WHAT CAUSES A RAINBOW?
As sunlight enters a water drop, the different wavelengths of light are bent by slightly different amounts. That is, the water drop acts like a prism that separates light into its different colors. To see a rainbow, the sun has to be in back of you and water drops have to be in the air in front. When you see a rainbow in the sky, the water drops are falling rain. You also can see rainbows in drops from a waterfall or spray from a sprinkler. USATODAY.com graphic shows how rainbows work. For more detail, go to our Understanding sky color and phenomena page.
