Evan Massaro, age 9, of Garden Grove, Calif., for his question:
What makes a star?
The nearest star to us bathes our world in sunlight every day. Our globe spins around like a top and turns to face it with first one side and then another. This shining star, of course, is our glorious sun. It shines day and night, whether our side of the Earth is facing it or not.
Our starry sun is big enough to gobble up our whole world a million times and still have room for more. Some of the faraway stars are big enough to gobble up our sun a million times, and some are no bigger than the Earth. But all the stars are fiery balls of blazing gases. They burn with the kind of fire and heat that comes from an atomic bomb. For the stars are nuclear power plants, and their radiant heat and light come from atomic energy.
Hydrogen and oxygen, iron and calcium are chemical elements. Our world is made from countless solids, liquids and gases. But all these substances are made from about 90 different elements. The stars also are made from these and perhaps a few other elements. But the fiery furnaces are too hot for the chemicals to become solids or liquids. Stars are made of gases, seething gases hotter than our hottest blast furnaces.
Hydrogen is the element made of the smallest atoms, and hydrogen makes up only a tiny fraction of our world. But hydrogen is the most plentiful of all the gases in a star. A star is made from about nine parts of hydrogen gas and one part of other seething gases. This hydrogen is the fuel for its furnace, which it burns by nuclear fusion. This process is the opposite of nuclear fission, which is the splitting apart of atoms.
In nuclear fusion, smaller atoms are joined together to make larger atoms. In a star, small atoms of hydrogen are fused to make larger atoms of helium. A few fragments of the hydrogen atoms are left over. They are the ashy waste from the fiery furnace, but they are very different from the ashes of a coal fire. In a star, the waste fragments of hydrogen are changed into seething atomic energy. They pour forth in all directions as heat and dazzling light. The sunbeams that fall upon our Earth have traveled to us from 93 million miles away. They are the atomic energy of our starry sun.
Astronomers tell us that the sky is populated with young stars, older stars and very ancient stars. A star is born from a vast cloud of hydrogen gas. As the vast cloud shrinks it may form a family of orbiting planets. It has enough hydrogen fuel to blaze away for billions of years, but finally it burns out and becomes a dark, dead ball of solid materials. Our beaming sun, we are told, has enough hydrogen fuel to keep blazing away for at least another 10 billion years.