The sun; a giant, glowing ball of gas some 850,000 miles in diameter. The temperature at its surface is over 11,000 F., hot enough to vaporize any material known to man. Deep within the sun, the temperature rises to over twenty million degrees, a heat we cannot begin to imagine or comprehend.
            The sun dominates our solar system, containing more than 99% of the system’s matter. The sun is a thousand times as massive as Jupiter, the largest planet, and 335,000 times as massive as the earth. And if the sun were hollow, 1,300,000 earths could be fitted inside!
           In short, the sun is immense; it is the unquestioned center of the solar system.
           And yet, when compared with other stars, the sun is nothing more than average. There are stars a dozen times as massive as the sun, and others but a tenth as large. There are stars that outshine our sun 50,000 times over, and others just a hundredth as bright.
           In fact, the sun is a very middling sort of star, not overly large, not overly small. But this average sort of star is of paramount importance to every living thing on earth. Without the sun, life here obviously not possible. Plants live and grow by means of photosynthesis, making direct use of the sun’s energy; animals survive by feeding on stored food produced by the plants. All our energy sources [save nuclear power] depend, in the end result, on the energy of the sun; even coal and oil are solar energy, trapped by primitive plants hundreds of millions of years ago and stored underground for years.
        Without the sun, we wouldn’t be here. That’s why the future behavior of the sun is of the utmost importance to us.
        The sun is, as I’ve said earlier, is an average star. It is now approaching middle age, having been around for about five billion years. The sun should continue to shine as it does now for about another five billion years before its fuel is exhausted.
      The sun, astronomers have told us in the past, is a stable star: its output of light and heat is unvarying over millions of years. That’s reassuring: as long as the sun remains as it is now, life on earth remains possible. Were the sun to heat up, let’s say, by only a small fraction of its total energy output, the oceans will boil and the earth would become a parched, uninhabitable wasteland. Were the sun to cool off by only a small fraction of its total output, the glaciers would descend from the poles and earth would turn into a frozen, icy world forever. All life would perish.
        But the sun, astronomers told us, is quiet and well-behaved. It won’t heat up, it won’t cool down, and we have nothing to fear.
         As recent as ten years ago, astronomers were completely sure of this point. But now their ideas about the stability of the sun have been challenged, and some of their new findings are unsettling and disturbing indeed.
                                                                            THE ENERGY MACHINE
            Deep within the core of the sun, nuclear reactions take place. In these reactions, hydrogen is converted to helium, and a small amount of matter is converted into energy. Every second some 616 million tons of hydrogen are changed to 612 million tons of helium. That difference of four million tons of matter is converted into energy –and this energy is responsible for the heat and the light of the sun.
            In these reactions various subatomic particles are produced. We are concerned here with only one, the NEUTRINO. The neutrino is a very strange sort of particle indeed. It seems to have mass, no weight; it always travels at the speed of light; and to the neutrino, matter is as transparent as empty space. The neutrino could travel through trillions of miles of solid lead before being stopped.
           The neutrino, once it is formed in the center of the sun, takes off at a speed of light, 186,000 miles per second. In two and a half seconds it has left the sun behind; in eight and a half minutes it has reached the orbit of the earth.
           While neutrinos are clear of the sun almost immediately, the same is not true of ordinary radiation. The energy released in the center of the sun must work its way to the surface; the particles are radiated and absorbed, radiated and absorbed; and only after a million years have passed does a ray of light make it to the surface of the sun, where it takes off into space. The sunlight which illuminates the earth was actually formed in the solar core a million years ago!
          This fact lends special importance to neutrinos, for while all the rest of the sun’s radiation is a million years old by the time it gets to us, the neutrinos have left the solar core just minutes ago. Scientists decided that to get a good idea of what’s going on in the center of the sun they’d somehow have to detect neutrinos.
          This is not an easy task, for as I have noted, an individual neutrino is virtually never stopped by matter. And yet the sun produces hundreds of billions of neutrinos every second, so that while an individual neutrino may almost never stop by matter, the odds are that at least a few of these hundreds of billions of neutrinos will be stopped.