What causes the formation of a rainbow?

Rainbows are formed when sunlight is refracted, or bent, as it passes through raindrops in the atmosphere. As the light is refracted, it is split into its component colors due to the different wavelengths of light. The light is then reflected off the inside surface of the raindrop and refracted again as it exits the drop. The result is a spectrum of colors, typically red, orange, yellow, green, blue, indigo, and violet, which appear in the sky as a circular arc. Rainbows are most commonly seen after a rainstorm when sunlight shines through the remaining rain.