Bibliography
[1] http://www.atractor.pt/mat/luzl/index-_en.html
[2] Nussenzweig, H. Moysés. "The Theory of the Rainbow". Scientific American, Vol. 236-No.4 (1977-Abril), 116-127
[3] http://apod.nasa.gov/apod/ap140930.html Aerial photograph of a circular rainbow