Foundations of Astronomy 13e Seeds Phys1411 Introductory Astronomy Instructor: Dr. Goderya Chapter 8 The Sun Topics we have covered I. Introduction A. Viewing the Sun B. General Definition C. General Properties D. Chemical Composition E. Basic Structure II. The Solar Atmosphere A. The Corona B. The Chromosphere C. Methods of Heat Transfer D. The Photosphere E. Temperature gradient in the Sun s atmosphere F. The Solar Wind III. Interior of the Sun - Helioseismology Topics for Today class IV. The Sunspot A. Sunspots and Solar Rotation V. Sunspot Activity A. The Solar Cycle B. Maunder Diagram C. Solar Rotation D. The Solar magnetic cycle VI. Nuclear Fusion in the Sun A. Nuclear Binding Energy B. Hydrogen Fusion C. The Solar Neutrino Problem Sun Spots Sunspots Tend to Occur in Groups or Pairs Visible 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 Northern Hemisphere. Ultraviolet 1
Solar Sunspot Cycles The number of spots visible on the Sun varies in a cycle with a period of 11 years. At maximum, there are often more than 100 spots visible. At minimum, there are very few or zero. The Maunder Butterfly Diagram Early in a cycle, spots appear at high latitudes north and south of the Sun s equator. Later in the cycle, new spots appear closer to the Sun s equator. If you plot the latitude of sunspots versus time, the graph looks like butterfly wings, as shown in this Maunder butterfly diagram, named after E. Walter Maunder of Greenwich Observatory The Sun s Magnetic Cycle Differential Rotation (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 speed. (b) Detailed analysis of the Sun s rotation from helioseismology reveals that the interior of the Sun rotates differentially as well, with regions of relatively slow rotation (blue) and rapid rotation (red). Differential rotation seems to be responsible for magnetic cycle of the Sun Babcock Model The Babcock model of the solar magnetic cycle explains the sunspot cycle as primarily a consequence of the Sun s differential rotation gradually winding up and tangling the magnetic field near the base of the Sun s outer, convective layer. The magnetic cycle is about 22 years. Solar Interior: Core and Envelope Sun Interior and Flow of Energy in the Sun Envelope This where almost all the energy is generated Core Near the center, nuclear fusion reactions sustain high 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 hot gas (red arrows) and sinking currents of cooler gas (blue arrows 2
Density Matters in the Sun Density and Temperature in the Sun Density =Mass/Volume 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 Pressure = (density)(temperature)(constant) Gas Pressure is the force of the gas particles colliding with the walls of its container Density and Temperature control the amount of pressure Gravity and Sun Hydrostatic Equilibrium A State When Gravity Compression = Gas Pressure 3
Energy in the Sun Where does the Sun gets its energy from? Coal? Chemical Burning? Comparing Oil, Coal and Fusion Nuclear Fusion is more Efficient Nuclear Fission? Or Nuclear Fusion? Fusionforenergy.com Fission or Fusion What kind of fuel can give such high temperatures and Pressure? Comparing fusion with burning Converting 1 kg of Hydrogen into Helium E = mc 2 = (0.007kg) (3 x 10 8 m/s) 2 = 6.3 x 10 14 joule 20,000 metric tons of coal (2 x 10 7 kg) is needed to produce this much energy Comparing The Sun with a Nuclear Bomb Total Output Power 4 x 10 26 watts 100 billion 1 megaton nuclear bombs per second 4 trillion-trillion 100W light bulbs World War II ClassAction: Cengage Astronomy Learning 2016 Education at the University of Nebraska-Lincoln Web Site (http://astro.unl.edu) 4
What Chemical Elements are Needed for Nuclear Fusion or Fission? What is Binding Energy? Energy needed to disassemble the nucleus of an atom. Binding Energy Curve Obtained by dividing the binding energy by the number of nucleons in the nucleus Fusion of Iron subtracts energy from the core Conditions for Fusion to Occur High Temperature (High Velocity) High Pressure High Density Proton-Proton (P-P) reaction http://astro.unl.edu/classaction/animations/sunsolarenergy/fusion01.html In the Sun s Core these conditions are met Converting Mass into Energy 4 H atoms = 6.693 x 10-27 kg -1 He atom = 6.645 x 10-27 kg Mass Lost = 0.048 x 10-27 kg 0.7% of mass converted to energy E = mc 2 = (0.048 x 10-27kg ) (3 x 10 8 m/s) 2 = 4.3 x 10-12 joule Lights up a 10-watt bulb for a one-half of a trillionth of a second 10 7 times larger than burning in a chemical reaction E = mc 2 Solar Neutrino Problem What is a Neutrino? It is a subatomic particle (Quarks and Leptons) with no charge. Neutrino s come in three flavors. The Sun produces 10 12 neutrino s that pass our bodies every second So why can we detect them? Is there a problem in our understanding of energy mechanics in the Sun? Solar neutrino can oscillate in these 3 flavors 5
Solar Neutrino Problem The Solar Constant On Earth only electron neutrino was detect the other two are not. But if neutrino can oscillate they must have mass and hence gravity. They could affect the evolution of the Universe. The Solar Constant Is the Amount of Energy We Receive From the Sun The energy we receive from the sun is essential for all life on Earth Solar Constant = F = 1360 J/m 2 /s F = Energy Flux = Energy received in the form of radiation, per unit time and per unit surface area [J/s/m 2 ] 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. 6