Walking on the Sun by Smash Mouth

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Walking on the Sunby Smash Mouth
Donna Kubik Spring, 2006
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Walking on what?

• What is the surface of the sun?
• Although astronomers talk about the surface of
  the Sun, the Sun is so hot that it has no liquid
  nor solid material
• It is comprised totally of gas that gets denser
  and denser toward the center
• The Sun contains gt99.85 of the total mass of the
  solar system

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Walking on the photosphere?

• The Sun appears to have a surface only because
  most of its visible light comes from one specific
  layer, called the photosphere.
• The photosphere is the lowest of 3 layers
  comprising the Suns atmosphere
• Because the upper 2 layers are transparent to
  most wavelengths of visible light, we see through
  them down to the photosphere.
• We cannot see through the photosphere, so
  everything below the photosphere is called the
  Suns interior

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Solar atmosphere

• Photosphere
• Chromosphere
• Corona

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Photosphere
400 km thick 5800K
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Limb darkening

• Sun appears darker near the edges
• This is called limb darkening

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Limb darkening

• At the edges, we are looking through more of the
  cooler atmosphere, so there is more absorption of
  the photons from the hottest (innermost) part of
  the photosphere
• In the center we can receive more photons from
  the hotter part of the photosphere

4000 K
5800 K
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Granulation

• Granulation is the fine grain structure of the
  photosphere.
• Individual granules are about 1000 km across.
• The granulation is constantly changing, usually
  over time scales of minutes or less.

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Granulation

• Each granule is a convective cell which
  consists of a bright, roughly-polygonal area of
  hot rising gas, and a cooler edge of descending
  gas
• The rising and descending is determined via
  Doppler shift of spectral lines

Darker because cooler
Brighter because hotter
Convection in photosphere
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Granulation

• The energy (E) and temperature (T) according
  to Stephan-Boltzman law ET4
• So more photons per area emitted from hot
  regions

Darker because cooler
Brighter because hotter
Convection in photosphere
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Chromosphere
2000 km thick 4000K
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The EUV Sun

• The name, chromosphere sphere of color is
  misleading
• The name suggests it is the layer we normally see
• But the chromospheres light is swamped by that
  of the photosphere

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The EUV Sun

• The chromosphere is only visible when the
  photosphere is blocked, as during a total solar
  eclipse, or when viewed at nonvisible wavelengths
  that the chromosphere is especially bright (as
  EUV), or when viewed through a filter (Ha) that
  blocks most of the photospheres light

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The EUV Sun

• Image taken at EUV wavelengths by SOHO (Solar and
  Heliospheric Observatory) operated by ESA and
  NASA.
• The UV light originates from the lower regions of
  the chromosphere
• These wavelengths also indicate active regions.

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Supergranulation

• The dark graininess seen in the image is due to
  supergranulation.
• Supergranules contain 900 granules
• Typical diameter of a supergranule is slightly
  larger than the earths diameter
• The source of this light is the chromosphere

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Spicules
Spicules
Supergranules

• High resolution images of the chromosphere, taken
  through an Ha filter, reveal numerous spikes,
  which are jets of gas called spicules
• Spicules are usually located on the edge of
  supergranules
• Spicules rise for several minutes at 45,000mph to
  a height of 10,000km

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Spicules

• The image shows spicules on the limb of the Sun
  as imaged by the Big Bear Solar Observatory.
• It shows a superposition of 11 limb images taken
  at different wavelengths

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Sunspots inhibit formation of supergranules
In these photos taken at the same time, there
are no supergranules where there are sunspots.
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Solar observatories

• The Big Bear Solar Observatory is located in the
  middle of Big Bear Lake (in CA) to reduce the
  image distortion which usually occurs when the
  Sun heats the ground and produces convection in
  the air just above the ground
• Turbulent motions in the air near the observatory
  are also reduced by the smooth flow of the wind
  across the lake instead of the turbulent flow
  that occurs over mountain peaks and forests.

Big Bear Solar Observatory
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Solar observatories

• In addition to the atmospheric effects, solar
  telescopes suffer from heating by sunlight of the
  optics and the air within the telescope tube.
• This causes the image to shiver and become
  blurred.
• Modern solar telescopes are either vacuum
  telescopes, filled with helium or use careful
  control of the optic's temperature to reduce
  heating of the air in the telescope.

Big Bear Solar Observatory telescopes
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Solar observatories

• The 65 cm and 25 cm telescopes are evacuated to
  avoid air turbulence inside the telescope tubes
  caused by the solar beam heating air molecules.
• Special white paint used inside and outside the
  observatory diffusely reflects sunlight and
  radiates heat away to reduce turbulence due to
  solar heating.

