Chapter 15

1. Chapter 15 The Sun Astro1010-lee.com UVU Survey of Astronomy twlee2016@gmail.com

2. Chapter 15 The Sun Radius: 700,000 km Mass: 2.0 × 1030 kg Density: 1400 kg/m3 or 1.4 xH2O Rotation: Differential Period: about a month Surface temperature: 5800 K The apparent surface of the Sun is the Photosphere UVU Survey of Astronomy Astro1010-lee.com twlee2016@gmail.com

3. Chapter 15 The Sun UVU Survey of Astronomy Astro1010-lee.com twlee2016@gmail.com

4. Chapter 15 The Sun Luminosity – total energy radiated by the Sun – can be calculated from the fraction of that energy that reaches Earth. This diagram illustrates how one can extrapolate from the radiation hitting Earth to the entire output of the Sun. UVU Survey of Astronomy Astro1010-lee.com twlee2016@gmail.com

5. Chapter 15 The Sun Mathematical models, consistent with observation and physical principles, provide information about the Sun’s interior. In equilibrium, inward gravitational force must be balanced by outward pressure UVU Survey of Astronomy Astro1010-lee.com twlee2016@gmail.com

6. Chapter 15 The Sun Although the average density of the Sun is only slightly more dense than water the density at the core is extremely high. The temperature is relatively low at the surface but is near 15 million K in the core. UVU Survey of Astronomy Astro1010-lee.com twlee2016@gmail.com

7. Chapter 15 The Sun The Solar interior has been understood theoretically for years. In recent years we have been able to investigate it by observation. Doppler shifts of solar spectral lines indicate a complex pattern of vibrations that can be used much like seismic waves on the Earth to determine the interior construction of the Sun. UVU Survey of Astronomy Astro1010-lee.com twlee2016@gmail.com

8. Chapter 15 The Sun Energy transport in gases is limited to convection and radiation. In the radiation zone the particles are so tightly packed that the energy can only pass by radiation. The radiation zone is relatively transparent; the cooler convection zone is opaque. UVU Survey of Astronomy Astro1010-lee.com twlee2016@gmail.com

9. Chapter 15 The Heart of the Sun Before we can discuss how the heat of the Sun is generated we have to consider the following: Four Forces of Nature Force Strength Strong Nuclear (pull) 1040 Electro-Magnetic 1028 Weak Nuclear(push) 1026 Gravitational 1 Einstein’s famous equation for the equivalence of matter and energy UVU Survey of Astronomy Astro1010-lee.com twlee2016@gmail.com

10. Chapter 15 The Sun This is the first step in the three-step fusion process that powers most stars. UVU Survey of Astronomy Astro1010-lee.com Proton –Proton Chain twlee2016@gmail.com

11. Chapter 15 The Sun The ultimate result of the process is: The helium stays in the core; The energy is in the form of gamma rays, which gradually share their energy with the body of the Sun as they travel out from the core, emerging in all of the wavelengths of the electromagnetic spectrum; The neutrinos escape without interacting. UVU Survey of Astronomy Astro1010-lee.com twlee2016@gmail.com

12. Chapter 15 The Sun The Solar Atmosphere The cooler chromosphere, is the pink layer above the photosphere. It is hard to see directly as the sun is too bright, unless Moon completely covers the photosphere. UVU Survey of Astronomy Astro1010-lee.com The much less dense corona can also be seen during a total eclipse. Temperatures here range from 1 to 4 million K. twlee2016@gmail.com

13. Chapter 15 The Sun Solar corona changes along with sunspot cycle; it is much larger and more irregular at sunspot peak UVU Survey of Astronomy Astro1010-lee.com twlee2016@gmail.com

14. Chapter 15 Features of the the Sun’s Surface UVU Survey of Astronomy Astro1010-lee.com twlee2016@gmail.com

15. Chapter 15 The Sun The visible top layer of the Sun, the Photo-sphere, is the top convection zone and is granulated. The areas of upwelling hot gas are light, surrounded by areas of sinking cooler gas. UVU Survey of Astronomy Astro1010-lee.com twlee2016@gmail.com

16. Chapter 15 The Sun Sunspots are the most fascinating of all the solar features. Galileo saw them in 1610 and they have been studied actively ever since. They appear dark because they are slightly cooler than the surroundings. The dark central part is the umbra and lighter surrounding part is the penumbra UVU Survey of Astronomy Astro1010-lee.com twlee2016@gmail.com

17. Chapter 15 The Sun The Sun reverses magnetic polarity every 11 years. Sun spots cycle through a maximum every polarity cycle . It takes two 11 year half-cycles to make one full 22 year cycle UVU Survey of Astronomy Astro1010-lee.com twlee2016@gmail.com

18. Chapter 15 The Solar Surface Schematic Formation of Sunspots : Notice the interaction between magnetic field lines and the differential rotation. Magnetic lines trapped in the plasma stretch and break to form Sun Spots Astro1010-lee.com UVU Survey of Astronomy They are like the ends of bar magnets with lines of force looping between them. twlee2016@gmail.com

19. Chapter 15 The Sun At the beginning of a half cycle most of the Sun spots are near 30 degrees north and south. By the end most are nearer the equator UVU Survey of Astronomy Astro1010-lee.com The number of Sunspots go through a maximum each half cycle. Some half cycles show more activity than others. twlee2016@gmail.com

20. Chapter 15 The Sun Over the years efforts have been made, with few successes, to correlate sun spot activity with events on the Earth. The coincidence of the Maunder minimum with the mini-ice-age in Europe is often designated as a cause-and-effect. UVU Survey of Astronomy Astro1010-lee.com twlee2016@gmail.com

21. Chapter 15 The Sun A Solar flare is a large explosion on Sun’s surface, driving matter into space in seconds or minutes. This matter adds to the Solar Wind, UVU Survey of Astronomy Astro1010-lee.com Hot matter escapes Sun often through coronal holes in Coronal Mass Ejections, which can be seen in X-ray images as bright white spots twlee2016@gmail.com

22. Chapter 15 The Sun Neutrinos are emitted directly from the core of the Sun, and escape, interacting with virtually nothing. Being able to observe these neutrinos would give us a direct picture of what is happening in the core. Unfortunately, they are no more likely to interact with Earth-based detectors than they are with the Sun; the only way to spot them is to have a huge detector volume and to be able to observe single interaction events. UVU Survey of Astronomy Astro1010-lee.com twlee2016@gmail.com

23. Chapter 15 The Solar Surface This is a large solar neutrino detector. Interactions (dim flashes) take place in the liquid, which reaches the top of the dome when full, Detection is by the glass photomultiplier tubes. UVU Survey of Astronomy Astro1010-lee.com twlee2016@gmail.com

24. Chapter 15 The Solar Surface • Detection of solar neutrinos has been going on for more than 30 years now; despite very different detection methods and energy sensitivities, all experiments agree that they are seeing about 30–50% of the expected number of neutrinos. Could be: • Problem with solar model • Problem with our understanding and detection of neutrinos • The second option seems more likely today. UVU Survey of Astronomy Astro1010-lee.com twlee2016@gmail.com

25. Chapter 15 In-Class Quiz The Sun ___________ magnetic polarity every 11 years. UVU Survey of Astronomy Astro1010-lee.com twlee2016@gmail.com

26. Chapter 15 End of Chapter 15 UVU Survey of Astronomy Astro1010-lee.com twlee2016@gmail.com