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I. OUR OWN SUN

I. OUR OWN SUN. (Space Climate School, Saariselka, March, 2009) Eric Priest (St Andrews). 1. Why Study the Sun ?. 1. Of great scientific interest in own right. 2. Influence on Earth. 3. Important for Astronomy. -- fundamental cosmic processes.

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I. OUR OWN SUN

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  1. I. OUR OWN SUN (Space Climate School, Saariselka, March, 2009) Eric Priest (St Andrews)

  2. 1. Why Study the Sun ? 1. Of great scientific interest in own right 2. Influence on Earth 3. Important for Astronomy -- fundamental cosmic processes 4. Many misconceptions….. Many basic properties still mystery (astrony) - interior, dynamo, corona, wind, flares So Sun is 1 of liveliest branches of space physics/astronomy

  3. Another Theme: Many surprises caused by magnetic field (B) Sun is NOT a normal gas Sun is in 4th state of matter ("PLASMA") behaves differently from normal gas: B and plasma -- coupled (intimate, subtle) B exerts force on plasma -- stores energy

  4. Vital Statistics 2. The SUN ? Chemical composition Radius Age --

  5. Overall Structure Interior: Core Convection zone (> 0.7 R0) Atmosphere:Photosphere, Chromosphere, Corona

  6. 3. Photosphere Temperature 6000 K Covered with turbulent convection cells: “Granulation” (1 Mm) “Supergranulation” (15 - 30 Mm)

  7. In close-up:points, flowers, ribbons(created by magnetic fields)

  8. SUNSPOTS Photosphere --> Sunspots Harriot discovered (1610) w. telescope Dark because cool But why cool ?

  9. New Model (Thomas & Weiss) Mixture: Dark filaments- (low) Bright filaments- (high)

  10. Map ofPhotospheric Magnetic Field White -- towards you; Black -- away from you Regions around sunspots -- bipolar "Active Regions"

  11. SURPRISES: -- 1. Intense magnetic fields over whole Sun B carried to edges of convection cells 2. Patterns of sunspots/act. regs -- large flux tube --> dynamo …

  12. Old Picture Atmosphere - static, T(r)

  13. But - atmosphere is inhomogeneous Many temperatures in same region

  14. 4. Chromosphere is dynamic (2D Simulation) [Hansteen & Carlsson] Corona Chromo- sphere Photo- sphere (light/ dense)

  15. Dynamic nature s. atmosphereSwedish Solar Telescope Quiet active region H-alpha 0.1 arcsec Continually-changing threads

  16. ("crown") -- See at ECLIPSE of Sun 5. CORONA Along open structures: -- fast solar wind SURPRISE (1940) -- Temperature is million degrees Students in St Andrews imaginative: Heating caused by magnetic field Structure outlines magnetic field

  17. Total Eclipse - March 29, 2006 - Motion of Moon’s shadow

  18. Over 1.5 hours: Light level decreases, Cooler, Shadows sharpen

  19. In last 10 minutes: Light level and temperature decrease more quickly Wind Start to see planets Just before totality (when Moon covers Sun) -- Baily beads Red chromosphere Prominences Corona - glowing against jet black disc !

  20. Just before totality 2nd Contact Magnetic tubes “prominences”

  21. CORONA: Normally need eclipse to see -- Glare of surface Observe direct with EUV/X-ray telescope As T increases (furnace), object becomes bluer

  22. Picture with X-ray telescope: Coronal holes -- loops -- bright points Bright --> Denser

  23. Hinode X-ray Telescope (2006--..)

  24. 6. SOHO (Solar & Heliospheric Observatory) Launched 1995. Orbiting Sun at point in phase with Earth Observing Sun continuously for 1st time (ESA/NASA) --> 1st comprehensive view of Sun MANY NEW SURPRISES

  25. QN. -- ? Earth Influenced by Solar Variability Number of Sunspots Oscillates w. 11-year Cycle

  26. Solar Cycle Sunspots - two zones between -35o and +35o latitude Leading spots have opposite polarities in 2 hemispheres [Hale] Leading polarity is closer to equator [Joy] Magnetic field reverses every 11 years

  27. Solar cycle (ii) Sunspot minm -- no spots -- polar fields Spots emerge at high latitudes w. opposite polarity [later at lower latitudes] 90% active region flux cancels --10 % migrates -- following flux reaches poles reduces & reverses polar field-- new minm Global coronal magnetic field goes thro’ complex set of 17 topologies (Maclean & Priest, 2007) [Polar Fields: * maximum extent at s. minimum * change polarity 1-2 years after s. maximum]

  28. Whole atmosphere varies with cycle Max Min Chromosphere Corona (Intensity Changes by 100) Schematic --> eq. streamers/polar holes

  29. FAST Solar Wind (700 km/s) in coronal holes SLOW Solar Wind (300 km/s) in equatorial streamers Solar wind velocity [polar plot, ULYSSES] Sunspot minimum [1994-95] [Red= inward field Blue= outward field]

  30. SURPRISE (1976) Realised NO sunspots in most of 17th centy "Maunder Minimum" -- Little Ice Age So B on Sun affects climate of Earth !! But mechanism not known !

  31. SOHO --> Total Emission (t) 1996-2000 Emission varies by 0.2% -- passage sunspots Increase by 0.1% from sunspot min to max Much too small to produce global warming ?? Real & ?? cause

  32. Solar cycle variations further back to: 1980 from several spacecraft [irradiance] 1400 from 10Be in ice cores 30, 000 yrs BP from 14C in tree rings (J Beer)

  33. CONCLUSIONS • Solar Physics - golden age - observations • Magnetic theory playing a key role • Sense of vitality will continue • amazing observations from space • (SOHO, TRACE, RHESSI, • Hinode, Stereo, • SDO, Orbiter) - bright new young students

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