Matt Groth, age 11, of Milwaukee, Wisconsin for his question:
Is it possible to see two rainbows at once?
Usually we see only one rainbow and often the glimmering arch is incomplete. But it is possible to see two rainbows, one outside the other. Even three or four rainbows are possible, one outside the other. Some people claim to have seen as many as five rainbows at the same time. This too is possible, though very rare.
Some experts regard a single rainbow as incomplete, even when the arch of colored ribbons is unbroken. A second rainbow is needed to complete the picture. The lowest and brightest one is called the primary bow. The blue bands are on the underside and the red band outlines the outside of the arch. The secondary bow is placed neatly outside the primary. Its colored ribbons are reversed to show the reds on the inside and the blues on the outside.
A lot of dramatic stage scenery is necessary to create one or more rainbows in the heavens. And you must be there, at just the right place to behold it. The morning or evening sun must be fairly low in a clear patch of sky. No rainbows are visible from the earth when the sun is higher than about 40 degrees above the horizon. Meantime on the opposite side of the sky there must be a curtain of weeping clouds.
The gorgeous display is possible because invisible sunlight is actually a blend of rainbow colored rays. When it passes through a glass prism, the different rays are refracted, or bent, and spread apart to display the separate colors of the rainbow spectrum. These refracted colors can be reflected by a shiny mirror. In that weeping cloud, millions of falling raindrops act as both prisms and mirrors.
When a sunbeam strikes the shiny surface of a raindrop it is refracted and its colors are separated. As it passes through, these refracted rainbow colors are reflected from inside the raindrop. This reflection bounces right out again—and more light is refracted as it leaves. The refraction and reflection from millions of raindrops is scattered at precise angles to arrange an orderly rainbow in the sky.
Light is an assortment of longer and shorter wavelengths. The shorter waves are angled least and display the blue bands of color. The longest waves are angled more sharply and display the reds. These differ¬ent angles arrange the colors of the primary bow in precise order, with the blues on the inside and the reds on the outside.
Some of the radiant sunbeams take different paths through the falling prisms and mirrors. Some bounce around and reflect twice from the inside of the raindrops. This reverses the angles of the spectrum to form the secondary bow. Here the longer red rays appear at the bottom and the shorter blue waves rim the outside edge of the arch.
The colored spectrum may be reflected several times to show three, four or even five rainbows at a time. All of them appear at precise angles, one outside the other. The angle of the primary bow is always 42 degrees; the second bow is 50 degrees. The rare extras appear at larger and still larger angles—measured from where you stand in relation to the view.