Anthony Singelis, age 11, of Dollard Des Ormeaux, P. Q. 970, Canada, for his question:
What does a spectroscope do?
It can identify the gases in a blazing star and reveal the chemical compounds present in rock samples. To a scientist, the spectroscope acts as a sort of fingerprinting system that makes a substance sign its own name in color. It accents certain bands in the rainbow spectrum. The substance being tested is burned in a colorless flame and its spectrogram signature is unique.
We behold the spectrum of ordinary white light in ribbons of the rainbow. If the beauteous bow is very vivid, we may be able to count seven colors red, orange and yellow, green and blue, indigo and violet. The spectroscope has a tube fitted with a glass prism and a system of lenses to view these colors in finer detail. It reveals not seven, but a multitude of colors as one band of ribbon merges with the next. When used to identify a substance, it also accents certain bands of color with vivid or dark hues.
Since spectrum colors are the colors of light, a substance being tested must be burned and changed to incandescent gas. It must be consumed in a colorless flame which has no color of its own to confuse the picture. The glass prism, of course, bends the wavelengths of light and spreads them apart in the banded rainbow. The incandescent substance scores lines on certain bands of the spectrum. This is photographed to give a spectrogram.
This picture of accented lines on the spectrum of ordinary white light is the undisputed signature of the substance being tested. Each chemical element writes its own signature. Chemical compounds reveal the signatures of the different elements they contain.
The spectrograph needs only a small fragment of material to reveal its contents. It takes a skilled expert to read some of the signs, but a few elements have bold, John Hancock type signatures. Sodium, for example, accents a vivid yellow line in the spectrum. We can see its yellow glow in the burning gas of sodium. But a precise scientist checks its with the spectroscope to make sure that its signature occurs in the correct part of the spectrum's yellow band.
Most elements accent two colors and the spectroscope reveals the bold signature of sodium to be two lines, close together in the yellow band of the spectrum. Helium also accents a line in the yellow band, close enough to sodium to fool the eye. But the spectrogram pinpoints it farther to the blue end of the spectrum.
The signatures of lithium and rubidium also can confuse the eye. Both accent lines of rich, vivid red but the spectrograph reveals that they cross different parts of the red color band. The spectrum of the sun has many light and dark lines that reveal the various substances in its blazing gases. The remarkable spectroscope detected helium in the sun before this element was discovered on the earth.