Chapter 9 The Sun
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Transcript of Chapter 9 The Sun
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Chapter 9The Sun
Chapter 9The Sun
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Sunspots
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Our SunOur Sun
• Is the nearest star
• 8 light minutes away
• Next nearest star is 4.3 light-years away (300,000X further than sun)
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Figure 9.1The Sun
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Table 9.1Some Solar Properties
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Solar RotationSolar Rotation
• Differential rotation
• Measure by timing sunspots
• Faster at equator
• Slower at poles
• X-ray and visible light movie of sun
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Figure 9.2Solar Structure
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Solar StructureSolar Structure• Core
• Radiation zone
• Convection zone
• Photosphere (“surface” we see)
• Chromosphere
• Transition zone
• Corona
• Solar wind
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Solar LuminositySolar Luminosity• Solar constant 1400 W/m2 above earth’s
atmosphere
• 1000 W/m2 at earth’s surface
• Solar constant and distance to sun gives luminosity of about 4 X 1026 W
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Figure 9.3Solar Luminosity
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Stellar balanceStellar balance• Outward pressure of hot gas
• Inward pull of gravity
• Balanced at every point in a star
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Figure 9.4Stellar Balance
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Standard solar modelStandard solar model• Mathematical and physical model of sun
• Based on observations and physical laws
• Predicts density and temperature
• Helioseismology allows knowledge of interior structure
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Figure 9.5Solar Oscillations
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Figure 9.6Solar Interior
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Sun’s temperature and densitySun’s temperature and density• Core density 150,000 kg/m3 (20X iron)
• Core temperature 15 million K
• Core is a gas (plasma)
• Photosphere is 0.0001X density of earth’s atmosphere
• Photosphere temperature 5780 K
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Discovery 9.1SOHO: Eavesdropping on the Sun
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SOHOSOHO• Solar and Heliospheric Observatory
• European Space Agency
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Solar energy transportSolar energy transport• Near core - very hot
• Gas is completely ionized (plasma)
• No photons captured - transparent to radiation
• Outer edge of radiation zone cool enough for electrons to re-combine with nuclei
• Photons all absorbed
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Convection ZoneConvection Zone• Energy transported by rising hot gases
• Cooler gas sinks
• Convection cells vary in size with depth in convection zone
• Tens of thousands of km to a thousand km convection cells
• Photons from photosphere escape into space
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Figure 9.7Solar Convection
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Evidence for convectionEvidence for convection• Solar granulation of photosphere
• Granules size of a large US state
• Last 5 to 10 minutes
• Bright regions - hot gas rising
• Dark regions - cool gas sinking
• 500 K difference between hot and cool
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Figure 9.8Solar Granulation
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Solar Granulation movieSolar Granulation movie• Near infrared
• 60 minute sequence sped up
• At http://www.bbso.njit.edu or click here
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Doppler shiftDoppler shift• Bright granules move up at about 1 km/s
• Dark granules move down at about 1 km/s
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SupergranulationSupergranulation• Larger scale flow beneath solar surface
• 30,000 km across
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Figure 9.9Solar Spectrum
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Composition of solar atmosphere
Composition of solar atmosphere
• Primarily H and He
• Also O, C, N, Si, Mg, Ne, Fe, S
• Similar to Jovian planets and rest of universe
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Table 9.2The Composition of the Sun
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Figure 9.10Solar Chromosphere
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Solar chromosphereSolar chromosphere• Above photosphere and less dense
• Pinkish hue from H emission
• Expelling jets of hot matter - spicules
• Last minutes
• 100 km/s
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Figure 9.11Solar Spicules
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CoronaCorona• Corona visible during total solar eclipse
• Emission spectrum visible against blackness of space
• Ionized atoms - high coronal temperatures
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Figure 9.12Solar Corona
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Transition ZoneTransition Zone• Minimum temperature of 4500 K in
chromosphere
• Temperature climbs through transition zone
• Reaches several million K in corona
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Figure 9.13Solar Atmospheric Temperature
