the sun
Post on 03-Jan-2016
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The Sun
Properties
• M = 2 X 1030 kg
= 300,000 MEarth
• R = 700,000 km
> 100 REarth
• 70% H, 28% He• T = 5800 K surface,
15,000,000 K core
Structure
Sun’s Atmosphere
Sun’s Atmosphere
• Solar Wind – stream of particles blown out from the sun
• Corona– Extends several million km above surface– T = 1,000,000 K– Emits X-Rays
• Chromosphere– T = 10,000 K– Emits UV
• Photosphere– T = 5,800 K– Emits visible light
Sun’s Interior
• Convection Zone– Energy travels up
toward the surface via rising hot gas
• Radiation Zone– Photons travel through
plasma 1/3 down from surface
• Core– Energy is produced
Sun’s Interior
• Convection Zone– Energy travels up
toward the surface via rising hot gas
• Radiation Zone– Photons travel through
plasma 1/3 down from surface
• Core– Energy is produced
Energy
• Measured in joules or calories
• Power is the rate energy is used
• 1 Watt = 1 joule/s
• We call the power output of a star it Luminosity
• LSun = 3.8 X 1026 watts
Hydrostatic Equilibrium
• Why doesn’t gravity just make the whole star collapse?– Gravity pulls in– Pressure from inside
the sun pushes out– These two things
balance perfectly
How does the Sun shine?
Historical Views
• Burning ball of coal or wood
• Energy release due to gravitational contraction– Kelvin-Helmholtz contraction
Nuclear fusion
• E=mc2
• Cloud of gas collapsed, releasing potential energy
• Gas heats• Gravity creates high
pressure• High pressure and
temperature allow nuclear fusion
• Need high temperature so particles move fast enough to collide
• Nuclear strong force keeps particles stuck together
Proton-Proton Chain
Solar Neutrinos
Solar Thermostat
Random Walk
• Radiation has to make it out of the sun
• Photon bounces randomly off of electrons– Density of Sun’s core
means lots of bounces
• Photons take a few hundred thousand years to get out
Solar Activity
Magnetic Fields
• Material can travel along magnetic field lines
• It is difficult to travel across field lines
Sunspots
Solar Prominence
Solar Prominence Video
Solar Flare
• Sometimes magnetic fields get too stretched and can’t handle the stress anymore
• They break, releasing trapped material
• Video
Coronal Mass Ejections
CME Video
Sunspot Cycle
• Cycle lasts ~11 years– 7-15 yrs
Sunspot Cycle
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