the sun as a star the “surface” of the sun and its structure outer layers – 3 distinct region...
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The Sun as a Star
The “Surface” of the Sun and Its Structure
Outer Layers – 3 distinct region
Photosphere
Chromosphere
Corona
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Photosphere -- light sphere
The surface in “visible” light
T ~ 6500 - 4000 K
Depth 100’s kms
Granulation – cellular pattern due to convection
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Chromosphere – color sphere, seen at solar eclipse
T ~ 6000 - 100,000 K, 2000 km thick
Hot, low density gas, also granular appearance – supergranulation
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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
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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
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The 11 yr sunspot cycle -- magnetic cycle every 22 yrs.
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Maunder Minimum and the
“ little ice age”
the Thames 1677 -- frozen
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Solar Activity – Prominences associated with large spot groups
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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
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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.
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Sunspots, prominences, flares all associated with magnetic fields
All increase and reach maximum with 11 yr solar activity cycle
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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
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the Maunder minimum and the “little ice age”
1645 -- 1715
global cooling 0.2o C
N. Europe ~ 1 - 2o C
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Dalton minimum 1800 – 1830
year without a summer 1816
but in 1815 Tambora volcano – middle of Dalton minimum
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the Solar irradiance – energy flux watts/m2 at upper atmosphere
0.1 – 0.2% variation in fluxEarth’s surface temperature vary by 0.1 – 0.2o C
During little ice age global cooling 0.2o C
Sunspots and short term climate change?
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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
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The impact on global warming ?
Or – our perception of it
slight increase in solar output ~1900 - 1950
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Zero degree reference is 30yr average ~ 1950 - 80
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Most recent sunspot curve
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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
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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+ + 3He+ 4He+ + 2 p+
Net Result -- 4H 1He
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Alternative -- CNO cycle in more massive stars > 2 Msun
The CNO cycle converts hydrogen to heliumThe 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.
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Beyond Hydrogen Fusion
He Fusion to Carbon, Oxygen3He4 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
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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
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Transfer of energy
Radiative (inner) and convection (outer)
Random walk of photons