I. OUR OWN SUN(Space Climate School, Saariselka, March, 2009)
Eric Priest (St Andrews)
1. Of great scientific interest in own right
2. Influence on Earth
3. Important for Astronomy
-- fundamental cosmic processes
Many basic properties still mystery (astrony) - interior, dynamo, corona, wind,
flares
4. Many misconceptions…..
1. Why Study the Sun ?
So Sun is 1 of liveliest branches of space physics/astronomy
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
Vital Statistics
? Chemical composition
2. The SUN
RadiusAge --
Interior:Core
Convection zone
(> 0.7 R0)
Atmosphere: Photosphere, Chromosphere, Corona
Overall Structure
Covered with turbulent
convection cells: “Granulation”
(1 Mm)“Supergranulation”
(15 - 30 Mm)
3. PhotosphereTemperature 6000 K
In close-up:
points, flowers, ribbons
(created by magnetic
fields)
Photosphere --> Sunspots
Harriot discovered (1610) w. telescope
Dark because cool But why cool ?
SUNSPOTS
New Model (Thomas & Weiss)
Mixture:
Dark filaments-(low)
Bright filaments-
(high)
Map of Photospheric Magnetic Field
White -- towards you;
Black -- away from you
Regions around sunspots --
bipolar "Active Regions"
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
Old Picture Atmosphere - static, T(r)
But - atmosphere is inhomogeneousMany temperatures in same region
4. Chromosphere is dynamic (2D Simulation) [Hansteen & Carlsson]
Corona
Chromo-sphere
Photo-sphere(light/dense)
Dynamic nature s. atmosphere
Swedish Solar Telescope
Continually-changing threads
Quiet active region H-alpha
0.1 arcsec
("crown") -- See at ECLIPSE of Sun
SURPRISE (1940) -- Temperature is million degrees
5. CORONA
Heating caused by magnetic fieldStructure outlines magnetic fieldAlong open structures: -- fast solar windStudents in St Andrews imaginative:
Total Eclipse - March 29, 2006 - Motion of Moon’s shadow
Over 1.5 hours:
Light level decreases,
Cooler,
Shadows sharpen
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
ProminencesCorona - glowing against jet black disc !
2nd ContactJust before totality
Magnetic tubes “prominences”
Normally need eclipse to see -- Glare of surface
Observe direct with EUV/X-ray telescope
As T increases (furnace), object becomes bluer
CORONA:
Coronal holes -- loops -- bright points Bright --> Denser
Picture with X-ray telescope:
Hinode X-ray Telescope (2006--..)
6. SOHO (Solar & Heliospheric Observatory)
Observing Sun continuously for 1st time (ESA/NASA)
Launched 1995. Orbiting Sun at point in phase
with Earth
MANY NEW SURPRISES
--> 1st comprehensive view of Sun
QN. -- ? Earth Influenced by Solar Variability
Number of Sunspots Oscillates w. 11-year Cycle
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
Solar cycle (ii)
Sunspot minm -- 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 polesreduces & reverses polar field-- new minm
Global coronal magnetic field goes thro’ complex set of 17 topologies(Maclean & Priest, 2007)
Whole atmosphere varies with cycle
Chromosphere
Corona (Intensity Changes by 100)
Max Min
Schematic --> eq. streamers/polar holes
Sunspot minimum [1994-95]
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]
SURPRISE (1976)
"Maunder Minimum" -- Little Ice Age
Realised NO sunspots in most of 17th centy
So B on Sun affects climate of Earth !! But mechanism not known !
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
Solar cycle variations further back to:
1400 from 10Be in ice cores30, 000 yrs BP from 14C in tree rings (J Beer)
1980 from several spacecraft [irradiance]
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