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The Surface of the Sun
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Author: priyanka ladha
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Description: Because the Sun produces so much energy in the visible spectrum, scientists must use different wavelengths to examine the surface and the atmosphere of the Sun. When astronomers look at the surface of the Sun in white light, or the visible part of the spectrum, they use special filters, which block all but approximately 0.0001% of the light from the Sun. On the surface we can see unusual dark and light texture, which is called solar granulation (see Figure 12). This granulation is a result of the convection of energy from the core through the interior, and each granule is only about 1000 km across. The bright areas are the hottest areas, where energy has just arrived at the surface as part of the convective cycle, and the darker areas are cooler zones, which are about to descend into the interior for warming.
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The Surface of the Sun
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Author: priyanka ladha
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Hits: 54
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Description: Because the Sun produces so much energy in the visible spectrum, scientists must use different wavelengths to examine the surface and the atmosphere of the Sun. When astronomers look at the surface of the Sun in white light, or the visible part of the spectrum, they use special filters, which block all but approximately 0.0001% of the light from the Sun. On the surface we can see unusual dark and light texture, which is called solar granulation (see Figure 12). This granulation is a result of the convection of energy from the core through the interior, and each granule is only about 1000 km across. The bright areas are the hottest areas, where energy has just arrived at the surface as part of the convective cycle, and the darker areas are cooler zones, which are about to descend into the interior for warming.
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The Solar Atmosphere
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Author: priyanka ladha
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Description: Corona
The corona is the outermost part of the Solar atmosphere and it extends far out into the solar system. Despite the high temperature of the corona, of about 1 million degrees Celsius, it contains very little heat energy as a result of the tenuous nature of the corona. The gases in the corona are so hot (although there are only a few particles) that they emit mostly X Rays. The corona contains mainly super heated gases, particularly Hydrogen and Helium as well as a few other light elements such as carbon, nitrogen and oxygen, which are completely ionised to leave only a bare nucleus.
There are actually three different types of corona, the White Light Corona, which we see as the wispy halo around the Sun during total eclipses, the Emission Line Corona, due to the emission spectra produced by the highly ionised light elements and the X Ray Corona which emitted as a result of the high temperatures in the corona
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The Solar Atmosphere
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Author: priyanka ladha
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Hits: 76
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Description: Corona
The corona is the outermost part of the Solar atmosphere and it extends far out into the solar system. Despite the high temperature of the corona, of about 1 million degrees Celsius, it contains very little heat energy as a result of the tenuous nature of the corona. The gases in the corona are so hot (although there are only a few particles) that they emit mostly X Rays. The corona contains mainly super heated gases, particularly Hydrogen and Helium as well as a few other light elements such as carbon, nitrogen and oxygen, which are completely ionised to leave only a bare nucleus.
There are actually three different types of corona, the White Light Corona, which we see as the wispy halo around the Sun during total eclipses, the Emission Line Corona, due to the emission spectra produced by the highly ionised light elements and the X Ray Corona which emitted as a result of the high temperatures in the corona
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The Solar Atmosphere
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Author: priyanka ladha
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Hits: 70
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Description: Corona
The corona is the outermost part of the Solar atmosphere and it extends far out into the solar system. Despite the high temperature of the corona, of about 1 million degrees Celsius, it contains very little heat energy as a result of the tenuous nature of the corona. The gases in the corona are so hot (although there are only a few particles) that they emit mostly X Rays. The corona contains mainly super heated gases, particularly Hydrogen and Helium as well as a few other light elements such as carbon, nitrogen and oxygen, which are completely ionised to leave only a bare nucleus.
There are actually three different types of corona, the White Light Corona, which we see as the wispy halo around the Sun during total eclipses, the Emission Line Corona, due to the emission spectra produced by the highly ionised light elements and the X Ray Corona which emitted as a result of the high temperatures in the corona
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The Solar Atmosphere
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Author: priyanka ladha
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Hits: 90
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Description: The solar atmosphere consists of two main regions, the Chromosphere and the Corona.
