chapter 14 our star
TRANSCRIPT
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Chapter 14Our Star
http://en.wikipedia.org/wiki/Sun
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14.1 A Closer Look at the Sun
• Our goals for learning
• How was the Sun’s energy source a major mystery?
• How does the Sun shine?
• What is the Sun’s structure?
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How come the Sun’s energy source a major mystery?
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Is it on FIRE?
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Is it on FIRE?
Luminosity~ 10,000 years
Chemical Energy Content
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Is it on FIRE? … NO!
Luminosity~ 10,000 years
Chemical Energy Content
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Is it CONTRACTING?
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Luminosity
Gravitational Potential Energy
Is it CONTRACTING?
~ 25 million years
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Luminosity
Gravitational Potential Energy
Is it CONTRACTING? … NO!
~ 25 million years
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How does the Sun shine?
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It can be powered by NUCLEAR ENERGY! http://en.wikipedia.org/wiki/Nuclear_Energy
Luminosity~ 10 billion years
Nuclear Potential Energy (core)
E = mc2
- Einstein, 1905
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Weight of upper layers compresses lower layers
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Gravitational equilibrium:
Energy provided by fusion maintains the pressurehttp://en.wikipedia.org/wiki/Nuclear_fusion
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Gravitational contraction:
Provided energy that heated core as Sun was forming
Contraction stopped when fusion began
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What is the Sun’s structure?
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Radius:
6.9 x 108 m
(109 times Earth)
Mass:
2 x 1030 kg
(300,000 Earths)
Luminosity:
3.8 x 1026 watts
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Solar wind:
A flow of charged particles from the surface of the Sun
http://en.wikipedia.org/wiki/Solar_wind
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Corona:
Outermost layer of solar atmosphere
~1 million K
http://en.wikipedia.org/wiki/Corona
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Chromosphere:
Middle layer of solar atmosphere
~ 104 - 105 K
http://en.wikipedia.org/wiki/Chromosphere
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Photosphere:
Visible surface of Sun
~ 6,000 K
http://en.wikipedia.org/wiki/Photosphere
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Convection Zone:
Energy transported upward by rising hot gas
http://en.wikipedia.org/wiki/Convection_zone
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Radiation Zone:
Energy transported upward by photons
http://en.wikipedia.org/wiki/Radiation_zone
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Core:
Energy generated by nuclear fusion
~ 15 million K
http://en.wikipedia.org/wiki/Solar_core
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What have we learned?
• Why was the Sun’s energy source a major mystery?– Chemical and gravitational energy sources
could not explain how the Sun could sustain its luminosity for more than about 25 million years
• Why does the Sun shine?– The Sun shines because gravitational
equilibrium keeps its core hot and dense enough to release energy through nuclear fusion. Stars are gravitationally control thermonuclear fusion reactors.
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What have we learned?
• What is the Sun’s structure?– From inside out, the layers are:
• Core
• Radiation Zone
• Convection Zone
• Photosphere
• Chromosphere
• Corona
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14.2 Nuclear Fusion in the Sun
• Our goals for learning
• How does nuclear fusion occur in the Sun?
• How does the energy from fusion get out of the Sun?
• How do we know what is happening inside the Sun?
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How does nuclear fusion occur in the Sun?
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Fissionhttp://en.wikipedia.org/wiki/Nuclear_fission Big nucleus splits into smaller pieces(Nuclear power plants)
Fusionhttp://en.wikipedia.org/wiki/Nuclear_fusion Small nuclei stick together to make a bigger one(Sun, stars)
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High temperature enables nuclear fusion to happen in the corePositively charge protons would repel each other as Benjamin Franklin taught us. Strong Nuclear Forcehttp://en.wikipedia.org/wiki/Strong_forceQCD, Quantum Chromo Dynamicshttp://en.wikipedia.org/wiki/Quantum_chromodynamics
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Sun releases energy by fusing four hydrogen nuclei into one helium nucleus Net Results
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Proton-proton chain is how hydrogen fuses into helium in Sunhttp://en.wikipedia.org/wiki/Proton-proton_reaction
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IN4 protons
OUT4He nucleus
2 gamma rays2 positrons2 neutrinos
Total mass is 0.7% lower
Net Results
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Thought Question
What would happen inside the Sun if a slight rise in core temperature led to a rapid rise in fusion energy?
A. The core would expand and heat up slightlyB. The core would expand and coolC. The Sun would blow up like a hydrogen bomb
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Thought Question
What would happen inside the Sun if a slight rise in core temperature led to a rapid rise in fusion energy?
