Solar Science Workshop

1
An Introduction to the Physics of Our Star The
Sun

• Distance from Earth
• 1 AU
• Travel time for Light to Earth
• About 8 minutes
• Travel time for solar wind to 1 AU
• A few days
• Mean surface temperature
• 5800K
• Temperature in the Center
• 1.55x107 K

2
The Sun

• Mass
• 333,000 Earth Masses
• More mass than all of the other objects in the
  solar system combined
• Diameter
• 218 Earth Diameters
• Average Density
• 1410 kg/m3
• Composition (by mass)
• 74 Hydrogen, 25 Helium, 1 other elements

Sun seen in Xrays
3
The Sun Seen From Earth by Amateurs

• COMMON SENSE WARNING
• NEVER LOOK DIRECTLY AT THE SUN WITHOUT A
  PROPER FILTER !!
• Looking directly at the Sun without the proper
  filter WILL cause permanent eye damage
• Safest to use the method of projection
• Project the image onto a piece of paper
• Can see sunspots, and even graph them easily

4
The Sun Seen From Earth by Amateurs

• Using a Baader solar filter
• Inexpensive
• Many solar observing glasses are made out of
  this material
• Used to see sunspots
• Similar to Mylar

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The Sun Seen From Earth by Amateurs

• Ha filters
• Much more pricey
• 100s-1000s of dollars
• Can see features in the solar chromosphere
• Used to see Prominences, filaments, flares
• Very impressive

Sun seen with an Ha filter
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How Old is the Sun ?

• Probably about the same age as Earth
• Has it been shining brightly the entire time?
• The luminosity has probably increased with time,
  but it has always been very bright
• What is the fuel that keeps it shining this
  long?

7
The Suns Energy Source is ThermonuclearFusion
in its Core

• Proton-proton chain
• Four hydrogen nuclei fuse to form a single
  helium nucleus
• There is a slight loss of mass in this process
  which is converted to energy according to
  Einsteins famous equation E mc2
• Thermonuclear fusion occurs only at the very high
  temperatures at the Suns core
• Fusion should not be confused with fission !
• Will continue to heat the Sun for another 5
  billion years

8
The Proton-Proton Chain
9
The Structure of the Sun

• The Interior
• Core
• Radiative zone
• Convection zone
• The Surface and Atmosphere
• Photosphere
• Chromosphere
• corona

10
The Suns Interior

• Hydrogen fusion takes place in a core extending
  from the Suns center to about 0.25 solar radius
• The radiative zone extends to about 0.71 solar
  radius
• Here energy travels outward through radiative
  diffusion
• The convective zone is a rather opaque gas
• Here energy travels outward primarily through
  convection

11
Where do the Neutrinos and ?-ray photons go ?

• Neutrinos exit the Sun, unimpeded
• Can be used to probe the solar interior
• Early attempts at detecting them found that their
  were about 3 times less seen at Earth than there
  should be
• THE SOLAR NEUTRINO PROBLEM !
• The gamma rays collide with matter and take
  millions of years to exit the Sun

12
Detecting Solar Neutrinos

• Underground detectors are used to avoid
  interference from cosmic rays

13
The Solution to the Solar Neutrino Problem

• Particle Physics gave us the answer
• Solar neutrinos oscillate and the original
  detectors could only see certain parts of the
  oscillations and not all of them
• New detectors were built to observe all neutrinos
• Two physicists won a Nobel Prize for their work
• Modern detectors are placed at different depths
  within the Earth to observe the actual
  oscillations

Raymond Davis Jr.
Masatoshi Koshiba
14
Solar Structure

• The standard solar model
• Theoretical model used to determine the physical
  properties of the Suns interior
• Assumes hydrostatic and thermal equilibrium

15
Solar Oscillations

• Waves can propagate through the Sun causing a
  variety of vibrations
• Like sound waves
• These are used to infer pressures, densities,
  chemical compositions, and rotation rates within
  the Sun

16
Helioseismology

• The branch of science that studies solar
  oscillations is known as Helioseismology
• The movie shows evidence of seismic activity on
  the Sun as seen by the SOHO MDI experiment

17
The Convection Zone

• The convection zone is just outside the radiative
  zone.
• Thickness is about 200,000 km
• Turbulent convective motions occur, similar to a
  pot of boiling water.
• Overturning (bubbling) motions inside the Sun are
  responsible for the granulation pattern seen on
  the Suns surface.

