Amber Reed's Notes

10.1 A closer look at the sun

Why does the sun shine?

Chemical energy content~10,000 years
Luminosity 

Gravitational potently energy~25 billion years 
Luminosity 

Nuclear potential energy (core)~ 10 billion years 
Luminosity  

-Weight of upper layers compress lower layers
-Gravitational equilibrium : gravity pulling in balances pressure pushing out
-energy balance : thermal energy released by fusion in core balances radiative energy lost from surface 
-gravitational contraction provided energy that heated the core of the sun 

What is the structure of the sun??

-Solar wind: flow of charged particles
-Corona: outermost layer of solar atmosphere~1million K
-Chromosphere: middle layer if solar atmosphere ~10^4-10^5 K
-Photosphere: visible surface of the sun ~6000 K
-Convection zone: energy transported upward by rising hot gas
-Radiation zone: energy transported upward by photons
-Core: energy generated by nuclear fusion ~15 million K

10.2 nuclear fusion in the sun 

How does nuclear fusion occur in the sun?

-Fission: big nucleus splits into smaller pieces ( nuclear power plants)
-Fusion: small nuclei stick together to make a bigger one ( sun and stars)
-High temps enable nuclear fusion to happen in the core 
-The sun releases energy by fusing four hydrogen nuclei into one helium nucleus 
Proton-proton chain is how hydrogen fuses into helium in the sun
In=4 protons
Out=He nucleus, 2 gamma rays , 2 positrons , 2 neutrinos
Mass is lower than .7%

Solar thermostat :
Decline in core temp causes fusion rate to drop, so core contracts and heats up
Rise in core temp causes fusion rate to rise, so core expands and cools down 

How does the energy form fusion get out of the sun?
-Energy gradually leaks out of the radiation zone in the form of randomly  bouncing photons 
-convection (rising hot gas) energy to the surface 

How do we know what is happening inside the sun?

-Making mathematical models
-Observing solar vibrations
-Observing solar neutrinos 

-Patterns of vibration on the surface tell us abut what the sun is like inside 
-data on solar vibrations agree with mathematical models of solar interior
-neutrinos created during fusion fly directly through the sun
-observations of these solar neutrinos can tell us whats happening in the core

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  

10.3 the sun-earth connection

What causes solar activity?
-solar activity is like "weather" on earth
-sunspots : are cooler than other parts of the sun's surface (4000K). Are regions with strong magnetic fields
-solar flares:
-solar prominences
( all these phenomena are related to magnetic fields )

-Zeeman effect: we can measure magnetic fields in sunspots by observing the splitting of spectral lines 
-Loops of bright gas often connect sunspot pairs
-Magnetic activity also causes solar prominences that erupt high above the sun's surface 
-The corona appears bright in x-ray photos in places where magnetic fields trap hot gas

Coronal mass ejections: send bursts of energetic charged particles out to the solar system 
-charged particles streaming from the sun can distrust electrical power grids and disable communications satellites 

How does solar activity vary with time?

-The number is sunspots rises and falls in 11 year cycles
-the sunspot cycle has something to do with the winding and twisting of the sun's magnetic field 


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