How are rainbows formed?

Sunlight is composed of light of varying wavelengths. Short wavelength light appears blue, violet and indigo, and long wavelength light appears red, orange and yellow.

When sunlight enters a raindrop in the air, the light splits into a multitude of colors. each rain droplet behaves like an independent prism which splits sunlight into its constituent colors.This light then reflects off the back surface of the raindrop and then goes back to the other side in which the light first passed, forming an arch. 


When light enters water it bends (refracts). The amount of bending depends on the wavelength of light. As a result, the light splits into its component colors.