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 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 B 0 (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 But why the active region patterns ?

In interior, plasma dominates --> moves B Rotation shears B Magnetic Field (B) and Plasma Coupled B 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 ~ G, but most is strong (1 kG) & vertical (i) ACTIVE REGION FLUX Emerges as sunspots (B = 3 kG, flux = Mx) * active regions --> faculae (bright)

Solar Cycle Sunspots vary with period 8-15 years (average 11.1 yr) Two zones between -35 o and +35 o 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 (10 19 Mx) -- emerge & migrate to boundary --> network fragments (F = 2x10 18 Mx, B = 1 kG) -- at edges of cells internetwork fragments (F = 6x10 16 Mx, B = G ?) -- inside cells

Chromosphere

("crown") -- See at ECLIPSE of Sun Faint open structures -- Bright closed structures SURPRISE (1868) -- Light from new element "Helium " SURPRISE (1940) -- Temperature is million degrees !!!! 3. CORONA

ECLIPSE

T = Million --> Corona is NOT a normal gas !!! 3 states of matter... B here -- unaware -- no effect B 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 (C 0 ) = x Photosphere Corona at 1 R o = x Photosphere Full Moon = 2 x x Photosphere = 0.2 C o Sunspot: Umbra = 0.2 Photosphere Penumbra = 0.75 Photosphere Lang: Moon = 0.1 x Sunspot ?? So Moon = Sunspot

Normally need eclipse to see -- Glare of surface Observe direct with X-ray telescope As T increases (furnace), object becomes bluer CORONA:

Skylab ( )

Coronal holes -- loops -- bright pointsBright --> Denser Picture with X-ray telescope:

A magnetic world Yohkoh

Eclipse seen by Yohkoh

Movie

From Photosphere to Corona

Movie + photosphere

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 ? Plasma Motions

TRACE - zoom

TRACE - flux emerge

To Finish