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I was out shooting sights with a variety of sextants yesterday and today in my 
backyard, a very enjoyable activity.  In order to get
the best sights I measured the outside air temperature and pressure using my 
Casio watch, you know, the one that says that noon is
PM... ;-)

Anyway, the question is, how does one calculate refraction at higher altitudes 
on land?  Do I just use the actual barometric
pressure or do I somehow factor in elevation explicitly?

It is my understanding that the more atmosphere, the more refraction, hence 
higher elevations have less pressure and thus less
refraction.  Bowditch and other sources do not say much about refraction as a 
function of elevation above sea level.  I did notice
one comment about Air Almanacs having extra columns in their refraction tables 
to allow an elevation to be entered, but I do not
have an Air Almanac to check on this.

My guess is that if refraction is stricly due to atmospheric thickness, the 
barometric pressure is sufficient, but if there are
geometrical aspects to refraction (which I know there are since there is no 
refraction for a body directly overhead), then elevation
much above sea level needs to be accounted for separately from barometric 
pressure.  The question then is, by how much?

Does anyone know the story about high altitude refraction?

Thanks,

Dan

Daniel K. Allen
mailto:danallen46@attbi.com
http://home.attbi.com/~danallen46/
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