Download The Sun

The Sun
Our Sun is an
ordinary star.
Many stars are much more
massive.
Many stars are much less
massive.
What is the name of our
Sun?
What is the difference
between a star and a sun?
Do You Know…….
• Where the Sun came from?
• How old is the Sun?
• If the Sun has a surface?
• What are the layers of the Sun’s interior and exterior?
• The nature of sunspots?
• The connection between sunspots and the Sun’s magnetic field?
• What powers the Sun?
The Solar Nebula
The Cosmic Abundance
Angular Momentum
Cloud
Cloud
Cloud
Collapses
Begins
Flattens
to Flatten
in to disk
Slowly
Solar Data Table
What powers the Sun?
Nuclear Fusion
E = mc2
Know as the
“P – P Chain”
Matter is turned into
anti-matter and energy
What Keeps the Star From Collapsing?
Hydrostatic
Equilibrium
The outward pressure
force balances the
inward gravitational
force everywhere
inside the Sun.
How Do We Know?
Is thermonuclear fusion really taking place?
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Detect the subatomic particles – Neutrinos
Nuclear burning produces ~1038 neutrinos/s
~ 1014 neutrinos pass thru each m2 of Earth/s
~1012 neutrinos pass thru your body each second
neutrinos have no electric charge
Neutrinos interact very weakly with matter
Rarely, a neutrino hits a neutron converting it into a proton
37Cl + neutrino => 37Ar Isotope reaction
Rate of formation of 37Ar is proportional to neutrino flux
Found 1 neutrino per day Expected 3 per day
1,000 tons of heavy water
9,600 light detectors
The Solar Interior
Three main interior layers
• Core
• Radiation Zone
• Convective Layer
Core
• Central region of the Sun
• Nuclear fusion occurs
(also called hydrogen burning)
• Star is born when fusion begins
(about 1 million degrees)
• Temp of core now about 15 million degrees
Radiative Zone
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Section directly above the core
Energy moves by “radiation transport”
Photons travel ~1 cm before being absorbed
Photons take 106 to 108 yrs to reach surface
Random walk
Convective Region
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Volume between radiative zone and surface
Energy is transported by convection
Cooler near the surface
Brings heat from interior to the surface
Similar to a pot of boiling water
The Surface of the Sun
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Called the Photosphere
Bright visible surface from which light escapes
300 to 400 km thick
Shell of hot, opaque gas
Can’t see through this layer
Completely transparent above
Completely opaque below
• Photosphere pressure ~ 10% of Earth’s sea level
• Place where continuous spectrum is produced
• Not a solid surface, density gradually increases w/depth
Limb Darkening
The Sun’s three
interior layers.
The Sun also has a
surface and two
atmospheric layers.
Can you name them?
Computer Model Showing Solar Oscillations
Blue zones moving outward
Red zones moving inward
Oscillations extend to core
Study of Helioseismology
Sun vibrates at many frequencies
The Atmosphere of the Sun
Chromosphere
Corona
Chromosphere
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Color Sphere, red
Caused by bright red emission line
Lies immediately above the photosphere
Difficult to observe
Reddish glow seen during a solar eclipse
Coronograph – an occulting disk
Source of most of the solar emission lines
Composed of hot transparent gases – mostly H
About 2,500 km thick
Density decreases with altitude
Temp increases from about 4,400 K to 25,000 K with altitude
100,000,000 times less dense then out atmosphere
Corona
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Outer most layer of the Sun
Extends millions of km above the photosphere
Tenuous gas layer ~109 atoms/cc Earth ~1019 atoms/cc
About 1 millionth as bright as the photosphere
Temp in access of one million degrees
Shape changes from month to month
Spherical at sunspot maximum
•Pattern of light and dark areas on the photosphere
•Are the light or dark areas hotter?
•Lifetime about 5 to 10 minutes
•Granules typically 700 km to 1000 kn in size
•Granules are the tops of the convection currents of rising gas
through the photosphere
•Rise at about 2 to 3 km/s
Granulation
Granulation
Jets of gas surging
upward into the corona
Last about 15 minutes
Speed ~ 20 km/s
Chromosphere
Solar Wind
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The Sun’s gravity keeps most gases from escaping
But high coronal temp cause speeds of 106 km/hr
The highest speed gases can escape
Sun ejects 106 tons of mass into the solar wind /s
Solar wind originates from coronal holes
Coronal Hole Movie Clip
•Coronal hole is dark – devoid of material
Coronal Holes are usually found at the polar regions
12 X-Ray Images From 1991 – 1995 120 day Intervals
Sunspots
Sunspot Formation
Sunspot Groups
Overlapping
Sunspots
1999
By observing the same group of
sunspots, Galileo determined
that the Sun rotates about once
per week.
