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What Causes a Rainbow?

© Copyright 2000, Jim Loy

When light passes from air into water (or glass), or water into air, different colors are refracted (bent) a different amount. Red is refracted the least, and violet the most. And so, the colors are separated into a spectrum, or rainbow. When raindrops are in the air, most light is either reflected off of the drops or goes right through them. If the light enters at certain angles, the light enters the drop, is reflected inside, and then exits the drop. Entering and exiting the drop, the colors are separated. You see red light come from a raindrop because that drop is at just the correct angle (about 42 degrees) between your eye and the sun so that the red light coming from the sun is refracted, reflected, and refracted again right into your eye. Blue light comes from another raindrop at a slightly different angle. All the raindrops that are at a certain angle between your eye the sun form a circle in the sky. That is why the rainbow is a circle.

See How Far Away Is A Rainbow?

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