SUN COURSE - SLIDE SHOW 2

Show 1 -- photosphere & sunspots -->

SUN COURSE - SLIDE SHOW 2

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 fusionRadioactive 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

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Start with field B0(x) and watch diffuse.

Current density

Ionosphere --> Sun (8 light mins)

Learn basic behaviour of plasma from Sun

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

miles]

MOST of UNIVERSE is PLASMA:

? 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

Galileo discovered (1610) w. telescope

-- Greeks, Chinese

? Planets, clouds, smoke, slag

Dark because cool

Surprise (1908):

site of strong magnetic field

White -- towards you; Black -- away from you

Regions around sunspots -- "Active Regions"

SURPRISES: -- patterns of sunspots

-- intense magnetic fields over whole Sun

2. MAGNETIC MAP ("Magnetogram")

Movie

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are needed to see this picture.But why the active region

patterns ?

In interior, plasma dominates --> moves B

Rotation shears B

Magnetic Field (B) and Plasma CoupledB exerts force on plasma -- move together

--> 2 tubes B --> Emerge:

Magnetic Tube Emerges

Creates pair of sunspots +/-

Opposite pattern in s. hemisphere

Global Magnetic Field of Sun

Spreads out --> remnant active region

Merges --> unipolar region -- one dominant polarity

Migrates to the poles --> polar field

At photosphere <|B|> ~ 3 - 20 G, but most is strong (1 kG) & vertical

(i) ACTIVE REGION FLUX

Emerges as

•sunspots (B = 3 kG, flux = 1022

Mx)

* active regions --> faculae (bright)

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

("crown") -- See at ECLIPSE of Sun

Faint open structures -- Bright closed structuresSURPRISE (1868) -- Light from new element "Helium"SURPRISE (1940) -- Temperature is million degrees !!!!

3. CORONA

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ECLIPSE

T = Million --> Corona is NOT a normal gas !!!3 states of matter ...

B here -- unaware -- no effectB in plasma -- coupled (intimate, subtle)CORONA is in 4th state ("PLASMA")

PLASMA behaves differently from normal gas:Corona created by B (heat, structure) --

open/closed (iron filings round bar magnet)

Another ECLIPSE

How Bright is Corona/Full Moon ?

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

Lang: Moon = 0.1 x Sunspot ??

So Moon = 10-5 Sunspot

Normally need eclipse to see -- Glare of surface

Observe direct with X-ray telescope

As T increases (furnace), object becomes bluer

CORONA:

Skylab (1973-1974)

Coronal holes -- loops -- bright points Bright --> Denser

Picture with X-ray telescope:

A magnetic

world

Yohkoh

Eclipse seen by Yohkoh

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Movie

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From Photosphere to Corona

Movie + photosphere

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Original Skylab Images

Latest images from new satellite:

TRACE (Active region)

Active region at limb

of Magnetic Loops in Corona (TRACE)

B strong

Dominates plasma

Close-up

along Magnetic Loops

Conjuring trick --

plasma appearing by magic ?

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Plasma Motions

TRACE - zoom

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TRACE - flux emerge

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To Finish