September - rain You are here: Home Photo gallery Atmospheric optics Light in water droplets Supernumerary rainbows

A set of interference rainbows just inside the primary rainbow. Supernumerary bows occur when raindrops responsible for the main rainbow are much uniform in size. Slightly different ray paths through a raindrop yield slightly different path lengths and slightly larger exit angle. As a result, there is constructive and destructive interference of each color in the spectrum as a function of ray exit angle, and a set of bows become visible inside the primary rainbow. Usually, there is some variation in size of raindrops, and the supernumeraries are washed out altogether. There is almost always some washing out of colors, and the bows show much green and red in them, and not the other colors in the spectrum.

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