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

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Presentation on theme: "I. OUR OWN SUN (Space Climate School, Saariselka, March, 2009) Eric Priest (St Andrews)"— Presentation transcript:

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

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

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

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

5 Interior: Core Convection zone (> 0.7 R 0 ) Atmosphere: Photosphere, Chromosphere, Corona Overall Structure

6 Covered with turbulent convection cells:Granulation (1 Mm) Supergranulation ( Mm) 3. Photosphere Temperature 6000 K

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

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

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

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

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

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. atmosphere Swedish Solar Telescope Continually-changing threads Quiet active region H-alpha 0.1 arcsec

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

17 Total Eclipse - March 29, Motion of Moons shadow

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19 Over 1.5 hours: Light level decreases, Cooler, Shadows sharpen

20 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 !

21 2nd Contact Just before totality Magnetic tubes prominences

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

25 Coronal holes -- loops -- bright pointsBright --> Denser Picture with X-ray telescope:

26 Hinode X-ray Telescope ( )

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

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

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

30 Solar cycle (ii) Sunspot min m -- no spots -- polar fields [Polar Fields: * maximum extent at s. minimum * change polarity 1-2 years after s. maximum] 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 min m Global coronal magnetic field goes thro complex set of 17 topologies (Maclean & Priest, 2007)

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

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

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

34 SOHO --> Total Emission (t) 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

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

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


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