Chromosphere
The chromosphere, chromo meaning colour, is an irregular layer immediately above the photosphere where the temperature rises to about 20 000 degrees Celsius (see Figure 10). In 1997, researchers from the Stanford-Lockheed Institute for Space Research in America, announced that they believed that the dramatic increase in temperature between the photosphere at about 5700 degrees Celsius and the chromosphere was due to the 'loops of a magnetic carpet' created in the interface layer between the radiative and convective zones.
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The Sun’s Light
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Author: priyanka ladha
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Hits: 65
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Description: Figure shows how the strongest frequency of light that is emitted from an object changes with its temperature.
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The Sun’s Light
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Author: priyanka ladha
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Description: The light from the Sun is made up of many colours, called the visible spectrum and many shorter and longer wavelengths of light, collectively called the electromagnetic spectrum (see Figure 8). These other wavelengths are invisible to humans, but they can be measured with special detectors. These other wavelengths consist of Infrared (IR), Ultraviolet (UV), Micro, Radio, X, and Gamma. IR rays heat up matter. (IR light rays can be produced by specially modified light bulbs, and are used in many places that sell food.) Our atmosphere acts as an "infrared shield," and keeps this light from reaching the surface. UV light has become an increasing concern over the past few years. It is a form of radiation, and the hole in the ozone layer is allowing some of the normally blocked UV light to get through. UV light causes tans, sunburns, and skin cancer. Microwaves are put to use in most people's kitchens in the aptly named "microwave oven." They are used to heat foods quickly, and are more effective at doing so than IR. Radio waves are used in a whole branch of astronomy, for they can penetrate clouds of gas and dust that visible light can't. They are also used for transmitting radio and television shows, with television having a slightly higher frequency. X-rays are a form of radiation that are more powerful than UV, and are normally blocked by our atmosphere. X-rays are mainly used for medical purposes. Since they are a form of higher energy, they can penetrate denser objects than visible light can. Gamma rays are the most energetic form of radiation, and can pass through the human body. In cells, they can cause mutations and other severe damage. Luckily, they are blocked by our atmosphere. If they weren't, life as we know it, would be impossible
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The Sun’s Light
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Author: priyanka ladha
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Hits: 72
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Description: Energy is radiated away from the Sun mainly as electromagnetic radiation - that is light and heat (see Figure 8), which originate in the photosphere. In the Sun, the maximum amount of electromagnetic radiation is emitted in the visible part of the spectrum, which is a direct consequence of the temperature of the photosphere. The photosphere actually makes up the lowest part of the solar atmosphere and can be thought of as the Sun's surface.
The light that is currently reaching the Earth was generated in the Sun approximately 100,000 years ago. It takes that long to get to the surface because the Sun is so dense making it very difficult for the energy to escape. Once light leaves the Sun's surface, it takes approximately 8 minutes and 26 seconds to reach Earth.
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The Sun’s Structure
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Author: sweety shrivastav
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Hits: 39
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Description: The Sun is made up of different layers, which can broadly be described as the Corona, Chromosphere, Photosphere, the Radiative and Convective zones, and the Core, as shown in Figure.
The Core
The core of the Sun contains the innermost 10% of the Sun's mass and 25% of the diameter. As discussed previously, fusion is a process whereby lighter nuclei are fused or joined together into more massive nuclei. All of the elements present in the Sun are plasmas, as a result of the extremely high temperature of the core (around 15 million degrees Celsius) and the density of the core is about 150 grams per cubic centimetre, more than 20 times that of iron. Unlike the Earth, there is no molten rock or other liquid in the core.
The Interior
The interior of the Sun consists of three zones; the radiative zone, the interface layer and the convective zone.
Radiative Zone
In the radiative zone, (or radiative envelope) heat and energy is transported from the extremely hot core to the convective zone by the movement of photons (light) from the core towards the surface. It extends from the top of the core to about 70% of the Sun's diameter. The density in the radiative zone drops from 20 grams per cubic centimetre (about that of gold) near the core, to 0.2 grams per cubic centimetre (much less than water). In the same distance, the temperature drops from 7 million degrees Celsius to 2 million degrees Celsius.
