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THE SUN.
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Origin, nature, physical features, etc.... More...
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Paper Abstract:
Origin, nature, physical features, etc.

Paper Introduction:
Except for the Earth itself, the Sun is the one body in the Universe in whose fate human beings are most immediately concerned. Its light and heat make life on Earth possible, and the steadiness of that light and heat over four billion years of Earth's history made it possible for that life to evolve and survive. This paper will be devoted to a brief examination of the Sun's nature, origin, major characteristics, and probable fate. The sun is a star. It is often called an "average" star, though stars vary so much in size, energy output, and other characteristics that to call any star average is in a sense misleading. But the Sun is indeed roughly intermediate among the various classes of stars. The most luminous known stars are roughly a million times brighter than the Sun, while the least

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Part of the resulting heat escaped from the solar protostar, and itbecame identifiable from a distance as an infrared star. As the solar nebula collapsed and compressed, individual gasmolecules and dust particles collided with ever-increasing energy andfrequency, releasing heat in the form of infrared radiation. While the Sun shines steadily and shows great long-term stability, atsome energy wavelengths the Sun is extremely violent. When a large number of stars are plottedby color and luminosity, the majority of them form a band from bright-blueto faint-red, a band called the main sequence. "Main Sequence" stars (most of them) are fromten times to one tenth the Sun's size. The Sun's "surface" is essentially the thin zone in which energystops leaking outwards and breaks free in the form of solar radiation. The less massive the star, thefainter and redder its radiation. In the earlystages of collapse the infrared escaped freely, but as the dust grew denserit was trapped, and the material of the solar nebula, previously cold,began to heat up. These experiments, however, have persistently failed todetect the neutrino count, or flux, which theory says they should. Starlightcomes from heat, which in turn is produced in one of three basic ways.Early and late in life, stars shine from heat generated by their owngravitational compression. Any gain of interior energy would causean expansion, reducing interior pressure and temperature, and thus reducingfusion output. One such clump, which astronomers call the solar-nebula, wasdestined to form the Sun, along with everything else in the solar system(Friedman 229ff). The energythus released, in accordance with Einstein's famous relation of mass andenergy, is about 4 x 1 26 watts (Friedman 36-37). White dwarfs stars at the end of life -- shinefrom "fossil" heat produced eons earlier, and slowly radiating away.Through the major part of their lives, stars produce heat by thermonuclearreactions, and the Sun produces its heat by such a reaction. 232). The Sun steadied down to a relatively stable condition as a naturalfusion reactor, a process that took about a hundred million years (Ibid.).Its initial high luminosity faded back until a balance was reached betweentemperature and pressure near the center. Since that time, for four and a half billion years, the Sun's lighthas been steady, except for the very gradual increase in size andluminosity, and reddening and reduction in surface temperature mentionedabove. Two maintypes of reaction are believed to occur within ordinary active stars. Most solar energy isin visible light, but a small fraction, for example, is in X-rays. TheSun's activity could be observed through new instruments, but the solarstorms had a devastating effect on other spacecraft, causing somesatellites to age five years in seven days ("Devastating Solar ..." 584-85). Our exact understanding of how the Sun generates its heat has beencomplicated in recent years by the non-result of a series of scientificexperiments. The more massive the star,the brighter and bluer its radiation. This cycle is the main source of theSun's energy output. The Sun's gradual evolution will continue for another five billionyears, after which its core hydrogen will be largely depleted. Indeed, 1989 was one of the most active years for solar activity inmany years; the most active since the development of space flight. The Sun is of class G- or G-2, depending on thesystem of measurement. How the early Earth kept warm enough inthe light of a younger and fainter Sun is another unsettled question (Ibid.233). The Sun finally became visible to human-like eyes, to whom it wouldhave appeared as an irregular red variable. From an original mix of 75 percent hydrogen and 25 percenthelium, the core of the Sun is now 35 percent hydrogen and 65 percenthelium (Ibid.). onlythe thin outer atmosphere beyond this level is visible to us. How bright and hot a star is on reaching stabilitydepends almost entirely on its initial mass. "Supergiant" stars are a hundred to a thousand times largerin diameter than the Sun. Energy from the core "leaks" veryslowly to the surface, taking ten thousand years to make the trip (Zirin1 ). After a relatively shorttime, hydrogen will be depleted in the shell regions as well, and the sunwill collapse into a red dwarf star, small, hot and faint, gradually fadingfor hundreds of billions of years (Friedman 234-35). The outer layers willswell out, and the Sun will become a red giant star, a hundred times aslarge and a thousand times as bright as now. Inthe simpler "proton-proton" cycle, hydrogen fuses directly together to formhelium, releasing energy as it does. Sun