18
Convection Cells
19
Solar Granulation

• Convection cells that are about 1000 km wide
• These are part of the Suns atmosphere known as
  the Photosphere

20
Recent High-resolution Images of granulation
21
Flowers and Ribbons

• Produced by magnetic fields

22
The photosphere is the lowest of three main
layersin the Suns atmosphere

• The Suns atmosphere has three main layers the
  photosphere, the chromosphere, and the corona
• Everything below the solar atmosphere is called
  the solar interior
• The visible surface of the Sun, the photosphere,
  is the lowest layer in the solar atmosphere
• The photosphere undergoes differential rotation

23
Limb Darkening

• The edges of the Sun appear darker than that seen
  straight on
• This is called limb darkening
• It is due to the fact that the temperature in the
  photosphere decreases with altitude

24
The Origin of Limb Darkening

• The light we see at the limb originated higher up
  in the atmosphere where it is cooler
• Thus it will be less bright there

25
Sunspots

• Low temperature regions
• How do we know this ?
• Darkest part is called the umbra
• Just outside the umbra is the penumbra
• Associated with Intense magnetic fields

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Sunspots Often Come in Groups
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The Chromosphere

• Above the photosphere is a layer of less dense
  but higher temperature gases called the
  chromosphere
• Color Sphere
• characterized by spikesof rising gas
• Spicules extend upward from the photosphere into
  the chromosphere along the boundaries of
  supergranules

29
Chromospheric FeaturesPlages and Filaments

• Filaments are dark, thread-like features seen in
  the red light of hydrogen (H-alpha).
• Dense cooler material suspended at high altitudes
  by magnetic fields
• Plage (the French word for beach) are bright
  patches surrounding sunspots that are best seen
  in H-alpha.
• associated with concentrations of magnetic fields

30
Chromospheric Features Prominences

• Same as filaments, except that they are seen from
  the side rather than straight on

31
The Corona

• The outermost layer of the solar atmosphere, the
  corona, is made of very high-temperature gases at
  extremely low density
• The solar corona blends into the solar wind at
  great distances from the Sun

32
The 11-year Sunspot Cycle
Number of Sunspots versus time they come and go
every 11 years
Number of Sunspots versus latitude forms a
butterfly pattern
33
The Maunder Minimum

• Complete absence of sunspots for 50 years
  corresponds to a mini ice age
• There is a loose correlation between global man
  temperature and sunspots

34
These changes are caused by convection and the
Suns differential rotation The Solar Dynamo
35
The Buildup of magnetic field energy must be
released how?

• Coronal Mass Ejections and Flares
• Releases an enormous amount of energy
• A solar flare is a brief eruption of hot, ionized
  gases from a sunspot group
• A coronal mass ejection is a much larger eruption
  that involves immense amounts of gas from the
  corona
• These storms can interact with the Earth and
  create huge geomagnetic storms
• They also accelerate particles to very high
  energies

36
Coronal loops expand from the surface of the Sun
following a solar explosion (solar flare) on
April 21, 2002
TRACE movie
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The Halloween 2003 Flares were the Largest in
Modern History
Perhaps the most extreme flare ever seen erupted
on Nov. 4 ... IMAGES SOHO/NASA/ESA
... and then this coronal mass ejection was
hurled into space.
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Aurora
The pattern of auroral light around the north and
south magnetic poles is called the auroral oval.
It expands and contracts over a period of hours
and days, depending on geomagnetic activity.
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Aurora in Tucson
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Shock Waves in Space

• Analogy with sonic booms
• Can accelerate charged particles to very high
  energies
• Radiation Environment !
• Space Weather