Rainbow Prism

Parallel beams of light strike a prism whose width varies with time. Red, orange, yellow, green, blue, indigo, and violet (ROYGBIV) rays are refracted by slightly different amounts. This is called dispersion, and becomes more obvious when the prism is at its widest. Shorter wavelengths (blue, violet) are refracted more than the longer, red, wavelengths. If all the rays were the same colour, then they would emerge from the right side of the prism parallel to each other, but you can just see the spread. Simulated using refractive indices of flint glass.