But what is the Sun made of and how does our star emit such an enormous amount of energy? First, we should point out that for the innermost regions of the star we cannot use direct measurements nor rely on special instruments to make observations from the Earth or from space. So, astronomers have developed some reasonable theories to explain these phenomena. Below the photosphere, moving towards the interior of the Sun, the density gradually increases due to the enormous pressure exerted by the outer layers of the star: after a convective area, consisting of columns of gas at 6 000 degrees Celsius as indicated by the"grains" of the photosphere, and an even hotter radiating zone, we reach the core, where matter has a density hundreds of times greater than water and the temperature reaches 15 million degrees. It would seem easy to deduce that such a "kiln" would generate heat simply by burning. And in fact, up to the end of last century, this was one of the two mechanisms proposed by the scientific community. The other, more sophisticated theory, stated that the Sun is a mass of gas that is contracting under the effect of its own gravitational force: the fact that compresses itself generates heat. If this were really the case, making the necessary calculations and considering the dimensions of the Sun, our star should burn out in about twenty million years. And this is exactly what doesn't make sense. By studying the oldest rocks on the Earth, geologists have discovered that our planet is almost five billion years old, and that therefore the Sun must be at least that old. But how can it burn for such a long time without showing any sign of "fatigue"? No one was able to answer this question: it was only thanks to the development of nuclear physics that we began to understand something about the true nature of the Sun.
But what is the Sun made of and how does our star emit such an enormous amount of energy? First, we should point out that for the innermost regions of the star we cannot use direct measurements nor rely on special instruments to make observations from the Earth or from space. So, astronomers have developed some reasonable theories to explain these phenomena. Below the photosphere, moving towards the interior of the Sun, the density gradually increases due to the enormous pressure exerted by the outer layers of the star: after a convective area, consisting of columns of gas at 6 000 degrees Celsius as indicated by the"grains" of the photosphere, and an even hotter radiating zone, we reach the core, where matter has a density hundreds of times greater than water and the temperature reaches 15 million degrees. It would seem easy to deduce that such a "kiln" would generate heat simply by burning. And in fact, up to the end of last century, this was one of the two mechanisms proposed by the scientific community. The other, more sophisticated theory, stated that the Sun is a mass of gas that is contracting under the effect of its own gravitational force: the fact that compresses itself generates heat. If this were really the case, making the necessary calculations and considering the dimensions of the Sun, our star should burn out in about twenty million years. And this is exactly what doesn't make sense. By studying the oldest rocks on the Earth, geologists have discovered that our planet is almost five billion years old, and that therefore the Sun must be at least that old. But how can it burn for such a long time without showing any sign of "fatigue"? No one was able to answer this question: it was only thanks to the development of nuclear physics that we began to understand something about the true nature of the Sun.
