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Our Sun: Our Turbulent Active Star
•The Sun is not a static
body, but very active.
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•Solar activity can have
dramatic effects on the
Earth
Why Study the Sun?
• Understand how the Sun affects the Earth
and the solar system
SOHO
• Understand how stars work
• Understand more about the laws of nature
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SDO
STEREO
The Sun is the only star known to grow vegetables.
(Dr.Philip Scherrer, Stanford University)
Ask Students:
“How does the Sun Change?”
• Answers (selected answers from and 8th grade
classroom)
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Changes height in the sky
Changes in intensity
Changes in temperature
Changes distance from the Earth
• Many of these are “changes” of the Earth
• Students consider the Sun itself to be pretty constant.
– Not a bad assumption but certainly not correct
– Solar Constant: 1300 - 1400 W/m2
What makes the Sun hot?
Fusion in the Sun’s core produces heat/energy
6 protons -> He + 2 protons + 2 electrons + 2 neutrinos + energy
The Sun’s Roiling Surface
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Size of Earth, for
comparison
Like fudge or oatmeal cooking, the
Sun’s surface boils up with heat,
then crashes down
As the Sun turns
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Approximately 5 months worth of images from 2001
Like the Earth, the Sun rotates. However, unlike the Earth,
the Sun has a complex rotation mechanism.
Sunspots
Sunspots denote
regions of strong
magnetic fields. They
appear dark because
they are relatively cooler
than the surface.
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What color is the Sun?
1
The Sun appears white
to us
but it
radiates in all
wavelengths
(visible and
nonvisible
“colors”)
The electromagnetic spectrum
The Sun in Another Light
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Extreme Ultraviolet image of the Sun at 195 Angstroms
Visible Light has wavelengths between 4000 and 7000 Angstroms
Seeing Magnetic
Field lines
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Plasma emission
traces out magnetic
fields in the solar
corona
Solar Eruptions
Common during the
Sun’s active periods
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Huge flare of 28 October 2003
Solar prominence dwarfs Earth
in size
The 11 year
sunspot cycle
The amount of
magnetic activity
on the Sun varies
in an 11 year cycle.
A regular cycle of sunspot numbers
over the past 300 years.
Dramatic changes occur
during the solar cycle
X-ray and magnetic activity
compared
CoronagraphsArtificial Eclipses
Explosions on the Sun
(Coronal Mass Ejections)
A billion tons of hot gas
being launched from the
Sun.
White circle in image indicates size and
location of Sun, which is blocked by a
metal disk in the instrument.
A solar “wind” streams into
the solar system and shapes
Earth’s magnetosphere
The Sun generates
Space Weather in our
solar system
Solar activity can have a dramatic impact on
communications, satellites, and astronauts.
Solar activity causes
colorful aurorae
Space Weather
affects the Moon
and other planets
we hope to explore.
Mars
Aurorae
on
Neptune,
Saturn,
and
Jupiter
Solar and Space Weather
Links on the Web
• NASA Link
– SOHO: http://sohowww.nascom.nasa.gov/
– SDO: http://sdo.gsfc.nasa.gov/
– STEREO: http://stereo.gsfc.nasa.gov/
• Stanford Solar-Center: http://solar-center.stanford.edu/
– SID home page: http://solar-center.stanford.edu/SID/
• CISM Home Page: http://www.bu.edu/cism/
• Windows to the Universe: http://www.windows.ucar.edu/
• Exploritorium:
http://www.exploratorium.edu/spaceweather/index.html
• SWPC: http://sec.noaa.gov/