Interface Layer
As the name suggests, this thin layer lies between the radiative zone and the convective zone. In recent years, this layer has become the focus of much research, as it is now believed to be home to a magnetic dynamo, which is the source of the Sun's magnetic field. As an intermediary between the turbulent convective zone and the calm radiative zone, there are significant changes in the velocity of the fluid, which result in a large shear and a stretching in the magnetic field lines, which increases the field strength.
Convective Zone
The convective zone (or convective envelope) extends for about the last 200 000 km up to the start of the photosphere. Energy in the outer convective zone is transported by a process of convection. At a temperature of about 2 million degrees Celsius at the innermost edge, the heavy ions of elements such as C, N, O, Ca and Fe retain some of their electrons which makes it more difficult for the radiative transfer of energy, so convection processes become more important.
The Photosphere
The photosphere is the deepest part of the Sun that we can see and is analogous to the Earth's crust. It is only about 100 km thick. Unlike the Earth, there is no solid foundation, and the photosphere consists of approximately 94% H, 6% He and 0.13% other gases at a temperature of about 5700 K (or ~ 6000 degrees Celsius). The term photosphere comes from the Greek word photos - meaning light.
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The Sun’s Structure
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Author: sweety shrivastav
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Hits: 63
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Description: The Sun is made up of different layers, which can broadly be described as the Corona, Chromosphere, Photosphere, the Radiative and Convective zones, and the Core, as shown in Figure.
The Core
The core of the Sun contains the innermost 10% of the Sun's mass and 25% of the diameter. As discussed previously, fusion is a process whereby lighter nuclei are fused or joined together into more massive nuclei. All of the elements present in the Sun are plasmas, as a result of the extremely high temperature of the core (around 15 million degrees Celsius) and the density of the core is about 150 grams per cubic centimetre, more than 20 times that of iron. Unlike the Earth, there is no molten rock or other liquid in the core.
The Interior
The interior of the Sun consists of three zones; the radiative zone, the interface layer and the convective zone.
Radiative Zone
In the radiative zone, (or radiative envelope) heat and energy is transported from the extremely hot core to the convective zone by the movement of photons (light) from the core towards the surface. It extends from the top of the core to about 70% of the Sun's diameter. The density in the radiative zone drops from 20 grams per cubic centimetre (about that of gold) near the core, to 0.2 grams per cubic centimetre (much less than water). In the same distance, the temperature drops from 7 million degrees Celsius to 2 million degrees Celsius.
Interface Layer
As the name suggests, this thin layer lies between the radiative zone and the convective zone. In recent years, this layer has become the focus of much research, as it is now believed to be home to a magnetic dynamo, which is the source of the Sun's magnetic field. As an intermediary between the turbulent convective zone and the calm radiative zone, there are significant changes in the velocity of the fluid, which result in a large shear and a stretching in the magnetic field lines, which increases the field strength.
Convective Zone
The convective zone (or convective envelope) extends for about the last 200 000 km up to the start of the photosphere. Energy in the outer convective zone is transported by a process of convection. At a temperature of about 2 million degrees Celsius at the innermost edge, the heavy ions of elements such as C, N, O, Ca and Fe retain some of their electrons which makes it more difficult for the radiative transfer of energy, so convection processes become more important.
The Photosphere
The photosphere is the deepest part of the Sun that we can see and is analogous to the Earth's crust. It is only about 100 km thick. Unlike the Earth, there is no solid foundation, and the photosphere consists of approximately 94% H, 6% He and 0.13% other gases at a temperature of about 5700 K (or ~ 6000 degrees Celsius). The term photosphere comes from the Greek word photos - meaning light.
