Presentation on theme: "4 - The Sun NEVER LOOK DIRECTLY AT THE SUN! EYE DAMAGE CAN RESULT!"— Presentation transcript:
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 = 2x10 30 kg = 300,000M Radius R = 7x10 8 m = 7x10 5 km = 111R Mean Density = Mass/Volume = M/((4/3) R 3 )= 1400 kg/m 3 = 1.4 g/cm 3 Distance = 1.5x10 11 m = 1.5x10 8 km = 8.3 light-minutes Luminosity L = 3.9x10 26 W (Solar Constant = 1350 W/m 2 ) Mean Surface Temperature = T effective = 5780 K CompositionBy MassBy Number H~68%~90% He~31%~10% “Heavies” ~1% ~1%
ATMOSPHERE (general) Photosphere - “sphere of light” - T average = T eff ~ 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 T 4 (Stefan-Boltzmann Law!)
Chromosphere - “sphere of color” - T drops to ~ 4300 K When seen edge-on we see the 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, ,000,000 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: C 0 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 = km/s T = 50, ,000 K* density = /m 3 sea level - ~2.5x10 25 /m 3 ) Solar wind expands outward, creating the heliosphere Listen to Voyager 1 crossing “dense” regions herehere * Why don’t we cook?
The Active Sun Sunspots: Appear in groups T~ 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 global warming is due to the Sun? cosmic rays can induce cloud formation & cover cloud chambers
Maunder Minimum ( ) & “Little Ice Age” Can lead to errors in radio-carbon dating See Wikipedia for more on the "Little Ice Age""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 Observatoryherehere)
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 Expel trillions of tons at hundreds of km/s! Potential damage to: satellites & astronauts power grids radio communication etc.
INTERIOR Sun produces 4x10 26 W for 4x10 9 yrs. How? Chemical - would last only 10 4 yrs Gravitational - would last 25-50x10 6 yrs Thermonuclear - can last yrs! Einstein finds that matter & energy are different aspects of the same thing - E=mc ’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 kg He + ENERGY equivalent to the missing kg (i.e. 0.7% of the original amount) - this is equivalent to burning 6000 tons of chemical fuel! L = 3.9x10 26 W 4.3x10 9 kg/s lost 6x10 11 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!
proton-proton chain CNO cycle
PPI (91% of time) PPII (8% of time) PPIII (1% of time) Proton-proton chain in detail……
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: T c ~15x10 6 K, P c ~3x10 11 Atm, density c ~160 g/cm 3 !!
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????
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!