THE SUN

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THE SUN

• http//www.whfreeman.com/universe6e/con_index.htm?
  18http//www.chara.gsu.edu/http//sohowww.nascom
  .nasa.gov/

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Guiding Questions

• What is the source of the Suns energy?
• What is the internal structure of the Sun?
• How can astronomers measure the properties of the
  Suns interior?
• How can we be sure that thermonuclear reactions
  are happening in the Suns core?
• Does the Sun have a solid surface?
• Since the Sun is so bright, how is it possible to
  see its dim outer atmosphere?
• Where does the solar wind come from?
• What are sunspots? Why do they appear dark?
• What is the connection between sunspots and the
  Suns magnetic field?
• What causes eruptions in the Suns atmosphere?

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The Sun is the nearest star to the Earth.

• It is a fairly typical star, middle sized and
  middle aged.
• All energy on Earth comes from the Sun except
  Earths own internal energy!
• In appearance the Sun is about the same size as
  the Moon (hence eclipses).

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It is 1 AU or about 150 million km from the
Earth.

• Its angular diameter from Earth is 31?59.
• The diameter of the Sun is 1.39 million km (110
  times Earths diameter and bout 10 times that of
  Jupiter).

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This is a radius of about 700,000 km 1 RO.

• The mass of the Sun is
• 1.99 1030 kg ? 2 1030 kg 1 Mass of the Sun
  1 MO,
• which is over 300,000 times the mass of the
  Earth.

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Rough Rule

• About 1000 Earths will fit by volume into
  Jupiter, about 1000 Jupiters will fit into the
  Sun.
• About how many Earths will fit into the Sun?

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The Suns density (mass/volume) is 1.41 g/cm3.

• Water has a density of
• 1.0 g/cm3and Earth has a
• density of 5.5 g/cm3.

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The Sun rotates differentially

• the parts of the Sun on the equator rotate faster
  than parts at the poles.
• Jupiter, Saturn, Uranus, and Neptune also rotate
  differentially.

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The Sun rotates differentially

• This means that there can be no solid surface
  on the Sun or any of these worlds.
• They are fluid throughout.

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The Suns equator rotates in 24.4 days

• and the poles rotate in about 40 days.
  Differential rotation arises because the sun is
  NOT SOLID.
• It is gaseous (or fluid) throughout.

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A straight line from pole to pole becomes
progressively more tangled over many solar
revolutions because of differential rotation.
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The rotation coupled

• with the Suns magnetic field is the prime cause
  of sunspots. Galileo observed sunspots.http//an
  twrp.gsfc.nasa.gov/apod/ap020801.html

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The temperature is 6000? C ? 5800 K.

• The total power output of the Sun, the
• LUMINOSITY 1 LO 3.9 10 W. A change of 1
  of the luminosity of the Sun could cause a change
  on Earth of 1? to 2? C.
• This emission is in all portions of the spectrum.
  http//zebu.uoregon.edu/soper/Sun/luminosity.htm
  l

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 THE CORE AND ENERGY GENERATION

• See fig. 18-5 and next slide.
• You will be expected to recreate the next slide
  on the midterm and final exams.
• This is the simplest cross section of the Sun
  available.

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THE CORE AND ENERGY GENERATION

• The Sun is about 4.6 BILLION years old and should
  continue to emit radiation for another 5 BILLION
  years!
• How can this be?

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THE CORE AND ENERGY GENERATION

• In the mid 1800s, it was proposed by von
  Helmholtz and Kelvin that a slow gravitational
  contraction is the source of the Suns energy.
• This could only power the Sun for a few hundred
  million years.

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THE CORE AND ENERGY GENERATION

• Gravitational contraction is what is believed to
  power the radiation from Jupiter.
• Since the Earth was proved in the early 20th
  century to be at least billions of years old, the
  theory had to be abandoned.

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THE CORE AND ENERGY GENERATION

• In 1905 Einstein proposed his General Theory of
  Relativity, that mass and energy are
  interchangeable
• (E mc2).
• E is energy, m is mass, and c is the speed of
  light, c 3 108 m/s (KNOW THIS
  NUMBER!). http//www.drphysics.com/relativity.html

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THE CORE AND ENERGY GENERATION

• During the thirties physicists worked out the
  theories of nuclear reactions.
• Nuclear fusion is the process that powers the Sun.

