OUR ENIGMATIC SUN

1
OUR ENIGMATIC SUN
(Bozeman, July, 2004) Eric Priest
2
(No Transcript)
3
1. INTRODUCTION
For centuries we have worshipped the Sun
4
(No Transcript)
5
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 astronomy
Many students attracted
6
Traditionally
close link Mathematics - Astronomy
e.g., Gregory Chair of Maths James Gregory
(1638-1675)
Invented Reflecting Telescope
Co-founder of Calculus
7
James Gregory

• Elected FRS (Academician) 1668 (age 30)

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

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

8
But left in 1674 --gt Edinburgh
The affairs of the Observatory of St Andrews
were in such a bad condition, the reason of which
was, a prejudice the masters of the University
did take at the mathematics. After this, my
salary was also kept back from me,
and scholars of most eminent rank were violently
kept from me, contrary to their own wills, the
masters persuading them that their brains were
not able to endure it.
9
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
10
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
11
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
12
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
13
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
14
Overall Structure
Interior --gt Core, Convection zone
Atmosphere --gt Photosphere, Chromosphere, Corona
15
Photosphere
Temperature 6000 K
Covered with turbulent convection cells
Granulation (1 Mm) Supergranulation (15
Mm)
16
New Swedish Telescope
Scharmer
on La Palma (Canaries)
17
Amazing images at 0.1from La Palma
18
In close-up points, flowers, ribbons (created
by magnetic fields)
19
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
Simply vertical magnetic flux tubes
Because magnetic field (B) stops granulation
? Planets, clouds, smoke, slag
Not so simple !
20
Stunning Imagefrom La Palma
Penumbral structure created by B
Close-up of penumbra -gt new surprises
21
Points moving along lanes Bright flows
in/out Strange dark cores
22
New Model
(Weiss, Thomas, Brummel, Tobias, Hurlburt)
Dark filaments- (low) held down by granule flux
pumping
Bright filaments- (high) flows travelling
convection ?
23
See below sunspot by t-distance seismology
Wave speed slower than normal - cooler
faster - magnetic field
24
Map of Photospheric Magnetic Field
White -- towards you Black -- away from you
Regions around sunspots -- bipolar "Active
Regions"
25
SURPRISES --
1. Intense magnetic fields over whole Sun
B carried to edges of convection cells
2. Patterns of sunspots/act. regs ? Why
26
Magnetic Field (B) and Plasma Coupled
In interior, plasma dominates --gt moves B
Rotation shears B
--gt 2 tubes B
--gt Emerge
27
Magnetic Tube Emerges
Creates pair of sunspots /-
Opposite pattern in s. hemisphere
28
Temperature Structure
29
The classical picture of chromosphere

• Plane parallel, multi-component atmosphere (HSRA,
  VAL, FAL)
• A gentle rise in temperature between Tmin and
  corona.

Fontenla et al. 1993
30
Dynamic models

• Time dependent excitations
• Start with piston in CZ, consistent with obs. of
  photospheric oscillations
• High resolution adaptive grid needed to resolve
  shock waves
• Carlsson Stein 1993, 1995, 1997, 2001

31
Classical Picture of Transition Region
Thin static layer between chromosphere and corona
But
32
4. CORONA
("crown") -- See at ECLIPSE of Sun
SURPRISE (1940) -- Temperature is million degrees
!!!!
33
ECLIPSE Movie
34
ECLIPSE in Turkey, 1999
In corona B dominates plasma
B heats corona, creates structure
Magnetic tubes prominences
Next Egypt, March 2006
35
CORONA
Normally need eclipse to see -- Glare of surface
Observe direct with X-ray telescope
As T increases (furnace), object becomes bluer
36
Skylab (1973-1974)
37
Picture with X-ray telescope
Coronal holes -- loops -- bright points
Bright --gt Denser
38
Yohkoh
A magnetic world
Amazingly rich variety of MHD phenomena
39
From Photosphere to Corona
40
Original Skylab Images
Images from TRACE satellite
41
TRACE (Active region) - from above

42
From side
Corona is made up of loops
Magnetic field dominates plasma
creates intricate structure
43
Close-up of plasma motions
Conjuring trick -- plasma appearing by magic ?
44
? Studying Sun Entails
45
? THOUGHT of MATHS FILL with CONFIDENCE
46
5. Eqns of Magnetohydrodynamics
Model interaction of B and plasma (conts medium)
PDE's for v and B as functions of x,y,z,t
As beautiful as the Sun !! -- Nonlinear
Impossible to solve completely
So approximate in imaginative ways --
Construct models for many dynamic phenomena on Sun
47
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
48
Suite 11 Instrument Packages
Solar wind - SWAN, CELIAS, CEPAC
Atmosphere LASCO - Visible Light
Coronagraph - UVCS - Ultraviolet Coronagraph -
EIT - Extreme UV telescope - global images-
CDS - Spectrum EUV -gt n, T, v raster
SUMER - Spectrum EUV -gt n, T, v raster
Interior MDI - Oscillations Imager B
GOLF - Global Velocity Oscillations
VIRGO - Irradiance Variations
49
The SUN this week
The photo sphere
50
Magnetic Field
51
Corona at 1.6 MK(195 A)
52
Corona at 2.0 MK (284 A)
53
QN. 1 -- ? Earth Influenced by S Variability
Number of Sunspots Oscillates w. 11-year Cycle
54
SURPRISE (1976)
Realised NO sunspots in most of 17th centy
"Maunder Minimum" -- Little Ice Age
So B on Sun affects climate of Earth !! How ??
55
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
56
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
57
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 --gt

Human-produced greenhouse effect by burning
fossil fuels
58
QN. 2 -- ? Structure of Solar Interior
Guitar string can oscillate in different normal
modes
Sun too Recently discovered several million
59
SOHO
Measures velocity of Sun's surface at
million pts/min
Deduces frequencies Deduced T(r) --
agrees with model to lt 1
60
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
61
QN.3 -- ? How Do Flares CMEs Occur
SOHO Coronagraph -- Artificial eclipse
Discovered huge ejections of plasma
Can reach Earth - communications / satellites
62
Spoof
Information propagates from the left w. very
little interference !
63
Comet coronal mass ejection
64
QN. 4 -- HOW is CORONA HEATED ?
Bright Pts, Loops, Holes
Recon-nection likely
65
IN FUTURE -- MAYBE
66
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
67
Future for the Sun (7 b years)
68
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, Coronas-F..,
• ATST, Solar B, Stereo, SDO, Orbiter)

- bright new young students (esp. theory)
69
(No Transcript)