Tim Kocsis, age 12, of Gallup, N.M., for his question:
WHAT IS THE THEORY OF RAINBOW COLORS?
A theory is an educated guess based on a mass of reasonable evidence. When we get enough evidence to prove it to be true, it graduates from the theory class and becomes a known scientific fact. After generations of patient research scientists can explain the cause of rainbow colors as fact rather than theory.
The rainbow is called the spectrum of white light and it reveals all the colors visible to the human eye. White light is actually ordinary colorless light, which is known to be a fantastic bundle of electromagnetic energies. It fans out from its source in all directions, traveling in straight lines at the breakneck speed of about 186,000 miles per second.
But this is not the whole story. Far from it. Light travels along in pulses of energy, somewhat like the ups and downs of the heaving ocean waves. A wavelength is the distance from the crest of one pulse to the next. A beam of light is an assortment of numerous wavelengths. Traveling together at the same speed, the multitude of different wavelengths blends together and becomes invisible.
When the various wavelengths in a beam of invisible light are separated, they are forced to show themselves as the. splendid colors of the rainbow. This happens, for example, when a beam of white light passes through a glass prism. As the different wavelengths strike its sloping sides, they are bent at different angles—which sends them off in different directions.
The shorter wavelengths bend at sharper angles and reveal themselves as rays of blue light. Slightly longer and still longer wavelengths bend at wider angles and reveal themselves as bands of green, yellow and orange. The longest wavelengths are bent least—and angle off to reveal themselves as glorious rainbow reds.
These bending exercises give us the rainbow spectrum of white light. Other things happen to give us the colors of everyday scenery. For example, leafy foliage absorbs all the colors except the greens, which bounce back for our eyes to see.
The wavelengths of light are measured by the angstrom unit, which is a 100 millionth part of a centimeter. The rainbow colors of the spectrum range from short blue wavelengths of about 3,800 angstroms step by step up to long red wavelengths of around 7,000 angstroms.