The Sun and its Effect on Earth

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The Sun and its Effect on Earth
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Why Study the Sun ?

• Influence on Earth
• Important for Astronomy/Planetary Sciences
• Only star that we can see closely
• The source of many interesting and important
  physics problems
• Many PhD theses!
• For Me?
• Many basic properties are a mystery!
• Space radiation environment, space weather,
  acceleration of high-energy charged particles

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How does the Sun Influence Earth?

• Provides the energy that creates life, warms the
  planet, drives the dynamic atmosphere and oceans
• Sun-climate connection?
• 11-year cycles (Snowshoe hare, sperm whales,
  homing pigeons, lake water levels, and others )
• Geomagnetic storms
• Aurora
• Power-grid failures (Canada, 1989)
  Telecommunications failures
• High-energy solar particles
• can destroy ozone
• lethal radiation dosages to astronauts and
  passengers/pilots on polar air-travel routes
• examples of how scientific discovery (flares
  and high-energy solar cosmic rays) influences
  technology

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The Sun Basic Facts

• 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 (11,000 oF)
• Temperature in the Center
• 1.55x107 K (28,000,000 oF)
• Temperature in the Corona
• A few million K

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The Sun Basic Facts

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

Sun seen in Xrays
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How Old is the Sun ?

• Probably about the same age as Earth
• 4.6 billion years
• Has it been shining brightly the entire time?
• The luminosity has increased with time
• Young faint-sun paradox
• What is the fuel that keeps it shining this
  long?

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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
• Will continue to heat the Sun for another 5
  billion years

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Where do the Neutrinos and 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 !
• Light particles collide with matter and take
  millions of years to exit the Sun

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The Solar Neutrino Problem

• Underground detectors are used to avoid
  interference from cosmic rays
• For a long time, it was not clear why there were
  fewer neutrinos observed than predicted. We now
  know why this is.
• 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
• This is an example of how science is an ongoing
  process

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The Structure of the Sun

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

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How do we probe the Solar Interior?

• The standard solar model
• Other than solar neutrinos, there is no means to
  directly probe the interior of the Sun
• The standard solar model is a theoretical
  construct that has been developed to determine
  the physical properties of the Suns interior

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Solar Oscillations

• Waves can propagate through the Sun causing a
  variety of vibrations
• Like sound waves
• These oscillations constrain the standard solar
  model
• 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

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Convection in the Solar Interior

• Below the visible surface of the Sun is a region
  known as the convection zone
• Here, turbulent convective motions occur, similar
  to a pot of boiling water.
• These bubbling motions are responsible for the
  granulation pattern seen on the Suns surface.

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1000 km wide occur in the Solar
Photosphere
Solar Granulation
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The Solar Atmosphere

• The Suns atmosphere has three main layers
• photosphere,
• chromosphere
• 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

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Sunspots

• Regions of low temperature and intense magnetic
  fields
• Darkest part is called the umbra
• Just outside the umbra is the penumbra
• Sunspots are most-easily seen in the photosphere

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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 called
  spicules which are seen as a ragged fuzz in
  H-alpha images of the Sun

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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
• Because the corona is very hot, it is best viewed
  in the x-ray part of the spectrum
• What heats the corona remains an open question!

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The Solar Wind

• Prior to the early 1960s, the prevailing theory
  was that space was a vacuum
• This was proven to be wrong and, in fact, there
  is a stiff wind blowing, called the Solar Wind
• Discovered by Gene Parker, who recently won the
  Kyoto Prize for his achievement
• First measured directly by Mariner 2, a
  Venus-bound spacecraft
• This is an example of how scientific knowledge is
  subject to change

The blue comet tail is an ion tail that points
directly away from the Sun and is influenced by
the solar wind
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Viewing the Sun

• Safest to use the method of projection
• Project the image onto some paper
• Can see sunspots, and even graph them easily

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Viewing the Sun

• Using a Baader solar filter
• Inexpensive
• Many solar observing glasses are made out of
  this material
• Used to see sunspots
• Often the film is purchased in a sheet and one
  makes their own filter especially suited for
  their own telescope

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Viewing the Sun

• 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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The Sun in X-rays seen from space
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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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• Sun also emits radio signals. These bursts are
  associated with magnetically active regions on
  the Sun

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The Sun seen with various space telescopes
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An example of a Solar Measurement The solar
constant

• What is the solar constant?
• How can it be measured on Earth?
• Is the Sun really a constant?

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The Solar Constant

• Solar Luminosity
• Total energy emitted by the Sun per second
• L 3.9 x 1026 W
• Solar Flux
• Luminosity divided by Suns surface area (the
  amount radiated per area)
• Solar Constant
• The amount of Solar Flux arriving at Earth
• 1370 W/m2

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The solar constant
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Basics of the measurement

• Any material that receives energy from the Sun
  will be heated (provided that it is cool, or room
  temperature, to begin with)
• If the experiment is designed properly (i.e. well
  isolated), the only source of energy is that from
  the Sun.
• What remains then, is to determine the rate at
  which the Suns energy is heating the system
• Can use a thermometer and determine the heating
  rate. If the heat capacity of the material is
  known, it is a simple matter to determine the
  incoming solar energy (plug and chug).
• The experiment involves graphing, measuring
  slopes, unit conversions, and some basic math.

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A link to this activity
http//stargazers.gsfc.nasa.gov/pdf/activities/spa
ce_weather/grades_7_12/Activity_3.pdf
Other solar-related activities can be found a few
levels up at http//stargazers.gsfc.nasa.gov/pdf/a
ctivities/space_weather/
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What can we do with this measurement?

• Can determine the temperature of the Sun
• Can work backwards to get the energy flux at the
  Sun, by knowing how far the Sun is from the
  Earth, and then use the Stefan-Boltzman
  (blackbody radiation) law to get the Suns
  temperature
• Can determine the temperature of the Earth
• Balance energy coming into Earth and energy out
  (via Earth radiating like a blackbody)
• One gets an answer that is a little low why?
  Because of the greenhouse effect!

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But the Sun is not really constant !

• Solar luminosity varies
• What causes this variability is an active area of
  research

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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
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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

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Sunspots Often Come in Groups
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These changes are caused by convection and the
Suns differential rotation The Solar Dynamo
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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

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SOHO/LASCO (C3) movie of the Halloween Solar
Storms of 2003
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Shock Waves in Space

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

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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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To Finish