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Copyright 2012 Pearson Education, Inc. Chapter 10 Our Star 1 Slide 2 Copyright 2012 Pearson Education, Inc. 10.1 A Closer Look at the Sun Our goals for learning: Why does the Sun shine? What is the Suns structure? 2 Slide 3 Copyright 2012 Pearson Education, Inc. Why does the Sun shine? 3 Slide 4 Copyright 2012 Pearson Education, Inc. Is it on FIRE? 4 Slide 5 Copyright 2012 Pearson Education, Inc. Is it on FIRE? Luminosity ~ 10,000 years Chemical Energy Content 5 Slide 6 Copyright 2012 Pearson Education, Inc. Is it on FIRE? NO! Luminosity ~ 10,000 years Chemical Energy Content 6 Slide 7 Copyright 2012 Pearson Education, Inc. Is it CONTRACTING? 7 Slide 8 Copyright 2012 Pearson Education, Inc. Is it CONTRACTING? Luminosity Gravitational Potential Energy ~ 25 million years 8 Slide 9 Copyright 2012 Pearson Education, Inc. Is it CONTRACTING? NO! Luminosity Gravitational Potential Energy ~ 25 million years 9 Slide 10 Copyright 2012 Pearson Education, Inc. It is powered by NUCLEAR ENERGY! Luminosity ~ 10 billion years Nuclear Potential Energy (core) E = mc 2 Einstein, 1905 10 Slide 11 Copyright 2012 Pearson Education, Inc. Weight of upper layers compresses lower layers. 11 Slide 12 Copyright 2012 Pearson Education, Inc. Gravitational equilibrium: Gravity pulling in balances pressure pushing out. Energy balance: Thermal energy released by fusion in core balances radiative energy lost from surface. 12 Slide 13 Copyright 2012 Pearson Education, Inc. Gravitational contraction provided energy that heated the core as the Sun was forming. Contraction stopped when fusion started replacing the energy radiated into space. 13 Slide 14 Copyright 2012 Pearson Education, Inc. What is the Suns structure? 14 Slide 15 Copyright 2012 Pearson Education, Inc. Radius: 6.9 10 8 m (109 times Earth) Mass: 2 10 30 kg (300,000 Earths) Luminosity: 3.8 10 26 watts 15 Slide 16 Copyright 2012 Pearson Education, Inc. Solar wind: A flow of charged particles from the surface of the Sun 16 Slide 17 Copyright 2012 Pearson Education, Inc. Corona: Outermost layer of solar atmosphere ~1 million K 17 Slide 18 Copyright 2012 Pearson Education, Inc. Chromosphere: Middle layer of solar atmosphere ~ 10 4 10 5 K 18 Slide 19 Copyright 2012 Pearson Education, Inc. Photosphere: Visible surface of the Sun ~ 6000 K 19 Slide 20 Copyright 2012 Pearson Education, Inc. Convection zone: Energy transported upward by rising hot gas 20 Slide 21 Copyright 2012 Pearson Education, Inc. Radiation zone: Energy transported upward by photons 21 Slide 22 Copyright 2012 Pearson Education, Inc. Core: Energy generated by nuclear fusion ~ 15 million K 22 Slide 23 Copyright 2012 Pearson Education, Inc. What have we learned? Why does the Sun shine? Chemical and gravitational energy sources could not explain how the Sun could sustain its luminosity for more than about 25 million years. The Sun shines steadily because nuclear fusion in the core maintains both gravitational equilibrium between pressure and gravity and energy balance between thermal energy released in core and radiative energy lost from the Suns surface. 23 Slide 24 Copyright 2012 Pearson Education, Inc. What have we learned? What is the Suns structure? From inside out, the layers are Core Radiation zone Convection zone Photosphere Chromosphere Corona 24 Slide 25 Copyright 2012 Pearson Education, Inc. 10.2 Nuclear Fusion in the Sun Our goals for learning: How does nuclear fusion occur in the Sun? How does the energy from fusion get out of the Sun? How do we know what is happening inside the Sun? 25 Slide 26 Copyright 2012 Pearson Education, Inc. How does nuclear fusion occur in the Sun? 26 Slide 27 Copyright 2012 Pearson Education, Inc. Fission Big nucleus splits into smaller pieces. (Nuclear power plants) Fusion Small nuclei stick together to make a bigger one. (Sun, stars) 27 Slide 28 Copyright 2012 Pearson Education, Inc. High temperatures enable nuclear fusion to happen in the core. 28 Slide 29 Copyright 2012 Pearson Education, Inc. The Sun releases energy by fusing four hydrogen nuclei into one helium nucleus. 29 Slide 30 Copyright 2012 Pearson Education, Inc. Protonproton chain is how hydrogen fuses into helium in the Sun. 30 Slide 31 Copyright 2012 Pearson Education, Inc. IN 4 protons OUT 4 He nucleus 2 gamma rays 2 positrons 2 neutrinos Total mass is 0.7% lower. 31 Slide 32 Copyright 2012 Pearson Education, Inc. Thought Question What would happen inside the Sun if a slight rise in core temperature led to a rapid rise in fusion energy? A. The core would expand and heat up slightly. B. The core would expand and cool. C. The Sun would blow up like a hydrogen bomb. 32 Slide 33 Copyright 2012 Pearson Education, Inc. Thought Question What would happen inside the Sun if a slight rise in core temperature led to a rapid rise in fusion energy? A. The core would expand and heat up slightly. B. The core would expand and cool. C. The Sun would blow up like a hydrogen bomb. Solar thermostat keeps the rate of fusion steady. 