Ch. 6: The Sun. Chemical energy? The Sun’s luminosity is about 4x10 26 joules per second. Its mass...
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Transcript of Ch. 6: The Sun. Chemical energy? The Sun’s luminosity is about 4x10 26 joules per second. Its mass...
Ch. 6: The Sun
Chemical energy?
The Sun’s luminosity is about 4x1026 joules per second.Its mass is about 2x1030 kg. What is its energy source?
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
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≈17,000 years
Is it CONTRACTING?
Luminosity
Gravitational Potential Energy~ 25 million years
It can be powered by NUCLEAR ENERGY!
Luminosity~ 10 billion years
Nuclear Potential Energy (core)
E = mc2
- Einstein, 1905
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
Weight of upper layers compresses lower layers
The Sun is in hydrostatic equilibrium
Gravity pushes inward
Fusion generates energy
- heats the gas
- increases the pressure
- balances the inward force of gravity
Core:
Energy generated by nuclear fusion
~ 15 million K
Radiation Zone:
Photons don’t know which way is up - they escape by a “random walk”
Energy gradually leaks out of radiation zone
Convection Zone:
Energy transported upward by rising hot gas
Photosphere:
Visible surface of Sun
~ 6,000 K
Chromosphere:
Middle layer of solar atmosphere
~ 104 - 105 K
Corona:
Outermost layer of solar atmosphere
~1 million K
Solar wind:
A flow of charged particles from the surface of the Sun
Limb darkening
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The layers of the Sun are determined by how energy is transported through and out of that layer
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I = I0e−τ
Radiation transport (radiative transfer)
Sunspots
cooler than other parts of the Sun’s surface (~4000 K)
Contain strong magnetic fields
cool gas is sinking
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
Why do the lines split?
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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
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μ =e
2mL
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L = mvr = nh
Potential energy of this interaction:
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U = −r μ ⋅
r B
Loops of bright gas often connect sunspot pairs
X-ray emission
Magnetic activity causes solar flares that send bursts of X-rays and charged particles into space
Magnetic activity also causes solar prominences that erupt high above the Sun’s surface
Corona appears bright in X-ray photos in places where magnetic fields trap hot gas
Insert TCP 5e Figure 14.20
Coronal mass ejections send bursts of energetic charged particles out through the solar system
Charged particles streaming from Sun can disrupt electrical power grids and can disable communications satellites
Number of sunspots rises and falls in 11-year cycle
Solar activity varies with time
Little Ice Age1300-1850
Winter sports became very popular!
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