Dispersion

Dispersion, optical phenomenon whereby a beam of white light is broken up into its component colors when it passes through a triangular glass prism. Each color has a different index of refraction; that is, it bends at a characteristic angle when passing from one medium to another (air to glass, for instance). Since white light is made up of all the colors of the spectrum, the colors separate when they pass through glass prisms. Rainbows are formed by the refraction and dispersion of sunlight through raindrops.