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Fusion Reactions in the Sun
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Author: sweety shrivastav
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Description: The most important series of fusion reactions are those converting hydrogen to helium in a process known as hydrogen burning. The chances of four protons fusing together to form helium in one go are completely negligible. Instead, the reaction must proceed through a series of steps. The two main hydrogen-burning reaction chains are the proton-proton (PP) chain and the carbon-nitrogen (CNO) cycle. The PP chain divides into three main branches, which are called the PPI, PPII and PPIII chains. The first reaction is the interaction of two protons (p or 1H) to form a nucleus of heavy hydrogen (deuteron, d, or 2H), consisting of one proton and one neutron, with the emission of a positron (e+) and a neutrino (n). The deuteron then captures another proton and forms the light isotope of helium with the emission of a gamma ray (Dhillon, 1999). The PPI reaction occurs 69% of the time, the PPII reaction occurs around 30% of the time, and the PPIII reaction is very rare, only representing 0.093% of the proton-proton reactions in the Sun. The huge release of gamma rays from these processes is what we call “sunlight”. For a pictorial representation of all three proton-proton chains, see Figure1.
The average proton in the Sun will undergo the PPI reaction approximately once in the lifetime of the Sun, i.e. once every 1010 years. The subsequent reactions occur much more quickly, with the second step of the PP chain taking approximately 6 seconds and the third step approximately 106 years in the Sun. The relative importance of the PPI and PPII chains depend on the relative importance of the reactions of 3He with 3He in PPI, as compared to the reactions of 3He with 4He in PPII. For temperatures in excess of 1.4 x 107 K, 3He prefers to react with 4He. At lower temperatures, the PPI chain is more important. The PPIII chain is never very important for energy generation, but it does generate abundant high-energy neutrinos (Dhillon, 1999).
The other hydrogen burning reaction of importance is the CNO cycle. For more massive stars than the Sun, the proton-proton chain can still occur, but there is another sequence of reactions that become favourable for converting hydrogen to helium. In stars, the primary constituents are hydrogen and helium, however there are relatively minute amounts of heavier elements. Carbon (C), Nitrogen (N), and Oxygen (O) ions, if they are present, can partake in the sequence of reactions illustrated in the figure below. The reaction starts with a carbon nucleus, to which are added four protons successively. In two cases the proton addition is followed immediately by beta decay, with the emission of a positron and a neutrino, and at the end of the cycle a helium nucleus is emitted and a nucleus of carbon remains (Dhillon, 1999). The reactions of the CNO cycle are shown pictorially in Figure 2.
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Fusion Reactions in the Sun
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Author: sweety shrivastav
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Hits: 109
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Description: The most important series of fusion reactions are those converting hydrogen to helium in a process known as hydrogen burning. The chances of four protons fusing together to form helium in one go are completely negligible. Instead, the reaction must proceed through a series of steps. The two main hydrogen-burning reaction chains are the proton-proton (PP) chain and the carbon-nitrogen (CNO) cycle. The PP chain divides into three main branches, which are called the PPI, PPII and PPIII chains. The first reaction is the interaction of two protons (p or 1H) to form a nucleus of heavy hydrogen (deuteron, d, or 2H), consisting of one proton and one neutron, with the emission of a positron (e+) and a neutrino (n). The deuteron then captures another proton and forms the light isotope of helium with the emission of a gamma ray (Dhillon, 1999). The PPI reaction occurs 69% of the time, the PPII reaction occurs around 30% of the time, and the PPIII reaction is very rare, only representing 0.093% of the proton-proton reactions in the Sun. The huge release of gamma rays from these processes is what we call “sunlight”. For a pictorial representation of all three proton-proton chains, see Figure1.
The average proton in the Sun will undergo the PPI reaction approximately once in the lifetime of the Sun, i.e. once every 1010 years. The subsequent reactions occur much more quickly, with the second step of the PP chain taking approximately 6 seconds and the third step approximately 106 years in the Sun. The relative importance of the PPI and PPII chains depend on the relative importance of the reactions of 3He with 3He in PPI, as compared to the reactions of 3He with 4He in PPII. For temperatures in excess of 1.4 x 107 K, 3He prefers to react with 4He. At lower temperatures, the PPI chain is more important. The PPIII chain is never very important for energy generation, but it does generate abundant high-energy neutrinos (Dhillon, 1999).
