lecture15_08 - AST210 Announcements Term Test 2 is on...

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AST210 Announcements Term Test 2 is on Wednesday 12 th November. Help sessions will be announced today or tomorrow. Unclaimed tests: please collect today, here! Final Exam: Tuesday 16 December 9-11 am (in EX100 & EX200) Question re test 1: TA hours today, 12-1, Nick MP1416 and Daniela Goncalves.
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Lecture 15 The Sun's Atmosphere Helioseismology The Solar Wind The Sunspot Cycle Effects on Earth's Climate.
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(11-5) The Solar Atmosphere The Photosphere 1. The solar atmosphere is conveniently divided into three regions; the photosphere, the chromosphere, and the corona.
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Figure 11.16a: The solar disk, the photosphere, in visible light. Courtesy of NASA/JPL-Caltech 2. Photosphere is the visible “surface” of the Sun. It is the part of the solar atmosphere from which light is emitted into space. The photosphere is a very thin layer—400 km thick.
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The Photosphere (cont.) 3. When observing the limb of the Sun (the apparent edge of the Sun as seen in the sky), it appears darker than the center of the solar disk. That’s because when we observe the limb of the Sun we see to a lesser depth because the line of sight is at a grazing angle. 4. The photosphere varies in temperature from about 6,500 K at its deepest to 4,400 K near its outer edge. Overall, the light received from the photosphere is representative of an object with temperature of about 5,800 K.
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See deeper into photosphere Light comes from higher, cooler layers
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Figure 11.17: Intensity vs wavelength for Sun (continuum)
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The Photosphere (cont.) 5. The pressure at one level of the outer photosphere is 0.01 the pressure of the Earth’s surface. Knowing the pressure and temperature we can calculate the density of particles in the outer photosphere: It is about 0.0005 of the density of air at sea level on Earth.
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6. The base of the photosphere shows granulation ; the Sun’s surface is divided into small convection cells. Granules are areas where hot material (light areas) is rising from below and then descending (dark surroundings). T.Rimmele (NSO), M.Hanna (NOAO)/AURA/NSF Sunspot and granules.
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Granulation (time-lapse imagery). Granules have lifetimes of about 10-20 minutes.
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Figure 11.18b: Flow of material in granules, effect of convection in Sun's envelope.
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7. The chemical composition of the photosphere is (by mass) 78% hydrogen and 20% helium; the remaining 2% consisting of 60 elements found on Earth. The similarity in composition between Earth and Sun points to their common origins. Of course, Earth has lost most of its H and He, but the other elements have more similar proportions, allowing for differentiation (some elements “sink”, others “float”).
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From our knowledge of nuclear fusion, we know the Sun’s core must hold more helium. Overall
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This note was uploaded on 04/22/2009 for the course AST 210 taught by Professor Prof.stefanmochnacki during the Fall '08 term at University of Toronto.

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lecture15_08 - AST210 Announcements Term Test 2 is on...

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