I. OUR OWN SUN

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I. OUR OWN SUN
(Space Climate School, Saariselka, March,
2009) Eric Priest (St Andrews)
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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
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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
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2. The SUN
Vital Statistics
? Chemical composition
Radius
Age --
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Overall Structure
Interior Core Convection zone (gt 0.7 R0)
Atmosphere Photosphere, Chromosphere, Corona
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3. Photosphere
Temperature 6000 K
Covered with turbulent convection cells
Granulation (1 Mm) Supergranulation (15
- 30 Mm)
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In close-up points, flowers, ribbons (created
by magnetic fields)
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SUNSPOTS
Photosphere --gt Sunspots
Harriot discovered (1610) w. telescope
Dark because cool But why cool ?
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New Model (Thomas Weiss)
Mixture Dark filaments- (low)
Bright filaments- (high)
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Map of Photospheric Magnetic Field
White -- towards you Black -- away from you
Regions around sunspots -- bipolar "Active
Regions"
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SURPRISES --
1. Intense magnetic fields over whole Sun
B carried to edges of convection cells
2. Patterns of sunspots/act. regs -- large flux
tube --gt dynamo
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Old Picture Atmosphere - static, T(r)
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But - atmosphere is inhomogeneous
Many temperatures in same region
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4. Chromosphere is dynamic (2D Simulation)
Hansteen Carlsson
Corona
Chromo- sphere
Photo- sphere (light/ dense)
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Dynamic nature s. atmosphere Swedish Solar
Telescope
Quiet active region H-alpha 0.1 arcsec
Continually-changing threads
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5. CORONA
("crown") -- See at ECLIPSE of Sun
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
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Total Eclipse - March 29, 2006 - Motion of
Moons shadow
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Over 1.5 hours
Light level decreases,
Cooler,
Shadows sharpen
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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 !
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2nd Contact
Just before totality
Magnetic tubes prominences
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CORONA
Normally need eclipse to see -- Glare of surface
Observe direct with EUV/X-ray telescope
As T increases (furnace), object becomes bluer
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Picture with X-ray telescope
Coronal holes -- loops -- bright points
Bright --gt Denser
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Hinode X-ray Telescope (2006--..)
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6. SOHO (Solar Heliospheric Observatory)
Launched 1995. Orbiting Sun at point in phase
with Earth
Observing Sun continuously for 1st time (ESA/NASA)
--gt 1st comprehensive view of Sun
MANY NEW SURPRISES
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QN. -- ? Earth Influenced by Solar Variability
Number of Sunspots Oscillates w. 11-year Cycle
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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
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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
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Whole atmosphere varies with cycle
Max Min
Chromosphere
Corona (Intensity Changes by 100)
Schematic --gt eq. streamers/polar holes
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Solar wind velocity polar plot, ULYSSES
Sunspot minimum 1994-95
Red inward field Blue outward field
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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 !
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SOHO --gt 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
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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)
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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