Transcript SUN COURSE - SLIDE SHOW 2

SUN COURSE - SLIDE SHOW 2
Show 1 -- photosphere & sunspots -->
1. Introduction, 2. Magnetic fields, 3. Corona
1. INTRODUCTION: PS Age of Sun ?
 If Sun consists of coal, it could generate heat/light for …
a few thousand yrs
 Kelvin (1862) - if Sun slowly contracts (grav. Energy ->
heat), it could have illuminated Earth for … 100 m yrs !
 Radioactivity discovered -> Earth rocks older than this !!
 Paradox resolved - new source heat discovered - nuclear
fusion
Radioactive dating method (eg uranium --> lead):
- measure ratio masses + rate of decay
--> time since rocks have formed
 Oldest rocks in s. system (Moon/meteorites) formed 4.6b
yrs ago -- when Sun thought to have been born
PS
Diffusion
Start with
field B0(x)
and watch
diffuse.
Current
density
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MOST of UNIVERSE is PLASMA:
Ionosphere --> 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
? THOUGHT of Vector Calculus FILL with
CONFIDENCE
Eqns of Magnetohydrodynamics
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 -ODE's or PDE's and
solve (standard techs)
--> Construct models
for many dynamic
phenomena on Sun
Temperature Structure
ATMOSPHERE
Photosphere -->
Sunspots
Dark because cool
Galileo discovered
(1610) w. telescope
Surprise (1908):
-- Greeks, Chinese
site of strong
?magnetic
Planets, clouds,
field
smoke, slag
2. MAGNETIC MAP ("Magnetogram")
White -- towards
you;
SURPRISES:
-Black
-- away
patterns
of sunspots
from you
Regions around
-intense--magnetic
sunspots
"Active
fields
over whole
Regions"
Sun
Movie
But why the
active region
patterns ?
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YUV420 codec decompressor
are needed to see this picture.
Magnetic Field (B) and Plasma Coupled
B exerts force on plasma -- move together
In interior, plasma dominates --> moves B
Rotation shears B
--> 2 tubes B --> Emerge:
Magnetic Tube Emerges
Creates pair of sunspots +/Opposite pattern in s. hemisphere
Global Magnetic Field of Sun
At photosphere <|B|> ~ 3 - 20 G, but most is strong (1 kG) & vertical
(i) ACTIVE REGION FLUX
Spreads out --> remnant
Emerges
as
active
region
•sunspots
= 3 kG,region
Merges
-->(B
unipolar
22 Mx)
flux
=
10
-- one dominant polarity
* active regions
--> -->
Migrates
to the poles
faculae
(bright)
polar
field
Solar Cycle
Sunspots vary with period 8-15 years (average 11.1 yr)
Two zones between -35o and +35o latitude
In opposite hemispheres, leading spots have opposite polarities (Hale)
Leading polarity is closer to equator (Joy)
New spots emerge at start of cycle at high latitudes w. opposite
polarity
As cycle progresses, spots form at lower latitudes (Sporer)
Polar Fields:
* maximum extent at s. minimum
* change polarity 1-2 years after s. maximum
No sunspots
varies 11-year
cycle
Also cycle in
X-rays
And in shape
of corona:
(ii) Quiet Sun - Network
mixed polarity -- at edge
of supergranule cells -covers Sun at s. minimum
ephemeral active regions
(1019 Mx) -- emerge & migrate
to boundary
--> network fragments (F =
2x1018 Mx, B = 1 kG) -- at
edges of cells
internetwork fragments (F =
6x1016 Mx, B = 10-100 G ?) -inside cells
Chromosphere
3. CORONA
("crown") -- See at ECLIPSE of Sun
SURPRISE
SURPRISE
(1940)
(1868)
----Temperature
Light
fromclosed
new
is million
element
degrees
"Helium
!!!!"
Faint open
structures
-- Bright
structures
ECLIPSE
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Another ECLIPSE
Corona
created
by state
B
T =CORONA
Million
B here
-->
isCorona
--inunaware
4th
is (heat,
NOT
-- ("PLASMA")
no structure)
aeffect
normal -gas !!!
open/closed
PLASMA
B in plasma
behaves
coupled
differently
(intimate,
from
subtle)gas:
3 -states
of matter
... normal
(iron filings round bar magnet)
How Bright is Corona/Full Moon ?
Lang: Moon = 0.1 x Sunspot ??
Base corona (C0) = 10-5 x Photosphere
Corona at 1 Ro = 10-8 x Photosphere
Full Moon = 2 x 10-6 x Photosphere = 0.2 Co
Sunspot: Umbra = 0.2 Photosphere
Penumbra = 0.75 Photosphere
So Moon = 10-5 Sunspot
CORONA:
Normally need eclipse to see -- Glare of surface
Observe direct with X-ray telescope
As T increases (furnace), object becomes bluer
Skylab (1973-1974)
Picture with X-ray telescope:
Coronal holes
Bright---->
loops
Denser
-- bright points
Yohkoh
A
magnetic
world
Eclipse seen by Yohkoh
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Movie
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From Photosphere to Corona
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Movie + photosphere
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Original Skylab Images
Latest images from new satellite:
TRACE (Active region)
Active
region
at limb
Close-up of Magnetic Loops in Corona (TRACE)
B strong
Dominates
plasma
Plasma Motions along Magnetic Loops
Conjuring
trick --
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plasma
appearing
by magic ?
TRACE
- zoom
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TRACE - flux emerge
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To Finish