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Chapter 15 (15.1), Chapter 16 (16.1-16.3), Chapter 17, Chapter 18, Chapter 19 (19.2).pdf

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15.1 THE STRUCTURE AND COMPOSITION OF THE SUNCOMPOSITION OF THE SUN'S ATMOSPHEREChapter 15 (15.1), Chapter 16 (16.1-16.3), Chapter 17Chapter 19 (19.2)Sunday, October 21, 201811:35 AM
7, Chapter 18,
Similarity between Sun and other stars shown by Cecilia Payne-Gaposchkin (1925)The Sun is hot enough that most atoms are ionized (hot ionized gas is plasma)In the 19th century, we observed a spectral line at 530.3 nmWe figured out that this was due to highly ionized iron (lost 13 electrons)Sun's atmosphere is more than a million degreesTHE LAYERS OF THE SUN BENEATH THE VISIBLE SURFACE
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The core produces nuclear energyIt is about 20% of the Sun's size with temperature of 15 million KThe radiative zone starts at 25% of the distance to the solar surface and extends to about 70%Light generated in the core is slowly transported through the radiative zone due to the high densityThe convective zone transports energy from the radiative zone to the surface through giant convection cellsAbout 200,000 km deepPlasma gets heated, rises to surface, cools, and sinks back downTHE SOLAR PHOTOSPHEREThe Sun becomes opaque in this layerAbout 400 km thickDiameter of Sun is the size of the region surrounded by the photospherePressure is less than 10% of Earth's pressure at sea levelDensity is about 1/10000ths of Earth's atmospheric density at sea levelStructure is known as granulationGranules are 700-1000 km in diameterLifetime is 5-10 minutesSupergranules are 35,000 km in diameterLifetime is about 24 hoursBright granules are columns of gas rising from below the photosphere at 2-3 km/sSpreads out, cools, and sinks into dark regions between granulesCenters of granules are 50-100 K hotter than intergranular regionsTHE CHROMOSPHERERegion above the photosphere
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Until now, it was only visible during solar eclipses2000-3000 km thickBright emission lines show it is composed of hot gases emitting light at discrete wavelengthsReddish color comes from hydrogen emissionHelium was discovered on the chromosphere in 1868, it was only discovered on Earth in 1895Temperature is about 10,000 KTHE TRANSITION REGIONRegion where temperature rapidly risesNASA launched Interface Region Imaging Spectograph (IRIS) to study (2013)
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THE CORONAObserved first during total eclipsesExtends millions of km above photosphere, emits half the light of a full moonCoronagraphs are used to photograph it now (occulting disk that removes the Sun's glare)Low density (10^10 less atoms per cm^3 compared to sea level in Earth's atmosphere)THE SOLAR WINDOutward stream of protons and electrons at 400 km/sThe Sun loses about 10 million tons of material per yearX-ray and UV pictures show that the corona has loops, plumes, bright and dark regionsLarge dark regions are coronal holesMagnetic field lines stretch into space rather than looping backGas can stream without hindrance from magnetic fieldsMagnetic field lines come into Earth at the north and south magnetic polesParticles can follow the field into our atmosphere

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Term
Fall
Professor
LARSON,ANNA

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