A. The core would expand and heat up slightlyB. The core would expand and coolC. The Sun would blow up like a hydrogen bomb
Solar thermostat keeps burning rate steady
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Solar Thermostat
Decline in core temperature causes fusion rate to drop, so core contracts and heats up
Rise in core temperature causes fusion rate to rise, so core expands and cools down
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How does the energy from fusion get out of the Sun?
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Energy gradually leaks out of radiation zone in form of randomly bouncing photons Photon Diffusion:http://en.wikipedia.org/wiki/Photon_diffusion
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Convection (rising hot gas) takes energy to surface http://en.wikipedia.org/wiki/Convection
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Bright blobs on photosphere are where hot gas is reaching surface
Granular Solar Physicshttp://en.wikipedia.org/wiki/Granule_%28solar_physics%29
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How we know what is happening inside the Sun?
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We learn about inside of Sun by …
• Making mathematical models
• Observing solar vibrations
• Observing solar neutrinos http://en.wikipedia.org/wiki/Solar_neutrinos
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Patterns of vibration on surface tell us about what Sun is like insidehttp://gong.nso.edu/info GONG, Global Oscillation Network Group
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Data on solar vibrations agree very well with mathematical models of solar interior
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Neutrinos created during fusion fly directly through the SunThe Sun is transparent to neutrinos.Observations of these solar neutrinos can tell us what’s happening in core
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Solar neutrino problem:
Early searches for solar neutrinos failed to find the predicted number. Down by a factor of three. This experiment was done deep underground only neutrinos could penetrate that far. Cl was transformed to Ar when a neutron was transformed into a proton and an electron by the absorption of a neutrino.http://en.wikipedia.org/wiki/Solar_neutrino_problem
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Solar neutrino problem:
Early searches for solar neutrinos failed to find the predicted number
More recent observations find the right number of neutrinos, but some have changed formNeutrino Oscillations:http://en.wikipedia.org/wiki/Neutrino_oscillation Neutrinos http://en.wikipedia.org/wiki/Neutrino
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What have we learned?
• How does nuclear fusion occur in the Sun?– The core’s extreme temperature and density are
just right for nuclear fusion of hydrogen to helium through the proton-proton chain
– Gravitational equilibrium acts as a thermostat to regulate the core temperature because fusion rate is very sensitive to temperature
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What have we learned?
• How does the energy from fusion get out of the Sun?– Randomly bouncing photons carry it through
the radiation zone– Rising of hot plasma carries energy through the
convection zone to photosphere
• How do we know what is happening inside the Sun?– Mathematical models agree with observations
of solar vibrations and solar neutrinos
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14.3 The Sun-Earth Connection
• Our goals for learning
• What causes solar activity?
• How does solar activity affect humans?
• How does solar activity vary with time?
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What causes solar activity?http://en.wikipedia.org/wiki/Solar_activity
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Solar activity is like “weather”
• Sunspots http://en.wikipedia.org/wiki/Sunspots • Solar Flares
http://en.wikipedia.org/wiki/Solar_flares • Solar Prominences
http://en.wikipedia.org/wiki/Solar_Prominence • All are related to magnetic fields
http://en.wikipedia.org/wiki/Magnetic_field
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Sunspots
Are cooler than other parts of the Sun’s surface (4000 K)
Are regions with strong magnetic fields
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Zeeman Effect
We can measure magnetic fields in sunspots by observing the splitting of spectral lineshttp://en.wikipedia.org/wiki/Zeeman_effect
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Charged particles spiral along magnetic field lines
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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 Sun’s surface
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Corona appears bright in X-ray photos in places where magnetic fields trap hot gas
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How does solar activity affect humans?
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Coronal mass ejections send bursts of energetic charged particles out through the solar systemhttp://en.wikipedia.org/wiki/Coronal_mass_ejection
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Charged particles streaming from Sun can disrupt electrical power grids and can disable communications satellites
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How does solar activity vary with time?
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Number of sunspots rises and falls in 11-year cycle
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Sunspot cycle has something to do with winding and twisting of Sun’s magnetic field Babcock Model: http://en.wikipedia.org/wiki/Babcock_Model
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What have we learned?
• What causes solar activity?– Stretching and twisting of magnetic field lines
near the Sun’s surface causes solar activity
• How does solar activity affect humans?– Bursts of charged particles from the Sun can
disrupt communications, satellites, and electrical power generation
• How does solar activity vary with time?– Activity rises and falls with an 11-year period