The Sunspot Cycle
Where Do Sunspots Form?
Sunspots and Earth Temperature
The Corona Changes Shape
Spherical at
sunspot maximum
Irregular at
sunspot minimum
How Do We Know the Sun has a Magnetic Field?
Magnetic Fields deflect charged particles
Dark Blue = Strong North Pole
Yellow = Strong South Pole
Highly magnetic areas in (B) correlate with (A)
Differential Rotation
Sunspots are used to measure solar
rotation rates
25 days at the equator
28 days at 40 degrees latitude
36 days at 80 degrees latitude
The Sun does not rotate like a rigid body
Differential rotation cause B in the photosphere to become
wrapped around the Sun. As a result, B becomes concentrated
at certain latitudes on both sides of the equator.
Rotation of
the Solar
Interior
Magnetic Reconnection – Adds Energy to the Corona
One arch contains as much as E as a power plant generates in 106 yrs.
Plages are hot spots in the
chromosphere forming
just before sunspots.
Plages are created when B
push upward from the
Sun’s interior, compressing
and heating a portion of the
chromosphere.
Eielson Air Force Base, Alaska — The Aurora
Borealis, or Northern Lights, shines above Bear Lake
Transient of Mercury 11/15/1999
UV image
Visible
Recap – Parts of the Sun
Key Ideas
• Hydrogen Fusion in the Sun’s Core: The Sun’s energy is
produced by hydrogen fusion, a sequence of thermonuclear
reactions in which four hydrogen nuclei combine to produce a
single helium nucleus.
• The energy released in a nuclear reaction corresponds to a slight
reduction of mass according to Einstein’s equation E = mc2.
• Thermonuclear fusion occurs only at very high temperatures; for
example, hydrogen fusion occurs only at temperatures in excess
of about 107 K. In the Sun, fusion occurs only in the dense, hot
core.
Key Ideas
• Models of the Sun’s Interior: A theoretical description of a
star’s interior can be calculated using the laws of physics.
• The standard model of the Sun suggests that hydrogen fusion
takes place in a core extending from the Sun’s center to about
0.25 solar radius.
• The core is surrounded by a radiative zone extending to about
0.71 solar radius. In this zone, energy travels outward through
radiative diffusion.
• The radiative zone is surrounded by a rather opaque
convective zone of gas at relatively low temperature and
pressure. In this zone, energy travels outward primarily
through convection.
Key Ideas
• Solar Neutrinos and Helioseismology: Conditions in the
solar interior can be inferred from measurements of solar
neutrinos and of solar vibrations.
• Neutrinos emitted in thermonuclear reactions in the Sun’s
core have been detected, but in smaller numbers than
expected. Recent neutrino experiments explain why this is
so.
• Helioseismology is the study of how the Sun vibrates. These
vibrations have been used to infer pressures, densities,
chemical compositions, and rotation rates within the Sun.
Key Ideas
• The Sun’s Atmosphere: The Sun’s atmosphere has three
main layers: the photosphere, the chromosphere, and the
corona. Everything below the solar atmosphere is called the
solar interior.
• The visible surface of the Sun, the photosphere, is the
lowest layer in the solar atmosphere. Its spectrum is similar
to that of a blackbody at a temperature of 5800 K.
Convection in the photosphere produces granules.
Key Ideas
• Above the photosphere is a layer of less dense but higher
temperature gases called the chromosphere. Spicules extend
upward from the photosphere into the chromosphere along
the boundaries of supergranules.
• The outermost layer of the solar atmosphere, the corona, is
made of very high-temperature gases at extremely low
density.
• Activity in the corona includes coronal mass ejections and
coronal holes. The solar corona blends into the solar wind at
great distances from the Sun.
Key Ideas
• The Active Sun: The Sun’s surface features vary in an 11year cycle. This is related to a 22-year cycle in which the
surface magnetic field increases, decreases, and then
increases again with the opposite polarity.
• Sunspots are relatively cool regions produced by local
concentrations of the Sun’s magnetic field. The average
number of sunspots increases and decreases in a regular
cycle of approximately 11 years, with reversed magnetic
polarities from one 11-year cycle to the next. Two such
cycles make up the 22-year solar cycle.
Key Ideas
• The magnetic-dynamo model suggests that many features of
the solar cycle are due to changes in the Sun’s magnetic
field. These changes are caused by convection and the Sun’s
differential rotation.
• A solar flare is a brief eruption of hot, ionized gases from a
sunspot group. A coronal mass ejection is a much larger
eruption that involves immense amounts of gas from the
corona.