OUR SUN

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OUR SUN

• Chapter 7
• Mr. Saks
• Astronomy

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Photosphere

• Part of the sun that we see
• Thin layer of gas less than 500Km deep.
• Average temperature 6000 K
• Were we get most of our sunlight from
• The sun, like all stars, has a spectra line

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Photosphere

• Granulation
• Convection cells working in the sun
• Hot gases rise and cold gases sink
• How do we know? Doppler effect
• Size of Texas
• 10-20 minutes

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Chromosphere

• The Color Sphere
• Irregular layer above photosphere where
  temperature rises from 6000C to 20,000C
• At higher temp. hydrogen emits light that gives
  off a reddish color. This can be seen easily
  during a total solar eclipse.
• Located above the photosphere it is about
  10,000km thick

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Chromosphere

• Nearly invisible so really only seen during an
  eclipse
• Much hotter than photosphere
• Has SPICULES- flame like structures 100-1000m in
  diameter extending 10,000km above the photosphere
  for short durations (about 5 minutes)
• Seem to be prominent near Supergranules

The basic structure of a spicule. The edges of
granules and the motion of the gas in the
convecting bubble can help form the flame-like
spicule structures.
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Corona

• Also known as the Crown
• Only seen during an eclipse it can extend as far
  as 12 times the Suns radius
• Low density but extremely hot 1,000,000K on
  average
• varies from about 500,000-2,000,000K
• Why so hot?
• Maybe because the interaction between the Suns
  rotation and magnetic field. (friction?)
• The Corona is so hot Suns gravity cannot hold
  onto the gas.
• High velocity atoms stream out from Sun in all
  directions (H, He, H, and e- particles)

Only in the brief darkness of a total solar
eclipse is the light of the solar corona easily
visible from Earth. Normally overwhelmed by the
bright solar disk, the ever-changing solar corona
is a fascinating sight.
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These images were made by the EIT camera onboard
the SOHO spacecraft, a space observatory that is
continuously observing the Sun. Notice the
complicated structure of the Sun's atmosphere.
The upper right image shows a close-up of a solar
flare (Image courtesy of SOHO).
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Solar Wind

• The continuous flow of particles
• Come past the Earth at nearly 300-800 km/sec
• Gusts can reach 1000 km/sec
• This is hot stellar wind
• Breeze of ionized atoms
• Solar wind causes Sun to loose mass

The structure of the corona is controlled by the
Sun's magnetic field which forms the bright
active regions and the ray-like structures
originating in the coronal holes. The composite
image allows one to trace these structures from
the base of the corona to millions of kilometers
above the solar surface. The dark areas, known as
coronal holes, represent the regions where the
highest speed Solar Wind originates. (Image
courtesy of SOHO).
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Helioseismology

• Almost no light emerges from below the
  photosphere
• We can use vibrations to explore the depth
• Helioseimology
• We detect vibrations by observing doppler shifts
  in solar surface

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Global Oscillation Network Group(GONG)

• Solar astronomers need large amounts of data for
  helioseismology
• GONG uses a network of telescopes around the
  world to observe the Sun continuously
• SOHO spacecraft gives us uninterrupted
  observations of Sun day and night

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SOHO

• Solar and Heliospheric Observatory satellite
• Has allowed
• Temperature
• Density
• Rate of rotation

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Solar Activity
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Sunspots

• Chinese knew, Galileo knew, and ancient
  astronomers noticed changing nature of Sun
• Sunspots are dark spots on the photosphere

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Sunspots

• These spots will grow and shrink over a period of
  days
• A typical large group can last as long as 2
  months
• Umbra is the dark center of sunspot
• Penumbra is the lighter region of sunspots
• Typical sunspots are about 2xs the diameter of
  the Earth

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Sunspot

• Sunspots look dark because they are cooler than
  the photosphere
• 4240 K compared to photosphere which is 5800 K
• Remember black body radiation
• Small temperature difference produces huge
  differences in brightness
• Sunspot by itself with no Sun would be brighter
  than moon and glow orange-red

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Sunspots

• Sunspots appear in pairs
• They have a North magnetic and South magnetic pole

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Heinrich Schwabe

• 1843 German Astronomer
• Noticed the number of sunspots varies with a
  period of about 11 years
• This is called the sunspot cycle
• At maximum there can be as many as 100 spots
  visible
• At minimum there are only a few spots

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Sunspots

• At beginning sunspots begin to appear at middle
  latitude of Sun (35 above and below the Suns
  equator)
• As the cycle continues the sunspots tend to get
  closer to the Suns equator (about 5)

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Maunder Butterfly Diagram

• Plotting the sunspots over the cycle the appear
  to look like butterfly wings known as Maunder
  Butterfly Diagram
• Last maximum was in 2001
• Next Maximum is?
• 2012-2013

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Little Ice Age

• Records show that between 1645 and 1715 there
  were very few sunspots
• Modern studies show that the Maunder Minimum
  coincide with periods of reduced solar activity
• Little Ice Ages
• Unusual cool weather in Europe and North America

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Suns Rotation

• Sun is not a solid object
• When spins, not all parts spin equally
• Photosphere
• Equator 25 days
• 45 Lat. 27.8 days
• Poles slower yet
• Heliosiesmology shows these rates are slower
  below the photosphere
• This moving gas is highly ionized
• Good conductor of electricity

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Dynamo Effect

• Rapid rotation of a conductor stirred by
  convection produces a magnetic field
• Process inside the Earths core that gives
  Earths magnetic field
• Sunspots tend to occur in magnetic pairs

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Babcock Model

• Theorizes the progressive tangling of the solar
  magnetic field
• The field becomes so tangled that regions of the
  sun close to each other can have opposing
  magnetic fields
• After 11 years the field is so tangled it is so
  tangled the regions begin to breakdown and the
  fields have to reorganize themselves by bursting
  up from the from the surface

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• The causes magnetic pair boundaries (SPOTS) in
  the photosphere trapping gases that cool allowing
  us to see sunpots
• Basically we are seeing magnetic field breakdowns

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Chromosphere Activity

• Prominences
• Hot ionized gas trapped in a magnetic arch over
  or around sunspots

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Solar Flare

• Eruptions from the Sun surface
• 107 tons of TNT
• Can heat up to millions of degrees
• Occur near sunspots in between the dividing line
• Affects the Earths magnetic field
• Blasts us with X-Ray and UV radiation
• Boosts solar wind

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Coronal Activity

• Active during high peak of sunspots and settles
  during solar sunspot minimum
• Coronal Mass Ejections (CME)
• Recombining of magnetism can cause massive
  release of ionized air out from the Sun

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CME and Solar Wind

• These violent gusts, when blowing past the Earth,
  can create electrical currents
• Up to a million megawatts
• These flow down into Earths magnetic poles and
  excite atoms in upper atmosphere to emit photons
• Auroras

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