十万个为什么·科学启蒙30篇（1）
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Why Do We See Rainbows After It Rains?
为什么雨后会出现彩虹？
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Rainbows form when sunlight passes through raindrops hanging in the air after a storm.
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Each drop bends the light, separates it into colors, and reflects it back toward your eyes.
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Red light bends the least, so it appears on the outer edge of the rainbow.
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Violet light bends the most, which is why it always sits on the inner edge.
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You must stand with your back to the sun and face the rain to see a full arc.
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Double rainbows happen when light reflects twice inside a raindrop, reversing the color order.
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Rainbows are actually full circles, but the ground usually blocks the lower half.
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No two people see the exact same rainbow because each views light from different drops.
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The size and brightness depend on drop size, sun height, and air clarity.
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Photographers sometimes use mist machines to create tiny rainbows for science demos.