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Solar windSolar wind• Starts 10 million km above photosphere
• Hot coronal gas escapes sun’s gravity
• Millions of tons of sun ejected each second
• Only lost 0.1% of mass in 4.6 billion years
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X-rays in coronaX-rays in corona• Photosphere emits primarily visible light
• Hotter corona emits primarily X-rays
• Coronal holes - visible in X-rays
• Solar wind escapes in coronal holes
• Related to magnetic fields
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Figure 9.14Sunspots
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Figure 9.15Sunspots, Up
Close
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SunspotsSunspots• In photosphere
• Cooler (darker) than surrounding material
• Dark umbra (4500 K)
• Grayish penumbra (5500 K)
• Typically 10,000 km across (size of earth)
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Sunspot magnetismSunspot magnetism• Magnetic field of photosphere stronger
than earth’s
• Magnetic field in sunspots is 1000X greater than surrounding photosphere
• Field lines perpendicular to surface
• Strong fields interfere with convective flow
• Causes sunspots to be cooler
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Sunspot magnetic polaritySunspot magnetic polarity• Sunspots in pairs at same latitude
• Pair members have opposite polarity N&S
• Leading spot in a hemisphere always has same polarity
• Leading spot in other hemisphere has opposite polarity
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Figure 9.16Sunspot Magnetism
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Magnetic field wrappingMagnetic field wrapping• Differential rotation “wraps” magnetic field
• North-south re-oriented to east-west
• Convection lifts field to surface
• Twisting and tangling results
• Some kinks rise out of photosphere
• Forms sunspot pair
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Figure 9.17Solar Rotation
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Analogy 9.1A tangled garden hose
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Figure 9.18Sunspot Cycle
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Maunder minimumMaunder minimum• Cycle varies from 7 to 15 years
• Overall activity varies
• Solar inactivity from 1645-1715
• Maunder minimum caused “Little Ice Age”
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Figure 9.19Maunder Minimum
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Solar prominencesSolar prominences• Loops or sheets of gas ejected into lower
corona
• Maybe due to magnetic fields near sunspots
• Typically 100,000 km (10X diameter of earth)
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Figure 9.20Solar Prominences
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Solar prominence movieSolar prominence movie• Big Bear Solar Observatory
• At http://www.bbso.njit.edu or click here
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Solar flaresSolar flares• More violent than prominences
• Sweeps across active region in minutes
• Temperature of millions of K
• Material blasted into space
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Figure 9.21Solar Flare
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Solar flare movieSolar flare movie• Big Bear Solar Observatory
• Go to http://www.bbso.njit.edu or click here
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Corona activityCorona activity• Coronal mass ejection
• Several times per day during sunspot maximum
• Can cause communication and power disruption on earth
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Figure 9.22Coronal Mass Ejection
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Figure 9.23Coronal Hole
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Figure 9.24Active Corona
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SOHO Coronal mass ejectionSOHO Coronal mass ejection• White ring is size of sun
• Play movie or go to
• http://sohowww.nascom.nasa.gov/data/LATEST/current_c2.mpg
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Sun’s energy sourceSun’s energy source
• Nuclear fusion reactions in core
• Two nuclei combine forming 3rd nucleus plus energy
• 3rd nucleus has less mass than sum of two nuclei
• Mass converted to energy E = mc2
• Need high temperature to overcome charge repulsion
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Figure 9.25Proton Interactions
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Proton-Proton chainProton-Proton chain• 4 protons helium-4 + 2 neutrinos +
energy
• Neutrino is chargeless and virtually massless particle
• Neutrinos easily pass through sun
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Figure 9.26Solar Fusion
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Energy generatedEnergy generated• 600 million tons of H fused into He every s
• Sun can sustain this another 5 billion years
• Energy produced in core as gamma rays
• Neutrinos also carry off energy
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Figure 9.27a Neutrino Telescope in Japan
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Figure 9.27bNeutrino Telescope in Ontario, Canada
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NeutrinosNeutrinos• Less neutrinos detected at earth than
predicted by standard solar model
• Neutrinos oscillate into new types during journey to earth
• Latest neutrino detectors can find all types
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More Precisely 9.2Energy Generation in the Proton–Proton Chain