Conley C. Kelty, Jr., age 11, of Houston, Texas, for his question:

What causes the colors of sunset?

At age 11, you can understand the wave theory of light and also a tiny measurement called the angstrom. These two concepts will help you grasp the cause of the orange red glows of dawn and sunset. But they are not necessary for you to appreciate these gorgeous spectacles.

The wave theory suggests that light travels out from its source in waves, or pulses, like hills and valleys. White light from the sun is a blend of assorted rays. Each ray has its oven color and each travels on its own wave length. The wave length .is the distance from the top of one crest to the top of the next.

The colors blended. in white light are the rainbow colors of the spectrum. Our eyes can pick out six or seven clear bands of color in the spectrum but there are countless tints and tones as one color fades into the next. Each of these colors and tones travels on its own wave length.

At the red end of the spectrum the wave length is about 0,00004 of a centimeter. At the opposite blue end, the wave lengths are about 0.00007 of a centimeter. The red wave lengths, then, are almost twice as long as the blue wave lengths. Imagine the thickness of a sheet of note paper. This distance is equal to about 130 waves of red rays and about 260 waves of blue light. But this is a clumsy way to measure. Instead, the experts use the angstrom, abbreviated as A,

The Angstrom unit is equal to one hundred millionth part of a centimeter. Our eyes cannot see such a small unit and even our minds find it hard to grasp. But it does allow us to write the wave lengths of light in whole numbers. The wave lengths of visible light range all the way from 4000 4'1 to 7000

Traveling through space at about 186,000 miles a second, the different rays of sun‑Light blend together as white or colorless light. But remember, each color is traveling on its own wave length, longer or shorter than its neighbors. Before it strikes the earth, the sunlight must pass through miles and miles of atmosphere. .rind air is made of tiny molecules and floating in it are particles of dust, smoke, soot, pollen, pores, salt and ice. Some of these fragments are smaller and some are thousands of times larger than an Angstrom. They snag the waves in the speeding light.

"'he blue waves are shortest. They are snagged first and. scattered through the high atmosphere. That is why the daytime sky looks blue. Noon sunshine comes straight down from the top of the sky. As the sun slopes 30 degrees, a quarter of the distance over the sky, the rays pierce the air at a slant. They must travel through twice the distance of atmosphere.

At sunset they must pierce a still thicker layer of air. More and more blue rays are scattered and subtracted from the spectrum. The yellow, orange and red tones become more noticeable. These are the rays with longer wave lengths. They are caught and reflected by clouds and we see the flaming beauty of the sunset.