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    Re: Refraction
    From: Robert Eno
    Date: 2005 Sep 3, 13:38 -0400

    Most bubble sextants will measure negative altitudes. My RAE MK IXA goes as
    low as -13 degrees. My A-10 goes to - 2 degrees 55 minutes. I believe that
    most marine sextants are also capable of measuring negative altitudes to at
    least - 5 degrees.
    
    A small clarification to my earlier comments regarding refraction in the
    polar regions: your sextant would not yield a negative reading, the
    calculated altitude would be negative. It is only at (height of eye)
    altitudes of several thousand feet asl (as in an aircraft) that one would
    observe a negative altitude.
    
    Robert
    
    ----- Original Message -----
    From: "Fred Hebard" 
    To: 
    Sent: Thursday, August 04, 2005 12:50 PM
    Subject: Re: Refraction
    
    
    > Marcel,
    >
    > OK, I got it.  Ignore my last post.  You might want to look at the
    > Introduction to the Air Almanac, which should give instructions for its
    > use, and should discuss this case.  I've never seen a bubble sextant,
    > so I don't know whether they measure negative altitudes.
    >
    > Fred
    >
    > On Aug 4, 2005, at 12:20 PM, Marcel E. Tschudin wrote:
    >
    >> Yes, how do I get in this? Just trying to cover in a self-made program
    >> the
    >> situation from an object at the horizon (over sea level) as seen from a
    >> mountain or air craft.
    
    
    

       
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