Sunlight_and_Stars

Science of the Sunlight and Stars University of Phoenix January 14, 2008 Science of the Sunlight and Stars The Milky Way Galaxy has over 100 billion stars. The Sun is the largest star in the Milky Way located about 28,000 light-years from the galactic center. Astronomers have been able to learn more about the attributes of the Sun in the recent twentieth century. They have been able to determine through radioactive dating of the Earth, Moon, and meteorites that the Sun, a G-2 V. type star, has been shinning for almost five billion years. The Sun, which contains more that 99.9% of the solar systems mass, is not a solid object even though on the surface it appears as one. Compared to Earth, the sun is about 333,000 times the mass and is almost 10 times the size of Jupiter. Because the Sun has so much mass it is able to produce its own light. In fact, almost all the visible light that is received in space comes from hot objects like the Sun and the stars. Internal Structure Before the twentieth century astronomers were able to determine the density and temperature structure of the interior of stars through principles of gas physics but they did not know where the energy of the Sun came from and how energy is produced. Helping to unlock this secret, scientists have studied the interior structure of the Sun. The Sun is gaseous - made up of mostly hydrogen and helium. Deep in the center of the Sun is the solar core. The core makes up about 10% of the mass of the Sun. Temperatures are extreme in the core with internal temperatures around15 million Kelvin (K). The core is very dense – “more than 100 times that of water and the pressure is 200 billion times that on the surface of Earth” (Bennett, Donahue, Schneider & Voit, 2007, p. 482). The extreme heat in the core produces nuclear reactions where hydrogen gases are turned into helium. As this energy moves outward on its way to the surface it enters the radiative zone. The radiative zone is an area of the Sun that covers approximately 85% of its radius and is where the energy moves outward through photons of light. Temperatures at this point rise to almost 10 million K (Bennett, Donahue, Schneider & Voit, 2007). It takes many years for the radioactive photons to pass through this level of the Sun to get to the next layer called the convection zone. It makes up about 15% of the Sun’s radius (astronomynotes.com, 2007). The convection zone is named for the process of heat being cooled through gas. The convention layer gives off the appearance that the surface is seething and churning in the solar sky (Bennett, Donahue, Schneider & Voit, 2007). The gases of helium and hydrogen are most apparent at this level while the other materials are calcium, iron, sodium, and magnesium. Temperatures range from one million degrees to around 6,000 degrees. Once the energy of the Sun passes through the convection zone it reaches the surface. This is where the photons are able to escape into space. Astronomers have been able to gather information about the Sun and its interior through the use of optical and radio telescopes, computers, observatories, and from specially designed space equipment. These scientists can now observe changes in the Sun, its atmosphere, wind shifts, and flares that occur on the surface. Computers can calculate temperatures, changes in the gas and heat, and analyze the Sun’s magnetic fields and winds. Observation pictures can now be taken which give the astronomers the ability to gain a closer look at this massive star. Energy Output The energy that the Earth receives from the Sun has been a mystery for many centuries. Long ago it was believed that the Sun was an actual fire in the sky. Other scientists and astronomers had different ideas of what the sun was made of and where the energy came from but it took until the late 1930’s to work out the details. Today, science has proven that the Sun’s energy is produced by nuclear fusion. Nuclear fusion is the “process in which two (or more) small nuclei slam together and make one larger nucleus” (Bennett, Donahue, Schneider & Voit, 2007, p.G-9). The sun converts hydrogen into helium. “Each second about 700,000,000 tons of hydrogen are converted to 695,000,000 tons of helium and 5,000,000 tons of energy in the form of gamma rays” (Arnett, para.7). In order for nuclei to be joined; the nuclei must be close together, have high temperatures and high density. “The only place these extreme conditions occur