A rainbow is a colorful arc of light that appears in the sky when sunlight shines through water droplets in the air, usually during or right after a rainstorm. The water droplets act like tiny prisms, splitting the white sunlight into its component colors: red, orange, yellow, green, blue, indigo, and violet, always in that same order.

You might spot a rainbow when the sun breaks through clouds during a passing shower, or see a small one in the spray from a garden hose on a sunny day. Rainbows always appear opposite the sun: if the sun is behind you, the rainbow forms in front of you where rain is falling.

Ancient people created myths to explain rainbows, not understanding the science behind them. Today we know that each color of light bends at a slightly different angle as it passes through the water droplets, separating the colors we normally see blended together as white light. Scientists call this refraction.

If you're lucky, you might see a double rainbow, where a second, fainter arc appears above the first with its colors reversed. No matter how far you walk toward a rainbow, though, you can never reach it. A rainbow exists only in the relationship between the sun, the water droplets, and your eyes.