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4 - The Sun

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:

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4 - The Sun

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  1. 4 - The Sun NEVER LOOK DIRECTLY AT THE SUN! EYE DAMAGE CAN RESULT!

  2. 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!

  3. 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%

  4. ATMOSPHERE (general) Photosphere - “sphere of light” - Taverage = Teff ~ 5780 K ~1000 km across Few X 100 Km thick • 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)

  5. 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!)

  6. Chromosphere - “sphere of color” - T drops to ~ 4300 K Special H filter used to image whole Sun 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)

  7. Solar Spectrum Kirchhoff’s Laws…

  8. 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 C0 C I C+1 C II C+2 C III C+3 is C IV *NOTE: spectroscopists use a special notation:

  9. 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?

  10. The Active Sun • Sunspots: • Appear in groups • T~4000-4500 K • Darker than surrounding photosphere (WHY?) • Large magnetic fields inhibit convection • umbra • penumbra

  11. note polarity reversed in N and S magnetic field 

  12. 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

  13. But the cycle seems to be getting shorter!

  14. Effects on Earth’s Climate What fraction of global warming is due to the Sun? cosmic rays can induce cloud formation & cover cloud chambers

  15. Maunder Minimum (1645-1715) & “Little Ice Age” Can lead to errors in radio-carbon dating See Wikipedia for more on the "Little Ice Age" cycle seen in sedimentary rock samples 650 million yrs old - due to variations in deposition of glacial meltwater

  16. Plages - heated by rising magnetic field - compresses gas Filaments - cool streamers of gas above photosphere Prominences - filaments seen from the side

  17. 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

  18. 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

  19. Coronal Mass Ejections Expel trillions of tons at hundreds of km/s! • Potential damage to: • satellites & astronauts • power grids • radio communication • etc.

  20. INTERIOR • Sun 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

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

  22. proton-proton chain CNO cycle

  23. Proton-proton chain in detail…… PPI (91% of time) PPII (8% of time) PPIII (1% of time)

  24. CNO Cycle

  25. 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 !!

  26. The Standard Solar Model (SSM)

  27. 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?

  28. Helioseismology to the Rescue! Measured Oscillation Modes - Global Oscillation Network Group (GONG) Convection deeper than once thought Differential rotation goes deep! But SSM not endangered

  29. 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????

  30. Super-K - gets about 1/2 the predicted amount Sudbury Neutrino Observatory (SNO) - sensitive to all “flavors” - agrees with SSM!!

  31. 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!

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