The Sun

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The Sun
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The Suns Atmosphere
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Surface of the sun Most of the visible light
comes from this layer
Photosphere
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Granulations

• Blotchy pattern on the photosphere caused by
  convection

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Chromosphere

• Dim layers of less dense gas above the
  photosphere
• Glows red
• Visible during a total solar eclipse
• Temperature rises from 6000C to about 20,000C.
  due to strong magnetic fields
• Spicules small jet like eruptions that eject
  material into the corona

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Corona

• Seen during a total solar eclipse.
• Also seen using a coronograph
• Thin gas at millions of degrees
• Parts of the corona that escape into space is
  called the solar wind.

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The Suns Interior
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Thermonuclear reactions in the Suns core turn
mass into energy.
At extremely high temperatures and pressures, 4
Hydrogen atoms can combine to make 1 Helium atom
and release energy by E mc2 4H ? He
energy HYDROGEN FUSION (page 283)
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Radiative Zone

• Energy generated by nuclear fusion in the core
  moves outward as electromagnetic radiation.
• Very Dense! It takes 170,000 years for energy
  from the core to get to the surface (50cm/hr)
  (20x slower than a snail)

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Convective Zone

• A region of turbulent plasma through which energy
  is transferred by convection.
• Hot plasma rises, cools as it nears the surface,
  and falls to be heated and rise again.

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The Active Sun
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SUNSPOTS

• cooler areas within photosphere
• caused by magnetic fields
• occur on an 11 year cycle
• Can last hours or several months

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• The average sunspot is about the size of Earth,
  though the largest can be 20 times the size of
  Earth.

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Extreme peaks or absences of sunspots may change
Earths climate

• Maunder Minimum 1650
• Few sunspots
• Colder climate
• Famine in Europe
• Thames froze

• Medieval Maximum 1100
• Many sunspots
• Hotter climate
• Famine in N. America
• Ancient Pueblo people abandoned Chaco canyon
• Icemelt permitted Vikings to reach N. America

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The latitude at which new sunspots appear changes
throughout the sunspot cycle. Starts at 30
degrees north and south and moves toward the
equator
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The last solar cycle
Many cycles are double peaked but this is the
first in which the second peak in sunspot number
was larger than the first. We are currently over
five years into Cycle 24. The current predicted
and observed size makes this the smallest sunspot
cycle since Cycle 14 which had a maximum of 64.2
in February of 1906.

• Dotted lines show range of prediction solid
  curve is the average jagged lines are monthly
  counts

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The daily movement of sunspots reveals that the
Suns rotation takes about 4 weeks.
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Rotation

• The sun does not rotate at the same rate
  everywhere because it is a gas (average 27 days)
• Poles are slower than equator
• This causes the magnetic fields to be stretched
  and solar storms develop

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The sunspot cycle is partly due to the Suns
differential rotation. This helps solar magnetic
fields twist up, intensify, emerge, cancel, then
repeat the cycle.

• Rotates faster at equator and slower at poles

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Sunspots are produced by a 22-year cycle in the
Suns magnetic field.

• Charged particles, such as electrons, will move
  along magnetic field lines.
• The Suns positive pole is in the North for 11
  years, then switches to the South for 11 years

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Helioseismology.

• Exploring the Suns interior by studying its
  vibrations.
• Computer generated images blue moving outward,
  red moving inward

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Astronomers probe the solar interior using the
Suns own vibrations.
Sections of the Suns surface quickly oscillate
up on down.
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Solar Prominences

• - Clouds of glowing gas
• Form huge loops from one sunspot to
  another
• Follow magnetic field lines
• Anchored to the Sun's surface in the photosphere,
  and extend outwards into the Sun's corona.

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Solar Flares

• The most violent solar disturbance
• Sudden outward eruption of plasma

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Coronal Mass Ejection

• Parts of the corona are thrown off the sun.
• Can be larger than the sun.
• Can cause a disturbance in the earths magnetic
  field

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Visible photosphere, sunspots
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Ultraviolet upper chromosphere and lower corona
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Infra-red chromosphere, sunspots are cooler and
darker
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Microwave
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X-Ray - corona
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UV
Infrared
Visible
Radio
X-Ray