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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.

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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
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
PS Diffusion

Start with field B0(x) and watch diffuse.

Current density

most of universe is plasma
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

eqns of magnetohydrodynamics
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

atmosphere
ATMOSPHERE

Photosphere --> Sunspots

Dark because cool

Galileo discovered (1610) w. telescope

Surprise (1908):

-- Greeks, Chinese

site of strong magnetic field

? Planets, clouds, smoke, slag

2 magnetic map magnetogram
2. MAGNETIC MAP ("Magnetogram")

White -- towards you;

Black -- away from you

SURPRISES: -- patterns of sunspots

Regions around sunspots -- "Active Regions"

-- intense magnetic fields over whole Sun

movie
Movie

But why the active region patterns ?

magnetic field b and plasma coupled
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
Magnetic Tube Emerges

Creates pair of sunspots +/-

Opposite pattern in s. hemisphere

global magnetic field of sun
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 active region

Merges --> unipolar region -- one dominant polarity

Migrates to the poles --> polar field

  • Emerges as
  • sunspots (B = 3 kG,
    • flux = 1022 Mx)
  • * active regions --> faculae (bright)
solar cycle
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)

slide15

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
No sunspots varies - 11-year cycle

Also cycle in X-rays

And in shape of corona:

ii quiet sun network
(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

3 corona

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

3. CORONA

SURPRISE (1940) -- Temperature is million degrees !!!!

SURPRISE (1868) -- Light from new element "Helium"

Faint open structures -- Bright closed structures

another eclipse
Another ECLIPSE

Corona created by B (heat, structure) --

open/closed

(iron filings round bar magnet)

B here -- unaware -- no effect

B in plasma -- coupled (intimate, subtle)

CORONA is in 4th state ("PLASMA")

PLASMA behaves differently from normal gas:

T = Million --> Corona is NOT a normal gas !!!

3 states of matter ...

how bright is corona full moon
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
CORONA:

Normally need eclipse to see -- Glare of surface

Observe direct with X-ray telescope

As T increases (furnace), object becomes bluer

picture with x ray telescope
Picture with X-ray telescope:

Coronal holes -- loops -- bright points

Bright --> Denser

yohkoh
Yohkoh

A magnetic world

original skylab images
Original Skylab Images

Latest images from new satellite:

plasma motions

along Magnetic Loops

Plasma Motions

Conjuring trick --

plasma appearing by magic ?