Transcript 12-Sun
The Sun as a Star The “Surface” of the Sun and Its Structure Outer Layers – 3 distinct region Photosphere Chromosphere Corona Photosphere -- light sphere The surface in “visible” light T ~ 6500 - 4000 K Depth 100’s kms Granulation – cellular pattern due to convection Chromosphere – color sphere, seen at solar eclipse T ~ 6000 - 100,000 K, 2000 km thick Hot, low density gas, also granular appearance – supergranulation The Corona or Halo T ~ 1-2 x 106 K , extends millions kms Very hot, low density gas Source of energy to heat chromosphere and corona ?? Coronal holes -- in X ray images Flux of charged particles – solar wind - from the holes, governed by magnetic fields Heating via magnetic waves and mechanical flux from convective layers deep in interior Sunspots and the Solar Activity Cycle Appear dark – lower temp. ~ 4500 K vs 6000 K Strong magnetic fields ~ several thousand Gauss – normal Sun – few Gauss Opposite polarity between sides of a large spot group Magnetic disturbance or storm The 11 yr sunspot cycle -- magnetic cycle every 22 yrs. Maunder Minimum and the “ little ice age” the Thames 1677 -- frozen Solar Activity – Prominences associated with large spot groups Solar Flares -- most violent form of solar activity A sudden brightening, above large spot group, between regions of opposite polarity Outburst of charged particles (cosmic rays), increase in high energy radiation The Carrington Event or solar super storm 1859 most powerful solar storm and solar flare recorded Coronal mass ejection – directly toward Earth aurora seen around world as far south as Caribbean so bright it woke people , telegraph systems failed all over Europe and N. America, telegraph machines threw sparks and some telegraph poles caught fire. Sunspots, prominences, flares all associated with magnetic fields All increase and reach maximum with 11 yr solar activity cycle lack of spots, aurora, < 50 spots 1672-1699 Normal in 30 yrs 30,000 – 40,000 Galileo 1614 ~ 100 spots observed Hevelius 1652-1685, Picard 1653-1685 (LaHire 1718), Flamsteed 1676-1699 LaHire and Durham noted surge in activity 1715 the Maunder minimum and the “little ice age” 1645 -- 1715 global cooling 0.2o C N. Europe ~ 1 - 2o C Dalton minimum 1800 – 1830 year without a summer 1816 but in 1815 Tambora volcano – middle of Dalton minimum Sunspots and short term climate change? the Solar irradiance – energy flux watts/m2 at upper atmosphere 0.1 – 0.2% variation in flux Earth’s surface temperature vary by 0.1 – 0.2o C During little ice age global cooling 0.2o C Sunspot Cycle 24 Cycle 23 minimum 2008.0 but then a lack of spots solar irradiance at 2008 minimum – lower 0.1% global magnetic field at minimum weaker solar wind weakening Is the Sun Missing Its Spots? NY Times 7/21/2009 The impact on global warming ? Or – our perception of it slight increase in solar output ~1900 - 1950 Zero degree reference is 30yr average ~ 1950 - 80 Most recent sunspot curve The Solar Interior and the energy source of the Sun and Stars Gravitational (contraction/collapse) Nuclear Fission --- radioactive elements Nuclear Fusion --- ??? p+ + p+ -> ? How? the Coulomb barrier Nuclear Fusion and Nucleosynthesis in the Stars The proton-proton chain or hydrogen fusion, requires 107o K 1. p+ + p+ np+ + e+ + neutrino np+ = deuteron (deuterium) 2. d+ + p+ n2p+ + gamma ray n2p+ = 3He 3. Net Result -- 4H 1He 3He+ + 3He+ 4He+ + 2 p+ Alternative -- CNO cycle in more massive stars > 2 Msun The CNO cycle converts hydrogen to helium The mass-12 isotope of C captures a proton and emits a gamma-ray producing the mass-13 isotope of N. N-13 is unstable and beta decays to the mass-13 isotope of C with a half-life of approximately 10 minutes. The mass-13 isotope of C captures a proton and emits a gamma-ray to become the mass-14 isotope of N. The mass-14 isotope of N captures another proton and emits a gamma-ray to become the mass-15 isotope of O. The mass-15 isotope of O undergoes a beta decay to become the mass-15 isotope of N. The mass-15 isotope of N captures a proton and emits an alpha-particle (that is, a nucleus of helium) to close the cycle and return to C-12. Beyond Hydrogen Fusion He Fusion to Carbon, Oxygen 3He4 C12 C12 + He4 O16 requires 108o K C, O fusion to heavier elements up to Fe (iron) requires 5 x 108o K C12 + C12 Mg24 , O16 + He4 Ca20 The Solar Interior Hydrostatic Equilibrium (Pressure) gas pressure out = gravity in Thermal Equilibrium (Temperature) Energy (heat) in = Energy out => Energy production rate = luminosity of the star Transfer of energy Radiative (inner) and convection (outer) Random walk of photons