Big Bear Solar Observatory telescopes
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Solar observatories

• Some solar telescopes look very different from
  other optical telescopes

Kitt Peak National Observatory
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Solar observatories

• Close to the ground the heating effect of the Sun
  causes a layer of hot, turbulent air, which makes
  images formed by mirrors near the ground
  unsteady, so the first mirror (heliostat) is
  often placed on a tall tower

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Solar towers
National Solar Observatory Sunspot, New Mexico
National Solar Observatory Kitt Peak, Arizona
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The Radio Sun

• Radio image taken from Japans Nobeyama Radio
  Observatory
• The most active regions are the most luminous.
• The radio image provides information about the
  transition region between the chromosphere and
  corona.

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Corona
Several million km thick 1-2 million K
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Corona viewed during eclipse

• The glow of the corona is a million times less
  bright than that of the photosphere
• Like the chromosphere, the corona can only be
  seen when the photosphere is blocked by special
  filters, at non-visible wavelengths at which the
  corona is especially bright, or when the disk of
  the Sun is blocked during a total solar eclipse.

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Coronagraph

• ..or by using a special instrument called a
  coronagraph that artificially blocks the disk of
  the Sun so that it can image the region
  surrounding the photosphere

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Coronagraph

• A very common way to observe the corona is to
  cover the bright disk of the Sun.
• This creates a sort of mini-eclipse and allows us
  to see the Sun's fainter outer atmosphere

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What can you see with a coronagraph?

• Streamers are structures formed by the Sun's
  magnetic field. They can last for months.
• Sometimes streamers go unstable and erupt in huge
  magnetic bubbles of plasma known as coronal mass
  ejections (or CMEs) that blow out from the Sun's
  corona and travel through space at high speed.

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Corona

• It seems that the temperature should decrease as
  one rises through the Suns atmosphere (moving
  away from the apparent heat source
• It does decrease from the photosphere (5800K) to
  the chromosphere (4000K), but then it rises to
  much higher temps in the corona
  (1-2 million K)!

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Corona

• Unexpected increase in temperature was discovered
  in about 1940 when Fe XIV (an iron atom stripped
  of 13 e-) was detected in the spectrum of the
  corona
• Takes lots of energy to strip so many electrons
  from an atom, so the corona must be very hot

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Corona

• Astronomers have mounting evidence that the
  corona is heated by energy carried aloft and
  released there by the Suns complex magnetic
  fields (more on that later)

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TRACE

• TRACE (Transition Region and Coronal Explorer)
  is a NASA space telescope designed to provide
  high resolution images and observation of the
  photosphere and transition region to the corona.
• The satellite, launched in April 1998

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TRACE

• The telescope is designed to take images in a
  range of wavelengths from visible light, through
  the Lyman alpha line to far ultraviolet.
• The different wavelength passbands correspond to
  plasma emission temperatures from 4,000 to
  4,000,000 K.
• Sun-synchronous (98) orbit of 600650 km.

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Sun-synchronous orbit

• Sun-synchronous (98) orbit of 600650 km.
• This type of orbit is designed to keep the
  satellite in full sun light for nine months a
  year.
• The orbit moves the satellite to the west at the
  exact same rate that the sun appears to move
  across the Earth's surface.

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Corona

• If the temperature is to high, why doesnt the
  corona outshine the photosphere?
• According to according to Stephan-Boltzman law
  ET4
• So more photons should be emitted per area
  emitted from hot regions!?
• But the density of the corona is very, very, very
  low, otherwise it would outshine the photosphere!

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Solar wind

• The Suns gravity keeps most of its atmosphere
  from escaping to space, but some of the gas in
  the corona is moving fast enough to escape.
• This is the solar wind

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Space weather

• The solar wind is one aspect of space weather
• You can view the current space weather conditions
  and the space weather forecast at
• http//spaceweather.com

SPACE WEATHERCurrentConditions Solar Wind
speed 330.9 km/s density 2.5 protons/cm3
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Solar wind

• The solar wind is comprised mostly of hydrogen
  and helium nuclei
• Hydrogen nuclei are protons

SPACE WEATHERCurrentConditions Solar Wind
speed 330.9 km/s density 2.5 protons/cm3
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Solar wind

• The solar wind particles reach speeds up to 805
  km/s
• The wind achieves these high speeds in part by
  being accelerated by the Suns magnetic field

SPACE WEATHERCurrentConditions Solar Wind
speed 330.9 km/s density 2.5 protons/cm3
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Solar wind

• The Sun ejects a million tons of matter each
  second
• Even at this rate of emission, the mass loss due
  to the solar wind will amount to only a few
  tenths of a percent of the Suns total mass
  throughout its lifetime

SPACE WEATHERCurrentConditions Solar Wind
speed 330.9 km/s density 2.5 protons/cm3
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SOHO

• SOHO (Solar and Heliospheric Observatory),
  operated by NASA and ESA, is designed to study
  the internal structure of the Sun, its extensive
  outer atmosphere and the origin of the solar
  wind, the stream of highly ionized gas that blows
  continuously outward through the Solar System.

