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 ~ K Depth 100’s kms Granulation – cellular pattern due to convection

Chromosphere – color sphere, seen at solar eclipse T ~ ,000 K, 2000 km thick Hot, low density gas, also granular appearance – supergranulation

The Corona or Halo T ~ 1-2 x 10 6 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 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 Normal in 30 yrs 30,000 – 40,000 Galileo 1614 ~ 100 spots observed Hevelius , Picard (LaHire 1718), Flamsteed LaHire and Durham noted surge in activity 1715

the Maunder minimum and the “little ice age” global cooling 0.2 o C N. Europe ~ o C

Dalton minimum 1800 – 1830 year without a summer 1816 but in 1815 Tambora volcano – middle of Dalton minimum

the Solar irradiance – energy flux watts/m 2 at upper atmosphere 0.1 – 0.2% variation in flux Earth’s surface temperature vary by 0.1 – 0.2 o C During little ice age global cooling 0.2 o C Sunspots and short term climate change?

Sunspot Cycle 24 Cycle 23 minimum 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 ~

Zero degree reference is 30yr average ~

Most recent sunspot curve

Gravitational (contraction/collapse) Nuclear Fission --- radioactive elements Nuclear Fusion --- ??? p + + p + -> ? How? the Coulomb barrier The Solar Interior and the energy source of the Sun and Stars

Nuclear Fusion and Nucleosynthesis in the Stars The proton-proton chain or hydrogen fusion, requires 10 7o K 1. p + + p +  np + + e + + neutrino np + = deuteron (deuterium) 2. d + + p +  n2p + + gamma ray n2p + = 3 He 3. 3 He He +  4He p + Net Result -- 4H  1He

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  3He 4  C 12 C 12 + He 4  O 16 requires 10 8o K C, O fusion to heavier elements up to Fe (iron) requires 5 x 10 8o K C 12 + C 12  Mg 24, O 16 + He 4  Ca 20

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