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The science behind our Sun and its interaction with Earth 1 The science behind our Sun and its interaction with Earth The limited amount of the Sun's energy that reaches Earth gives us heat and light, without which Earth would be lifeless. Nicholas Guillerm Monica Seoane Alex Reed Physics 1010 Salt Lake Community College The science behind our Sun and its interaction with Earth 2 Abstract This paper explores solar research. For thousands of years the human race has felt a significant connection to the Sun. Although astronomy is as ancient as recorded history itself, it was long separated from the study of physics. In ancient times people observed celestial bodies in the sky that seemed to be perfect spheres moving in perfectly circular orbits. Early astronomers and scientists such as Archimedes (287 BC-212 BC), Nicolaus Copernicus (1473 – 1543), Galileo Galilei (1564 – 1642) and Isaac Newton (1643-1727) were equipped with crude tools, yet their scientific deductions were brilliant and laid the groundwork for the experimental researchers who followed them. Recently, through technological and scientific advances, scientists have uncovered many mysteries behind the Sun's energy. Albert Einstein (1879 – 1955), Carl Sagan (1934 – 1996) and Stephen Hawking (Born 1942) continued scientific research and made enormous contributions to the ancient study of astrophysics. The availability of observational data led to research and then to theoretical explanations. The study of our very own star “The Sun” has a special place in observational astrophysics. Due to the tremendous distance of all other stars, the Sun can be observed in detail unparalleled by any other star. Our understanding of our own Sun serves as a guide to our understanding of planets and of other stars. The science behind our Sun and its interaction with Earth 3 The limited amount of the Sun's energy that reaches Earth gives us heat and light, without which Earth would be lifeless. How The Sun affects Life On Earth. Our Sun has lived for approximately 4.6 billion years. It is about halfway through its lifespan (Frank, 2008). The Sun's light and heat are absolutely vital to human existence, yet most of us take them for granted. The Sun is the most important factor in Earth supporting life. We have come a long way in the study of our star, and have learned much. Understanding our Sun has led to many breakthroughs in science and technology, and in our understanding of the physical universe. Our Sun, while completely vital to our lives, to the point that for most of human history it was an object of worship or seen as the center of the Universe, is for the most part just an average star. There are innumerable stars in the universe, many far larger than our Sun while many others are smaller. The energy from this glowing sphere of gas produces climates on Earth capable of supporting life. The radiant energy given off by the Sun warms and lights Earth, heating its solid and liquid surfaces as well as its atmosphere. Warmth is distributed because the air in our atmosphere is always moving. The same is true of our oceans. Water absorbs heat from the Sun's rays and carries warmth through ocean currents. The Sun also emits radiant energy at a high frequency, much of which is in the visible portion of the electromagnetic spectrum. We can therefore observe the effects of light illuminating the Earth. Although we know there are connections between solar activity and Earth's climate, humans have yet to discover all the implications of those effects. Only through continued research and a collaboration between researchers from multiple scientific fields can we gain a more complete understanding. Photosynthesis is a process by which plant life on Earth converts light energy from the Sun into chemical energy for fuel. This process allows plants to convert water and carbon The science behind our Sun and its interaction with Earth 4 dioxide into carbohydrates and oxygen creating a well balanced ecosystem. For many millions of years plant life has evolved the ability to convert energy from the Sun into fuel but now, in a much shorter period of time, the human race has begun doing the same. With the invention of solar power technology we are now harnessing sunlight and converting it into electricity through a process called photovoltaics. Due to the increased demand for renewable and pollution free energy, the manufacturing techniques in solar panel technology have advanced in recent years while the cost has declined since the first solar cells were manufactured. Although the Sun's energy supports life by warming Earth's surface, solar radiation is deadly to humans. The