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    Re: Astronomical Refraction: Computational Method for All Zenith Angles
    From: Marcel Tschudin
    Date: 2005 Aug 23, 01:52 +0300

    Frank, you wrote
    > Today, I coded  up a much better way of dealing with all of this
    > atmospheric
    > structure. I  generate a density table directly from the temperature
    > profile
    > of the atmosphere  (this is the principal independent variable) and the
    > condition of hydrostatic  equilibrium and the ideal gas law which is how
    > atmosphere
    > models are  derived usually. While these equations can be integrated
    > analytically in  important special cases you then have to do a lot of work
    > patching
    > together the  pieces. But if you do the integration numerically from the
    > ground
    > up, it's  trivial to modify the temperature profile, generate new
    > atmosphere
    > data, and  then re-run the refraction tables.
    Added what you proposed. Density values look resonable, BUT ...
    > And that's it. This model can then be used  as input to the refraction
    > integration. Using a lapse rate of 5.70 deg C per  kilometer below 11km
    > altitude and
    > a rate of zero above that altitude, I was able  to replicate almost
    > exactly
    > the refraction tables in the Auer-Standish article.  The differences were
    > mostly less than one-tenth of a second of arc.
    I would have wished to get such results, mine are substancially higher...
    I checked and checked and can still not findout why.
    Further you wrote
    > By the way, Marcel, thanks for raising this  issue. It's led me to all
    > sorts
    > of interesting things.
    ...and I did not imagine that I finally would spend so much time on it. Your
    "interesting things" gave me courage and the input to start writing a
    program for it. At the moment, it looks as I am stuck half way.

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