ch. 6: the sun. chemical energy? the sun’s luminosity is about 4x10 26 joules per second. its mass...
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Ch. 6: The Sun
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Chemical energy?
The Sun’s luminosity is about 4x1026 joules per second.Its mass is about 2x1030 kg. What is its energy source?
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Chemical energy?
The Sun’s luminosity is about 4x1026 joules per second.Its mass is about 2x1030 kg. What is its energy source?
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= 10 Cal/g= 108 J/kg
2x1030 kg
4x1026 Joules
second
108 joules
kgx 1 year
3x107 secondsx
€
≈17,000 years
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Is it CONTRACTING?
Luminosity
Gravitational Potential Energy~ 25 million years
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It can be powered by NUCLEAR ENERGY!
Luminosity~ 10 billion years
Nuclear Potential Energy (core)
E = mc2
- Einstein, 1905
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The fusion of hydrogen via the proton-proton chain
positron
neutrino
4He nucleu
s
• Neutrinos created during fusion fly directly through the Sun
• Observations of these solar neutrinos can tell us what’s 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 don’t 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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The layers of the Sun are determined by how energy is transported through and out of that layer
€
I = I0e−τ
Radiation transport (radiative transfer)
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Sunspots
cooler than other parts of the Sun’s 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?
€
rμ =I
r A
Magnetic moment of a current carrying loop:
I
Current I = charge/time
•Electrons are moving charges•They respond to external B•Their energy levels change when in a B
€
μ =e
2mL
€
L = mvr = nh
Potential energy of this interaction:
€
U = −r μ ⋅
r B
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Loops of bright gas often connect sunspot pairs
X-ray emission
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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 Sun’s 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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Number of sunspots rises and falls in 11-year cycle
Solar activity varies with time
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Little Ice Age1300-1850
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