Earth's atmospheric ozone layer contains carbon dioxide and water vapor which reflect harmful rays back into space and protect us from extreme temperatures and ultraviolet light, however some UV rays make it through to the surface. While plant life feeds on light photons, humans and other animal life can suffer adverse effects from excessive UV exposure. Too much sunlight can trigger DNA damaging molecules and cause skin cancer. Solar flares and storms sometimes eject large numbers of highly energetic particles and X rays towards Earth that our protective layer of atmosphere can not stop. Geomagnetic storms can damage Earth’s orbiting satellites, and have been known to knock out electrical power and radio communications over large regions. Among the observable effects of these storms in the Earth’s atmosphere are the Auroras, geomagnetic disturbances that appear as beautiful lights that The science behind our Sun and its interaction with Earth 5 may drift to lower latitudes, becoming more brilliant and concentrated, as the magnetic force on the magnetosphere is increased. Structure of the Sun. The Sun is a giant ball of hot gas that generates energy and releases it into space in all directions. With the help of Einstein's Special Theory of Relativity, along with the ideas of other scientists in the late 1930s, the human race learned that the Sun's energy comes from a process called nuclear fusion, in which mass is converted into energy. Our Sun is just a typical middle aged, middle sized star that in another 5 billion years or so will exhaust its hydrogen resources and begin to expand and fuse helium into carbon as it nears its end. The Sun formed about four and a half billion years ago from a collapsing cloud of interstellar gas. The contraction of this cloud released gravitational potential energy in the form of thermal radiation. The remaining energy was trapped inside the cloud causing its interior temperature and pressure to rise. The cloud reached a state of gravitational equilibrium becoming capable of sustaining nuclear fusion and the Sun was born. At this point the pressure of hot gas pushing outward precisely balanced the inward pull of gravity as the energy generation came into balance with the energy lost from the surface in the form of electromagnetic radiation. The source of the Sun's energy is its plasma core, which is one hundred times as dense as water with a temperature of about 15 million degrees kelvin. The core, while only a fraction of the Sun's volume, contains half of its mass. Positively charged hydrogen atoms move within the Sun at very high speeds and collide with one another transforming into helium, while also generating light photons. Approximately four hundred million tons of hydrogen are turned into helium each second in the Sun's core. The science behind our Sun and its interaction with Earth 6 The energy from the core radiates outward, passing into the next layer of the Sun, the radiative zone. Here the heat can only travel as electromagnetic radiation due to the extreme density and heat of the area. In the radiative zone the energy made in the core, comprised of gamma rays, radiates out in the form of photons. Throughout the radiative zone these photons are bounced around so much they make take hundreds of thousands of years to leave the radiative zone, despite moving at the speed of light. As they bounce, photons lose energy, becoming less energetic photons. This is fortunate for us as gamma rays aren't exactly good for us. Beyond the radiative zone is the convective zone. As the name implies, here the energy is transferred via convection towards the outer edges of the star. The convection zone is responsible for the “boiling” of the Sun, and can cause matter to be ejected outwards in solar flares, also creating the granulated surface that is seen in detailed pictures of the Sun. The photosphere is the layer of the Sun that we actually see. In general, although the Sun has no surface, it is the photosphere that is being referred to when we speak about the surface of the Sun. The diameter of the photosphere is usually used to measure the diameter of the Sun. It is the coolest part of the star at an average temperature of 6050 degrees Kelvin. The pressure of the photosphere is very low, for the most part less than 1% the pressure of the Earth's The science behind our Sun and its interaction with Earth 7 atmosphere. It is the layer where electromagnetic radiation is emitted on the spectrum that we can actually see. Finally, there are the Sun’s outer layers, the chromosphere and the corona. The chromosphere is where most of the Sun's hydrogen emissions take place. It is visible during a solar eclipse as a dim ring around