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Therefore, I have adapted them, expecting only Julians dates starting from 1.Jan. 2000.
 
Therefore, I have adapted them, expecting only Julians dates starting from 1.Jan. 2000.
 
These calculations I have put into another library (Helios.h)
 
These calculations I have put into another library (Helios.h)
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==SPA Algorithm==
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A much more accurate solar algorithm seems to be from Reda, I.; Andreas, A. (2003):
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''Solar Position Algorithm for Solar Radiation Applications. NREL Report No. TP-560-34302,
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''Revised January 2008. The algorithm is supposed to work for the years -2000 to 6000,
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''with uncertainties of +/-0.0003 degrees.''
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In this paper methods have been worked out according to the book from
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''Jean Meeus: Astronomical Algorithms, Willmann-Bell, Richmond 2000 (2nd ed., 2nd printing)''
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a widely accepted text book for astronomic calculations.
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The calculations are, however, quite involved; for Arduino I chose the simpler PSA.
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Implementations and references for both algorithms I found thanks to the code from
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[http://klaus.e175.net/solarpositioning Klaus Brunner]. It was also a valuable help for debugging
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the Arduino implementation.