Monochrome rainbowA monochrome or red rainbow is an optical and meteorological phenomenon and a rare variation of the more commonly seen multicolored rainbow. Its formation process is identical to that of a normal rainbow (namely the reflection/refraction of light in water droplets), the difference being that a monochrome rainbow requires the sun to be close to the horizon; i.e., near sunrise or sunset. The low angle of the sun results in a longer distance for its light to travel through the atmosphere, causing shorter wavelengths of light, such as blue, green and yellow, to be scattered and leaving primarily red.[1] In the lower light environment where the phenomenon most often forms, a monochrome rainbow can leave a highly dramatic effect.[2][3] In July 1877, Silvanus P. Thompson witnessed a red and orange rainbow over Lake Lucerne in Switzerland:
And there were a few more reports:.[5][6][7] In the background of Madonna of Foligno, there is a monochrome rainbow in orange. References
Further reading
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