Rainbows are formed opposite to the sun by the refraction and reflection of the sun's rays in drops of falling rain. The raindrops are responsible for the colors of rainbows. They break the sunlight up into the full spectrum of colors, each drop acting as a sort of miniature prism. Each color emerges at a slightly different angle on each raindrop. When millions of raindrops gather, the spectrum shows up as distinct bands of color -- each with a different length. Red is the longest and violet the shortest band. The arc is most pronounced when the Sun is close to the horizon.