Rainbows are produced when sunlight is reflected and refracted by raindrops in a manner similar to the refraction occurring when light passes through a prism. The light rays making up the main, or primary, rainbow experience single internal reflection from the back surfaces of the drops. The light composing the secondary bow undergoes two reflections from the raindrops. As you know from looking in a mirror, the action of reflection is to cause an inversion of an image. Your right hand appears to be your left hand. The second reflection in a raindrop reverses the order of the colors in the rainbow. In rare cases, you can see a very weak third bow. It is explained by three reflections and exhibits the same order of colors as does the primary bow. At each reflection, only part of the incident light is actually reflected, therefore, the more the reflections, the less bright the bow.
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