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    Re: Lunar distance accuracy
    From: Alexandre Eremenko
    Date: 2007 Oct 22, 13:19 -0400

    
    Jim,
    On Mon, 22 Oct 2007, Jim wrote:
    
    > Looking for some qualitative comments
    > regarding the accuracy of lunar
    > distances. I have been looking through the archives
    > and not found
    > quite what I am looking for.
    
    I posted very many messages on the archive on this subject
    in the recent years. Both qualitative and raw observation
    data, and statistics.
    
    > I have noticed that the sun moon lunars seem to be
    > more accurate than star moon lunars which are
    > in turn better than the
    > planet moon lunars.
    
    I agree with the first part. But not with the second.
    The Sun lunars are most accurate, indeed.
    I think this has simple explanation:
    our eye has better resolution in daylight.
    On the planets my experience is different:
    the best night results I achieve with Venus and Jupiter.
    (It's true this required a lot of practice, about two years
    of frequent observations).
    The point is that for Venus and Jupiter, you see discs
    rather than points. And you can learn to make these discs
    divided by the Moon edge in exactly equal halves.
    As I said, this requires a lot of practice, and a decent
    sextant with a good scope.
    
    > 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.
    
    Yes, I confirm this. And I posted a lot of statistics
    related to this. My sights are better than that
    ON THE AVERAGE, but I can say that 0.3-0.5 accuracy I can
    obtain with reasonable degree of confidence.
    
    > Using
    > planets I find that getting reliable
    > results consistently <1.0' is
    > getting to be a challenge.
    
    I agree that this is a challenge.
    But I can do bright planets (Jupiter and Venus)
    to 0.2' MOST of the time, but SOMETIMES the
    errors of up to 0.6' occur.
    As I said it took me about two years of practice
    from my balcony.
    
    Two questions:
    1. Have you tried star-to-star distances?
    2. What sextant and what TELESCOPE do you use.
    I find that 6x telescopes are VERY MUCH superior
    to the standard sextant 3x-4x scopes when you do
    the lunars. I always use a 6x inverting scope
    for all my land observations.
    
    There is a long running argument between Frank and
    me about lunars accuracy. Frank essentially claims
    that a NOVICE (a person who never tried before,
    after 2-3 days of practice) can take lunars
    with 0'2 accuracy RELIABLY (with averaging 3-5 observations).
    I disagree with this. And I cite several XIX century
    authorities who did some research on the subject.
    
    But of course I can be wrong:
    1. My eye sight is not perfect (I am 54 years old)
    2. My sextant is probably not the best one
    (I have no way of knowing this! I did not have many
    opportunities to try other sextants).
    Speaking of the "authorities", despite my efforts I did not
    find any thorough and convincing scientific research
    on the subject
    of Lunars accuracy.
    I mean large series of observations from an exactly
    known place, by many different obsevvers, with various
    sextants under various conditions.
    
    In fact my observation books contain more material
    than anything I've seen published, combined.
    But this is by ONE observer, with ONE sextant.
    
    Alex.
    
    
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