The Sun Our Extraordinary Ordinary StarGuiding QuestionsSlide Number 3The Sun’s energy is generated by thermonuclear reactions in its coreThe Sun’s energy is produced by hydrogen fusion, not in a single step, but in a sequence of thermonuclear reactions in which four hydrogen nuclei combine to produce a single helium nucleusSlide Number 6Slide Number 7Slide Number 8A theoretical model of the Sun shows how energy gets from its center to its surface Slide Number 10Slide Number 11How do we know about the solar interior?Slide Number 13Slide Number 14A Subatomic InterludeA Subatomic Interlude IIA Subatomic Interlude IIIA Subatomic Interlude IVNeutrino FactoidsNeutrino DetectionNeutrinos reveal information about the Sun’s core—and have surprises of their own The Photosphere - the lowest of three main layers in the Sun’s atmosphere The Sun is a sphere, although it appears as a disk. This leads to a phenomenon known as limb darkening.Convection in the photosphere produces granulesSlide Number 25The Chromosphere - characterized by spikes of rising gasSlide Number 27Slide Number 28The corona ejects mass into space to form the solar wind Activity in the corona includes coronal mass ejections and coronal holes Sunspots - low-temperature regions in the photosphereSlide Number 32Sunspots are produced by a 22-year cycle in the Sun’s magnetic fieldSlide Number 34Slide Number 35The solar magnetic changes are caused by convection and the Sun’s differential rotationSlide Number 37Slide Number 38Slide Number 39Slide Number 40Rotation of the Solar InteriorThe Sun’s magnetic field also produces other forms of solar activity Jargon1The Sun Our Extraordinary Ordinary Star2Guiding Questions1. What is the source of the Sun’s energy?2. What is the internal structure of the Sun?3. How can astronomers measure the properties of the Sun’s interior?4. How can we be sure that thermonuclear reactions are happening in the Sun’s core?5. Does the Sun have a solid surface?6. Since the Sun is so bright, how is it possible to see its dim outer atmosphere?7. Where does the solar wind come from?8. What are sunspots? Why do they appear dark?9. What is the connection between sunspots and the Sun’s magnetic field?10. What causes eruptions in the Sun’s atmosphere?3An Overview of the Details4The Sun’s energy is generated by thermonuclear reactions in its core• The energy released in a nuclear reaction corresponds to a slight reduction of mass according to Einstein’s equation E = mc2• Thermonuclear fusion occurs only at very high temperatures; for example, hydrogen fusion occurs only at temperatures in excess of about 107 K• In the Sun, fusion occurs only in the dense, hot core5The Sun’s energy is produced by hydrogen fusion, not in a single step, but in a sequence of thermonuclear reactions in which four hydrogen nuclei combine to produce a single helium nucleus6789A theoretical model of the Sun shows how energy gets from its center to its surface • Hydrogen fusion takes place in a core extending from the Sun’s center to about 0.25 solar radius• The core is surrounded by a radiative zone extending to about 0.71 solar radius– In this zone, energy travels outward through radiative diffusion• The radiative zone is surrounded by a rather opaque convective zone of gas at relatively low temperature and pressure– In this zone, energy travels outward primarily through convection10Understanding Hydrostatic Equilibrium11Understanding Hydrostatic Equilibrium II12How do we know about the solar interior?• Helioseismology is the study of how the Sun vibrates• These vibrations have been used to infer pressures, densities, chemical compositions, and rotation rates within the Sun By using the Sun’s own vibrations13Solar Model Results1415A Subatomic Interlude16A Subatomic Interlude II17A Subatomic Interlude III18A Subatomic Interlude IV• Neutrinos are produced in the “Weak Interaction”, for example– Neutrinos from Earth• natural radioactivity– “Man-made” neutrinos• accelerators, nuclear power plants.– Astrophysical neutrinos• Solar neutrinos• Atmospheric neutrinos• Relic neutrinos– left over from the big bang.19Neutrino Factoids• The earth receives about 40 billion neutrinos per second per cm2 from the sun.– About 100 times that amount are passing through us from the big bang.• This works out to about 330 neutrinos in every cm3 of the universe!• By comparison there are about 0.0000005 protons per cm3 in the universe.• Our body emits about 340 million neutrinos per day from 40K.• Neutrinos don’t do much when passing through matter.• Remember, it is very difficult to observe neutrinos.20Neutrino Detection• The neutrino is observed by detecting the product of its interactio n with matter.neElectronnMuon21Neutrinos reveal information about the Sun’s core—and have surprises of their own• Neutrinos emitted in thermonuclear reactions in the Sun’s core have been detected, but in smaller numbers than expected• Recent neutrino experiments explain why this is so22The Photosphere - the lowest of three main layers in the Sun’s atmosphere• The Sun’s atmosphere has three main layers– the photosphere– the chromosphere– the corona• Everything below the solar atmosphere is called the solar interior• The visible surface of the Sun, the photosphere, is the lowest layer in the solar atmosphereThe spectrum of the photosphere is similar to that of a blackbody at a temperature of 5800 K23The Sun is a sphere, although it appears as a disk. This leads to a phenomenon known as limb darkening.24Convection in the photosphere produces granules25MoreConvection26The Chromosphere - characterized by spikes of rising gas• Above the photosphere is a layer of less dense but higher temperature gases called the chromosphere• Spicules extend upward from the photosphere into the chromosphere along the boundaries of supergranules27CrossSectionalView of theSolarAtmosphere28• The solar corona blends into the solar wind at great distances from the SunThe Corona –outermost layer of the solar atmosphere, made of very high-temperature gases at extremely low density29The corona ejects mass into space to form the solar wind30Activity in the corona includes coronal mass ejections and coronal holes31Sunspots - low-temperature regions in the photosphere32Sunspot Cycle -Sunspots on the move33Sunspots are produced by a 22-year cycle in the Sun’s magnetic