Transcript Part 1

The Sun
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Chapter 10
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.)
Major Regions of the Sun
• Interior
– Core
– Radiative Zone
– Convective
Zone
• Atmosphere
– Photosphere
– Chromosphere
– Corona
Photosphere
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• 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
Most Detailed Sunspot Image Ever!
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Swedish Vacuum Telescope
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
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
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• 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
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– 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
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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
Why Does Sun Shine?
• Sun in Hydrostatic Equilibrium
– Pressure requires high temperature
– Sun is hot
• Hot objects
– Radiate (emit light)
– lose energy
Sun shines because
it is hot
• Solar Luminosity
– 1026 Watts
• Age of Sun
– greater than 4.5 billion years (age of earth)
• What is energy source?
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
Nuclear Reactions
• Fusion:
– two light nuclei joined
into one
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• Powers Sun
• Fission:
– massive nucleus splits
in two
• Powers nuclear
reactors (Davis-Besse)
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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
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• 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
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• mass decrease is energy source
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p-p Chain in the Sun