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    Re: 1st lunar attempt
    From: Fred Hebard
    Date: 2003 Apr 24, 21:48 -0400

    Doug,
    
    You should take elevation into account.  I also live at the same
    elevation.  The actual air pressure declines by about 2 inches of
    mercury at 2100 feet elevation.  The unusual conditions corrections
    table (A4) inside the front cover of the Nautical Almanac ranges down
    to 28.5 inches, which is pretty close to our "normal", just a bit under
    28 inches at 2100 feet.  The corrections amount to 0.1 to 0.3 minutes
    of arc under spring and summer temperatures.
    
    Other than the effect on refraction, there are no significant effects
    of 2100' of elevation on celestial altitudes.  The parallax of the moon
    might change by about 0.01 minutes of arc.
    
    It doesn't matter much what bodies you use.  If you can arrange for one
    to be at fairly low altitude, that can reduce contortions such as lying
    on your back and twisting sideways, which can be very tiring.  If you
    use a liquid horizon, other than mercury, you will be limited to
    brighter stars and planets, such as Jupiter or Sirius.  Bruce Stark
    recommends in his book that you ignore taking the altitudes and just
    focus on the distance, if you know where you are.  The methods in his
    book can accommodate either.  For use at sea, you would need to have
    altitudes to go along with the lunar, which then makes twilight
    observations desirable (but not necessary since the altitudes only need
    to be accurate to a minute or so, and you could advance a line of
    position).
    
    Take about eight distances, pretty much as fast as you can.
    Theoretically, you should get a straight line when plotting distance
    against the time of observation.  George Huxtable recently posted data
    of a very nice lunar observed about 150 years ago in Australia, to give
    you an idea of what an excellent set of data look like.
    
    Fred
    
    
    

       
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