Transcript 23sun3s

The Sun
Astronomy 311
Professor Lee Carkner
Lecture 23
Helios -- The God of the Sun
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The Sun was often
worshiped by
ancient people
WARNING !
NEVER LOOK DIRECTLY AT THE
SUN
NEVER LOOK AT THE SUN WITH
BINOCULARS OR A TELESCOPE
PERMANENT EYE DAMAGE CAN
RESULT
Observing the Sun
With a solar filter in place we can use a
telescope to get a high spatial resolution
optical image of the Sun
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Today’s Sun
The Sun From the Inside Out
We will examine the Sun from the core
to the diffuse outer layers
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Nuclear fusion and magnetic fields
play key roles in the energetics and
structure of the Sun
Why Does the Sun Shine?
From radioisotope dating we know that
the solar system is 4.5 billion years old
What could power the Sun for this
length of time?
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The Core
At the core of the Sun the temperature and
pressure are very high due to the weight of
the outer layers
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At these conditions the hydrogen atoms are
moving so fast and are packed together so
tightly that they can fuse together to make
helium:
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Hydrogen Fusion
How Does the Energy at the
Core Get Out?
In general energy is transported in 3
ways:
Conduction -Radiation -Convection --
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The Inner Structure of the Sun
Radiative and Convective Zones
Radiative Zone (0.25-0.71 Rsun)
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Convective Zone (0.71-1.00 Rsun)
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Hot material rises causing convection
The Photosphere
It takes about 170,000 years for the energy to reach
the surface of the Sun
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The photosphere has an average temperature of 5800
K
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The top layer will absorb some of the light from the
bottom layers producing absorption lines
Granulation in the
Photosphere
The photosphere is at the top of the
convective zone
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The photosphere is covered with
granules (each about 1000 km across)
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Solar Granulation
Granules
Sunspots in the Photosphere
The photosphere sometimes has small
dark regions called sunspots
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Sunspots are regions where the Sun’s
magnetic field inhibits the flow of
warmer material
Sunspots
Sunspot Cycles
Sunspots exist for a maximum of a few months
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There is a sunspot cycle of 11 years
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The sunspots move towards the equator over the
course of the cycle
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Sunspot Maximum and
Minimum
The Sunspot Cycle
Sunspot Cycles and
Differential Rotation
The Sun rotates differentially
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The magnetic field gets “wrapped-up” around the
equator
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The sunspots are caused by the magnetic field
“kinks”
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The Twisted Magnetic Field of
the Sun
The Sun’s Magnetic Field
The Sun’s magnetic field extends far
out beyond the surface
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These loops can break and reconnect
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The Chromosphere
The chromosphere is a diffuse layer of the
solar atmosphere extending from the
photosphere to about 2000 km
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It has a temperature of about 20000 K
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The Structure of the
Chromosphere
The chromosphere is composed of many
rising filaments of hot gas called spicules
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Between the chromosphere and the corona
is the transition region where the
temperature rises from 20,000 K to 1 million
K over a small region
Spicules in the Chromosphere
Temperature in the Sun’s
Atmosphere
The Corona
The corona is the outer layer of the Sun’s
atmosphere
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It is thinner and hotter than the chromosphere
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The high temperatures produce a hot ionized
gas called a plasma
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Flares and Magnetic Activity
The material in the corona is constantly
changing
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Flare activity is linked to sunspot activity
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Changes in magnetic activity seem to
effect climate
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Magnetic Activity Cycle
The Structure of the Corona
The high temperatures and irregular
structure of the corona are due to
magnetic fields
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The tangled, shifting magnetic loops
gives the corona its structure
Core
Radiative Zone
Convective Zone
Photosphere
Chromosphere
Corona
Structure of the Sun
Summary: Structure of the
Sun
Core
fusion converts H to
He and power the
Sun
Radiative Layer
transports energy
from the core
Convective Layer
transports energy to
the photosphere
Photosphere
visible surface of the
Sun
Chromosphere
hot middle
atmospheric layer
Corona
very hot outer layer
Summary: Solar Energetics
Thermonuclear Fusion
Energy is produced at the core of the Sun
by converting hydrogen to helium
Energy Transport
Energy is transported via radiation where
the opacity is low and via convection
where the opacity is high
Magnetic Fields
The outer layers of the Sun are composed
of hot plasma in magnetic loops