Why are there rainbows?
(Lansing State Journal, January 28, 1998)
The rainbows are caused by the refraction, or bending, of sunlight as it passes through the raindrops. The raindrops act like miniature prisms. As white light enters the prism, it is separated into the individual wavelengths of light, which we see as the different colors in a rainbow. Thus the spectrum, or band of colors which make up the "white light" exits the prism as separate bands of color. The more slowly a wavelength of light travels, the more it is bent by the prism. That is why the colors seen in the rainbow are always in the order: red; orange; yellow; green; blue; indigo and violet. The red light travels more slowly than violet light so it is bent more.
Since rainbows are made by sunlight passing through water droplets, it is possible to create your own miniature rainbow. Spray a fine mist of water in the direction of the sun and watch as the rainbow appears!