Mark Tuttle, age 10, of Montgomery, Alabama, for his question:
What is the sun made of?
Our cool planet is made from 92 chemical elements and the sun appears to be made of the very same basic ingredients. However, our most plentiful elements are very scarce on the sun and we are very short of the sun's most plentiful elements. Besides, all the earth's ingredients are liquids, frozen gas solids and coolish gases. While in the starry sun, all the atomic elements are seething gases. What's more, most of its atoms are densely packed ions, stripped of their electrons. Their condition is vastly different from our cool, gaseous atmosphere.
Three quarters of the sun is seething hydrogen gas and one quarter is helium gas. The earth is very short of these two elements. Our most plentiful ingredients include oxygen, silicon and assorted metallic elements. These and most of our remaining ingredients make up only one per cent of the sun. Within the sun's 99 per cent mixture of hydrogen and helium there are atoms of oxygen and neon. In smaller amounts there are carbon and nitrogen. Magnesium, silicon and iron are present in still smaller amounts. Traces of aluminum and sulphur, calcium, nickel and chromium have been identified plus atoms of most of the earth's other basic ingredients.
It appears that the seething sun and the cool earth are made of the same atomic elements though the ingredients are in vastly different proportions. The fascinating problem is how these tiny atoms were identified in the sun from a distance of 93 million miles. The answers were found in the rainbow spectrum of light. Atoms of incandescent hydrogen gas create brilliant lines across the yellow band of the spectrum. Burning gases of all the elements create identifying lines in their own colored bands of the spectrum.
All the sun's ingredients are incandescent gases. So you would expect to find all its elements identified by their vivid lines in the solar spectrum. But this is not so. The light comes from the sun's seething surface where each blazing element marks its own vivid color. But from our earthly point of view, this surface photosphere is below the red chromosphere and other layers of the sun's atmosphere. These thinner, cooler gases absorb the brilliant identification lines and replace them on the spectrum with dark lines. There are thousands of these dark lines across the solar spectrum.
They reveal the sun's ingredients because each one matches the vivid lines made by this or that atomic element.
Light is electromagnetic energy and the banded colors of the spectrum are different wavelengths. The blue end of short waves graduates to the red end of the longest visible rays. The banded rainbow is marked off in angstrom units and the range of visible light runs from about 4000 to somewhat higher than 7000 angstroms. Each element in the sun leaves its signature of dark lines, precisely where it can be identified in angstroms on the solar spectrum.