Raindrop optics for rainbow formation. Diagram of how a beam of sunlight is dispersed by a raindrop to produce a rainbow. Sunlight enters a raindrop as white light (upper left) and is refracted and split into its colour components. This is because the different colours refract at different angles. At the back of the raindrop (upper right) the light is reflected and the colours cross over. A second refraction (lower centre) splits the colours further. The red light (top part of the rainbow) is overall reflected at an angle of 42 degrees, while the blue light (inner part) is only reflected at 40 degrees. An observer of the rainbow sees the red part of this beam. The blue part of the rainbow is from a different raindrop.