Introduction - If you have any usage issues, please Google them yourself
This algorithm is based on numerical approximation of the exact equations.
The authors of the original paper state that this algorithm should be
precise at+/- 0.0003 degrees. I have compared it to NOAA solar table
(http://www.srrb.noaa.gov/highlights/sunrise/azel.html) and to USNO solar
table (http://aa.usno.navy.mil/data/docs/AltAz.html) and found very good
correspondance (up to the precision of those tables), except for large
zenith angle, where the refraction by the atmosphere is significant
(difference of about 1 degree). Note that in this code the correction
for refraction in the atmosphere as been implemented for a temperature
of 10C (283 kelvins) and a pressure of 1010 mbar. See the subfunction
un_topocentric_zenith_angle_calculation� for a possible modification
to explicitely model the effect of temperature and pressure as describe
in Reda & Andreas (2003).