4 - The Sun

NEVER LOOK DIRECTLY AT THE SUN! EYE DAMAGE CAN RESULT!

Major Regions:

Interior (“Inner-sphere”)

•Core

•Radiative Zone

•Convective Zone

Atmosphere (“Outer-sphere”)

•Photosphere

•Chromosphere

•Corona

No real “surface” - it is gaseous all the way to the center!

Basic Facts:

Mass M = 2x1030 kg = 300,000M

Radius R = 7x108 m = 7x105 km = 111R

Mean Density = Mass/Volume = M/((4/3)R3)= 1400 kg/m3 = 1.4 g/cm3

Distance = 1.5x1011 m = 1.5x108 km = 8.3 light-minutes

Luminosity L = 3.9x1026 W (Solar Constant = 1350 W/m2)

Mean Surface Temperature = Teffective = 5780 K

Composition By Mass By Number

H ~68% ~90%

He ~31% ~10%

“Heavies” ~1% ~1%

ATMOSPHERE (general)Photosphere - “sphere of light” - Taverage = Teff ~ 5780 K

Granulation - light & dark regions in photosphere

•upwelling is hotter & brighter

•downwelling is cooler & darker

•Flowing motion “convection”

Also see “supergranulation”

Surface pulsations - 5 min - 1 hr (measured via Doppler Effect)

Few

X

100

Km

thick

~1000 km across

Limb Darkening

The photosphere is hotter as you go deeper

We see deeper when looking at the center of the “disk”

Brightness increases as T4 (Stefan-Boltzmann Law!)

Chromosphere - “sphere of color” - T drops to ~ 4300 K

When seen edge-on we see the

656.3 nm Balmer line H

This is where Helium was discovered

(Helios - Greek god of the Sun)

Special H filter used to image whole Sun

Solar Spectrum

Kirchhoff’s Laws…

Corona - T rises to ~ 500,000 - 1,000,000 K !!

Highly ionized atoms, such as Fe+13 (also called Fe XIV)*

Light scattered by ions & electrons (inner) & dust grains (outer)

Heated by complex magnetic/particle activity

*NOTE: spectroscopists use a special notation:

C0 C I

C+1 C II

C+2 C III

C+3 is C IV

Solar Wind

Outer atmosphere is flowing away from the Sun - the solar wind

Speeds up to few million km/hr

Earth is inside the solar wind!

At Earth:

V = 400 - 700 km/s

T = 50,000-500,000 K*

density = 103 - 104/m3 (Earth @ sea level - ~2.5x1025/m3)

Solar wind expands outward,

creating the heliosphere

Listen to Voyager 1 crossing “dense” regions here

* Why don’t we cook?

The Active Sun

Sunspots:

•Appear in groups

•T~4000-4500 K

•Darker than surrounding photosphere (WHY?)

•Large magnetic fields inhibit convection

umbra

penumbra

magnetic field

note polarity reversed in N and S

Solar Cycle:

Number of spots = ~ 11 yrs

Latitude of spots = ~ 11 years

Magnetic polarity of spots = 22 years (to return to starting orientation)

Horace Babcock - Magnetic Dynamo via differential rotation

But the cycle seems to be getting shorter!

Effects on Earth’s Climate

What fraction of What fraction of global warming is global warming is due to the Sun?due to the Sun?

cosmic rays can induce cloud formation & cover

cloud chambers

Maunder Minimum

(1645-1715)

&

“Little Ice Age”

Can lead to errors in radio-carbon dating

See Wikipedia for moreon the "Little Ice Age"

cycle seen in sedimentary rock samples 650 million yrs old - due to variations in deposition of glacial meltwater

Plages - heated by rising magnetic field - compresses gas

Filaments - cool streamers of gas above photosphere

Prominences - filaments seen from the side

Flares - sudden release of energy equal to 100s of millions of megatons - radio through gamma rays! Temperatures exceed 10 million K

A couple (here & here) of nice movies from the Big Bear Solar Observatory

Magnetic field loops trap hot gas, area bright in X-rays

Open fields - gas flows & area is dark in X-rays - coronal holes

Look at this with 3D glasses (red-green) - from Yohkoh spacecraft

Coronal Mass Ejections

QuickTime™ and aYUV420 codec decompressor

are needed to see this picture.

