Rainbows are one of nature's most beautiful optical phenomena, yet the science behind them is relatively straightforward. A rainbow forms when sunlight interacts with water droplets suspended in the atmosphere. When light enters a water droplet, it slows down and bends, a process called refraction.

White sunlight is actually composed of many different colors, each with a different wavelength. As light enters the droplet, these colors bend at slightly different angles. Red light bends the least, while violet light bends the most. Inside the droplet, the light reflects off the back surface like a mirror, then bends again as it exits. This double refraction separates the colors enough for our eyes to perceive them as distinct bands.

The classic rainbow displays seven colors: red, orange, yellow, green, blue, indigo, and violet. Red appears on the outer edge because it bends the least, while violet appears on the inner edge. Observers see rainbows as arcs because only droplets at a specific angle relative to the sun can direct the separated light to their eyes.