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THE CORE AND ENERGY GENERATION

• An atoms nucleus is composed of
• PROTONS positively charged particles and
• NEUTRONS particles with no electric charge.

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THE CORE AND ENERGY GENERATION

• Nuclear reactions involve forces between these
  particles.
• Most hydrogen atom nuclei are composed of a
  single proton.
• Deuterium nuclei are composed of a proton and a
  neutron.

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THE CORE AND ENERGY GENERATION

• Four hydrogen atoms combine, or fuse, to create
  an atom of
• helium, giving off a tiny bit of energy, ?, two
  neutrinos, ?, and 2 positrons in the process.

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The Suns energy is generated by thermonuclear
reactions in its core.

• The Suns luminosity (energy output) is 3.9 X
  1026 watts (or joules per second) and written as
  L?
• The Sun is powered by thermonuclear fusion
  reactions in the core where hydrogen is being
  converted into helium and releasing energy in a
  process called the proton-proton-chain.
• Einsteins equation, E mc2 describes how much
  energy can be created from an amount of mass, m.

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The Suns energy is generated by thermonuclear
reactions in its core.
At extremely high temperatures and pressures, 4
Hydrogen atoms can combine to make 1 Helium atom
and release energy in the process according to E
mc2 4H ? He energy HYDROGEN FUSION
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THE CORE AND ENERGY GENERATION.

• The energy is in the form of gamma rays.
• Neutrinos are tiny, nearly massless particles

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THE CORE AND ENERGY GENERATION.

• Positrons are antimatter, positive electrons.
• They are almost instantly converted back to
  energy by interactions with the electrons.

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THE CORE AND ENERGY GENERATION

• Electrons are stripped from the nuclei by the
  high temperatures, and they form an electron
  sea.
• This energy comes from the mass conversion, E
  mc2, of about 0.7 of the total mass of the
  hydrogen atoms.

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THE CORE AND ENERGY GENERATION

• The formula that represents this is
• 4 H -gt 1 He 2? ?.
• This is the definition of a star.

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THE CORE AND ENERGY GENERATION.

• It fuses hydrogen to helium in its core.
• The process is called the Proton-Proton Cycle or
  the Bethe Cycle.
• See fig 18-2 and box 18-1. http//www.whfreeman
  .com/universe6e/con_index.htm?18

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THE CORE AND ENERGY GENERATION

• This process requires VERY HIGH TEMPERATURES
  (16Million K)
• AND PRESSURES (160g/cm3 or over a billion times
  sea-level atmospheric pressure).

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A theoretical model of the Sun shows how energy
gets from its center to its surface.
Thermonuclear fusion can only occur at very high
temperatures and pressures.
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A theoretical model of the Sun shows how energy
gets from its center to its surface through
the(1) core, (2) radiative zone, and the (3)
convective zone
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THE CORE AND ENERGY GENERATION

• To produce the Suns energy about 5 million tons
  of matter must be converted each second!
• 610 billion kg of hydrogen is transformed into
  606 billion kg of helium.

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THE CORE AND ENERGY GENERATION

• Fortunately, although this is a HUGE amount to
  us, it is a very tiny amount of the Sun.

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THE CORE AND ENERGY GENERATION

• The only place where these reactions take place
  is in the CORE or the Sun.

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THE CORE AND ENERGY GENERATION

• The rest of the star is there to create the
  temperatures and pressures required for fusion
  and to transport the energy created out of the
  Sun.

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THE CORE AND ENERGY GENERATION

• About 99 of the atoms in the Sun are hydrogen,
  but, by mass, the outer layers of the Sun are
  about
• 78 hydrogen, 20 helium, and 2 everything else
  (metallicity).

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THE CORE AND ENERGY GENERATION

• Because the Sun has been fusing hydrogen to
  helium in the cove for nearly 5 billion years, we
  know the inner parts must contain more helium.

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THE CORE AND ENERGY GENERATION

• Overall, the Sun (by mass) is theorized to be
  about
• 73 hydrogen, 25 helium, and 2 metallicity

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THE CORE AND ENERGY GENERATION

• Until recently the theory of fusion had some
  observational problems,
• The Neutrino Problem.
• Only about a third of the predicted neutrinos
  were seen.

