Roddy Wonder, age 11, of Danbury, Iowa, for his question:
Where does the rainbow get its colors?
For ages, the study of color was claimed by artists as their own special field. Then Isaac Newton claimed color for the field of physics. Tae now know that color is a built in property of light. Red roses and green grasses, blue skies and shimmering rainbows are colored by light, and only light.
Everyone has a bit of the artist in him and a bit of the thinker. The rainbow appeals first of all to the admiring eye of the artist. Its beauty is wonderous to behold. Then the thinker is prodded with curiosity about the nature of this phenomenon. It took the best brains of centuries to answer the natural questions about the rainbow and some of them are still unanswered. For the rainbow is a glamorous daughter of light. And modern scientists cannot explain the nature of light down to the last detail. Plenty of fascinating research is waiting for those who plan future careers in this branch of science.
Isaac Newton experimented with ordinary white, or colorless light. He let a beam of invisible light pass through one, then two glass prisms. The first prism produced a fan of rainbow stripes. The second prism made these colors disappear. Newton reasoned that the first prism separated the colors in 'a beam of light and the second prism blended them together again. He proved to his satisfaction that invisible white light actually is a blended rainbow that can be separated into strands of visible colors.
Later scientists discovered that the colors actually are different wavelengths of electromagnetic energy. Each tint is a small fraction of the radiant energy that pours from the sun. As it travels, it vibrates in pulses of energy to its own rhythm. Its basic pulse rate is measured in distance and time. Its wavelength is the distance from one crest of energy to the next. Its frequency is the number of vibrations per second. Each color hidden in a beam of white light has its own wavelength and frequency.
We need this basic information about wavelengths to understand how the spectrum colors are separated from white light. Actually, it is the wavelengths that are separated. The sloping sides of a prism bend these short, medium and long waves at different angles, forcing them to fan out in different directions. The assorted wavelengths become a visible spectrum. A weeping cloud sheds showers of crystal clear raindrops. Then when the sun shines from the opposite side of the sky, the showering raindrops act like glassy prisms.
They bend the assorted wavelengths of sunlight at assorted angles and force them to display the visible spectrum as a banded rainbow.
The wavelengths of visible light are so small that the infinitesimal Angstrom was invented to measure them. Created for scientists, it is based on the metric system. There are 100 million Angstroms in a centimeter and a centimeter is not quite half an inch:. The longest wavelengths of visible light are the red rays that range from 6,300 to 7,800 Angstroms. The shorter and still shorter wavelengths become visible as orange and yellow, green and blue. The shortest wavelengths are deep violets that range from 3,800 to 4,400 Angstroms.
The colored spectrum is merely 3 per cent of the total electromagnetic energy shed by the sun. Its assorted wavelengths range from 0.000014 to 0.000028 of an inch. Ultraviolet and X rays, gamma rays and cosmic rays are shorter and still shorter than the visible range of the spectrum. Infrared, heat and radio wavelengths are longer. Some of the longest waves of electromagnetic energy are measured in kilometers and miles. If extra long and extra short waves have rainbow colors to show, our eyes are not equipped to see them.