the Sun. Spicules of hot gas erupt above the photosphere with the temperatures climbing up to 10,000 degrees Kelvin (Franke, 2008). It is believed that this heat increase in the chromosphere is due to wave motion through the plasma of the Sun. The corona is a thin layer of gas, billions of times less dense than that of the atmosphere of the Earth at sea level, stretching far beyond what we see of the Sun. This is the layer of the Sun responsible for the solar winds. The corona is heated to 2 million degrees Kelvin (Franke,2008). It is known that the temperature of the corona is so high because the atoms observed with in it are found to be highly ionized, which can only occur in the range of millions of degrees. It is thought that this heating is caused by the solar magnetic field, which can store and transport energy from the inner regions of the core (utk edu, 2011), but this phenomenon is not fully understood. Because it is millions of times less bright than the rest of the Sun, the corona is normally invisible to us, although it can be seen during a total solar eclipse. Solar activity refers to the array of solar phenomena that can be observed from earth. This portion of the paper will be dedicated to the observation of three main phenomena: Sun spots, solar flares, and coronal mass ejection, and the relation between the three. Among the observable phenomena that occur on the Sun’s surface are sunspots. These spots are cooler, darker regions on the surface of the Sun created by bundles of magnetic energy being pushed to the surface. Sunspots are calculated to have a temperature of about 3700K The science behind our Sun and its interaction with Earth Figure 1. compared surface. 8 with 5700K for surrounding areas of the Sun’s The magnetic field of sunspots if calculated to to be almost 1000 times stronger than the surrounding photosphere. The spots consist of two main parts, these being the “umbra” and the “penumbra”. Umbra is the darkest innermost region of the sunspot, while “penumbra” refers to the outer, lighter region. Sunspots are perhaps the most easily observed solar phenomena, most often appearing in groups or in pairs with negative and positive polarities. Some of the larger spots can even be observed by the naked eye. Written records on the observation of sunspots can be traced back to almost 800 B.C. China (Bergman, 2005). They have been observed throughout recorded history by many curious astronomers who believed they were seeing clouds on or above the surface of the Sun. Galileo was one of these astronomers, and was among the first to deduce that the sunspots proved the rotation of the Sun, and the movement and activity of its surface. Galileo provided drawings of his observations, carefully tracking the movement of a group of sunspots over a series of weeks, shown in Figure 1 (Van Helden, 1995). In 1843 continuous observation of the Sun eventually lead an amateur German astronomer, Samuel Heinrich Schwabe, to the discovery of a sunspot cycle. The solar cycle can be measured in an 11 year span, coinciding with periods of greatest sunspot activity or highest sunspot count (“solar maximum”), and by contrast, the period of lowest sunspot count, or the “solar minimum”. This eleven year span periodically reverses, coinciding with the 22 year span of the Sun’s magnetic field cycle. The Sun’s eleven year cycle is influenced by surface flow, The science behind our Sun and its interaction with Earth which is influenced by several 9 Figure 2 components. Rotation, oscillation, cellular convection and meridional flow are all contributing components. The Royal Greenwich Observatory has provided detailed observations of sunspots since 1874. The data provided by the observatory show that sunspots do not in fact happen at random but form in concentration in two latitude bands on either side of the equator (Hathaway, 2013). Figure 2 shows the position of sunspots along the equator starting in 1874 and continuing until 2010. Other phenomena that coincide with the Sun’s 11 year cycle are solar flares. Solar flares are massive electromagnetic eruptions that occur when magnetic energy that has built up in the solar atmosphere becomes greatly pressurized and is then released. Solar flares usually occur near sunspots, in the neutral area between two oppositely directed magnetic fields. Energy released in a solar flare typically spans almost the entire electromagnetic spectrum, exerting waves and lengths throughout (Hathaway, 2012). Classification of solar flares is based on their x-ray light intensity using a series of letters with numerical value, A B C M or X, with A being the lowest classification, releasing the least intense x-rays, and X being the greatest