The other hydrogen burning reaction of importance is the CNO cycle. For more massive stars than the Sun, the proton-proton chain can still occur, but there is another sequence of reactions that become favourable for converting hydrogen to helium. In stars, the primary constituents are hydrogen and helium, however there are relatively minute amounts of heavier elements. Carbon (C), Nitrogen (N), and Oxygen (O) ions, if they are present, can partake in the sequence of reactions illustrated in the figure below. The reaction starts with a carbon nucleus, to which are added four protons successively. In two cases the proton addition is followed immediately by beta decay, with the emission of a positron and a neutrino, and at the end of the cycle a helium nucleus is emitted and a nucleus of carbon remains (Dhillon, 1999). The reactions of the CNO cycle are shown pictorially in Figure 2.
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The Hertzsprung-Russel diagram.
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Author: sweety shrivastav
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Description: About 5.5 billion years ago, a passing star or galaxy disturbed a calm and placid cloud of gas and dust, called a nebula. The star or galaxy caused the cloud to swirl around, causing small eddies to form. The swirl caused the gas to start to coalesce together. Gravity, one of the universe's four fundamental forces, caused more and more gas and dust to gather onto these masses. The masses kept getting bigger and bigger. At this stage, they were called protostars. As gravity caused the material to pile on, it also caused them to condense, which increased their gravitational force. The condensation caused the pressure in their cores to rise, and their internal heat increased. When the heat reached a temperature of 10,000,000 °C, nuclear fusion started, and our Sun was born (Case Western Reserve University, 2006).
After a lifetime of 9 billion years as a main-sequence star, approximately 10% of the hydrogen in the Sun's core will have been converted into helium, and nuclear fusion reactions will cease producing energy. The equilibrium between the total pressure force directed outwards and the gravitational force directed towards the centre of the Sun will be disturbed. The core of the Sun starts to slowly collapse under its own gravity and the fusion reactions move out towards shells surrounding the core, where hydrogen-rich material is still present. The gravitational energy from the collapse will be converted into heat causing the shell to burn vigorously and the Sun's outer layers swell. The surface will be far removed from the central energy source, and it will cool and appear to glow red. The Sun will then have evolved into the stage of a red giant (Encyclopedia of Planetary Sciences, 1997).
For a few hundred million years, the expansion of the outer solar layers will continue, and the Sun, as a red giant, will engulf the planet Mercury. The temperature on Venus and Earth will rise tremendously. Hydrogen fusion in the shell continues to deposit helium "ash" onto the core, which becomes even hotter and more massive. In the Sun's core nuclear fusion of helium into carbon and oxygen will start to trigger even further expansion of its outer layers. The helium-rich core, unable to lose heat fast enough becomes unstable. In a very short time of a few hours, the core will get too hot and is forced to expand explosively. Outer layers of the Sun will absorb the core explosion but the core will no longer be able to produce energy by thermonuclear burning. Helium fusion will then continue in a shell and the structure of the Sun will look like an onion: An outer, hydrogen-fusion layer and an inner, helium-fusion layer, which surrounds an inert core of carbon and oxygen. The old Sun may repeat the cycle of shrinking and swelling several times. In this stage of evolution the Sun is called an asymptotic giant branch star. Finally enough carbon will accumulate in the core to prevent the core explosion. Helium-shell burning will add heat to the outer layers of the Sun, mainly containing hydrogen and helium. The asymptotic giant Sun will eventually generate an intense wind that will begin to carry off its outer envelope. The precise mechanism behind this phenomenon is not yet well understood. The Sun will expand a final time, and after about 30 million years it will swallow Venus and Earth, outer layers will keep expanding outward and as much as half of the Sun's mass will be lost into space (Encyclopedia of Planetary Sciences, 1997).
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SUN
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Author: sweety shrivastav
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Description: The Sun is an ordinary star about half way through its lifetime. It generates energy by the process of nuclear fusion occurring in its core.
The Sun generates energy in the same way all other non-giant stars do, using the three main processes of hydrogen fusion. The basic process is to combine light atoms into heavier ones, but the mass of the heavier ones is slightly less than the sum of the lighter ones. The extra mass is lost as energy and radiated into space; this energy conversion is represented in the Einstein's famous equation of E = mc2 (Case Western Reserve University, 2006).
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