Ch. 6: The Sun

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Ch. 6 The Sun
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The Suns luminosity is about 4x1026 joules per
second. Its mass is about 2x1030 kg. What is its
energy source?
Chemical energy?
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The Suns luminosity is about 4x1026 joules per
second. Its mass is about 2x1030 kg. What is its
energy source?
Chemical energy?
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10 Cal/g 108 J/kg
2x1030 kg
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Is it CONTRACTING?
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E mc2 - Einstein, 1905
It can be powered by NUCLEAR ENERGY!
Nuclear Potential Energy (core)
10 billion years
Luminosity
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The fusion of hydrogen via the proton-proton chain

• Neutrinos created during fusion fly directly
  through the Sun
• Observations of these solar neutrinos can tell us
  whats happening in core

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Weight of upper layers compresses lower layers
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The Sun is in hydrostatic equilibrium Gravity
pushes inward Fusion generates energy - heats
the gas - increases the pressure - balances
the inward force of gravity
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Core Energy generated by nuclear fusion 15
million K
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Radiation Zone Photons dont know which way is
up - they escape by a random walk Energy
gradually leaks out of radiation zone
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Convection Zone Energy transported upward by
rising hot gas
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Photosphere Visible surface of Sun 6,000 K
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Chromosphere Middle layer of solar atmosphere
104 - 105 K
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Corona Outermost layer of solar atmosphere 1
million K
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Solar wind A flow of charged particles from the
surface of the Sun
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Limb darkening
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Radiation transport (radiative transfer)
The layers of the Sun are determined by how
energy is transported through and out of that
layer
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Sunspots cooler than other parts of the Suns
surface (4000 K) Contain strong magnetic
fields cool gas is sinking
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41.2 Zeeman effect
Atomic energy levels, and their spectral lines,
are split when the atoms are in a magnetic field
Experimental confirmation of the quantization of
angular momentum
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Why do the lines split?

• Electrons are moving charges
• They respond to external B
• Their energy levels change when in a B

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X-ray emission
Loops of bright gas often connect sunspot pairs
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Magnetic activity causes solar flares that send
bursts of X-rays and charged particles into space
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Magnetic activity also causes solar prominences
that erupt high above the Suns surface
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Corona appears bright in X-ray photos in places
where magnetic fields trap hot gas
Insert TCP 5e Figure 14.20
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Coronal mass ejections send bursts of energetic
charged particles out through the solar system
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Charged particles streaming from Sun can disrupt
electrical power grids and can disable
communications satellites
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Solar activity varies with time
Number of sunspots rises and falls in 11-year
cycle
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Little Ice Age 1300-1850
Winter sports became very popular!
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• Historical implications of the Little Ice Age
• Greenland settlement collapsed in 1400
• Glaciers advanced, crushing villages in
  Switzerland
• 1780 New York Harbor froze
• Stradivari built his famous violins
• Armies could march acropss frozen rivers and
  straits
• Snow fell in summer in Northern Europe famine
  ensued