Lecture 17
The Sun
November 2, 2015
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Basic Information
•
•
•
•
Mass = 330,000 M
Radius=109 R
Density=1400 kg/m3
Spins differentially
– P = 25 days at equator
– P = 36 days at poles
• Closest star to the Earth.
• Very strong magnetic
field
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Composition of the Sun
•
•
•
•
75% Hydrogen
24% Helium
1% Trace elements
How do we know?
– Spectroscopic measurements
– Analysis of solar wind
• Other important solar data comes from:
– Solar and Heliospheric Observatory (SOHO)
– Solar Dynamics Observatory (SDO)
4
Solar Atmosphere
Photosphere
Corona
Interior
Solar Wind
Chromosphere
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Photosphere
• Layer of gas seen from the Earth
• Temp ~5800 K
• Granules -- patches of gas experiencing
convection
Cooler gas
sinking
Warmer gas
rising
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Chromosphere
• Layer of less dense gas
– Seen only during solar eclipses or with special filter
– Light red or pink in color (because of atomic hydrogen)
– Rising jets of gas = spicules
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Corona
• Seen only during a solar
eclipse
• Thin, hot gas (over 1
million Kelvin)
• Why so hot???
– Energized by the Sun’s
complex magnetic field.
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The photosphere of the sun is
A.
B.
C.
D.
a thin pinkish gas with rising spicules.
a 5800 K layer with convective97%
granules.
a hot thin gas energized by the magnetic field.
a dense, hot layer enriched by helium.
2%
A.
0%
B.
C.
2%
D.
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Solar Wind
•
•
•
•
Outflow of particles from Sun into space
Mainly protons and electrons.
Sun ejects 1 million tons of mass per second
Greatest wind is emitted through coronal holes
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Sunspots
•
•
•
•
Dark, cooler (~ 4300 K) spots on surface of Sun.
Powerful magnetic field 5000× stronger than Earth’s
Lifetime of ~2 rotations (8 weeks).
More numerous in an ~11 year cycle.
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Solar Photosphere features
This time-lapse movie shows three and a half hours
in the life of a sunspot (note the clock at upper right).
A sunspot consists of a dark central umbra and a
feather-like penumbra. Around them, granules some
1000 km across rise and fall in the hot photosphere.
Each granule releases enough energy in its 8-minute
lifetime to supply the United States with its energy
needs for 300 years.
Sunspot groups, which may last for about two
months, are produced by cycles in the Sun's magnetic
field. To measure the Sun's rotation, observers can
track the motion of sunspot groups, much as Galileo
did four centuries ago. (This movie shows these
motions over a period of about two weeks.) Such
studies show that the equatorial regions of the Sun
rotate somewhat faster than the polar regions.
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Sunspot photo
Close up
image of
sunspot and
granules.
Click here for
more info on
this image
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Mega sunspot of November 2015
So you thought Halloween was over? Think again. There is a monster spot on the Sun. AR2443 has more than quadrupled in
size since it first appeared on Oct. 29th, and it now stretches more than 175,000 km from end to end. Philippe Tosi took this
picture of the active region on Nov. 1st from his backyard observatory in Nîmes, France.
The sunspot has more than a dozen dark cores, many of which are as large as terrestrial continents--and a couple as large as
Earth itself. These dimensions make it an easy target for backyard solar telescopes.
Of greater interest is the sunspot's potential for explosive activity. The spotty complex has a 'beta-gamma' magnetic field that
harbors energy for strong M-class solar flares. Any such explosions will be geoeffective as the sunspot turns squarely toward
Earth in the days ahead.
(www.spaceweather.com November 2, 2015)
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Solar Cycle
•Last solar maximum = 2001 Next: 2012
•Currently leaving solar activity minimum
http://solarscience.msfc.nasa.gov/SunspotCycle.shtml
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Solar Activity
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Solar Activity
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Solar Activity
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Formation of Sunspots
–
–
–
–
Sun rotates faster at the equator than at the poles
Magnetic field under surface becomes wound up
Magnetic field gets pushed above surface.
Magnetic field inhibits warmer gas from moving to
those areas where field pushes through surface.
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Sunspots are dark because
A. they are cool relative to the gas around them.
B. they contain 10 times more iron than the
87%
surrounding regions.
C. nuclear reactions occur in them at a slower rate
than in the surrounding gas.
D. they are clouds in the cool corona that block our
view of the solar surface.
E. absorption lines are clustered together there.
4%
A.
B.
6%
C.
1%
1%
D.
E.
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One major feature that distinguishes a sunspot
from other regions on the Sun is
A. faster rotation around the Sun's axis
66%
than neighboring regions.
B. its greater light emission compared to
the photosphere.
C. its very powerful magnetic field.
D. a coronal hole existing above it.
18%
10%
A.
B.
6%
C.
D.
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Prominences and Solar Flares
• Prominences
– Hot gas lofted upwards by
the magnetic field.
– Associated with sunspots
– The least energetic solar
atmosphere phenomenon
• Solar Flares
– Gas and particles erupt off
of the surface
– Produce sun quakes
– Associated with sunspot
groups
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Prominence -- SOHO
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Sunquake -- SOHO
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Coronal Mass Ejection
• Gigantic event sometimes set off by flares
• Can create disruption of satellites,
communications, and power grids
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Flares and CME Video
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Solar Dynamics Observatory
• Launched February 11, 2010
• Web site: http://sdo.gsfc.nasa.gov/
• Spectacular
4K video
published 11/1/15
• Daily information
at spaceweather.com
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Which of the following phenomena on the Sun do
NOT appear to be sources of particles traveling
out into the solar system from the Sun?
A.
B.
C.
D.
granules.
eruptive prominences
coronal holes
flares
63%
16%
21%
0%
A.
B.
C.
D.
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The Energy of the Sun
• Sun produces energy through the process of
nuclear fusion
• 4 hydrogen atoms are combined to form one
helium atom
He
H
H
p
p
H p
H
p
n n
p p
Energy
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• During fusion, some of the mass is
transferred into energy through
E = Energy
E  mc
2
m = mass
c = speed of light
• Fusion can only occur in the core of the Sun
– high gravitational pressure
– high temperatures
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Interior Structure of the Sun
• Core
– Nuclear
fusion
produces
energy
• Radiative
Zone
– Energy is
transported
by photons
of light
• Convective
Zone
– Warmer
gas moves
upward,
cool gas
sinks
Animation
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Hydrostatic Equilibrium
• Hydrostatic equilibrium is the balance between
pressure of out-flowing energy pushing outward
and inward pull of gravity.
• Keeps the Sun
from collapsing
due to gravity
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The energy produced in the central core of the
Sun is transported to the surface
A. by radiation in the layers just outside the central core
and by convection in the outer74%
layers.
B. by convection in the layers just outside the central
core and by radiation in the outer layers.
C. by convection from just outside the central core all
the way to the surface.
D. by radiation from just outside the central core all the
way to the surface.
10%
A.
B.
6%
C.
10%
D.
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Summary