Barbara Floyd., Age 12,, Of Westminstet Calif.., for her question:
What causes the spectrum?
The rainbow colors of the spectrum catch the eye in all kinds of ' odd places. Sometimes they appear in a puddle on the road where passing cars have left an oily film upon the water. They fan out in vivid ribbons when light strikes the surface of a glass prism., and they arch over the sky in the glimmering rainbow.
When scientists talk about the spectrum., they have a very large item in mind. They are referring to the many different wave lengths of electromagnetic energy. This is the kind of radiant energy which pours forth from the star which is our sun. The various,vave lengths of electromagnetic energy also give us radio, radar and carry our tv programs.
This vibrant energy is a union of the invisible forces of electricity and magnetism. On a large scale., it streams forth from the stars. On a small scale,, it is created around man made electric currents., as we see in a light bulb. It fans out in straight lines from its source in all directions., and it travels at the speed of light, radio and tv travel from the broadcasting station at 186.,000 miles a second ¬fast enough to whip around the equator seven times in a second.
Electromagnetic energy travels along in waves. A wave length is the distance between the crest of one wave and the next. The short wave lengths of x~rays are but a fraction of an angstrom unit which is one hundred millionth part of a centimeter. The wave lengths with colors of light range from 4000 to 8000 angstrom units. Other wave lengths can be measured in inches, yards and even miles,
Light is but a narrow band in the electromagnetic spectrum. As it whips through space the different wave lengths are blended together as white or colorless light. But when a beam of white light strikes an oily puddle., a falling raindrop or a glass prism., its different wave lengths are bent at different angles. We see the rainbow spectrum of white light when each wave length of light is bent and separated from the others., it shows itself as a color of the rainbow. The shortest wave lengths are bent at the sharpest angles. They give us the blues of the spectrum. The longest wave lengths of white light are bent least. They give the rosy colors of red and orange bands of the spectrum.
The spectrum of white light is priceless to the astronomer. A burning gas blazes with its own color., and each element can be identified by its own marks on the spectrum of white light. The spectrum of a distant star shows the elements present in its seething gases.