SOHO orbit is sunward of Earth Not to scale
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SOHO

• All previous solar observatories have orbited the
  Earth, from where their observations were
  periodically interrupted as our planet eclipsed'
  the Sun.
• A continuous view of the Sun is achieved by
  operating SOHO from a permanent vantage point 1.5
  million kilometers sunward of the Earth

SOHO orbit is sunward of Earth Not to scale
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Lagrange points

• The Italian-French mathematician Joseph-Louis
  Lagrange discovered five special points in the
  vicinity of two orbiting masses where a third,
  smaller mass can orbit at a fixed distance from
  the larger masses.

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Lagrange points

• Of the five Lagrange points, three are unstable
  and two are stable.
• The unstable Lagrange points - labeled L1, L2 and
  L3 - lie along the line connecting the two large
  masses.
• The stable Lagrange points - labeled L4 and L5 -
  form the apex of two equilateral triangles that
  have the large masses at their vertices.

SOHO
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Lagrange points

• The L1 point of the Earth-Sun system provide an
  uninterrupted view of the sun and is the location
  of SOHO

SOHO
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Lagrange points

• The L2 point of the Earth-Sun system is the
  location of WMAP and (perhaps by the year 2011)
  the James Webb Space Telescope.
• The L1 and L2 points are unstable on a time scale
  of approximately 23 days, which requires
  satellites parked at these positions to undergo
  regular course and attitude corrections.

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The quiet Sun vs. the active Sun

• Quiet Sun
• Granules, supergranules, spicules, and the solar
  wind occur continuously. They are features of
  the quiet Sun.
• Active Sun
• But the Suns atmosphere is periodically
  disrupted by magnetic fields that stir things up,
  creating the active Sun.

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Solar magnetic field

• In contrast to the Earth, the Sun has a very weak
  overall magnetic field (average dipole field).
• However, the solar surface has very strong and
  tremendously complicated magnetic fields.
• Because the surface magnetic fields are so
  complex, solar astronomers use computers to
  simulate the Sun's magnetic fields.

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Solar magnetic field

• It is the dynamics of the Suns magnetic fields
  that is thought to cause many of the features of
  the active Sun

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Discovery of sunspots

• Sunspots are one of the features of the active
  Sun
• Galileo looked at the Sun through his telescope
• One should NEVER look directly through a
  telescope at the Sun
• This caused Galileo to suffer from partial
  blindness.

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Discovery of sunspots

• Galileo did see spots on the Sun
• These were sunspots
• This animation shows a sequence of drawings made
  by Galileo as he observed the Sun from June 2nd
  to 26th, 1612.

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Sunspots are cooler spots
Umbra
Prenumbra

• A typical sunspot is 10,000 km across and lasts
  between a few hours and a few moths
• It is comprised of two parts
• The dark, central region is called the umbra
• The brighter ring around it is called the
  prenumbra

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Sunspots are cooler spots
Umbra
Prenumbra

• Seen without the surrounding very bright granules
  that outshine it, the umbra appears red and the
  penumbra orange
• From Weins Law lmax0.0029/T
• The orange umbra is 4300 K
• The red penumbra is 5000 K
• Both are cooler than the surrounding 5800 K
  photosphere

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Zeeman effect

• In 1908, George Ellery Hale discovered that
  sunspots are directly linked to magnetic fields
• When he observed the spectra from sunlight coming
  from a sunspot, he found that each spectral line
  in the normal solar spectrum was flanked by
  additional, closely-spaced spectal lines not
  usually observed

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Zeeman effect

• This splitting of a single spectral line into
  two or more lines is called the Zeeman effect
• Pieter Zeeman first observed such splitting in
  the laboratory in 1896

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Zeeman effect

• Zeeman showed that an intense magnetic field
  splits the lines of a light source if the source
  is inside the field
• The more intense the magnetic field, the more the
  split lines are separated