classification (Hathaway, 2013). The science behind our Sun and its interaction with Earth 10 Figure 3 Figure 4 Solar flares occur most frequently at the solar maximum of the 11 year cycle, as this is the time of greatest surface activity. In 1859, Richard C. Carrington was among the first to record a solar flare that happened to occur during his observation of sunspots. First believing the flare to be a trick of light entering through a screen, he then realized that the phenomena was actually happening on the surface of the Sun. After recording the time, he hastily searched for someone to observe the phenomena with him, only to return a minute later and realize the moment had passed. Figure 3 displays the points (A and B) at which “intensely white and bright light broke out…” (Carrington, 1859). Solar flares can occur very quickly, as Carrington’s experience proves, but they may also be extended, decreasing in brightness over hours or even days. These prolonged flares are often accompanied by another, much larger scale eruption called Coronal Mass Ejections or CME (Figure 4). Figure 4 displays a halo event, in which the entire Sun seems to be surrounded by the expanding CME. The “halo” occurs when the CME explodes in the direction of Earth. Although CMEs and solar flares are often observed together, CMEs can also occur independently of an extended The science behind our Sun and its interaction with Earth 11 solar flare. CMEs are large bubbles of magnetized gas which, when exploding, are comparatively much larger than solar flares. CMEs occur in many variations, some having a three-part structure, others a narrow jet, and still others appearing as global eruptions. CME’s essentially remove built up magnetic energy and plasma from the Sun’s corona (Webb & Howard , 2012). Coronal mass ejections can occur as frequently as several times a day during the solar maximum, and as infrequently as once every couple of days during the solar minimum. The magnetized plasma emitted during these eruptions can interrupt the solar winds creating a shock wave that accelerates solar winds and increases already existing solar activity. These mass explosions hurdle magnetic energy and particles towards Earth, expanding as they travel and disturbing the Earth’s magnetosphere, an onrush known as a geomagnetic storm. Observation of the connection between the three described phenomena, sunspots, solar flares and CMEs, helps us understand more about the structure of the Sun and how it distributes its energy. Learning about the distribution of our Sun's energy allows us to better understand how more distant stars across the universe work as well. Studying solar activity and the Sun as the source of life helps expand our knowledge of how the Sun directly affects us on the small planet we call home. Quote By Carl Sagan “The Earth and every living thing are made of star stuff”(Carl Sagan, Cosmos) “The nitrogen in our DNA, the calcium in our teeth, the iron in our blood, the carbon in our apple pies were made in the interiors of collapsing stars. We are made of star stuff.” (Carl Sagan). The science behind our Sun and its interaction with Earth References Bergman, J. (2005, September 06). History of sun spot observations. Retrieved from http://www.windows2universe.org/sun/activity/sunspot_history.html Carrington, R. C. (1859). Description of a singular appearance seen in the sun on september 1, 1859.Monthly Notices of the Royal Astronomical Society, Vol. 20, p.13-15, 20, 13-15. Retrieved from http://adsbit.harvard.edu/cgi-bin/nph-iarticle_query?bibcode=1859MNRAS..20...13C Hathaway, D. H. (2013, March 01). The sunspot cycle. Retrieved from http://solarscience.msfc.nasa.gov/SunspotCycle.shtml Hathaway , D. H. (2012, August 14). Photospheric features. Retrieved from http://solarscience.msfc.nasa.gov/feature1.shtml Van Helden, A. (1995). Sunspots. Retrieved from http://galileo.rice.edu/sci/observations/sunspots.html Webb , D. F., & Howard , T. A. (2012). Coronal mass ejections: Observations. Living Reviews in Solar Physics, 9(3), 1. Retrieved from http://www.livingreviews.org/lrsp-2012-3 The photosphere of the sun. (n.d.). Retrieved from http://csep10.phys.utk.edu/astr162/lect/sun/photosphere.html The university of michigan solar and heliospheric research group.. (n.d.). Retrieved from http://solar-heliospheric.engin.umich.edu/hjenning/Chromosphere.html utk edu.(2011). The solar corona. Retrieved from http://csep10.phys.utk.edu/astr162/lect/sun/corona.html Franke, T. (2008). Structure of the sun. Retrievedfrom http://cde.nwc.edu/SCI2108/course documents/the sun/structure/structure.htm Donahue, Bennett, Schneider Voit. The Cosmic Perspective. Massachusetts: Boston, 2008. Addison Wesley 12