OUR ENIGMATIC SUN

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OUR ENIGMATIC SUN
(Bozeman, July, 2005) Eric Priest
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1. INTRODUCTION
For centuries we have worshipped the Sun
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Why Study the Sun ?
1. Of great scientific interest in own
right
2. Influence on Earth
3. Important for Astronomy
-- fundamental cosmic processes -- the
only star can see closely
4. For me ...
Many basic properties still a mystery
So Sun is 1 of liveliest branches of
physics/astronomy misconceptions ??
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OUR ENIGMATIC SUN
(Theme Sun full of surprises)
CONTENT
1. Introduction 2. Structure of the Sun
3. Sunspots 4. Corona
5. Modern Surprises - SOHO satellite
Climate Interior Solar Flares and
CME's Heating Atmosphere Conclusions
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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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MOST of UNIVERSE is PLASMA
Ionosphere --gt Sun (8 light mins)

• stars (4 light years)
• At 186,000 miles per sec, 1 light year 6
  trillion miles

Learn basic behaviour of plasma from Sun
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2. The SUN
Vital Statistics
? Chemical composition
Radius
Age --
700 Mm (1Mm 1000 km) 100 x Earth
91 H, 8.9 He, minor elements (O, C, N, Fe ...)
4.6 billion years (1b 1000 million)
Ball of gas held together by gravity
? Mean distance from Earth
93 million miles 215 Ro
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Overall Structure
Interior --gt Core, Convection zone
Atmosphere --gt Photosphere, Chromosphere, Corona
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Photosphere
Temperature 6000 K
Covered with turbulent convection cells
Granulation (1 Mm) Supergranulation (15
Mm)
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New Swedish Telescope
Scharmer
on La Palma (Canaries)
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Amazing images 70 km from La Palma
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In close-up points, flowers, ribbons (created
by magnetic fields)
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3. SUNSPOTS
Photosphere --gt Sunspots
Surprise (1908)
site of strong magnetic field
Galileo discovered (1610) w. telescope
Dark because cool But why cool ?
-- Greeks, Chinese
Vertical magnetic flux tubes
Because magnetic field (B) stops granulation
Not so simple !
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Stunning Imagefrom La Palma
Penumbral structure created by B
Close-up of penumbra -gt new surprises
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New Model
Weiss et al
Dark filaments- (low) held down by granule flux
pumping
Bright filaments- (high)
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See below sunspot by t-distance seismology
Wave speed slower than normal - cooler
faster - magnetic field
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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 ? Why
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Magnetic Field (B) and Plasma Coupled
In interior, plasma dominates --gt moves B
Rotation shears B
--gt 2 tubes B
--gt Emerge
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Magnetic Tube Emerges
Creates pair of sunspots /-
Opposite pattern in s. hemisphere
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Old Picture Atmosphere - static, T(r)
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E.g., old model of chromosphere

• Temp (height)

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But- atmosphere is dynamic
Carlsson Stein

• Effect of motion in photosphere

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Also - atmosphere is inhomogeneous
Many temperatures in same region
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4. CORONA
("crown") -- See at ECLIPSE of Sun
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High-res. image (Turkey, 1999)
Fine structure
Magnetic tubes prominences
SURPRISE (1940) -- Temperature is million degrees
Next Egypt, March 2006
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CORONA
Normally need eclipse to see -- Glare of surface
Observe direct with 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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Yohkoh
A magnetic world
Amazingly rich variety of MHD phenomena
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Original Skylab Images
Images from TRACE satellite
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TRACE (Active region) - from above

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From side
Corona is made up of loops
Magnetic field dominates plasma
creates intricate structure/ heats
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5. 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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The SUN today
The photo sphere
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Magnetic Field
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Corona at 1.6 MK(195 A)
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Corona at 2.0 MK (284 A)
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Photo- sphere over past few weeks
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QN. 1 -- ? Earth Influenced by Solar Variability
Number of Sunspots Oscillates w. 11-year Cycle
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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 !! How ??
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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
? Contribution to global warming
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SURPRISE (2001)
Discovered that Global B of Sun doubled since 1900
? Effect on Global T of Earth
Observed increase in T (blue) Best estimate of
increase caused by Sun (yellow)
Only 1/3 global warming (1970 to 2000) caused by
Sun
? Mechanism couple Sun/climate
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So

• Sun is at its most active for 1000 years

• Over last 100 years Bsun increased,
• and so has Tearth

• Over past 20 years, number sunspots const.,
  while Tearth continued increase

Human-produced greenhouse effect by burning
fossil fuels
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QN. 2 -- ? Structure of Solar Interior
Guitar string can oscillate in different normal
modes
Sun too Recently discovered several million
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SOHO
Measures velocity of Sun's surface at
million pts/min
Deduces frequencies Deduced T(r) --
agrees with model to lt 1
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Deduce Internal Rotation
Observe Faster at equator --
Expect const. on cylinders B generated
throughout conv. zone
Surprise -- const on radial lines -- intense
shear layer ? site dynamo
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QN.3 -- ? How Do Flares CMEs Occur
SOHO Coronagraph -- Artificial eclipse
Discovered huge ejections of plasma
Can reach Earth - communications / satellites
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Spoof
Information propagates from the left w. very
little interference !
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Comet coronal mass ejection
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QN. 4 -- HOW is CORONA HEATED ?
Bright Pts, Loops, Holes
Recon-nection likely
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IN FUTURE -- MAYBE
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Future Space Observatories
STEREO (NASA) Two satellites Stereoscopic
images of corona
Solar B (Japan-US-UK) Connections surface/corona
Solar Dynamics Observatory Successor to
SOHO (super - MDI Trace)
Solar Orbiter (ESA) 3 times closer than Mercury
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Future for the Sun (7 b years)
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7. CONCLUSIONS

• Solar Physics - golden age - observations

• Magnetic theory playing a key role

• Sense of vitality will continue

• amazing observations from ground space
• (SOHO, TRACE, RHESSI, ..,
• ATST, Solar B, Stereo, SDO, Orbiter)

- bright new young students
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Traditionally
close link Mathematics - Astronomy
e.g., Gregory Chair of Maths James Gregory
(1638-1675)
Invented Reflecting Telescope
Co-founder of Calculus
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James Gregory

• Appointed 1st regius prof maths at St Andrews
  (1668)

• Given hall as lab -- see line for telescope
  along meridian

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James Gregory
- wrote 1st text book on Calculus -
discovered
-- General binomial theorem
-- Taylor expansions
-- Ratio test for convergence of a series
-- Series for sin x and tan x
-- Integral of log x and sec x
-- Differentiation is inverse of integration
-- How to use change of variable in integration