The 11/1/10 Solar Atmosphere
Suns
Atmosphere &
Sunspots
Regions of the Sun above
the photosphere are called
the Suns atmosphere
Just above the photosphere
lies the chromosphere
Above the
chromosphere is
the corona
The Chromosphere
The Chromosphere (2)
Region of suns atmosphere
just above the photosphere.
Temperature increases
gradually from 4500 K to
10,000 K, then jumps to 1
million K
Transition region
Spicules: Filaments
of cooler gas from
the photosphere,
rising up into the
chromosphere.
Visible in H
emission.
Each one lasting
about 5 15 min.
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11/1/10
Spicules on the Solar Limb
The Corona
The Magnetic Carpet of the Corona
Corona contains very low-density, very hot (1 million
oK)
A Very Active Star
gas
Coronal gas is heated through motions of magnetic
fields anchored in the photosphere below (magnetic
carpet)
Computer
model of
the
magnetic
carpet
The surface and atmosphere
of the Sun are extremely
active
Solar wind streams out of
coronal holes, regions of low
magnetic field
Active regions send arcades
of plasma shooting from the
surface. These are regions of
high magnetic field
Coronal mass ejections send
large quantities of mass out
into space
Solar flares release energy
into space
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11/1/10
How do we know all of this?
Naturally, weve
never seen the inside
of the Sun
Solar Activity
Computer models
suggest the layered
structure weve
discussed
We can probe the
interior using
helioseismology, the
study of sunquakes!
Copyright (c) The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Sun Spots
Sun Spots (2)
Active Regions
Cooler regions of the
photosphere (T 4240 K).
Only appear dark against the
bright sun. Would still be
brighter than the full moon when
placed on the night sky!
Visible
Ultraviolet
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11/1/10
Sun Spots (3)
The Suns Magnetic Dynamo
Magnetic field in sun spots is about 1000 times
stronger than average.
The sun rotates faster at the equator than
near the poles.
Magnetic Poles
Magnetic
South
Poles
In North sun spots, magnetic field lines emerge out of the
photosphere.
The Babcock Cycle
This differential rotation might be responsible for
magnetic activity of the sun.
The Solar Cycle
The Sun has an 11-year
sunspot cycle, during which
sunspot numbers rise, fall,
and then rise again:
Reversal of magnetic
polarity
After 11 years, North/
South order of
leading/trailing sun
spots is reversed
=> Total solar cycle
= 22 years
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Magnetic Loops
The Solar Cycle (3)
Maunder Butterfly Diagram
Magnetic field lines
Sun spot cycle starts out with spots at higher
latitudes on the sun
Evolve to lower latitudes (towards the
equator) throughout the cycle.
The Maunder Minimum
The sun spot number also fluctuates
on much longer time scales:
Prominences
Areas around sunspots are active; large
eruptions may occur in photosphere.
Solar prominence is large sheet of ejected
gas:
Historical data indicate a very quiet phase of the
sun,1645 1725: The Maunder Minimum
Corresponds to relatively lower temperatures
here on Earth, a little ice age
The reason for the Maunder Minimum and its
effect on climate are still unknown
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Prominences
Eruptive Prominences and Flares
(Ultraviolet
images)
Extreme events (solar
flares) can significantly
influence Earths
magnetic field structure
and cause northern lights
(aurora borealis).
Solar Flares
Flares Affect Earth
A Solar flare is a large explosion on Suns surface,
emitting a similar amount of energy to a
prominence, but in seconds or minutes rather than
days or weeks:
Can travel from the Sun to Earth in less than an hour!
Can damage satellites, spacecraft, and humans in space
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11/1/10
A Coronal Mass Ejection
The Solar Wind
Particles flow outward at
about 400 km/s.
Gases in the corona are
so hot and moving so fast
that they cannot be held by
solar gravity and escape
into space.
Sun is constantly
losing mass:
107 tons/year
( 10-14 of its mass per
year)
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