The Sun: Our Extraordinary Ordinary Star

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CHAPTER 10 The Sun Our Extraordinary Ordinary
Star
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WHAT DO YOU THINK?

• How does the mass of the Sun compare with that of
  the rest of the solar system?
• Are there stars nearer the Earth than the Sun?
• Does the Sun have a solid and liquid interior
  like the Earth?
• What is the surface of the Sun like?
• Does the Sun rotate?
• What makes the Sun shine?

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• You will discover
• why the Sun is a typical star
• how todays technology has led to a new
  understanding of solar phenomena, from sunspots
  to the powerful ejections of matter that
  sometimes enter our atmosphere
• that some features of the Sun generated by its
  varying magnetic field occur in cycles
• how the Sun generates the energy that makes it
  shine
• new insights into the nature of matter from solar
  neutrinos

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The bright visible surface of the Sun is called
the photosphere.
When looking at the Sun, the edges appear orange
and darker than the central yellow region. This
is known as limb darkening.
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Upon closer inspection, the Sun has a marbled
pattern called granulation, caused by the
convection of gases just beneath the photosphere.
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During an eclipse, sometimes you can see the
layers of the Suns atmosphere just above the
photosphere, which emits only certain wavelengths
of light, resulting in a reddish appearance. We
call this the sphere of color, or chromosphere.
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The solar chromosphere is characterized by jets
of gas extending upward called spicules.
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THE SOLAR CORONA
This x-ray image shows the million-degree gases.
Seen in visible light during an eclipse.
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The temperature of the solar gases increase with
distance from the solar surface. Within the
narrow transition region between the chromosphere
and the corona, the temperature increases by 100
times.
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Sunspots
Overlapping sunspots
Sunspots have two regions the inner, darker
umbra and the outer penumbra.
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The number of sunspots on the photosphere varies
over an eleven-year cycle.
Sunspot Maximum
Sunspot Minimum
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Sunspots can be used to determine the rate of the
suns rotation.
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During the sunspot cycle, the latitude at which
sunspots appear changes. A plot of the latitude
of appearing sunspots over time reveals that
early in the sunspot cycle, they appear away from
the equator, then slowly move toward the equator
as the cycle progresses.
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Sunspots are regions of intense magnetic fields
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The Sun undergoes differential rotation. The
rotation period of the Suns gases varies from 25
days in the equatorial region to 35 days near the
solar poles.
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Therefore, the magnetic field lines of the Sun
become intertwined after several rotations,
creating regions of intense magnetic fields and
thus producing sunspots.
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Viewing the Sun with an H-Alpha filter reveals an
active chromosphere during a sunspot maximum
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Ionized gases trapped by magnetic fields form
prominences that arc far above the solar surface.
Sometimes these gases are ejected into space.
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Coronal holes are conduits for gases to flow out
from the Sun
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Violent eruptions called solar fares eject huge
amounts of solar gases into space.
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By following the trails of gases released during
a solar flare, we can map the Suns global
magnetic field.
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Coronal Mass Ejections (CMEs) typically expel 2
trillion tons of matter at 400km per second.
It reaches Earth two to four days later, and is
fortunately deflected by our magnetic field.
An x-ray view of a coronal mass ejection
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The Sun is powered by thermonuclear fusion, which
converts hydrogen into helium.
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The Suns interior is held stable by a balance
between pressure forces and gravity, in a
condition called hydrostatic equilibrium.
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THE SOLAR INTERIOR
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Changes in Physical Properties of Solar Gases
from the Solar Core to the Photosphere
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A mystery involving undetected neutrinos produced
in the Suns core prompted an investigation into
the fundamental nature of these particles.
Subsequent experiments showed that neutrinos can
change as they travel through space.
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WHAT DID YOU THINK?

• How does the mass of the Sun compare with that of
  the rest of the solar system?
• The Sun contains 99.85 of the solar systems
  mass.
• Are there stars nearer the Earth than the Sun?
• No, the Sun is our closest star.
• Does the Sun have a solid and liquid interior
  like the Earth?
• No, the Sun is composed of hot gases.

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WHAT DID YOU THINK?

• What is the surface of the Sun like?
• The Sun has no solid surface, and no solid or
  liquids anywhere. The surface we see is composed
  of hot, churning gases.
• Does the Sun rotate?
• The Suns surface rotates differentially once
  every 35 days near its poles, and once every 25
  days near its equator.
• What makes the Sun shine?
• Thermonuclear fusion in the Suns core

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Key Terms
Cerenkov radiation chromosphere convective
zone core (of the Sun) corona coronal
hole coronal mass ejection filament granule helios
eismology hydrogen fusion hydrostatic equilibrium
limb (of the Sun) limb darkening magnetic
dynamo neutrino photosphere plage plasma positron
prominence radiative zone solar cycle solar
flare solar luminosity
solar model solar wind spicule sunspot sunspot
maximum sunspot minimum supergranule thermonuclear
fusion transition zone Zeeman effect