The Sun Chapter 10. The Sun - Our Star “Average” star Made entirely of gas –too hot for...
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The Sun
Chapter 10
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The Sun - Our Star
• “Average” star• Made entirely of gas
– too hot for liquids or solids• Surface temp = 5000 K• Center temp = 10 million K
• Composition (by mass):– 70% H– 28% He– 2% everything else (C, N, O, etc.)
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Major Regions of the Sun
• Interior– Core
– Radiative Zone
– Convective Zone
• Atmosphere– Photosphere
– Chromosphere
– Corona
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Photosphere
• Effective “surface” of sun– not solid– region we see by eye
• Thin atmospheric layer– Few hundred km
• Low density gas– 0.01% Earth’s atmosphere
• Close-up shows granulation– convection cells
• Sunspots– Cooler than surrounding gas
• appear dark
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Atmospheric Features
• Sunspots– Larger than Earth– Occur in groups– Associated with magnetic fields– Galileo used to measure solar
rotation • 25 days at equator• longer at poles
– Number of sunspots• Cyclical
– 11 yr period
• Correlated with solar activity– greatest activity at sunspot maximum– least at minimum
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Most Detailed Sunspot Image Ever!
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Swedish Vacuum Telescope
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Solar Rotation
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Atmospheric Features
• Sunspots– Larger than Earth– Occur in groups– Associated with magnetic fields– Galileo used to measure solar
rotation • 25 days at equator• longer at poles
– Number of sunspots• Cyclical
– 11 yr period
• Correlated with solar activity– greatest activity at sunspot maximum– least at minimum
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Atmospheric Features
• Prominences– Loops of hot gas– Base near sunspots – Trace magnetic fields
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Chromosphere
• Region just above photosphere
• Emission-line spectrum– indicates higher temperature
– reddish color from hydrogen line
• Temperature increases outward
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Transition Region
• Between chromosphere and corona
• Temperature increases– from 10,000 K to 106 K
• Spicules (“spikes”) – gas jets poking up from
photosphere– duration ~10 minutes– heights 5,000-20,000 km
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Corona
• Outermost region of atmosphere– Extends millions of km
• Seen during eclipse • Very high temperature
– millions of degrees K
– heated by solar magnetic field
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Solar Wind
• Gas flows away from sun– 10 million tons/yr– protons & electrons– speed 400-800 km/s
• Material goes outward into solar system– Hits Earth’s atmosphere
• guided by magnetic field• makes atmosphere glow
(aurorae)
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Solar Flare
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Solar Flares
• Eruptions caused by magnetic fields – may last 5-10 min
– release huge amounts of energy• gas heated to 107 K
– produces X-rays and UV radiation
• Coronal Mass Ejections– very large flares
– large mass of gas ejected from corona
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Solar Flares & Effects on Earth
• CME hits Earth’s Magnetic Field– Aurorae intensified
– affects magnetic field • produces power surges
– ’89 Quebec/Montreal power outage
– electrical interference• Disrupts radio communications
– Cell phone outage
• Danger to satellites/astronauts• Space Weather at:
http://www.sel.noaa.gov/today.html
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Solar Variability & Earth’s Climate
• Solar Luminosity Varies ~1%– Highest at sunspot maximum– Lowest at minimum activity
• Maunder minimum 1650-1700– Very few sunspots– “Little Ice Age” in Europe
• extreme cold temps• shorter growing season
• Still learning how Sun affects Earth’s climate QuickTime™ and aTIFF (Uncompressed) decompressorare needed to see this picture.
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Solar Interior
• Interior is gaseous
• Constant battle:– Gravity pulls in– Pressure pushes out
• Star shrinks – becomes hotter, until
• Pressure balances gravity
Hydrostatic Equilibrium
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Why Does Sun Shine?• Sun in Hydrostatic Equilibrium
– Pressure requires high temperature– Sun is hot
• Hot objects– Radiate (emit light)– lose energy
• Solar Luminosity– 1026 Watts
• Age of Sun– greater than 4.5 billion years (age of earth)
• What is energy source?
Sun shines because it is hot
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Sun’s Energy Source• Thermal energy (chemical reactions)?
– wood or fuel burning– Entire Sun used in a few thousand years NO
• Gravitational contraction?– energy released as Sun contracts– would suffice for 100 million years NO
• Nuclear Energy?– Einstein: E = mc2
– Can convert mass into energy• 1 gram of matter = energy of 15,000 barrels of oil
– Need 4 million tons/sec– Will suffice for 10 billion years YES
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Nuclear Reactions
• Fusion: – two light nuclei joined
into one• Powers Sun
• Fission: – massive nucleus splits
in two• Powers nuclear
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Converting Mass to Energy
• Nuclear reactions change mass– Mass increase consumes energy
– Mass decrease releases energy
• Mass decreases in
– Fission of heavy nuclei• Can occur spontaneously
• natural radioactivity
– Fusion of light nuclei• Like charges repel
• Fusion requires high speed
• Temperature > 10 million K
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Fusion: Sun’s Energy Source
• Sun’s core:– Temperature = 15 million K
– Large enough to fuse hydrogen
• p-p chain (proton-proton)– Series of fusion reactions
– Converts:4 hydrogen to 1 helium nucleus
– mass of 4 H > mass of 1 He• mass decrease is energy source
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p-p Chain in the Sun