On the Inside of a Rainbow

July 02, 2005

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Provided by: Dale Hugo
Summary authors & editors: Dale Hugo; Jim Foster

The above photo showing a high-arching rainbow was taken form Arlington Heights, Illinois on May 27, 2005. The rain came just as I started cooking on the grill, so our company retreated indoors while I kept a watchful eye on the grill. Though our get together was interrupted by the storm, we were later treated to a beautiful double bow. This is a very fine example of scattering of sunlight on the inside of the primary bow. While the rainbow itself is caused by the concentration of rays emerging from raindrops at the angle of minimum deviation (approximately 42 degrees), sunlight also emerges at smaller angles -- from raindrops on the inside of the primary bow. This results in a brightening inside the primary rainbow. A rainbow can only appear this high-arching if the Sun is very close to the horizon.

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