What is the Sun Like?

            The sun is a star. Though the sun is about 93 million miles away, it is our main source of heat and light, as well as the source of most of our other forms of energy. Without the sun, there would be no green plants, and without green plants there would be no food for other living things.
            Because the sun is the nearest of all the stars, it appears larger and brighter than the others. Actually, the sun is only a medium-sized star. Yet the diameter of the sun is over 100 times greater than the earth's diameter. If the sun were hollow, there would be room inside it for more than a million earths. The sun is much hotter than anything you can imagine. Scientists believe that near the center its temperature must be more than 20 million degrees F. At such a temperature, materials cannot exist in a solid or a liquid state. Not even gases can keep their ordinary properties. The sun's gases include large amounts of hydrogen, smaller amounts of helium, and much smaller amounts of oxygen, nitrogen, carbon, neon, and other elements.
            The surface of the sun is not equally bright all over. If you look at the sun through a piece of dark glass, you can often see dark spots on its surface. Telescopes show even more of these dark spots. Scientists call these dark places sunspots. the sunspots appear dark because they are cooler than the areas around them. They vary greatly in size. Some are no more than 500 miles in diameter, while others are more than 50,000 miles across. Sometimes the sunspots form groups that cover areas of several billion square miles. Scientists have not yet discovered what causes sunspots, but they do know that sunspots occur in cycles of about eleven years in length. During this period, the sunspots increase in number up to a certain point, and then they decrease in number. Often when there are large numbers of sunspots, telephone, radio, and even some other kinds of communications on the earth are severely disturbed. They also affect the working of magnetic compasses. Some scientists think that sunspots may even affect our weather.
            For many years scientists could not understand how the sun could keep on giving out enormous amounts of energy. If the sun were burning, it would have burned itself out long ago. Scientists now know that the sun produces heat and light by releasing atomic energy from some of its elements. Heat can be obtained from atomic energy. In atomic fission, large atoms such as uranium atoms split into smaller atoms. Another way that atomic energy is released is when small atoms, such as hydrogen, come together and fuse to make larger atoms. This is called atomic fusion. Huge amounts of heat and light are produced as a result of fusion. Most of the sun's energy seems to be produced when hydrogen atoms combine to form helium. Scientists think that this process of releasing atomic energy has been going on in the sun for several billion years and will probably go on for more than ten billion years.