Expel trillions of tons at hundreds of km/s!

Potential damage to:

•satellites & astronauts

•power grids

•radio communication

etc.

INTERIORSun produces 4x1026 W for 4x109 yrs. How?

•Chemical - would last only 104 yrs

•Gravitational - would last 25-50x106 yrs

•Thermonuclear - can last 1010 yrs!

1905 - Einstein finds that matter & energy are different aspects of the same thing - E=mc2

1920’s - Eddingtom calculates that the core of the Sun must have T ~ millions K, and proposes some type of atomic/nuclear process fuels the Sun’s energy

Atkinson suggests it is fusion of H into He

1 kg H 0.993 kg He + ENERGY equivalent to the missing 0.007 kg (i.e. 0.7% of the original amount) - this is equivalent to burning 6000 tons of chemical fuel!

L = 3.9x1026 W 4.3x109 kg/s lost 6x1011 kg/s H He

IF THE SUN COULD USE ALL OF ITS H FUEL:

Lifetime fuel supply

rate of fuel use

2x1030 kg

6x1011kg s 1

1yr

3.6x107 s yr 1

100x109 yrs

Later, we will see that the Sun will only be able to tap ~10% of its mass, but that’s still 10 billion years!

proton-proton chain

CNO cycle

A 1H 1H 2H e e

e e B 2H 1H 3HeC 3He 3He 4He21H

D 3He 4He 7BeE 7Be e 7Li e

F 7Li 1H 8Be* G 8Be* 24He * excited state

H 7Be 1H 8B I 8B 8Be* e e

J 8Be* 24He

PPI

(91% of time)

PPII

(8% of time)

PPIII

(1% of time)

Proton-proton chain in detail……

A 12C 1H 13N * 13N * 13C e e13C 1H 14N 14N 1H 15O 15O 15N e e

B 15N 1H 12C 4He

CNO Cycle

SOLAR INTERIOR MODELS

Mathematical descriptions of what the Sun should be like inside

Hydrostatic Equilibrium - balance of gravity & pressure

Thermal Equilibrium - balance of heat energy everywhere

Energy Transport (how does it get from the core to the surface?

•conduction - direct transfer through physical contact

•convection - transfer of energy through fluid motion

•radiation - transfer via photons

Equation of State - relates pressure, density, temperature

Opacity - how photon transfer are affected by the gas

Energy Generation - energy production vs. temperature, density, etc.

“Boundary Conditions” - L, M, R, etc. to look like a real star!

Results: Tc~15x106K, Pc~3x1011 Atm, density c~160 g/cm3 !!

The Standard Solar Model (SSM)

Solar Neutrino Problem

pp chain produces neutrinos

The measured rate of neutrinos is 1/3-1/2 that predicted by SSM

Something is wrong………..

•Experiments? - but many give similar “wrong” results

•Solar Models? - helioseismology says “probably not”

•New physics? - who asked for that?

Measured Oscillation Modes - Global Oscillation Network Group (GONG)

Helioseismology to the Rescue!

Convection deeper than once thought

Differential rotation goes deep!

But SSM not endangered

The Experiments

Ray Davis Homestake Mine - looks for from pp III - gets 1/3 predicted value

pp III very sensitive to T

Experiment only measures 1 “flavor” of - the “electron ”

What if ’s change in flight????

37Cl

e 37 Ar e

Super-K - gets about 1/2 the predicted amount

Sudbury Neutrino Observatory (SNO) - sensitive to all “flavors” - agrees with SSM!!

Sun only makes electron ’s

SNO Results show:

We detect ~1/3 of electron ’s predicted by SSM

We detect TOTAL number of predicted by SSM

2/3 of the electron ’s were converted into other flavors before they reached Earth (so the total number is conserved)

Requires revising “standard physics” of subatomic particles - New Physics!