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Neutrinos provide information about the Suns
core - and have surprises of their own.

• Current models of the solar interior predict that
  1038 neutrinos should be released every second if
  our current theories are correct.
• Current neutrino detectors on Earth watch for
  collisions between perchloroethylene cleaning
  fluid (C2Cl4) and neutrinos which produces
  radioactive argon.
• Only 1/3 of the expected neutrinos from the Sun
  are being detected.
• Astronomers do not know why this occurs.

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Mystery of the Missing Neutrinos

• Current models of the solar interior predict that
  1038 neutrinos are released every second.
• Current neutrino detectors on Earth watch for
  collisions between perchloroethylene cleaning
  fluid (C2Cl4) and neutrinos which produces
  radioactive argon.
• Only 1/3 of the expected neutrinos from the Sun
  are being detected.

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THE CORE AND ENERGY GENERATION

• Another theory said that neutrinos, which come in
  three types, oscillate between the types.

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THE CORE AND ENERGY GENERATION

• This has recently been confirmed, and the
  Proton-Proton Cycle is considered to be the most
  likely form of fusion in the Sun.

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THE CORE AND ENERGY GENERATION

• Hydrostatic Equilibrium is a balance within a
  star between the downward pressure caused by the
  gravity force of the overlying layers and the
  upward force of the radiation trying to escape
  from the core
• (PR FG).

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THE CORE AND ENERGY GENERATION

• Normal stars are in hydrostatic equilibrium.
  Without it a star will pulsate.

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RADIATIVE AND CONVECTIVE ZONES AND ENERGY
TRANSPORT

• Energy transport goes by two routes, convection
  (in the Convective Zone) and radiation
  (throughout the Sun).
• The energy is carried by tiny particles of light
  called photons.

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RADIATIVE AND CONVECTIVE ZONES AND ENERGY
TRANSPORT

• As the energy moves out from the core the photons
  bounce around hitting atoms on their way out.

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RADIATIVE AND CONVECTIVE ZONES AND ENERGY
TRANSPORT

• In the Radiative Zone these photons perform a
  statistical Random Walk or Drunkards Walk.

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RADIATIVE AND CONVECTIVE ZONES AND ENERGY
TRANSPORT

• If the photon didnt bounce around, it would only
  take about 2.3 sec. to escape to the photosphere.
• But, it takes anywhere from 30,000 to 100,000
  years for a photon to make it from its creation
  in the core to the visible surface of the Sun,
  the photosphere

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RADIATIVE AND CONVECTIVE ZONES AND ENERGY
TRANSPORT

• (It takes about 8 minutes for it to reach Earth
  after that).
• As the photon bounces it loses energy.

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RADIATIVE AND CONVECTIVE ZONES AND ENERGY
TRANSPORT

• It starts as a high-energy gamma ray,
• becomes an X-ray at the bottom of the convective
  zone,
• becomes ultraviolet light, and then visible
  light.

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RADIATIVE AND CONVECTIVE ZONES AND ENERGY
TRANSPORT

• Some photons degrade as far as radio wavelengths.
  
• The layers of the Sun exterior to the core change
  the lethal rays created by fusion to
• primarily life-giving visible light at the
  photosphere.

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• See the CLEA link
• in the lab for a
• statistical model
• of the photons
• movement.

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RADIATIVE AND CONVECTIVE ZONES AND ENERGY
TRANSPORT

• In the Radiative Zone the pressure is too high
  for much transport of solar material,
• but was we get into the Convective Zone the
  primary transport is by movement of the solar
  material
• the Sun boils.

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RADIATIVE AND CONVECTIVE ZONES AND ENERGY
TRANSPORT

• See the chicken noodle soup model.
• A granule is a division of the Suns
  photosphere into small convection cells.

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RADIATIVE AND CONVECTIVE ZONES AND ENERGY
TRANSPORT

• The center of a granule heats up and rises
  (bright center)
• as it gets higher it cools and sinks around the
  edges of the granule (darker edges).

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RADIATIVE AND CONVECTIVE ZONES AND ENERGY
TRANSPORT 18

• See figs. 18-11, 12, 13.
• You can see the tops of the granule cells in the
  photosphere.
• http//www.whfreeman.com/universe6e/con_index.htm?

