The Sun

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The Sun

• LASSO Summer 2007 Workshop

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http//stereo.gsfc.nasa.gov/classroom/classroom.sh
tml
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• The Sun
• Largest object in the solar system
• 99.8 of the total mass
• Jupiter contains most of the rest
• Radius is about 700,000 km
• 100 times the radius of the Earth
• Would take more than 1,000,000 Earths to fill
  it
• 75 H, 25 He by mass (92.1 H, 7.8 He by number
  of atoms). The remaining 0.1 contains all of
  the other elements
• About 4.5 billion years old, 5 billion years of
  life left

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• Masses of Things
• 2x1030 kg Sun
• 2x1027 kg Jupiter
• 6x1024 kg Earth
• 7x1022 kg Earths moon
• 1x108 kg Nimitz class Aircraft Carrier
• 2x106 kg Space Shuttle
• 2x103 kg Toyota Camry
• 4 kg newborn human
• The sun and moon look about the same size, but
  they are not!

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The Sun is the Heart of the Solar System
X-ray image of the sun from Yohkoh
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• The Sun
• The sun rotates
• 26 day period at the equator, slower above and
  below!
• The suns equator tilted 7? from Earths orbital
  plane.
• Distance to Earth 150,000,000 km
• Light takes 8 minutes to reach Earth
• Magnetic field in a sunspot 3000 gauss
• Compare Earth 0.25 gauss

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• Why study the Sun?
• All life on Earth depends on the Sun (Almost)
• The Earth is warming up under the influence of
  human activity. How would the global climate
  vary, if only influenced by solar variability?
• Not only are dynamic changes of the sun
  fascinating, but also they affects human
  activities
• Disrupt communication satellites
• Produce radiation hazards to astronauts
• Power outages, particularly at higher latitudes
• The Sun is the only nearby star, and so provides
  the only opportunity to directly study stars.

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Parts of the Sun Interior Core source of
energy (fusion) T 15,000,000 K Radiation
Zone energy travels outward by radiation T
5,000,000 K Convection Zone energy travels
outward by convection T 2,000,000
K Atmosphere Photosphere visible surface of
Sun T 6000 K Chromosphere hydrogen emits
red light T increases to 20,000 K Corona
Extends out far into space (solar wind) T
2,000,000 K
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Temperature of the Sun
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• 15 million degrees makes the core an unusual
  place
• Here on terrestrial Earth and upper atmosphere we
  more commonly encounter hydrogen and helium in
  lower energy states
• H2 (2 protons) or H (1 proton) w/o the extra
  neutrons
• 4He (2 protons 2 neutrons)
• Uncommon
• 3He (2 protons 1 neutron)
• D (1 proton 1 neutron)

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The Core Fusion
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Radiative Zone
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The Photosphere The Visible Surface
Granules - convection cells
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The ChromosphereThe Happening Place on the Sun
Prominence
Filament
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The Grand Daddy Prominence
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The Corona Gateway to Interplanetary Space
In white light
In x-rays
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Solar Output
Visible, IR, and UV Radiation
Radio Waves
Solar wind plasma
Neutrinos
High-Energy Charged Particles
X-ray and gamma-rays
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• The Sun has a magnetic field
• Magnetic fields create arches, arcades, loops in
  the corona. These are visible in X-rays and UV
  because they trap hot plasma.
• Field structure
• Dipole-like near the equator coronal helmet
  streamers
• Open field lines near the poles coronal holes
• Field extends out into space with the corona,
  carried by solar wind
• The field changes polarity with an 11-year cycle
• Changes thought to be due to differential
  rotation of the Sun (poles rotate faster than
  equator)
• Variation with solar cycle
• Near solar minimum field most dipolar, dipole
  aligned with rotation axis
• Pre-minimum dipole is tilted relative to the
  rotation axis
• Near solar maximum field is less dipolar

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Emergent Magnetic Fields
Earth to scale
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Coronal StructureSolar Maximum vs. Solar Minimum
Polar Coronal Hole
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The Sun is variable in space and time 11-year
solar cycle Magnetic north and south poles
flip Solar minimum -- poles stable, little solar
activity Solar maximum -- field in transition,
lot of activity Sunspots Cooler (darker)
regions of the photosphere (4000 K) Strong
magnetic field (x1000) emerging from Sun Seen in
two zones, on either side of the equator Coronal
Mass Ejections (CMES) Ejection of large amounts
of mass (1015 g) Responsible for most large
geomagnetic disturbances Can last several
days Flares Explosions on surface of the
Sun Release electromagnetic and particle
energy Last from minutes to hours
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Sunspot image from SOHO
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Solar Variability The Sunspot Cycle
11 years
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Solar cycle butterfly diagram of sunspot
occurrence
solar latitude
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Solar Variability The X-Ray Sun
Solar Minimum (1995)
Solar Maximum (1991)
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The Sun-Climate Connection? (Did Sunspots Sink
the Titanic?)

• Sunspot correlated with
• Sea surface temperature
• Minimum latitude of icebergs

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Coronal StructureSolar Maximum vs. Solar Minimum
Polar Coronal Hole
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The Key to the Suns Activity Magnetic Fields
Convection
Active Region
Flux tubes rise through surface
Field carried to surface
Field generation
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Magnetic flux emergence
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Emergent Magnetic Fields
Earth to scale
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Sunspots
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Sunspots
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http//stereo.gsfc.nasa.gov/classroom/matching/mat
ching_activity.shtml
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MATCHING MAGNETIC ACTIVITY AND ACTIVE REGIONS The
solution is A - 3 B - 4 C - 5 D - 2 E - 1
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Filaments/Prominences
cooler plasma
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Filaments/Prominences
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Solar Flares
overlying arcade
filament
two-ribbon flare
post-flare loops
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Magnetic Reconnection
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Solar Flares
overlying arcade
filament
two-ribbon flare
post-flare loops
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Solar Flare and Post-Flare X-ray Loops
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Helmet Streamers
Underlying Prominence
Helmet Streamers
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Coronal Mass Ejections (CMEs)Erupting Helmet
Streamers
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Erupting Prominence
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Coronal Holes
open field easy escape fast flows
closed field inhibited escape slow flows
cool (dark)
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Evolution of coronal hole Extension to low
latitudes
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Whats wrong with the sun? Is the new sunspot
cycle late?
July 1, 2008
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• We are forgetting how long a minimum can last.
  This is not another Maunder Minimum. (David
  Hathaway MSFC)
• 1933 was considered unremarkable.

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We live with a very dynamic star!
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• Outstanding Questions
• What causes the solar cycle? Why does it
  disappear at times?
• Why is the corona so hot? We know its tied to
  magnetic energy, but what are the exact
  mechanisms?
• What accelerates the solar wind to speeds of up
  to 1000 km/s, or more?
• Will we ever be able to predict when CMEs will
  erupt, and how powerful they will be?

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BACKUP MATERIAL
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Earth-Sun Distance varies from 146 million km to
152 million km
146 million km (91 million mi) 0.286 Viewed
from Earth
152 million km (94.5 million mi) 0.275 Viewed
from Earth

• J

Astronomy Picture of the Day http//antwrp.gsfc.na
sa.gov/apod/astropix.html
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Moon and Sun from Stereo B spacecraft
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Convection Zone Where the Sun Boils