1. Outer Layers of the Sun Photosphere –Limb darkening –Sun spots Chromosphere Corona Prominences, flares, coronal mass ejections Reading 18.5-18.10

2. The Sun’s Atmosphere Photosphere - the 5800 K layer we see. Chromosphere – a thin layer, a few 1000 km thick, at a temperature of about 10,000 K. Can be seen during solar eclipse. Corona – Outermost layer, 1,000,000 km thick, at a temperature of about 1,000,000 K.

3. Outer layers of sun 1 = photosphere, 2 = chromosphere, 3 = corona Why the outer layers of the Sun’s atmosphere are hotter is a puzzle.

4. Photosphere

5. Chromosphere

6. Corona

8. Limb darkening

10. Sun spots are about 4000 K (2000 K cooler than solar surface) and have magnetic fields up 1000  the normal solar magnetic field. They can be as large as 50,000 km and last for many months. Sunspots are low temperature regions in the photosphere

11. Particles spiral around magnetic field lines Magnetic field Motion of charged particle (electron, proton, nucleus)

12. The large magnetic fields in sunspots decrease the flow of heat via convection causing the sunspot to become cool. Sunspots are low temperature regions in the photosphere

13. Sunspot cycle

14. Sunspots can be used to measure the rotation of the Sun Near the equator the Sun rotates once in 25 days. The poles rotate more slowly, about once every 36 days.

15. Sunspot cycle Each 11 years, the Sun’s magnetic field changes direction. Overall cycle is 22 years.

16. Granulation

17. What direct observational evidence supports the model of thermonuclear reactions in the Sun’s core? 1.Neutrinos 2.Gamma rays 3.Sun spot counts 4.WMD inspections

18. Solar magnetic fields also create other phenomena Prominences Flares Solar wind Coronal mass ejections

19. Particles spiral around magnetic field lines Magnetic field Motion of charged particle (electron, proton, nucleus) Particles, that we see, get trapped along magnetic field lines, that we don’t see, stretching out from the Sun.

20. Prominences - Cooler than photosphere.

21. Solar flares - Hotter, up to 40,000,000 K More energetic

22. Coronal mass ejections - eruption of gas, can reach Earth and affect aurora, satellites Movie

23. Coronal mass ejection Movie

24. Which statement is not correct? 1.The solar coronal temperature is about 10 6 K. 2.Sunspots are very cool and dark, with temperatures of about 300 K. 3.The Sun’s core has a temperature about 10 7 K. 4.The chromosphere is hotter than the photosphere.

25. Review Questions 1.Since the Sun is so bright, how is it possible to see its dim outer atmosphere (corona)? 2.Where does the solar wind come from? 3.What are sunspots? Why do they appear dark? 4.What is the connection between sunspots and the Sun’s magnetic field? 5.What is the sunspot cycle?