11/6/2018 Foundations of Astronomy | 13e Seeds Phys1411 – Introductory Astronomy Instructor: Dr. Goderya Chapter 8 The Sun © Cengage Learning 2016 Topics we have covered Topics for Today’ class I. Introduction A. Viewing the Sun IV. The Sunspot B. General Definition A. Sunspots and Solar Rotation C. General Properties V. Sunspot Activity D. Chemical Composition A. The Solar Cycle E. Basic Structure B. Maunder Diagram C. Solar Rotation II. The Solar Atmosphere D. The Solar magnetic cycle A. The Corona VI. Nuclear Fusion in the Sun B. The Chromosphere A. Nuclear Binding Energy C. Methods of Heat Transfer B. Hydrogen Fusion D. The Photosphere C. The Solar Neutrino Problem E. Temperature gradient in the Sun’s atmosphere F. The Solar Wind III. Interior of the Sun - Helioseismology © Cengage Learning 2016 Sun Spots Sunspots Tend to Occur in Groups or Pairs Active Regions • In sunspot groups, here simplified into pairs of major spots, the leading spot and the trailing spot have opposite magnetic polarity. • Spot pairs in the Southern Hemisphere have reversed polarity from those in the Visible Northern Hemisphere. © Cengage Learning 2016 Ultraviolet © Cengage Learning 2016 1 11/6/2018 Solar Sunspot Cycles The Maunder Butterfly Diagram The number of spots visible on the Sun varies in a cycle Early in a cycle, spots appear at high latitudes north and with a period of 11 years. At maximum, there are often south of the Sun’s equator. Later in the cycle, new spots more than 100 spots visible. At minimum, there are very appear closer to the Sun’s equator. If you plot the latitude of few or zero. sunspots versus time, the graph looks like butterfly wings, as shown in this Maunder butterfly diagram, named after E. Walter Maunder of Greenwich Observatory © Cengage Learning 2016 © Cengage Learning 2016 The Sun’s Magnetic Cycle – Differential Rotation Babcock Model The Babcock model of the • (a) The photosphere of the Sun rotates faster at the equator than at higher latitudes. Sunspot at different latitudes don’t move at the same solar magnetic cycle explains speed. the sunspot cycle as primarily • (b) Detailed analysis of the Sun’s rotation from helioseismology a consequence of the Sun’s reveals that the interior of the Sun rotates differentially as well, with regions of relatively slow rotation (blue) and rapid rotation (red). differential rotation gradually winding up and tangling the magnetic field near the base of the Sun’s outer, convective Differential layer. rotation seems to be responsible The magnetic cycle is about for magnetic 22 years. cycle of the Sun © Cengage Learning 2016 Solar Interior: Core and Envelope Sun Interior and Flow of Energy in the Sun • Near the center, nuclear fusion reactions sustain high Core temperatures. • Energy flows outward through the radiative zone as photons that gradually make their way to the surface as they are randomly deflected over and over by collisions with electrons. • In cooler, more opaque outer layers the energy is carried by rising convection currents of Envelope hot gas (red arrows) and sinking currents of cooler gas (blue arrows This where almost all the energy is generated © Cengage Learning 2016 2 11/6/2018 Density Matters in the Sun Density and Temperature in the Sun Density =Mass/Volume © Cengage Learning 2016 © Cengage Learning 2016 Gravity Pulls Matter Inward Gas Pressure Pushes Outwards What Keeps the Sun from Collapsing on itself? KCVS Where Does Pressure Come From? Indiana.edu Gas Pressure: Ideal Gas Law Gravity and Sun Hydrostatic Equilibrium Pressure = (density)(temperature)(constant) A State When Gravity Compression = Gas Pressure • Gas Pressure is the force of the gas particles colliding with the walls of its container • Density and Temperature control the amount of pressure © Cengage Learning 2016 3 11/6/2018 Energy in the Sun Comparing Oil, Coal and Fusion Where does the Sun gets its energy from? • Nuclear Fusion is Coal? more Efficient Chemical Burning? Nuclear Fission? Or Nuclear Fusion? Fusionforenergy.com© Cengage Learning 2016 Fission or Fusion Comparing fusion with burning What kind of fuel can give such high temperatures and Pressure? Converting 1 kg of Hydrogen into Helium E = mc2 = (0.007kg) (3 x 108 m/s)2 = 6.3 x 1014 joule 20,000 metric tons of coal (2 x 107 kg) is needed to produce this much energy © Cengage Learning 2016 Comparing The Sun with a Nuclear Bomb • Total Output Power 4 x 1026 watts – 100 billion 1 megaton nuclear bombs per second – 4 trillion-trillion 100W light bulbs World War II © Cengage Learning 2016 ClassAction:© Cengage AstronomyLearning 2016 Education at the University of Nebraska-Lincoln Web Site (http://astro.unl.edu) 4 11/6/2018 What Chemical Elements are Needed for Binding Energy Curve Nuclear Fusion or Fission? What is Binding Energy? Energy needed to disassemble the nucleus of an • Obtained by atom. dividing the binding energy by the number of nucleons in the nucleus • Fusion of Iron subtracts energy from the core © Cengage Learning 2016 © Cengage Learning 2016 Conditions for Fusion to Occur Proton-Proton (P-P) reaction http://astro.unl.edu/classaction/animations/sunsolarenergy/fusion01.html • High Temperature (High Velocity) • High Pressure • High Density In the Sun’s Core these conditions are met © Cengage Learning 2016 © Cengage Learning 2016 Converting Mass into Energy Solar Neutrino Problem What is a Neutrino? It is a subatomic particle (Quarks and Leptons) with no charge. Neutrino’s come in three flavors. 4 H atoms = 6.693 x 10-27kg E = mc2 -1 He atom = 6.645 x 10-27kg • The Sun produces 1012 neutrino’s that pass our bodies _______________________ every second Mass Lost = 0.048 x 10-27kg • So why can’ we detect them? 0.7% of mass converted to energy • Is there a problem in our 2 -27kg 8 2 -12 understanding of energy E = mc = (0.048 x 10 ) (3 x 10 m/s) = 4.3 x 10 joule mechanics in the Sun? Lights up a 10-watt bulb for a one-half of a trillionth of a second • Solar neutrino can oscillate in these 3 flavors 107 times larger than burning in a chemical reaction © Cengage Learning 2016 © Cengage Learning 2016 5 11/6/2018 Solar Neutrino Problem The Solar Constant • On Earth only electron neutrino was detect the other two are not. • The Solar Constant Is the Amount of • But if neutrino can oscillate they Energy We Receive From the Sun must have mass and hence gravity. • The energy we receive from the sun is • They could affect the evolution of essential for all life on Earth the Universe. • Solar Constant = F = 1360 J/m2/s – F = Energy Flux = Energy received in the form of radiation, per unit time and per unit surface area [J/s/m2] © Cengage Learning 2016 © Cengage Learning 2016 Acknowledgment • The slides in this lecture is for Tarleton: PHYS1411/PHYS1403 class use only • Images and text material have been borrowed from various sources with appropriate citations in the slides, including PowerPoint slides from Seeds/Backman text that has been adopted for class. © Cengage Learning 2016 © Cengage Learning 2016 6.