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Thank you, Wolfgang for the code snippet.

The program from Mr. Umland is for use in CN. It uses Bennett's
formula for calculating the refraction from the observed *apparent*
altitude in order to obtain true altitude. I solve this problem with
my positional astronomy program differently, the other way round. I do
this by first calculating the sun's position in topocentric,
astrometric coordinates providing the *true* altitude which then, by
adding refraction, is converted to apparent altitude. The solution is
then found iteratively until the calculated apparent altitude agrees
with the observed one. A different refraction formulae has to be used
for each of the two cases.

Marcel

   

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