33 Slide 34 Copyright 2012 Pearson Education, Inc. Solar Thermostat Decline in core temperature causes fusion rate to drop, so core contracts and heats up. Rise in core temperature causes fusion rate to rise, so core expands and cools down. 34 Slide 35 Copyright 2012 Pearson Education, Inc. How does the energy from fusion get out of the Sun? 35 Slide 36 Copyright 2012 Pearson Education, Inc. Energy gradually leaks out of the radiation zone in the form of randomly bouncing photons. 36 Slide 37 Copyright 2012 Pearson Education, Inc. Convection (rising hot gas) takes energy to the surface. 37 Slide 38 Copyright 2012 Pearson Education, Inc. Bright blobs on photosphere where hot gas reaches the surface 38 Slide 39 Copyright 2012 Pearson Education, Inc. How do we know what is happening inside the Sun? 39 Slide 40 Copyright 2012 Pearson Education, Inc. We learn about the inside of the Sun by making mathematical models observing solar vibrations observing solar neutrinos 40 Slide 41 Copyright 2012 Pearson Education, Inc. Patterns of vibration on the surface tell us about what the Sun is like inside. 41 Slide 42 Copyright 2012 Pearson Education, Inc. Data on solar vibrations agree with mathematical models of solar interior. 42 Slide 43 Copyright 2012 Pearson Education, Inc. Neutrinos created during fusion fly directly through the Sun. Observations of these solar neutrinos can tell us whats happening in the core. 43 Slide 44 Copyright 2012 Pearson Education, Inc. Solar neutrino problem: Early searches for solar neutrinos failed to find the predicted number. 44 Slide 45 Copyright 2012 Pearson Education, Inc. Solar neutrino problem: Early searches for solar neutrinos failed to find the predicted number. More recent observations find the right number of neutrinos, but some have changed form. 45 Slide 46 Copyright 2012 Pearson Education, Inc. What have we learned? How does nuclear fusion occur in the Sun? The cores extreme temperature and density are just right for the nuclear fusion of hydrogen to helium through the protonproton chain. Gravitational equilibrium and energy balance together act as a thermostat to regulate the core temperature because the fusion rate is very sensitive to temperature. 46 Slide 47 Copyright 2012 Pearson Education, Inc. What have we learned? How does the energy from fusion get out of the Sun? Randomly bouncing photons carry it through the radiation zone. The rising of hot plasma carries energy through the convection zone to the photosphere. How do we know what is happening inside the Sun? Mathematical models agree with observations of solar vibrations and solar neutrinos. 47 Slide 48 Copyright 2012 Pearson Education, Inc. 10.3 The SunEarth Connection Our goals for learning: What causes solar activity? How does solar activity vary with time? 48 Slide 49 Copyright 2012 Pearson Education, Inc. What causes solar activity? 49 Slide 50 Copyright 2012 Pearson Education, Inc. Solar activity is like weather on Earth. Sunspots Solar flares Solar prominences All these phenomena are related to magnetic fields. 50 Slide 51 Copyright 2012 Pearson Education, Inc. Sunspots Are cooler than other parts of the Suns surface (4000 K). Are regions with strong magnetic fields. 51 Slide 52 Copyright 2012 Pearson Education, Inc. Zeeman Effect We can measure magnetic fields in sunspots by observing the splitting of spectral lines. 52 Slide 53 Copyright 2012 Pearson Education, Inc. Charged particles spiral along magnetic field lines. 53 Slide 54 Copyright 2012 Pearson Education, Inc. Loops of bright gas often connect sunspot pairs. 54 Slide 55 Copyright 2012 Pearson Education, Inc. Magnetic activity causes solar flares that send bursts of X rays and charged particles into space. 55 Slide 56 Copyright 2012 Pearson Education, Inc. Magnetic activity also causes solar prominences that erupt high above the Suns surface. 56 Slide 57 Copyright 2012 Pearson Education, Inc. The corona appears bright in X-ray photos in places where magnetic fields trap hot gas. 57 Slide 58 Copyright 2012 Pearson Education, Inc. Coronal mass ejections send bursts of energetic charged particles out through the solar system. 58 Slide 59 Copyright 2012 Pearson Education, Inc. Charged particles streaming from the Sun can disrupt electrical power grids and disable communications satellites. 59 Slide 60 Copyright 2012 Pearson Education, Inc. How does solar activity vary with time? 60 Slide 61 Copyright 2012 Pearson Education, Inc. The number of sunspots rises and falls in 11-year cycles. 61 Slide 62 Copyright 2012 Pearson Education, Inc. The sunspot cycle has something to do with the winding and twisting of the Suns magnetic field. 62 Slide 63 Copyright 2012 Pearson Education, Inc. What have we learned? What causes solar activity? The stretching and twisting of magnetic field lines near the Suns surface causes solar activity. Bursts of charged particles from the Sun can disrupt communications, satellites, and electrical power generation. How does solar activity vary with time? Activity rises and falls in 11-year cycles. 63 Slide 64 Copyright 2012 Pearson Education, Inc. Homework Quick Quiz: 27-36 p. 306 Quantitative problems: 52 p. 307 Review questions 64