Phillip Coppock, age 11, of Colorado Springs, Colo., for his question:
WHAT IS A STAR MADE OF?
Largest star in the heavens is about 1 billion miles in diameter, or about 1,000 times larger than our sun. The smallest has a diameter of about 5,200 miles. Nearest star to the earth, excluding the sun, is Proxima Centauri which is 4.3 light years away. Farthest one is in a galaxy billions of light years away from earth.
A star is a ball of glowing gas. The sun is a star and there are more than 200 billion more of them. From earth, only about 4,000 can be seen most of them as pinpoints of light.
A star is made of two gases: hydrogen and helium. You see a star shining because atomic energy makes these gases very hot. A star will continue to shine until it runs out of helium gas and the fuel used to make atomic energy.
Astronomers tell us that most stars started shining between 3 million and 10 billion years ago. New stars continue to form within the clouds of gas and dust left over from old stars. The sun, the scientists tell us, probably took shape from the remains of an old star.
Scientists also say that the earth might have taken shape from the same material as the sun. They say that the earth, and all living things on it, is made up of atoms that once were part of a star.
Starlight has a wide variety of color. Some stars are blue while others are white, yellow, orange or red. The star's color depends on surface temperature of the star. A red star will be about 5,000 degrees Fahrenheit while a blue star will be 50,000 degrees. Our sun, which is a yellowish star, has a temperature of about 10,000 degrees Fahrenheit.
Brightness depends on the amount of light energy that a star sends out, not on its size. A small distant star can look larger from earth than a large, nearer star if it is hotter.
Nuclear energy is produced in a star with a changing of hydrogen into hellium. This happens in two ways: the proton proton reaction and the carbon cycle.
In the proton proton reaction, the nuclei of hydrogen atoms collide with one another and combine to produce nuclei of helium atoms.
In the carbon cycle, first the nuclei of hydrogen atoms collide with carbon nuclei to form nitrogen atoms. Then additional collisions change the nitrogen to oxygen and back to nitrogen. Finally, each nitrogen nucleus breaks down into a carbon nucleus and a helium nucleus.
Stars shine until they use up all of their hydrogen. Astronomers tell us that most stars have enough hydrogen to last billions of years.
Nuclear fusion produces so much energy that the temperature at the center of a star can reach millions of degrees. They are cooler on their surfaces.