Dave Cooper, age 12, of Minnedosa, Manitoba, Canada, for his question:
WHEN WILL THE SUN RUN OUT OF HEAT AND LIGHT?
Our sun is only one of billions of stars in the universe, and it is the closest star to earth. The huge ball of gases lets most of its heat and light disappear in space with only about two billionths reaching earth. How hot is the sun? Astronomers can't be sure exactly but they figure the temperature at the sun's center is about 27 million degrees Fahrenheit.
When the sun's energy reaches the surface, it is sent out into space as radiant energy in the form of light and heat. We once thought this heat and light came from something burning within the sun, but we now know that the light and heat come from thermonuclear reactions in the center of the sun.
Scientists say that the sun is about 4.6 billion years old, while the Milky Way was formed between 10 and 15 billion years ago.
Thermonuclear reactions change the sun's hydrogen into helium. At the rate of its current expenditure of energy, scientists estimate that the sun can shine for at least 10 billion years with little or no change in its size or brightness. This means that the sun will most likely shine for at least another 5 billion years.
Scientists have been able to predict what will happen when the sun uses up all of its energy. The center of the sun will shrink and become hotter while the surface temperature will fall slightly. Higher temperatures at the center will increase the rate at which hydrogen changes into helium, and the amount of energy given off by the sun will also increase.
Then the outer regions of the sun will expand about 30 to 40 million miles. The sun will then be a red giant star, and the earth's temperature will become too hot for life to exist there.
When the sun uses all of its thermonuclear energy as a red giant, it will begin to shrink. Eventually it will shrink to about the size of earth and then become a white dwarf. In this state, the sun will have entered a final stage of its existence.
After billions of years as a white dwarf, the sun will have used up all of its energy and lost all of its heat. It will then be called a black dwarf. When this happens, all of the planets in our solar system will be cold and dark. If atmosphere should still remain on earth, the gases of the atmosphere would be frozen.
Solar storms occur on the surface of the sun. Some occur in the form of arches of gas called prominences. The arches rise from the edge of the disk and flow back into the sun. Other solar storms happen in areas of gas called sunspots. They seem to appear and disappear in regular cycles. A third type of storm takes place as bright bursts of light called flares. Flares release large amounts of solar energy.