1. The Sun

2. Properties M = 2 X 10 30 kg = 300,000 M Earth R = 700,000 km > 100 R Earth 70% H, 28% He T = 5800 K surface, 15,000,000 K core

3. Structure

4. Sun’s Atmosphere

5. Solar Wind – stream of particles blown out from the sun Corona –Extends several million km above surface –T = 1,000,000 K –Emits X-Rays Chromosphere –T = 10,000 K –Emits UV Photosphere –T = 5,800 K –Emits visible light

6. Sun’s Interior Convection Zone –Energy travels up toward the surface via rising hot gas Radiation Zone –Photons travel through plasma 1/3 down from surface Core –Energy is produced

7. Sun’s Interior Convection Zone –Energy travels up toward the surface via rising hot gas Radiation Zone –Photons travel through plasma 1/3 down from surface Core –Energy is produced

8. Energy Measured in joules or calories Power is the rate energy is used 1 Watt = 1 joule/s We call the power output of a star it Luminosity L Sun = 3.8 X 10 26 watts

9. Hydrostatic Equilibrium Why doesn’t gravity just make the whole star collapse? –Gravity pulls in –Pressure from inside the sun pushes out –These two things balance perfectly

10. How does the Sun shine?

11. Historical Views Burning ball of coal or wood Energy release due to gravitational contraction –Kelvin-Helmholtz contraction

13. Nuclear fusion E=mc 2 Cloud of gas collapsed, releasing potential energy Gas heats Gravity creates high pressure High pressure and temperature allow nuclear fusion

16. Need high temperature so particles move fast enough to collide Nuclear strong force keeps particles stuck together

17. Proton-Proton Chain

20. Solar Neutrinos

21. Solar Thermostat

22. Random Walk Radiation has to make it out of the sun Photon bounces randomly off of electrons –Density of Sun’s core means lots of bounces Photons take a few hundred thousand years to get out

23. Solar Activity

24. Magnetic Fields Material can travel along magnetic field lines It is difficult to travel across field lines

25. Sunspots

26. Solar Prominence

27. Solar Prominence Video

28. Solar Flare Sometimes magnetic fields get too stretched and can’t handle the stress anymore They break, releasing trapped material Video

29. Coronal Mass Ejections

30. CME Video

31. Sunspot Cycle Cycle lasts ~11 years –7-15 yrs

32. Sunspot Cycle