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3/18/2017 Foundations of Astronomy | 13e Seeds Phys1411 – Introductory Astronomy Instructor: Dr. Goderya Chapter 8 The Sun © Cengage Learning 2016 Keep your voting card ready Topics in Chapter 8 that we will cover • General Properties • Solar Atmosphere and Surface – Temperature variation • Solar Interior – Energy Flow – Methods of Energy Flow • Density • Pressure © Cengage Learning 2016 Topics in Chapter 8 that we will cover The Sun Is Just a Normal Star • Energy Productions – Nuclear Fission – Nuclear Fusion – Comparing Fusion with Burning Coal • Hydrostatic Equilibrium – Gravity – Gas Pressure • The Sun’s Future (Briefly) • The remaining topics: Read it on your own. © Cengage Learning 2016 © Cengage Learning 2016 A Giant Ball of Gas on Fire 1 3/18/2017 General Properties Observing the Sun – Warning! • Average star • Never look directly at the sun through a telescope or binoculars! • Spectral type G2 • Only appears so bright because it is so close. • Absolute visual magnitude = 4.83 (magnitude if it were at a distance of 32.6 light years) – Use a projection technique or a special sun viewing filter • 109 times Earth’s diameter • 333,000 times Earth’s mass • Consists entirely of gas (av. density = 1.4 g/cm3) • Central temperature = 15 million 0K • Surface temperature = 5800 0K © Cengage Learning 2016 © Cengage Learning 2016 The Solar Atmospheric Temperature Apparent surface of the sun Heat Flow Only visible during solar eclipses Solar interior © Cengage Astronomy Learning 2016 ClassAction: Education at the University of Nebraska-Lincoln Web Site (http://astro.unl.edu) © Cengage Learning 2016 Temp. incr. inward Solar Interior: Core and Envelope Core Envelope This where almost all the energy is generated © Cengage Astronomy Learning 2016 ClassAction: Education at the University of Nebraska-Lincoln Web Site (http://astro.unl.edu) 2 3/18/2017 Gravity Pulls Matter Inward What Keeps the Sun from Collapsing on itself? KCVS Gas Pressure Pushes Outwards Where Does Pressure Come From? Indiana.edu Density Matters in the Sun Density =Mass/Volume © Cengage Astronomy Learning 2016 ClassAction: Education at the University of Nebraska-Lincoln Web Site (http://astro.unl.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 Energy in the Sun Where does the Sun gets its energy from? Coal? Chemical Burning? Nuclear Fission? Or Nuclear Fusion? 3 3/18/2017 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 Fission or Fusion What kind of fuel can give such high temperatures and Pressure? World War II © Cengage Learning 2016 Fusion vs. Fission Comparing Oil, Coal and Fusion • Nuclear Fusion is more Efficient © Cengage Learning 2016 Fusionforenergy.com Proton-Proton (P-P) reaction http://astro.unl.edu/classaction/animations/sunsolarenergy/fusion01.html © Cengage Astronomy Learning 2016 ClassAction: Education at the University of Nebraska-Lincoln Web Site (http://astro.unl.edu) © Cengage Learning 2016 4 3/18/2017 Conditions for Fusion to Occur Density and Temperature in the Sun • High Temperature (High Velocity) • High Pressure • High Density © Cengage Learning 2016 Three Ways of Heat Transfer © Cengage Astronomy Learning 2016 ClassAction: Education at the University of Nebraska-Lincoln Web Site (http://astro.unl.edu) © Cengage Learning 2016 Sun Interior and Flow of Energy in the Sun • 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 © Cengage Learning 2016 © Cengage Astronomy Learning 2016 ClassAction: Education at the University of Nebraska-Lincoln Web Site (http://astro.unl.edu) 5 3/18/2017 Attendance © Cengage Astronomy Learning 2016 ClassAction: Education at the University of Nebraska-Lincoln Web Site (http://astro.unl.edu) Gravity and Sun © Cengage Learning 2016 Campus.kellerisd.net Life Time of the Sun Hydrostatic Equilibrium A State When Gravity Compression = Gas Pressure • So How Long will the Sun Live with its Nuclear Fuel? T Life = 1010 /Msun2 If M sun = 1, then T Life = 1010 years © Cengage Learning 2016 What will happen when the Sun runs out of nuclear fuel? © Cengage Learning 2016 Common Misconception • Nuclear fusion in the Sun is tremendously powerful – Truth: Only a tiny fraction of the hydrogen atoms are fusing into helium and are spread through a large volume in its core – Truth: Gram for gram, you are a much more efficient heat producer than the Sun • The Sun produces a lot of energy because it contains many grams of matter in its core © Cengage Learning 2016 © Cengage Learning 2016 6 3/18/2017 Test your Learning Test your Learning Another name for an isolated proton might be a ________ a) hydrogen ion b) hydrogen isotope c) helium ion d) neutron The Sun's luminosity comes primarily from a) chemical burning. b) the mechanical energy of turbulence. c) nuclear fusion. d) gravitational contraction. e) all of the above are comparable in importance. http://hea-www.harvard.edu/~pgreen/educ/ http://hea-www.harvard.edu/~pgreen/educ/ Test your Learning Test your Learning The chemical composition of the Sun 3 billion years ago was different from what it is now in that it had a) more hydrogen b) more helium c) more nitrogen d) molecular hydrogen The energy emitted by the Sun is produced a) uniformly throughout the whole Sun. b) throughout the whole Sun, but more in the center than at the surface, as 1/r^2. c) in a very small region at the very center of the Sun. d) from radioactive elements created in the Big Bang. http://hea-www.harvard.edu/~pgreen/educ/ http://hea-www.harvard.edu/~pgreen/educ/ Test your Learning Acknowledgment Tremendous pressure is created at the Sun's center due to its own gravity. What keeps it from collapsing? a) neutrinos and other particles generated by nuclear fusion b) a hard inner core c) thermal (gas) pressure generated by nuclear fusion d) thermal (gas) pressure left over from the formation of the Sun http://hea-www.harvard.edu/~pgreen/educ/ • 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 7
