PYTS/ASTR 206 – The Sun1AnnouncementszAnnouncements Late homework #1 due now (50% credit) Homeworks returned on Thursday Grades were well distributed – Average was a high CThe SunPTYS/ASTR 206 – The Golden Age of Planetary ExplorationShane Byrne – [email protected]/ASTR 206 – The Sun3In this lecture…In this lecture…z Introduction to the Sunz Powering the SunThe core and nuclear fusionThe core and nuclear fusionz Solar interiorz Photosphere and Solar Atmospherez Magnetic effects Sunspots, flares etc…SunspotszSunspots 11 year cycle Longer cycles and climatez Comparing the Sun to other stars Hertzsprung Russell DiagramPYTS/ASTR 206 – The Sun4IntroductionIntroductionz The sun contains ~98-99% of all the material in the solar systemPYTS/ASTR 206 – The Sun5z The sun dominates the solar system Contains almost all the mass Is huge compared to any other objectSupplies almost all the energySupplies almost all the energy Other sources – contraction of planets e.g. Jupiter Other sources – Radioactive elements e.g. Earth’s interior Dominates the orbits of almost all solar system objectsyj Except those of planetary Moonsz Long argument about where the sun’s energy comes fromPYTS/ASTR 206 – The Sun6z The sun can be divided up into…It iInterior Nuclear fusion reactions Energy transported radiation and convection Temperatures up to 15 million degrees (Kelvin) “Surface”- photosphere Not solid – really part of the atmosphere About 6000K Magnetic field effects Sunspots, flares etc Energy transported convection “Atmosphere” Chromosphere and CoronaVthiVery thin Up to 1 million degrees Energy transported radiation Solar windPYTS/ASTR 206 – The Sun7Solar interior – Powering the SunSolar interior – Powering the Sunz Atoms have nuclei surrounded by electron cloudsz Atomic nuclei contain protons (with a + electric charge) and neutrons Held together by the ‘strong’ nuclear forceforce Repelled from other nuclei by electromagnetic forcesIf you can get two nuclei close enoughIf you can get two nuclei close enough then the strong nuclear force will winz How do you force two nuclei together?High temperatures++High temperatures A lot of energy Nuclei move fast High pressures++ Atoms are closely packed Nuclei collide often++++Low energy – nuclei repel each otherHigh energy –nuclei combinePYTS/ASTR 206 – The Sun8z Temperature and density are very (very very) large in the center of the sunPYTS/ASTR 206 – The Sun9zHow dense is the sun on average?zHow dense is the sun on average?The SunThe EarthA rockPYTS/ASTR 206 – The Sun10zHow dense is the sun on average?zHow dense is the sun on average?The SunThe EarthArockThe Sun1400 Kg m-3The Earth5500 Kg m-3A rock~3000 kg m-3AditfthSil!zAverage density of the Sun is low! z It’s the enormous mass of the Sun (330,000 Earth Masses) that generates the high pressures at its centerz Gravity does the workz Gravity is weak so stars need to be big to make this workPYTS/ASTR 206 – The Sun11z All the energy is produced in the dense, hot, corez >90% of the sun’s mass is in the central halfPYTS/ASTR 206 – The Sun12z Two main players to think btabout Hydrogen Helium%f S 99.9% of the atoms in the SunzNumber of protons decideszNumber of protons decides what the element isz Number of neutrons decides the isotopethe isotopeZeroNeutronsOneNeutronTwoNeutronsHydrogen (H)1 – protonH1Regular HydrogenH2DeuteriumH3TritiumHelium (He)2 – protonsHe3Helium 3He4Regular HeliumPYTS/ASTR 206 – The Sun13z Nuclear fusion releases energyTh tthiHd lif it hli lThe proton-proton chain –Hydrogen nuclei fuse into a helium nucleusWindows to the universeHydrogen Bombz Other reaction chains exist in bigger starsWindows to the universePYTS/ASTR 206 – The Sun14z Net effect? 4 hydrogen nuclei go in… …1 helium nuclei comes out With some other sub-atomic junk But…. 4 x H1has more mass than 1 x He4 What happened to the extra mass? It was converted to energyIt was converted to energy… E = m c2z Nuclear fusion – small atoms fusing togetherz NOT nuclear fission – big atoms splitting apart Plutonium, Uranium etc… Nuclear fission is used in power plants (and bombs) Nuclear fusion will be used in power plants in the near-future (and bombs)PYTS/ASTR 206 – The Sun15z Nuclear fusion produces the energy…. Now what?Eit tdthhthEnergy is transported through the sunz Radiative zone No organized gas motion Photons carry the energy Zig-zag path due to collisions with atomsz Convective zone Organized gas motion Many convection cells Extends up to the ‘surface’ Driven by density differenceswww.physics.arizona.eduPYTS/ASTR 206 – The Sun16Solar “surface” – the photosphereSolar “surface” – the photospherez Hot gases convected up from below Hot – 6000K Tenuous – Density of 0.01% of room air Radiates like a blackbody in the visible portion of the spectrum We can’t see through the photosphere with lightwith light Photosphere is about 400km thick Very thin compared to the solar radius 700,000kmPYTS/ASTR 206 – The Sun17z Convection cells create granules~1000 km across lasts a few minutes~1000 km across, lasts a few minutes Larger collections of cells exist - supergranules 35,000km across, lasts 1 dayPYTS/ASTR 206 – The Sun18Solar AtmosphereSolar Atmospherez Divided into the: ChromosphereCoronaCoronaPYTS/ASTR 206 – The Sun19z Chromosphere2000k hi k2000km thick Temperature inversion Heated from below – photosphereHeated form above–CoronaHeated form above Corona Much more tenuous than photosphere 1/10,000thof the densityPYTS/ASTR 206 – The Sun20z CoronaStarts 2000km above the photosphereStarts 2000km above the photosphere Extremely hot – 2 million degrees Very Tenuous1011atoms per cubic meter1011 atoms per cubic meter 1,000,000,000,000 times less dense than the photosphere No upper edgeG d ll fd it it l t diGradually fades into interplanetary medium How is the Corona heated ?? Magnetic field effectsPYTS/ASTR 206 – The Sun21z Recap the different parts of the SunSolar radius 700,000km So a ad us 00,000Region Position/Thickness Temperature NotesThermonuclear Core 0 - 0.25 Solar radii 15-8 million K Fusion reactionsRadiative zone
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