1. The Sun as a Star The “Surface” of the Sun and Its Structure
Outer Layers – 3 distinct region
Photosphere
Chromosphere
Corona

2. Photosphere -- light sphere
The surface in “visible” light
T ~ K
Depth 100’s kms
Granulation – cellular pattern due to convection

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

4. T ~ 1-2 x 106 K , extends millions kms Very hot, low density gas
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

5. 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

6. The 11 yr sunspot cycle -- magnetic cycle every 22 yrs.

7. Maunder Minimum and the “ little ice age”
the Thames frozen

8. Solar Activity – Prominences associated with large spot groups

9. 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

10. 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.

11. Sunspots, prominences, flares all associated with magnetic fields
All increase and reach maximum with 11 yr solar activity cycle

12. lack of spots, aurora, < 50 spots 1672-1699
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

13. the Maunder minimum and the “little ice age”
global cooling 0.2o C
N. Europe ~ 1 - 2o C

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

15. 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

16. 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

17. The impact on global warming ?
Or – our perception of it
slight increase in solar output ~

18. Zero degree reference is 30yr average ~ 1950 - 80

21. Most recent sunspot curve

22. 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

23. 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. 3He He+  4He p+
Net Result -- 4H  1He

24. The CNO cycle converts hydrogen to helium
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.

25. C12 + He4  O16 requires 108o K 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

26. 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

27. Transfer of energy
Radiative (inner) and convection (outer)
Random walk of photons