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    Re: U.S. Standard Atmosphere Supplements
    From: Frank Reed CT
    Date: 2005 Aug 27, 02:05 EDT

    Fred you wrote:
    "Frank (or should I say,  Frank I :)"
    
    Soon we will be forced to invent the "surname".   ;-)
    
    You wrote:
    "That's very nice evidence for the anomalous dip that  George Huxtable is
    so fond of mentioning, wouldn't you say?  The most  convincing
    demonstration I have seen at least.  I wonder how far below  "ref" the
    refraction at 0 degrees altitude would go.  Seven minutes  above is
    astounding."
    
    The variability of refraction right at the  horizon is distinct from
    anomalous dip, since the light ray from an astronomical  source traverses the whole
    atmosphere, grazes ground level, and then travels the  last few miles to the
    observer's eye. The light ray from the horizon itself only  does the last part of
    the trip. It could be calculated in more or less the same  way though.
    
    So if a single day's difference in atmospheric conditions at  a site chosen
    at random can yield a six arcminute difference in refraction right  at the
    horizon and one arcminute at half a degree altitude, why don't we notice  it? I
    think the simple answer is that we never measure any astronomical  objects down
    that low except the Sun and the Moon and them very rarely. The  variability in
    refraction will change the exact time of sunrise/set and  moonrise/set by
    something like a half a minute (depending on latitude) for a six  arcminute
    change in refraction. I think the time of sunset is as  variable as that on a
    regular basis.
    
    -FER
    42.0N 87.7W, or 41.4N  72.1W.
    www.HistoricalAtlas.com/lunars
    
    
    

       
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