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THE OUTER LAYERS

• The Sun does not have a hard surface as we are
  used to on Earth.
• The Photosphere is the visible surface we see
  when we look at the Sun.

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THE OUTER LAYERS

• It is only about 400 km thin, too thin to draw on
  your diagram of the Sun.
• It is the place in the Sun where the Sun becomes
  transparent to visible light.

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Granulation caused by convection
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THE OUTER LAYERS

• The Limb of the Sun is the edge and is
  noticeably darker than the central section.
• This is because we can see to a greater depth due
  to the angle of sight.

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Annular Eclipse on October 3, 2005
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THE OUTER LAYERS

• The temperature of the photosphere is generally
  taken to be
• 5800? C 6000 K.

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THE OUTER LAYERS

• The pressure there is about one hundredth that at
  Earths surface with a thousandth the density.
• http//www.whfreeman.com/universe6e/con_index.htm?
  18

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THE OUTER LAYERS

• The Sun shakes. It has seismic events. It has
  a great many harmonics and could be thought of as
  a giant drum.
• http//www.whfreeman.com/universe6e/con_index.htm?
  18

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Astronomers probe the solar interior using the
Suns own vibrations.
Sections of the Suns surface quickly oscillate
up on down.
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Astronomers probe the solar interior using the
Suns own vibrations.

• Exploring the Suns interior by studying its
  vibrations is called HELIOSEISMOLOGY.
• Because we can not actually see inside the Sun,
  helioseismology provides theoreticians with a way
  to check to be sure their models of the solar
  interior are correct.

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THE OUTER LAYERS

• Flares are huge hydrogen explosions on the
  photosphere.
• They can even poke holes in the outer atmosphere
  and send particle flux to the Earth.

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THE OUTER LAYERS

• A very large flare a couple of years ago fried
  the new IBM communications satellite in Earth
  orbit.

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THE OUTER LAYERS

• Flares, sunspots and prominences originate on the
  photosphere

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THE OUTER LAYERS

• The Chromosphere is a region of the solar
  atmosphere lying about 2 to 3 thousand km
• above the photosphere and
• inside the Corona, the outer atmosphere.

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THE OUTER LAYERS

• The chromosphere is usually observed during solar
  eclipse.
• It is visibly pinkish and is the coolest part of
  the Sun.
• It is in the chromosphere where the absorption
  lines in the Suns spectrum originate.

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The chromosphere is characterized by spikes of
rising gas.

• The chromosphere is the thin, pinkish layer of
  SPICULES just above the photosphere.
• Spectrum is dominated by Ha emission lines
  suggesting it is quite tenuous.
• The temperature is higher in the chromosphere
  than the photosphere (which is opposite one would
  expect where it should get cooler with increasing
  distance).

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THE OUTER LAYERS

• Spicules are narrow jets of gas originating in
  the chromosphere and extending 6 to 10 thousand
  km into the corona.
• See fig. 14 15.

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THE OUTER LAYERS

• Spicules last only a few minutes and are not well
  understood.
• Plages are bright areas above the photosphere.

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THE OUTER LAYERS

• Filaments are high arching segments of solar
  material seen in darker relief against the
  chromosphere.
• See fig 18-18.

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THE OUTER LAYERS

• The Corona is the outer atmosphere of the Sun.
  
• It is about 1 to 2 million Kelvins in temperature
  with temperature increasing with height.

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The corona ejects mass into space to form the
solar wind.

• Most easily seen during an eclipse.
• Thin gas at millions of degrees more than
  photosphere.
• The outflow of mass from the Sun is called the
  solar wind.

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THE OUTER LAYERS

• It also is observed well on Earth only during
  eclipses.
• Prominences are eruptions of solar material from
  the photosphere into the corona.

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THE OUTER LAYERS

• Prominences are often enormous, rising thousands,
  even millions of kilometers above the
  photosphere.
• See fig 18-19 20.

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THE OUTER LAYERS

• They can reach speeds of 1500 km/s, and slower
  moving ones may last several days.
• http//www.whfreeman.com/universe6e/con_index.htm?
  18

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THE OUTER LAYERS

• The solar wind boils off the corona and extends
  throughout the solar system.
• It can vary from a breeze to a gale depending
  of the sunspot cycle and flares.