and Earth. It is often called an "average" star, thoughstars vary so much in size, energy output, and other characteristics thatto call any star average is in a sense misleading. The storms had more earthly effects as well, disruptingcommunications and electric power over wide areas. A basicquestion mark thus lies at the very heart of our understanding of the Sun.Either our understanding of the solar thermonuclear reaction is incorrect,or our understanding of the neutrino is incorrect (Zirin 1 -1 2). Cambridge, MA: Harvard University Press, 1982.Zirin, Harold. It was for a while severalhundred times brighter than the Sun we know today, shining from the immenseheat energy released by and trapped in its collapse. The birth of the Sun very probably began with the death of anotherstar, a luminous supergiant that blew itself apart in a supernovaexplosion. In theprocess, some four million tons are "lost": turned into energy. At this time, the solar nebula made the gradualtransition into a protostar. Astrophysics of the Sun. "The Violent Sun." Astronomy, 18 (February, 199 ), 32-34.Noyes, Robert W. Eventually this dark outer cloak was drivenaway by the solar wind, and the Sun became a visible star. Cold opaque dustin the outer portion of the nebula still made it undetectable at thewavelengths of visible light. Thus, solar energy output is held steady by a feedbackprocess. The Sun, Our Star. The sun is a star. This self-stabilizing process occurs to all young stars, which thenshine with a relatively constant luminosity during the major portion oftheir active lives. A belt ofoutlying matter survived in a ring around the proto-Sun's equator to formthe planets and other bodies of the Solar System -- including, ultimately,ourselves. This core is only a quarter the size of the whole Sun, but is thesource of ninety percent of its energy. The Sunwill not then go out. The interioreventually became hot enough to sustain nuclear reactions -- at first inrelatively scarce materials such as lithium and deuterium (used in hydrogenbombs because it is easily induced to fuse into helium), and at last tosustain the carbon cycle reaction. Hydrogen fusion should result in the emission of ghostlysubatomic particles, without mass or electric charge, called neutrinos.These are hard to detect, since a typical neutrino can pass through sixlight-years (thirty trillion miles) of solid lead without being stopped ordeflected. But the Sun is indeedroughly intermediate among the various classes of stars. In the core of the sun, the supply of hydrogen has been partlydepleted. New York: Scientific AmericanLibrary, 1986.Golub, Leon. But in the enormous quantities in which the Sun must producethem, some of these neutrinos should be detected by sensitive instrumentshere on Earth. Stars hotter and brighter than the Sun derive most oftheir energy, it is believed, from a more complex thermonuclear cycle inwhich carbon atoms function as a "catalyst" to join hydrogen atoms and formhelium atoms (Zirin 99-1 ). A sounding rocket launched in the fall of 1989 brought backspectacular photographs of solar X-ray storms (Golub 32-34). About half a million years had passed since thebeginning of the collapse. When the Sun stabilized, it was slightly bluer andhotter, but also smaller and fainter, than it is now. The explosion took place in a spiral arm of the Milky Waygalaxy, among clouds of galactic gas and dust, from which the exploded starhad itself formed in the relatively recent past. Any loss of interior energywould cause a reduction in diameter, increasing pressure and temperature,and stimulating increased fusion. Instead, the core will partly collapse, and hydrogenfusion will spread to a shell around the hot core. Except for the Earth itself, the Sun is the one body in the Universein whose fate human beings are most immediately concerned. Its light andheat make life on Earth possible, and the steadiness of that light and heatover four billion years of Earth's history made it possible for that lifeto evolve and survive. The Sun lies about midwayalong the main sequence, which runs (blue to red) through spectral types ,B, A, F, G, K, and M. Each second, in the interior of the Sun,about six hundred million tons of hydrogen are turned into helium. These clumps then further collapsed of their own weight, fallingin upon themselves with ever-increasing force as they grew smaller anddenser. The expanding shock wavefrom the supernova disturbed and disrupted the nebulae around it,compressing some portions of it together to form clumps at a higherdensity. Blockedfrom Earth's surface by the atmosphere, they are visible only to telescopesin space. The temperature increased most rapidlytowards the center of the solar nebula-protostar, reaching thousands andeventually millions of degrees (Ibid. "White dwarf" stars are a hundredtimes smaller than the Sun (about the size of the Earth), while "neutronstars" are only a few miles across (Noyes 7-11). The basic characteristic of stars is that they shine. Its luminosity wasabout seventy percent of its present level -- enough less that the Earth'soceans should have frozen over. This paper will be devoted to a brief examinationof the Sun's nature, origin, major characteristics, and probable fate. Continued study of theSun will shed new light on the effects of solar storms and radiation, andthe relationship between solar radiation and Earth's climate. The most luminousknown stars are roughly a million times brighter than the Sun, while theleast luminous known stars are three hundred thousand times less brightthan the Sun. Works Cited"Devastating Solar Activity in 1989." Sky and Telescope, 79 (June, 199 ),584-85.Friedman, Herbert. New York: Cambridge University Press, 1988.----------------------- 8

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