[1] A.J. Preetham, P. Shirley, and B. Smits, A Practical Analytic Model for Daylight, SIGGRAPH 1999, Computer Graphics Proceedings; An online version can be found at at http://www.cs.utah.edu/~shirley/papers/sunsky/ This paper includes source code examples and is the base for the VRaySun and VRaySky plugins.
[2] R. H. B. Exell, The intensity of solar radiation, 2000 This document is available at http://www.jgsee.kmutt.ac.th/exell/IntensitySolarRad.pdf(Please note that this link is no longer valid). This document contains information about the average intensity of the solar radiation, as well as some specific measurements.
[3] R. Cahalan, Sun & Earth Radiation This page can be found at http://climate.gsfc.nasa.gov/static/cahalan/Radiation/ (Please note that this link is no longer valid). These pages contain a list of accurate solar irradiances across a large portion of the electromagnetic spectrum.
[4] D. Robinson-Boonstra, Venus Transit: Activity 3, Sun & Earth Day 2004 This document can be found online at http://sunearth.gsfc.nasa.gov/sunearthday/2004/2004images/VT_Activity3.pdf (Please note that this link is no longer valid). Among other things, this document gives the distance from the Sun to the Earth and the size of the Sun derived from astronomic observations. [5] Hosek L, et al, An Analytic Model for Full Spectral Sky-Dome Radiance This document can be found online at http://cgg.mff.cuni.cz/projects/SkylightModelling/HosekWilkie_SkylightModel_SIGGRAPH2012_Preprint_lowres.pdf Describes the Hosek sky model used by the VRaySun and VRaySky
