

    Jim you wrote:
    "Standing on land in good conditions, no averaging, I have found that
    obtaining sun moon lunars with an accuracy of <0.5' can be obtained
    routinely with many sights well within this. Using stars I would have
    to estimate a slight increase in error putting it at <0.7'. Using
    planets I find that getting reliable results consistently <1.0' is
    getting to be a challenge."
    My own experience is that I can get individual Sun-Moon lunars accurate with
    a standard deviation of about 0.25 minutes of arc. By averaging four in a
    row, the net accuracy is nearly doubled. Sun-star lunars are worse for the
    bright stars (e.g. Regulus) by a factor of two and for the fainter stars
    (e.g. alpha Arietis) by a factor of three. For the planets, I get excellent
    results with Jupiter, Mars when its bright, as it is now, and Venus when it
    does not have much phase. For all of these, especially Moon-Jupiter lunars,
    the results are just as good as the very best Sun-Moon lunars. I would
    recommend trying some more Jupiter lunars to see if you can improve your
    In the first month when I joined this group, nearly four years ago, I posted
    about Moon-Jupiter lunars. The thread starts here:
    Incidentally, when you look through old logbooks, you find that something
    like 80% of lunar observations were Sun-Moon, at least for American
    commercial vessels. Celestial navigation was largely a daytime activity in
    the 19th century. They also shot the standard lunars stars now and then, but
    I have not yet found a single attested Moon-planet lunar. I'm sure some
    navigators tried them, but since the ephemerides of the planets were less
    accurate back then, using them may have been seen as one more layer of
    uncertainty (which would have been true 175 years ago, but not today).
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