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2. Biometeorology, ESPM 129, Lecture 9: Solar, Radiation, Part 2: Earth-Sun Geometry. http://nature.berkeley.edu/biometlab/espm129/pdf/Lecture%209%20espm%20129 .
3. Solar Concepts. http://www.usc.edu/dept/architecture/mbs/ools/vrsolar/Help/solar-concepts.html
4. http://rredc.nrel.gov/solar/spectra/am1.5/ASTMG173.html ; http://www.lehigh.edu/imi/docs-pitt/pdf-Pitt/T2f-Fangman.pdf
5. Christian Gueymard, SMARTS2: A Simple Model of the Atmospheric Radiative Transfer of Sunshine: Algorithms and Performance Assessment (1995). http://www.fsec.ucf.edu/en/publications/pdf/FSEC-PF-270-95.pdf