When white sunlight is intercepted by a drop of water, the light is diffused. As with a prism, this diffusion separates the sunlight into its component colors. (The “prism” in this case, would be a spherical one.) The result, when viewed at the correct angle, is a rainbow. The observer must be between the water droplets and the Sun. Incident light is diffused back at an angle that is approximately 40° away from the angle at which the original, incident light beam struck the droplet.
Click on to advance through a sequence of different animations.
At the end of the last animation, click individual raindrops.