How Do Rainbows Form?

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By By Steve Pool

SEATTLE - Rainbows area one of the most pleasant benefits from our usual shower-and-sunbreak pattern. But for rainbows to work, you have to have the sun behind you, and the rain in front of you.

The sun's light is made up of several colors ranging from red though green and into blue and violet. You see the sun's light as white because you're seeing all the colors combined.

But raindrops can act like a prism in separating the sun's light into its individual colors. Each individual color of light gets bent slightly different when it hits the raindrop, spreading out the colors into what you see as a rainbow.

Double rainbows occur when the sun's light gets refracted twice inside the same raindrop. Since some of the light has already escaped to make the first rainbow, double rainbows are generally dimmer. Their colors are also inverted.

For More Information:

www.wrh.noaa.gov

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Evening rainbow from Queen Anne using fisheye lens, 17 April 2014
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A large rainbow formed over the ferry Wenatchee while headed from Bainbridge Island to Seattle.