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    Re: lunars from Mt. Everest?
    From: Ken Muldrew
    Date: 2003 Dec 18, 09:43 -0700

    On 17 Dec 2003 at 21:09, Frank Reed wrote:
    
    > If you observe an object in the sky at an
    > altitude of 15 degrees, the sea level refraction is 3.6 minutes at sea
    > level, but in Denver it would be 3.1 minutes.  That's not a big deal
    > for standard line of position sights, but it would be a major source
    > of error for land-based lunars practice.
    
    I would guess that many locations at high altitude are also going to
    be in mountainous country where the lunar stars might be just above
    the raised horizon of a mountain. In such cases the refraction due to
    temperature changes will probably be signficant (at least, the stars
    twinkle a lot when they're close to the mountain (in an angular
    sense)). I wonder what the minimum angle is that one could get away
    with before the error becomes intolerable. Is refraction a big
    problem for navigation at sea when sighting the horizon?
    
    The celebrated land-based navigator David Thompson used temperature
    and altitude to correct for refraction. His altitudes came from
    occasional boiling-point measurements and estimated reckoning. They
    were sometimes out by several thousand feet (although they were
    usually better than that).
       \----------------------------+---------------------------------+
    o_,
     O_/ \    Ken Muldrew, PhD      | Voice: (403) 220-5976           |
    <\__/7
     <\__  \  Dept. of Cell Biology | Fax:   (403) 270-0617           |
      | /
      "\ L  | University of Calgary | kmuldrew{at}acs.ucalgary.ca        |
    / /
       <    +-----------------------+---------------------------------+ /
    /
                   Morning coffee recapitulate phylogeny               L/
    
    
    

       
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