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The corona ejects mass into space to form the
solar wind.

• Most easily seen during an eclipse.
• Thin gas at millions of degrees more than
  photosphere.
• The outflow of mass from the Sun is called the
  solar wind.

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THE OUTER LAYERS

• In a sense the Sun is evaporating.
• The outer limits of the wind were found in 1995
  by the Pioneer spacecraft far beyond the orbit of
  Pluto.

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THE OUTER LAYERS

• Near the Earth the wind travels at about 400 km/s
  and has only 2-10 particles/cm3.
• When the wind hits the Earths magnetic field
  auroras form near the poles.

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THE OUTER LAYERS

• Only about a tenth of one percent (0.1) of the
  original mass of the Sun has been lost since the
  Suns formation.

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SUNSPOTS, THE MAGNETIC FIELD, AND CYCLE OF THE
SUN

• http//www.whfreeman.com/universe6e/con_index.htm?
  18
• http//www.hao.ucar.edu/public/slides/slide17.html
  

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Sunspots are low-temperature regions in the
photosphere.
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SUNSPOTS

• The Chinese have seen spots on the Sun as early
  as the fifth century BC.
• The first sunspots were seen telescopically by
  Galileo and by Harriott in the 17th century.

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SUNSPOTS

• Sunspots are very hot, but look dark in
  comparison to the photosphere because they are
  about 1500 K cooler.
• They are temporary and last only a few hours to a
  few months.

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SUNSPOTS

• Sunspots are caused by kinks in the magnetic
  field of the Sun.
• They have magnetic fields a thousand times
  greater than the surrounding photosphere.

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SUNSPOTS

• The smallest ones in fig. 21 are larger than the
  Earth.
• Sunspots usually come in pairs with opposite
  magnetic polarities, one north and one south.

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SUNSPOTS

• The pairs are usually aligned in an east-west
  direction.
• Sunspots have a cycle of about 11 years,
• discovered by Schwabe in 1851.

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SUNSPOTS

• The inner, darker part of the spot is called the
• umbra (T ? 4500K), and the outer part is the
• penumbra (T ? 5500 K).
• http//www.whfreeman.com/universe6e/con_index.htm?
  18

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Sunspots are low-temperature regions in the
photosphere.
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The daily movement of sunspots reveals that the
Suns rotation takes about 4 weeks.
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SUNSPOTS

• We measure the Suns magnetic field using the
• Zeeman Effect,
• which is the splitting of a spectral line by a
  strong magnetic field.
• See fig. 18-23

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SUNSPOT CYCLE

• The sunspot cycle is composed of two sub-cycles
  of about 11 years each.
• The overall cycle is about 22 years long.

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The cyclical change in the latitude of sunspots
also reveals that the Sun experiences an 11-year
solar cycle.
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SUNSPOT CYCLE

• In the beginning of the first cycle
• 1. Few or no sunspots
• form at about 35? latitude
• north and south. The
• North magnetic pole
• is near the North geographic
• pole.

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Sunspot minimum
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SUNSPOT CYCLE.

• 2. More an more
• spots form at lower
• and lower latitudes
• as the cycle advances.

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Middle of 11 year cycle
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SUNSPOT CYCLE

• 3. Sunspot maximum after about 11 years with
  many large spots near the equator with many
  large flares

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SUNSPOT CYCLE

• 4. The first sub-
• cycle ends with the
• polarity of the Sun
• reversing the North
• magnetic pole is now
• near the South geographic pole.

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First sunspot maximum after 11 years, poles swap
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SUNSPOT CYCLE

• 5. Few or no sunspots
• form at about 35?
• latitude north and south.

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Second sunspot minimum
123

• 6. More an more spots form at lower and lower
  latitudes as the cycle advances.

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Second middle of cycle
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SUNSPOT CYCLE

• 7. Sunspot maximum
• after about 11 years
• with many large spots
• near the equator with
• many large flares.

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SUNSPOT CYCLE

• 8. The second sub-
• cycle ends with the
• polarity of the Sun
• reversing the North
• magnetic pole is now
• back near the North geographic pole.

