Elaine Jefferson, age 10, of Missoula, Mont., for her question:
HOW IS A RAINBOW FORMED?
A rainbow is an arch of bright colors that appear in the sky when the sun shines after a shower of rain. It forms in that part of the sky opposite the sun. If the rain has been heavy, the bow may spread all the way across the sky, and its two ends seem to rest on the earth.
Seven colors appear in each rainbow: violet, indigo, blue, green, yellow, orange and red. But these colors blend into each other so that often you rarely see more than four or five of the colors clearly.
The amount of space each color takes up varies and depends chiefly on the size of the raindrops in which the rainbow forms.
Sunlight is a combination of the seven colors you find in a rainbow. Each color has a certain range of wave lengths. You see the rainbow when the sun is behind you and the rain is in front of you. As a ray passes into a drop of rain, the water acts like a prism.
The ray is refracted or bent as it enters the drop and is dispersed or separated into different colors. As it strikes the inner surface of the drop, it is reflected or turned back. On leaving the drop, it is further refracted and dispersed.
Many drops produce a rainbow. Each color is formed by rays that reach the eye at a certain angle and the angle for a particular color never changes.
A complete bow shows two bands of colors. The inner and brighter one is called the primary bow. The outer and less distinct one is known as the secondary bow. The primary bow has the red coloring on the outside and the violet on the inside of the arch, while in the secondary bow, the colors appear as just the opposite.
The higher the sun, the lower the bow, and if the sun rises higher than 40 degrees, no bow can be seen. When the sun is near the horizon, an observer on a high mountain might see the whole circle of the rainbow.
Rainbows are often observed in the spray that flies from a garden hose or from a lawn sprinkler. Beautiful rainbows often may be seen on sunny days at Niagara Falls.
Occasionally, the light of the moon forms a rainbow. The feebleness of the light creates faint colors, which are difficult to observe. This type rainbow differs only in intensity of color from the one produced in sunlight.
The rainbow has different names in different parts of the world. "The Italians, for example, call it "the flashing arch." In Sanskrit, it is called the "bow of Indra."
The people of Annam call a rainbow "the little window in the sky."
North African tribes call the rainbow "the bride of the rain." And in the various languages of central Europe, the rainbow is called "the arch of Saint Martin," "the bridge of the Holy Spirit," "the crown of Saint Bernard" and "the girdle of God."
In southern Utah, one of the world's best known natural bridges is called the Rainbow Bridge National Monument. This bridge is 309 feet above the bottom of the gorge and has a 278 foot span.