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What Makes a Rainbow?

Rainbows are seen when raindrops, falling in the distance, bend and bounce sunlight back towards your eye.

Raindrops reflect sunlight, like a mirror. However raindrops also bend, or refract, light, like a lens. The reflection is spread into a cone of light. The edge of this cone is bright, because sunlight is concentrated at this angle (called the rainbow angle).

Each colour of sunlight is bent and bounced in a slightly different direction. The colours separate around the bright edge of the reflection.

The collection of raindrops that send the same bright colour towards your eye is curved. The centre of the curve is the shadow of your head (called the anti-solar point). The rainbow always appears at the same distance from this central point, at the rainbow angle.

Multiple raindrops creating a rainbow
magnifyMultiple raindrops creating a rainbow

Light reflected by a raindrop
magnifyLight reflected by a raindrop

Dispersion of sunlight through a raindrop
magnifyDispersion of sunlight
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