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Second maximum, end of magnetic cycle, poles back
at original orientation.
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SUNSPOT CYCLE

• Total magnetic sunspot cycle of the Sun is
  complete.
• This sunspot cycle can be represented by a
  butterfly diagram of sunspot latitude vs. time.

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The cyclical change in the latitude of sunspots
also reveals that the Sun experiences an 11-year
solar cycle.
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DIAGRAM SOURCE NASA RECENT SUNSPOT PLOT
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DIAGRAM SOURCE UK
132
Sunspots are produced by a 22-year cycle in the
Suns magnetic field.

• Charged particles, such as electrons, will move
  along magnetic field lines.
• The Sun experiences 11 years of magnetic fields
  in one direction, then 11 years of field in the
  opposite direction.

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SUNSPOTS

• The current model of sunspot formation has the
  magnetic field lines fastened the material of the
  Sun.
• As the Sun rotates differentially the lines form
  tubes that become gradually twisted within the
  Sun.

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The interior of the Sun rotates at different
rates than the exterior as well as differentially
at various latitudes. The radiative zone seems
to rotate as a rigid sphere.
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SUNSPOTS

• When the tubes are forced to the surface, they
  become visible as sunspots.
• Breaking out in this sunspot kink weakens the
  lines and the sunspots die out

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The sunspot cycle maybe be due in part to the
Suns differential rotation which might cause the
magnetic fields to wrap, intensify, then become
chaotic and cancel itself.
137
SUNSPOTS

• The kinks also appear to cause flares. See fig.
  18-24 through fig. 18-29.
• As new lines form deep within the Sun, the
  magnetic field direction in the emerging tubes
  will reverse over time, leading to the 22 year
  cycle.

138
This X-ray image of the Sun shows bright regions
where gas is moving along magnetic field lines.
139
SUNSPOTS

• Sunspot cycles are NOT constant,
• some are shorter, some longer, some stronger, and
  some nonexistent.

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SUNSPOTS

• The Maunder Minimum occurred in the late middle
  ages from about 1600 to about 1850.

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SUNSPOTS

• During part of the minimum almost no sunspots
  were observed,
• and far fewer sunspots were observed during the
  entire minimum.

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SUNSPOTS

• This time corresponds to the Little Ice Age in
  Europe when temperatures were much lower than
  average.
• Other cool minimums have been deduced for earlier
  periods including

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MAUNDER MINIMUM INFORMATION

• Oort minimum 1010 1050 AD
• Wolf Minimum 1280 1340 AD
• Spoerer Minimum 1420 1530 BC
• Maunder Minimum 1410 1720 AD.
• Apparently these periods of cold hot are
  cyclical and somewhat due to the Sun.

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SUNSPOTS

• There also may be a connection to our global
  warming cycle,
• since the last two sunspot cycles have been the
  most active on record.
• We have been at record warmth during these cycles.

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SUNSPOTS

• There is no evidence that sunspots are related to
  real ice ages.
• These appear to be due to geographical, axial,
  and orbital changes.

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SUNSPOTS

• Sunspots, flares and solar wind have other
  effects on the Earth among which are

147
SUNSPOTS

• 1. Communications Disruptions (EMFs)Satellite
  destruction2. Aurora (Northern and Southern
  Lights)3. Atmospheric expansion4. Cooler (and
  hotter?) overall Earth temperatures.

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The Suns magnetic field also produces other
forms of solar activity.

• plages
• filaments

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Solar magnetic fields also create other
atmospheric phenomena.

• plages
• filaments
• prominences

150
Solar magnetic fields also create other
atmospheric phenomena.

• plages
• filaments
• prominences
• solar flares
• coronal holes

151
Solar magnetic fields also create other
atmospheric phenomena.

• plages
• filaments
• prominences
• solar flares

• coronal holes
• coronal mass ejections (CMEs)

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Guiding Questions

• What is the source of the Suns energy?
• What is the internal structure of the Sun?
• How can astronomers measure the properties of the
  Suns interior?
• How can we be sure that thermonuclear reactions
  are happening in the Suns core?
• Does the Sun have a solid surface?
• Since the Sun is so bright, how is it possible to
  see its dim outer atmosphere?
• Where does the solar wind come from?
• What are sunspots? Why do they appear dark?
• What is the connection between sunspots and the
  Suns magnetic field?
• What causes eruptions in the Suns atmosphere?