Dale Rosebush, age 13, of P eterboro, Ontario, Canada, for his question:

How much energy is in the sun?

This question may mean either how much energy the sun has left, or how much it pours forth, moment by moment. Astrophysicists can estimate both these figures, though the amount of remaining energy in the fiery furnace is based on some guesswork. The constant output of solar energy can be computed more precisely. It is estimated from the amount of radiation that falls upon the surface of the earth    at a distance of almost 93 million miles.

If our sun were encased in a glacier 39 feet thick, all that ice would vaporize in about a minute. This imaginary situation gives some idea of the amount of energy that continuously radiates from the sun. Astronomers assume that the blazing star is a nuclear furnace, consuming its original hydrogen fuel at a steady rate. Each square centimeter on its enormous surface radiates energy equal to about eight horsepower. Its total output equals the nuclear energy from four million tons of hydrogen every second.

These estimates are based on small samples here on earth and traced back to the sun. It is possible to measure perpendicular rays and figure how much solar energy they shed on a square centimeter of the earth's surface. An average sample allows for other rays slanted by the curved earth, for day and night, and the effects of the atmosphere. These and other figures are computed to give the total amount of energy that the sun sheds upon our planet. I comes to about 126 million million horsepower  ¬or roughly 54,000 horsepower per person.

Naturally there is a vast difference between the radiation that reaches us and the amount poured fourth from the surface of the sun. Radiation diminishes at a set ratio as it fans out from its source. To reach the earth, the sun's energy must traverse 92,956,000 miles through space. If the sun were hollow, it could swallow more than a million earth sized planets    which gives us some idea of its enormous surface.

These are some of the known facts used to compute the sun's constant outpouring of energy. It sheds energy equal to about 1.8 horsepower on every square meter of the earth's surface. Tracing this back, we find that every square meter of the sun's surface must be pouring forth energy equal to about 8,000 horsepower. Actually, the earth gets only one in two billions parts of the continuous energy poured from the sun.

Spectrum analysis of the sun's incandescent gases indicates that about half its original hydrogen fuel has been consumed. At its present rate, it could have done this in about 4 1/2 billion years. Perhaps it can continue to radiate energy for another five billion years or so. Though astronomers are not certain what changes may occur as the furnace subsides. Some suspect that it may slow down and burn for another ten billion years or so.