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Supernumerary Rainbows

The banded fringes seen on the inside edge of a rainbow.

These bands of light are an interference pattern. The dark bands in the supernumerary rainbow are where light waves cancel each other out, while the bright bands are where the light waves reinforce each other.

Supernumerary rainbows are stronger when each raindrop makes a similar interference pattern. This happens when all raindrops are of a similar size. In fact you can use the visibility of supernumerary rainbows to estimate the size of the falling raindrops!

Supernumerary rainbows are often visible, but many people have never noticed them. An explanation for them was developed in the nineteenth century. This explanation was only possible after Thomas Young discovered the phenomenon of interference.

Supernumerary rainbows
magnifySupernumerary rainbows

Interference of wavefronts
magnifyInterference of wavefronts
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