Rose Emershaw, age 12, of Visalia, Calif., for her question:

What is a rainbow made of?

The rainbow is always far away over the fields or out of reach above the distant hills. The pretty spectacled never comes close enough to be touched, and for this reason it is natural to wonder what it really is. But there is no sense in trying to catch it, even in an airplane.

The shimmering arch seems to be made from bands of colored glass. But it is not. If it were possible to touch a rainbow, we would feel nothing solid at all. However, we would get thoroughly soaked with water. For the main ingredient in a rainbow is a shower of falling raindrops. The second necessary ingredient is a host of streaming sunbeams. In order for the shimmering bow to form, these two ingredients must be placed in exactly the right positions. The weather also must be just right.

The rainbow appears when the sky is partly clear and partly spotted with small rain clouds. The sun must be in the clear and beaming from rather low in the sky. In the opposite part of the sky there must be a showering cloud. This weeping cloud is the dark curtain against which the multicolored rainbow appears.

Raindrops, of course, are glassy drops of falling water. And glass tends to play tricks with sunbeams and other white light. Curved glass lenses bend the rays of light to magnify an image or to make faraway objects seem nearer. A glass prism splits the rays of white light apart and reveals their separate colors. The glassy drops of falling rain act like prisms and separate the strands of white light into their rainbow colors.

The light that comes from the sun is a form of electromagnetic energy. It travels in pulsing wavelengths at about 186,000 miles a second. As a rule its many different wavelengths are blended together and the sunlight is invisible to our eyes. But when the wavelengths are separated, we see them as different colored rays of light. The raindrops falling from the weeping cloud separate the colored strands of white light, and some of these rainbow colors are reflected back for our eyes to see.

The rainbow is made of sunbeams and falling rain. But the sunbeams must strike the raindrops from just the right angle. This is why we never see the bow when the sun is shining from directly overhead. It forms when the sunbeams slope across to the distant cloud when the sun is rather low in the east or west.

All the colors we ever see or imagine are blended together in the rainbow. We call these colors the spectrum of white light, and, of course, they are closely related to the wavelengths of light. The shortest wavelengths are the violet and the deep blue rays of white light. In the shimmering rainbow these rays appear on the inside of the arch. The longest wavelengths are the red rays that appear on the outer side of the rainbow.