Outer Layers of the Sun

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Outer Layers of the Sun

• Photosphere
• Limb darkening
• Sun spots
• Chromosphere
• Corona
• Prominences, flares, coronal mass ejections
• Reading 18.5-18.10

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The Suns Atmosphere

• Photosphere - the 5800 K layer we see.
• Chromosphere a thin layer, a few 1000 km thick,
  at a temperature of about 10,000 K. Can be seen
  during solar eclipse.
• Corona Outermost layer, 1,000,000 km thick, at
  a temperature of about 1,000,000 K.

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Outer layers of sun
1 photosphere, 2 chromosphere, 3 corona Why
the outer layers of the Suns atmosphere are
hotter is a puzzle.
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Photosphere
5
Chromosphere
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Corona
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Corona
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Limb darkening
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Limb darkening
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Sunspots are low temperature regions in the
photosphere
Sun spots are about 4000 K (2000 K cooler than
solar surface) and have magnetic fields up 1000?
the normal solar magnetic field. They can be as
large as 50,000 km and last for many months.
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Particles spiral around magnetic field lines
Magnetic field
Motion of charged particle (electron, proton,
nucleus)
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Sunspots are low temperature regions in the
photosphere
The large magnetic fields in sunspots decrease
the flow of heat via convection causing the
sunspot to become cool.
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Sunspot cycle
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Sunspots can be used to measure the rotation of
the Sun
Near the equator the Sun rotates once in 25
days. The poles rotate more slowly, about once
every 36 days.
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Sunspot cycle
Each 11 years, the Suns magnetic field changes
direction. Overall cycle is 22 years.
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Granulation
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What direct observational evidence supports the
model of thermonuclear reactions in the Suns
core?

• Neutrinos
• Gamma rays
• Sun spot counts
• WMD inspections

18
Solar magnetic fields also create other phenomena

• Prominences
• Flares
• Solar wind
• Coronal mass ejections

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Particles spiral around magnetic field lines
Magnetic field
Motion of charged particle (electron, proton,
nucleus)
Particles, that we see, get trapped along
magnetic field lines, that we dont see,
stretching out from the Sun.
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Prominences -Cooler than photosphere.
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Solar flares -Hotter, up to 40,000,000 KMore
energetic
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Coronal mass ejections -eruption of gas, can
reach Earth and affect aurora, satellites
Movie
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Coronal mass ejection
Movie
24
Which statement is not correct?

• The solar coronal temperature is about 106 K.
• Sunspots are very cool and dark, with
  temperatures of about 300 K.
• The Suns core has a temperature about 107 K.
• The chromosphere is hotter than the photosphere.

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Review Questions

• Since the Sun is so bright, how is it possible to
  see its dim outer atmosphere (corona)?
• Where does the solar wind come from?
• What are sunspots? Why do they appear dark?
• What is the connection between sunspots and the
  Suns magnetic field?
• What is the sunspot cycle?