十万个为什么·科学启蒙30篇（3）

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彩虹是怎么出现的

A rainbow appears when sunlight enters a raindrop, bends, reflects off the back, and bends again while exiting.
Each color of light bends by a slightly different amount, separating white light into its full spectrum.
Red light bends the least and exits at about 42 degrees, while violet bends the most at 40 degrees.
Your eyes see red higher in the arc and violet lower because of these precise exit angles.
You must stand with your back to the Sun and face falling rain to see a rainbow at all.
The center of the rainbow’s circle lies directly opposite the Sun from your viewpoint.
Double rainbows happen when light reflects twice inside the drop, reversing the color order in the outer bow.
Rainbows are not physical objects—they exist only where light, raindrops, and your eyes align perfectly.
Fogbows look white because tiny fog droplets scatter light too broadly to separate colors clearly.
At sunrise or sunset, the Sun’s low angle can make rainbows appear fuller and more vivid.