Rainbows: Why Do You Need Sun and Rain?

To see a rainbow, you must have the sun behind you and rain in front of you. When sunlight enters a raindrop, it slows down and bends—a process called refraction. The light then hits the back of the drop, reflects forward, and spreads out into its hidden colors as it exits the water.

Because each color of light bends at a slightly different angle, they always appear in the same order: Red, Orange, Yellow, Green, Blue, Indigo, and Violet (ROYGBIV). Red always sits on the outside of the arc because it bends the least, while violet sits on the inside because it bends the most sharply.

We usually see rainbows as arches because the ground gets in the way. However, if you were in an airplane or looking down from a high mountain, you would see that a rainbow is actually a perfect circle! The center of that circle is always the spot directly opposite the sun from your eyes.