Matthew Rowley, age 10, of Salt Lake City, Utah, for his question:
What do they mean by color wave lengths?
Our wonderful world is arrayed in an endless assortment of lovely colors or so it seems. But scientists tell us that leaves are not really green and the sky is not really blue. They say that these and other beautiful bits of the scenery actually borrow their colors from the rainbow.
We know that we cannot see colors without the help of some light. Scientists call a sunbeam white light because it has no color and we cannot see it. But white light of some sort is needed to show the color of mice and marigolds, trees and tigers and all the other colorful items that fill the world. Colors fade as the light lessens. The flowers in a moonlit garden turn pasty pale because moonbeams shed less light than dazzling sunbeams.. It seems, then, that the secrets of color must be hidden in that invisible white light. And so they are.
White light from the sun is a form of energy. The sun sheds it out in all directions, along with a whole range of other forms of energy. Radio and ultraviolet and invisible infrared energy also arrive with the beaming sunshine. All these radiant energies are in a great hurry. They travel along together at about 186,000 miles per second. But each of the fellow travelers is different from all the others. It is different because its wave length is different.
Radiant energy pulses along in miniature spurts that resemble the ups and downs of the wavy sea. A wave length is the measure from the crest of one pulse of energy to the next. And each form of solar energy travels along on its own wave length. The wave lengths of X rays are shorter and those of radio are longer than light. But light itself is made up from a wide range of different, wave lengths. Some are almost twice the length of others but all of them are infinitesimal. Scientists measure the wave lengths of light in angstroms and four billion angstrom units equal about one inch. The wave lengths composing white light range from roughly 4,000 to 7,000 angstroms.
A glass prism can separate these wave lengths and force them to show their colors. Each wave length strikes its shiny sides at a different angle. This makes them fan out in slightly different directions. The separated wave lengths show us the spectrum colors of the rainbow. The shortest wave lengths are bent at the sharpest angles. When separated from white light, we see them as violet rays. The longest wave lengths are bent least. We see them as red rays. Wave lengths around 6,000 angstroms reveal bands of orange and yellow. Wave lengths in the 5,000's show themselves as greens. The shortest wave lengths reveal bands of blues ranging from bright to velvety purples.
The rainbow colors hidden in a colorless sunbeam play all sorts of tricks on the scenery. But they do not choose to shed their greens on the foliage and their reds on the roses. Far from it. Everything gets a full quota of wave lengths. But chemical substances select and absorb only certain wave lengths of light. The rest they bounce back for our eyes to see. Leaves absorb the reds and some blues and reflect back the greens. Black ink absorbs all the colors. A white lily absorbs none and its surface shows nothing but colorless light.