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    Star sparkle in sextant image
    From: Jim Thompson
    Date: 2004 Sep 27, 08:48 -0300

    I am still working to get my intercepts down to acceptable distance from a
    known position on land or at anchor.  All too often I am about 2-4 miles
    away. Perhaps my biologics are against me?  Even when I think that I have
    perfectly lined up the sun's limb with a clear horizon, my sights tend to be
    out by that much at times.  Perhaps I cannot see the limb and horizon as
    clearly as my brain thinks it can.
    
    For now, though, I would like to explore star image quality.  We have
    discussed star sparkle before on this list, but I finally got around to
    attempting to draw what I actually seem to see.  Sparkle makes it difficult
    for me to precisely line up the star's images on top of each other. This
    means that I have to take a series of sights to obtain an Index Error before
    and after each round of sights, and then average them. Typically my
    variation in a series of IE attempts ranges to about +/- 0.5' of arc, which
    seems like a lot to me.  I would have thought that a navigator could expect
    less variation, say +/ 0.2' or even 0.1'?
    
    How do the images on the following page compare with what you see through
    your sextant?  Is there more sparkle, or less?
    http://jimthompson.net/boating/CelestialNav/CelestNotes/UsingSextant.htm
    
    
    
    Jim Thompson
    jim2{at}jimthompson.net
    www.jimthompson.net
    Outgoing mail scanned by Norton Antivirus
    -----------------------------------------
    
    
    

       
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