naturally is in the cores of stars” (Strobel, p.3). In the core of the sun, “positively charged atomic nuclei and negatively charged electrons are moving round at extremely high speeds and may collide with other nuclei and stick together” (Bennett, Donahue, Schneider & Voit, 2007. p.482, ¶8). When these nuclei stick together this is the nuclear fusion process. This process depends on the high temperature in the sun’s core to allow the nuclei to move at high rates of speed in the core. Because the nuclei are moving around at a high speed, this allows the nuclei to come close together to allow the fusion to occur when they collide. “The higher the temperature, the harder the collisions, makes fusion reactions more likely at higher temperatures” (Bennett, Donahue, Schneider & Voit, 2007. p.483-484). The nuclear fusion process occurs in several steps. “The first step takes two protons which fuse together to make a nucleus consisting of one proton and on neutron, this is called a deuterium nucleus. The second step occurs when the deuterium nucleus created in step one collides with a proton and fuses together. The end result of this collision is a nucleus of helium-3 consisting of two protons and one neutron. This helium-3 is a rare form of helium. The next step, step three occurs when two helium-3 nuclei collide with another helium-3 nuclei to form a helium-4 consisting of two protons and two neutrons and the process releases the two excess protons during the process” (Bennett, Donahue, Schneider & Voit, 2007, p.484). “Fusion of hydrogen into helium generates energy because a helium nucleus has a mass slightly less than the combined mass of four hydrogen nuclei” (Bennett, Donahue, Schneider & Voit, 2007. p.485). The slightly less mass that occurs during this process becomes the energy which is identified in Einstein’s formula of E=mc². Equilibrium Equilibrium is “a condition in which all acting influences are canceled by others, resulting in a stable, balanced, or unchanging system” (Equilibrium, 2008). Many different types of equilibrium exist including hydrostatic equilibrium, thermal equilibrium, and nuclear equilibrium. Hydrostatic equilibrium is the balance between a star’s gas pressure and gravity; gas pressure pushes outward while gravity is pulled inward. The Sun is in a state of hydrostatic equilibrium because the Sun is neither collapsing nor exploding. A star will collapse if more gravity exists than pressure. A star will explode if more pressure than gravity exists. The Sun is not in perfect equilibrium because the Sun is not completely still due to prominences, flares, and vibrations (Equilibrium, 2007). Thermal equilibrium occurs when a star maintains a steady temperature (Thermal Equilibrium, 2008). “The Sun is about 6,000 K at the surface, radiating into a 3 K blackbody, and is about 1.5 x 10 to the 7th K in its center. These temperature differences mean that energy has a one-way flow from hot to cold, so this is clearly a non-equilibrium situation” (Equilibrium, 2007). The Sun is not far from equilibrium because the temperature does not change randomly over a few seconds. However, the Sun is losing energy to radiation. Because the Sun is not made primarily of iron this means that the Sun is not in nuclear equilibrium (Equilibrium, 2007). “The term equilibrium does not mean that there isn’t any change in the star. It just means that there is not a net overall change in the star” (Equilibrium: Life Goal of a Star, 2008). The Sun is not in perfect equilibrium but is very close to being in equilibrium. Evolution Stars have been around for billions of years traces of the first generation of stars have not been found in this lifetime do to the fact that first generation stars were born in high temperatures of molecular clouds, which caused these stars to have a short lifespan (Bennett, Donahue, Schneider & Voit, 2007, p.536). The evolution of stars or star births comes from studying young stars and stellar birthplaces, in studying young stars and stellar birthplaces astronomers were able to find that dark clouds of gas and dust is the birthplace of stars (Bennett, Donahue, Schneider & Voit, 2007, p.527). The interstellar medium, which is “the gas and dust that fill the spaces between stars within a galaxy” help form molecular clouds (Bennett, Donahue, Schneider & Voit, 2007, p.528). The gas in the interstellar medium is composed of mostly hydrogen and helium and this can be traced back to the Big Bang Theory (Bennett, Donahue, Schneider & Voit, 2007, p.528). Stars are born “in the coldest and highest density types of interstellar clouds” which are known as molecular clouds (Bennett, Donahue, Schneider & Voit, 2007, p.528). Molecular clouds are “cold enough and dense enough to combine together and form molecules,” the temperature is usually about 10-30 K and the density has typically about 300 molecules occupying each cubic centimeter (Bennett, Donahue, Schneider & Voit, 2007, p.528). Hydrogen molecules are the most abundant in these clouds and helium atoms are also very abundant in these clouds the rest is interstellar dust (Bennett, Donahue, Schneider & Voit, 2007, p.528). Stars form because “gravity causes the cloud to contract, and the contraction continues until the central object becomes hot enough to sustain nuclear fusion in its core,” which becomes a star (Bennett, Donahue, Schneider & Voit, 2007, p.530). As pressure begins to push back, the contractions “slows down and the central part of the cloud becomes a protostar (Bennett, Donahue, Schneider & Voit, 2007, p. 544). A protostar is a clump of gas that will eventually become a star (Bennett, Donahue, Schneider & Voit, 2007, p.536). Meanwhile, “matter from the surrounding cloud rains down upon the protostar, increasing its mass” (Bennett, Donahue, Schneider & Voit, 2007, p.544). Just like human beings stars are born and eventually die. During a stars life a star can go through many phases such as the intermediate mass phase, the t-tauri phase, main sequence phase, red giant phase, asymptotic phase, the white dwarf phase, the black dwarf phase, supernovae, neutron stars, and black holes (NASA.gov, 2007). The T-Tauri phase is a variable star that varies in brightness (NASA.gov, 2007). The main-sequence phase occurs when there is greater mass, and “the more rapidly the hydrogen in its core is used up, and therefore the shorter is its stay on the main sequence” (NASA.gov, 2007). The red giant phase occurs “as the star expands, its outer layers become cooler, so the star becomes redder. And because the star’s surface area expands greatly, the star also becomes brighter” (NASA.gov, 2007). The Sun, which is also a star currently in its life cycle, is in the intermediate mass phase. The sun “has enough nuclear fuel to remain much as it is for another 5 billion years (NASA.gov, 2007). Then the sun will enter the red giant phase, then the white dwarf phase, and finally the black dwarf phase (NASA.gov, 2007). Conclusion The stars are an amazing part of the universe and the Sun is the largest star in the Milky Way Galaxy. The Sun is made up of mostly hydrogen and helium. Extreme temperatures range from 15 million K at the core to 6000 K at the surface. The Sun’s energy is produced by nuclear fusion, which involves several steps. Equilibrium is found in stars and in the Sun. The Sun does not have perfect equilibrium do to certain factors such as flares and prominences. The evolution of stars goes back billions of years. The Sun and stars go through many phases in there lifetime before they burn out. Because of recent technology scientist have been able to understand why and how the Sun and stars get their energy. The beauty of stars can be captured through a telescope, a film, a textbook, a picture, or by simply looking up to the sky. References Arnett, Bill. (2006). The Sun, retrieved January 11, 2008 from www.nineplanets.org/sol.html Astronomynotes. (2007 June 2). The sun-the closest star. Retrieved December 29, 2007, from http://www.astronomynotes.com/starsun/s2.htm Bennett, J., Donahue, M., Schneider, N., & Voit, M. (2007). The Cosmic Perspective, Pearson Education, Inc. Equilibrium. (2007). Astro. Retrieved January 13, 2008 from http://www.astro.umd.edu/~miller/teaching/astr320/lecture16.pdf Equilibrium. (2008). The Free Dictionary. Retrieved January 12, 2008 from http://www.thefreedictionary.com/equilibrium Equilibrium: Life Goal of a Star. (2008). Stars. Retrieved January 13, 2008 from http://aspire.cosmic-ray.org/labs/star_life/starlife_equilibrium.html NASA. Sun retrieved January 8, 2008 from www.nasa.gov/worldbook/sun_worldbook.html NASA. Star retrieved January 8, 2008 from www.nasa.gov/worldbook/star_worldbook.html Strobel, Nick (2001). The Sun and Stellar Structure, retrieved January 11, 2008 from www.astronomy notes.com/starsun/s3.htm Thermal Equilibrium. (2008). Zebu. Retrieved January 13, 2008 from http://zebu.uoregon.edu/~imamura/208/jan27/thermal.html