Wednesday, June 30, 2010

Understanding Sun

An evening spent looking up under dark skies will convince you that stars can be breathtaking in their loveliness. We can appreciate why, for thousands of years, human beings thought that the stars were embedded in a perfect sphere, spinning and changeless. Yet, because of their great distance, theirs is a remote beauty. Many amateur astronomers are disappointed to discover that stars (other than the sun) look pretty much the same through even the best telescope. Our common sense sees little similarity between the distant, featureless points of light against a sable sky and the great yellow disk of daytime, whose brilliance overwhelms our vision and warms our world. Yet, of course, our sun is a star—and, as stars go, not a particularly remarkable one. We now turn our attention to the very center of our solar system, the parent of the terrestrial and jovian planets and their rings and moons. We have spent the last three chapters discussing the planets and their moons. But taken together, these objects represent only 0.1 percent of the mass of the solar system. The other 99.9 percent of the mass is found in the sun. Peoples of many times and cultures have worshipped the sun as the source of all life, and in some sense, they were right. The sun is our furnace and our light bulb: the ultimate source of most energy and light here on the earth. And because it contains almost all of the mass, it is the gravitational anchor of the solar system. Indeed, its very matter is ours. The early sun was the hot center of a swirling disk of gas and dust from which the solar system formed some 4.6 billion years ago. If the sun were a cake, the earth and the rest of the planets would be some flour left on the counter. But the sun is only one star in a galaxy containing hundreds of billions of stars. Astronomers feel fortunate that the sun is so nondescript a citizen of the galaxy. It is, of course, the star closest to us and its very averageness lets us generalize about the many stars that lie far beyond our reach. In this chapter we examine our own star, and begin to explore how the sun (and stars in general) generate the enormous energies that they do.

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