Bill Strickland, age 13, of Cartersville, Ga., for his question:

HOW CAN THE SUN BURN IF IT HAS NO OXYGEN?

Andy's faithful readers have certain favorite questions which get asked all the time. And this is one of them. Each has been answered several years ago, though usually for a reader of a different age group and always from a different point of view. In any case, it seems only fair to repeat the old favorites for those who missed them the last time.

We are told that we live in the Atomic Age, alias the Nuclear Age. We know about nuclear power plants that produce heat, plus other forms of energy, when the nuclei of tiny atoms are split asunder. This atom splitting is called nuclear fission   and the operation is not at all like ordinary fire.

For one thing, ordinary fire cannot burn without plentiful supplies of oxygen  and nuclear fission needs no oxygen at all. Its stupendous energy is released from the mighty forces that bind tiny particles together in the atomic nucleus.     The seething furnace of the sun also operates on energy from the atomic nucleus. It is not the same as nuclear fission, but it, too, needs no oxygen.

The sun's energy comes from nuclear fusion, which is the fusing or joining of small atomic nuclei to build larger atomic nuclei. Its fuel is hydrogen gas, which makes up more than half of the sun's total material. Fusion occurs when the nuclei of four hydrogen atoms combine to form the nucleus of one helium atom.

Each atom, of course, is made from an assortment of smaller particles. In the sun, the newly made larger atom of helium uses almost, but not quite all, of the particles in the hydrogen atoms. The unused portion is converted into solar radiation. This matter is converted into energy.

In the sun, this small operation involving just a few atoms is repeated zillions of times every second. The fusion of hydrogen to form helium occurs on a grand scale, and stupendous quantities of solar energy are released in the process. The operation is generated by fantastic heat in the core of the sun  and no oxygen is needed to run this nuclear activity.

Physicists estimate that the extravagant sun consumes 564 million tons of its hydrogen fuel every second. In every second, its nuclear fusion produces 560 million tons of helium gas, which is the ash of the solar furnace. And every second, 4 million tons of surplus matter are converted into the solar energy.