1. The Sun Astronomy 311 Professor Lee Carkner Lecture 23

2. Helios -- The God of the Sun   The Sun was often worshiped by ancient people

3. WARNING !  NEVER LOOK DIRECTLY AT THE SUN  NEVER LOOK AT THE SUN WITH BINOCULARS OR A TELESCOPE  PERMANENT EYE DAMAGE CAN RESULT

4. Observing the Sun  With a solar filter in place we can use a telescope to get a high spatial resolution optical image of the Sun   

5. Today’s Sun

6. The Sun From the Inside Out  We will examine the Sun from the core to the diffuse outer layers   Nuclear fusion and magnetic fields play key roles in the energetics and structure of the Sun

7. Why Does the Sun Shine?  From radioisotope dating we know that the solar system is 4.5 billion years old  What could power the Sun for this length of time?   

8. The Core  At the core of the Sun the temperature and pressure are very high due to the weight of the outer layers   At these conditions the hydrogen atoms are moving so fast and are packed together so tightly that they can fuse together to make helium: 

9. Hydrogen Fusion

10. How Does the Energy at the Core Get Out?  In general energy is transported in 3 ways:  Conduction --  Radiation --  Convection -- 

11. The Inner Structure of the Sun

12. Radiative and Convective Zones  Radiative Zone (0.25-0.71 R sun )    Convective Zone (0.71-1.00 R sun )    Hot material rises causing convection

13. The Photosphere  It takes about 170,000 years for the energy to reach the surface of the Sun    The photosphere has an average temperature of 5800 K   The top layer will absorb some of the light from the bottom layers producing absorption lines

14. Granulation in the Photosphere  The photosphere is at the top of the convective zone   The photosphere is covered with granules (each about 1000 km across) 

15. Solar Granulation

16. Granules

17. Sunspots in the Photosphere  The photosphere sometimes has small dark regions called sunspots   Sunspots are regions where the Sun’s magnetic field inhibits the flow of warmer material

18. Sunspots

19. Sunspot Cycles  Sunspots exist for a maximum of a few months   There is a sunspot cycle of 11 years    The sunspots move towards the equator over the course of the cycle 

20. Sunspot Maximum and Minimum

21. The Sunspot Cycle

22. Sunspot Cycles and Differential Rotation  The Sun rotates differentially   The magnetic field gets “wrapped-up” around the equator    The sunspots are caused by the magnetic field “kinks” 

23. The Twisted Magnetic Field of the Sun

24. The Sun’s Magnetic Field  The Sun’s magnetic field extends far out beyond the surface   These loops can break and reconnect 

25. The Chromosphere  The chromosphere is a diffuse layer of the solar atmosphere extending from the photosphere to about 2000 km   It has a temperature of about 20000 K  

26. The Structure of the Chromosphere  The chromosphere is composed of many rising filaments of hot gas called spicules    Between the chromosphere and the corona is the transition region where the temperature rises from 20,000 K to 1 million K over a small region

27. Spicules in the Chromosphere

28. Temperature in the Sun’s Atmosphere

29. The Corona  The corona is the outer layer of the Sun’s atmosphere   It is thinner and hotter than the chromosphere   The high temperatures produce a hot ionized gas called a plasma 

30. Flares and Magnetic Activity  The material in the corona is constantly changing   Flare activity is linked to sunspot activity   Changes in magnetic activity seem to effect climate 

31. Magnetic Activity Cycle

32. The Structure of the Corona  The high temperatures and irregular structure of the corona are due to magnetic fields     The tangled, shifting magnetic loops gives the corona its structure

33. Structure of the Sun Core Radiative Zone Convective Zone Photosphere Chromosphere Corona

34. Summary: Structure of the Sun  Core  fusion converts H to He and power the Sun  Radiative Layer  transports energy from the core  Convective Layer  transports energy to the photosphere  Photosphere  visible surface of the Sun  Chromosphere  hot middle atmospheric layer  Corona  very hot outer layer

35. Summary: Solar Energetics  Thermonuclear Fusion  Energy is produced at the core of the Sun by converting hydrogen to helium  Energy Transport  Energy is transported via radiation where the opacity is low and via convection where the opacity is high  Magnetic Fields  The outer layers of the Sun are composed of hot plasma in magnetic loops