4 - The Sun
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Transcript of 4 - The Sun
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4 - The Sun
NEVER LOOK DIRECTLY AT THE SUN! EYE DAMAGE CAN RESULT!
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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!
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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%
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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
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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!)
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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
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Solar Spectrum
Kirchhoff’s Laws…
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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
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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?
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The Active Sun
Sunspots:
•Appear in groups
•T~4000-4500 K
•Darker than surrounding photosphere (WHY?)
•Large magnetic fields inhibit convection
umbra
penumbra
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magnetic field
note polarity reversed in N and S
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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
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But the cycle seems to be getting shorter!
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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
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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
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Plages - heated by rising magnetic field - compresses gas
Filaments - cool streamers of gas above photosphere
Prominences - filaments seen from the side
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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
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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
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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.
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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
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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!
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proton-proton chain
CNO cycle
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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……
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A 12C 1H 13N * 13N * 13C e e13C 1H 14N 14N 1H 15O 15O 15N e e
B 15N 1H 12C 4He
CNO Cycle
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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 !!
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The Standard Solar Model (SSM)
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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?
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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
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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
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Super-K - gets about 1/2 the predicted amount
Sudbury Neutrino Observatory (SNO) - sensitive to all “flavors” - agrees with SSM!!
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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!