Slide 1The SunSlide 3Slide 4Slide 5Slide 6Slide 7Slide 8Slide 9Slide 10Slide 11Slide 12Slide 13Slide 14Slide 15Slide 16Slide 17Slide 18Slide 19Slide 20Slide 21Slide 22Slide 23Slide 24Slide 25Slide 26Slide 27Slide 28Slide 29Slide 30Slide 31Slide 32Slide 33Slide 34Slide 35Slide 36Slide 37PYTS/ASTR 206 – The Sun1AnnouncementsLate homework #1 due now (50% credit)Homeworks returned on ThursdayGrades were well distributed – Average was a high CPTYS/ASTR 206 – The Golden Age of Planetary ExplorationShane Byrne – [email protected] SunPYTS/ASTR 206 – The Sun3Introduction to the SunPowering the SunThe core and nuclear fusionSolar interiorPhotosphere and Solar AtmosphereMagnetic effectsSunspots, flares etc…Sunspots11 year cycleLonger cycles and climateComparing the Sun to other starsHertzsprung Russell DiagramIn this lecture…In this lecture…PYTS/ASTR 206 – The Sun4The sun contains ~98-99% of all the material in the solar systemIntroductionIntroductionPYTS/ASTR 206 – The Sun5The sun dominates the solar systemContains almost all the massIs huge compared to any other objectSupplies almost all the energyOther sources – contraction of planets e.g. JupiterOther sources – Radioactive elements e.g. Earth’s interior Dominates the orbits of almost all solar system objectsExcept those of planetary MoonsLong argument about where the sun’s energy comes fromPYTS/ASTR 206 – The Sun6The sun can be divided up into…InteriorNuclear fusion reactionsEnergy transported radiation and convectionTemperatures up to 15 million degrees (Kelvin)“Surface”- photosphereNot solid – really part of the atmosphereAbout 6000KMagnetic field effectsSunspots, flares etcEnergy transported convection“Atmosphere”Chromosphere and CoronaVery thinUp to 1 million degreesEnergy transported radiationSolar windPYTS/ASTR 206 – The Sun7Atoms have nuclei surrounded by electron cloudsAtomic nuclei contain protons (with a + electric charge) and neutronsHeld together by the ‘strong’ nuclear forceRepelled from other nuclei by electromagnetic forcesIf you can get two nuclei close enough then the strong nuclear force will winHow do you force two nuclei together?High temperaturesA lot of energyNuclei move fastHigh pressuresAtoms are closely packedNuclei collide oftenSolar interior – Powering the SunSolar interior – Powering the Sun++++++Low energy – nuclei repel each otherHigh energy – nuclei combinePYTS/ASTR 206 – The Sun8Temperature and density are very (very very) large in the center of the sunPYTS/ASTR 206 – The Sun9How dense is the sun on average?The SunThe EarthA rockPYTS/ASTR 206 – The Sun10How dense is the sun on average?The Sun1400 Kg m-3The Earth5500 Kg m-3A rock~3000 kg m-3Average density of the Sun is low! It’s the enormous mass of the Sun (330,000 Earth Masses) that generates the high pressures at its centerGravity does the workGravity is weak so stars need to be big to make this workPYTS/ASTR 206 – The Sun11All the energy is produced in the dense, hot, core>90% of the sun’s mass is in the central halfPYTS/ASTR 206 – The Sun12Two main players to think aboutHydrogenHelium99.9% of the atoms in the SunNumber of protons decides what the element isNumber of neutrons decides the isotopeZeroNeutronsOneNeutronTwoNeutronsHydrogen (H)1 – protonH1Regular HydrogenH2DeuteriumH3TritiumHelium (He)2 – protonsHe3Helium 3He4Regular HeliumPYTS/ASTR 206 – The Sun13Nuclear fusion releases energyThe proton-proton chain – Hydrogen nuclei fuse into a helium nucleusHydrogen BombOther reaction chains exist in bigger starsWindows to the universePYTS/ASTR 206 – The Sun14Net effect?4 hydrogen nuclei go in……1 helium nuclei comes outWith some other sub-atomic junkBut…. 4 x H1 has more mass than 1 x He4 What happened to the extra mass? It was converted to energy…E = m c2Nuclear fusion – small atoms fusing togetherNOT nuclear fission – big atoms splitting apartPlutonium, 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 Sun15Nuclear fusion produces the energy…. Now what?Energy is transported through the sunRadiative zoneNo organized gas motionPhotons carry the energyZig-zag path due to collisions with atomsConvective zoneOrganized gas motionMany convection cellsExtends up to the ‘surface’Driven by density differenceswww.physics.arizona.eduPYTS/ASTR 206 – The Sun16Solar “surface” – the photosphereSolar “surface” – the photosphereHot gases convected up from belowHot – 6000KTenuous – Density of 0.01% of room airRadiates like a blackbody in the visible portion of the spectrumWe can’t see through the photosphere with lightPhotosphere is about 400km thickVery thin compared to the solar radius 700,000kmPYTS/ASTR 206 – The Sun17Convection cells create granules~1000 km across, lasts a few minutesLarger collections of cells exist - supergranules35,000km across, lasts 1 dayPYTS/ASTR 206 – The Sun18Divided into the:ChromosphereCoronaSolar AtmosphereSolar AtmospherePYTS/ASTR 206 – The Sun19Chromosphere2000km thickTemperature inversionHeated from below – photosphereHeated form above – CoronaMuch more tenuous than photosphere1/10,000th of the densityPYTS/ASTR 206 – The Sun20CoronaStarts 2000km above the photosphereExtremely hot – 2 million degreesVery Tenuous1011 atoms per cubic meter1,000,000,000,000 times less dense than the photosphereNo upper edgeGradually fades into interplanetary mediumHow is the Corona heated ??Magnetic field effectsPYTS/ASTR 206 – The Sun21Recap the different parts of the SunSolar radius 700,000km Region Position/Thickness Temperature NotesThermonuclear Core 0 - 0.25 Solar radii 15-8 million K Fusion reactionsRadiative zone 0.25 – 0.7 Solar radii 8-2 million K Energy transported by photonsConvective zone 0.7 - 0.999 Solar radii 2 million – 6000K Energy transported by convectionPhotosphere 400km thick 6000K Opaque layerChromosphere 2000km thick ~6000K Tenuous atmosphereCorona Extends outwards 2 million K Very hotVery
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