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Announcements

Announcements. Scores for first exam are available on WebCT. Exams (A and B) with correct answers marked are available on usual course web site (not in WebCT). Two more days of observing for extra credit for first exam. Second exam will be on Friday, October 8 th .

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Announcements

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  1. Announcements • Scores for first exam are available on WebCT. • Exams (A and B) with correct answers marked are available on usual course web site (not in WebCT). • Two more days of observing for extra credit for first exam. • Second exam will be on Friday, October 8th. • Fourth exam will be on Wednesday, Nov. 17, instead of Friday, Nov. 19.

  2. Outer Layers of the Sun • Photosphere • Helioseismology • Sun spots • Chromosphere • Corona • Prominences, flares, coronal mass ejections • Reading 17.3-17.5

  3. 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.

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

  5. Photosphere

  6. Chromosphere

  7. Corona

  8. Corona

  9. Helioseismology is a way to probe the Sun’s interior using the Sun’s own vibrations. • The surface of the Sun vibrates up and down in oscillations which can go deep through the Sun. • We can observe these oscillations from Earth by looking at the Doppler shifts of different pieces of the Sun.

  10. Limb darkening

  11. Limb darkening

  12. Sunspots are low temperature regions in the photosphere 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.

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

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

  15. Sunspot cycle

  16. 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.

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

  18. Granulation

  19. What direct observational evidence supports the model of thermonuclear reactions in the Sun’s core? • Neutrinos • Gamma rays • Sun spot counts • WMD inspections

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

  21. 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.

  22. Prominences -Cooler than photosphere.

  23. Solar flares -Hotter, up to 40,000,000 KMore energetic

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

  25. Coronal mass ejection Movie

  26. Which statement is not correct? • The solar coronal temperature is about 106K. • Sunspots are very cool and dark, with temperatures of about 300 K. • The Sun’s core has a temperature about 107 K. • The chromosphere is hotter than the photosphere.

  27. Guiding Questions • Since the Sun is so bright, how is it possible to see its dim outer atmosphere (corona)? • Seen during eclipse, also with space instruments • Where does the solar wind come from? • Continuous ‘rain’ of charged particles from Sun • What are sunspots? Why do they appear dark? • Magnetically intense regions, 2000K cooler than surroundings (dark by contrast with hotter surface) • What is the connection between sunspots and the Sun’s magnetic field? • Sunspots are regions of intense magnetic field

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