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    Re: Vernier sextant
    From: Alexandre Eremenko
    Date: 2007 Mar 05, 16:07 -0800

    Bill,
    
    On Mar 3, 1:36 am, Bill  wrote:
    
    > I'm still waiting on more bubble sextant results.
    
    I have plenty. And I am ready to share them with you.
    I just do not post them on the list,
    because, apparently there is no interest in the raw
    numbers in this list.
    
    One of the ususual results I have is a daylight
    observation of Venus. I mean before the sunset.
    
    Since my childhood I know (theoretically) that you can see bright
    stars in daylight. If you know precisely where to look.
    If you do not know where to look, you can miss even a very well
    visible object:-) This I know by experience as a anti-aircraft
    artillery
    officer:-) A low flying plane comes, you hear the sound (which comes
    from
    a deceptive direction if the airplane is fast enough). You lookouth.
    at the sky
    and you see nothing. Until someone spots it, points at it, and then
    you suddenly see it.
    
    Same with stars. Very bright stars are well visible in daylight.
    The star navigation authorities (Chichester and Lecky) recommend
    the following. You pre-compute the time and alt of meridian passage.
    You preset this alt on your sextant. Then, at a pre-computed time you
    point it North or S. And you see the star!
    
    Instead, I pre-computed the Sun-Venus distance and pointed my sextant
    at the Sun, rocking it and trying to find Venus.
    I failed 1 hour before sunset but succeeded twice 1/2 hour before the
    sunset.
    I could even measure the Sun-Venus distance with my sextant.
    
    Returning to my vernier sextant.
    So far my Lunars are bad. I mean VERY bad. Several minutes off.
    Only now I really understand the advantages of the modern sextants:-)
    (Large FILTERS (I do not care about large mirrors!), good optics,
    and easy reading scale). And light weight for alluminium ones:-)
    But I continue my experiments.
    
    Alex.
    
    
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