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 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
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: 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 = 400 - 700 km/s T = 50,000-500,000 K* density = 10 3 - 10 4 /m 3 (Earth @ 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~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
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 (1645-1715) & “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 10 10 yrs! 1905 - Einstein finds that matter & energy are different aspects of the same thing - E=mc 2 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 = 3.9x10 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!
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 !!
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!