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Sunspots

• The intense magnetic field below a sunspot
  strangles the normal up-flow of energy from the
  hot solar interior, leaving the spot cooler and
  therefore darker than its surroundings

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Sunspots

• The suppression of the bubbling convective
  motions forms a kind of plug that prevents some
  of the energy in the interior from reaching the
  surface.
• As a result, the material above the plug cools
  and becomes denser, causing it to plunge downward
  at up to 3,000 miles per hour, according to new
  observations from SOHO

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Sunspots

• This time-lapse movie shows in five seconds what
  happens in 20 minutes on the Sun's surface near a
  sunspot.
• This sunspot measured about 25,000 kilometers
  across.
• Visible is boiling granulation outside the
  sunspot, inward motion of bright grains in the
  outer penumbral region toward the sunspot, and
  the churning of small magnetic elements between
  solar granules.

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Sunspots

• Sunspots themselves are relatively cool regions
  of the solar surface depressed by magnetic
  fields.
• The dark lanes surrounding the sunspot are called
  penumbral filaments, and recent computer
  simulations have shown that their behavior is
  also dominated by magnetic fields.
• The movie was taken with the Dutch Open Telescope

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Sunspots

• Sunspots reveal
• The solar cycle
• The Suns rotation

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Differential rotation

• Sun rotates differentially
• 25 days for one rotation at equator
• 27 days at latitude 30 deg
• 33 days at latitude 75 deg
• 35 days near poles

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The Solar Cycle

• Sunspot maximum and minimum occur on 11-year
  cycle
• Orientation of the Suns magnetic field flips
  every 11 years
• Solar cycle is 22 years

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Butterfly diagram

• Sunspots do not appear at random locations over
  the surface of the sun but are concentrated in
  two latitude bands on either side of the equator.

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Butterfly diagram

• A butterfly diagram showing the positions of the
  spots for each rotation of the sun since May 1874
  shows that these bands first form at
  mid-latitudes, widen, and then move toward the
  equator as each cycle progresses

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The Solar Cycle

• Prominences, flares, and plages vary with the
  same 11-year cycle as sunspots
• Coronal mass ejections, the major source of
  hazardous particles from the Sun, occur with
  varying frequency, but never totally cease.

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Filaments, plages, and prominences

• Hotter, therefore brighter, regions in
  chromosphere
• Created by magnetic fields under the photosphere
  just before they they emerge
• Prominences are filaments viewed from the side
• All associated with sunspots

Prominences
Plages
Filaments
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Filaments, plages, and prominences

• This image of 1,000,000K gas in the Sun's thin,
  outer atmosphere indicates ionized iron at 171 Å
• The loops of energized particles clearly follow
  magnetic field lines around an active region.

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Filaments, plages, and prominences

• This image of 1-million degrees Kelvin gas in the
  Sun's thin, outer atmosphere which detects
  ionized iron here at 171 Å
• The loops of energized particles clearly follow
  magnetic field lines around an active region.

Compare loops and prominences (left) to models of
Solar magnetic fields (right)
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The x-ray Sun

• This x-ray image was obtained by the Japanese
  observatory Yohkoh (Sunbeam), a collaborative
  effort with the US and UK.
• The x-rays originate from the Suns corona.

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Yohkoh

• The Japanese satellite, known as Yohkoh
  ("Sunbeam"), a cooperative mission of Japan, the
  USA, and the UK, was launched in 1991 (ended
  operation in 2005)
• The scientific objective has been to observe the
  energetic phenomena taking place on the Sun,
  specifically solar flares in x-ray and gamma-ray
  emissions

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The x-ray Sun

• The brightest regions correspond to violent solar
  flares which send high energy particles to Earth.
• Darker regions denote cooler areas which are
  called coronal holes, because gases can escape
  this region.

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Solar flares in the chromosphere

• Violent eruptive events, solar flares, send out
  vast quantities of high-energy particles as well
  as x-rays and UV radiation.
• Lots of flares at sunspot maximum
• Can last for hours

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Solar flares vs. prominences

• Solar flares are more sudden and violent events
  than prominences.
• While they are thought to also be the result of
  magnetic kinks, flares do not show the arcing or
  looping pattern characteristic of
  prominences

Flares
Prominences (which are filaments viewed from the
side)
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Solar flares vs. prominences

• Flares are explosions of incredible power, rising
  local temperatures to 100,000,000 K
• Prominences release their energy over days or
  week, while flares release their energy in
  minutes or hours

Flares
Prominences (which are filaments viewed from the
side)
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Coronal mass ejections

• In the foreground of the 15 degree wide field of
  view, a bubble of hot plasma, called a coronal
  mass ejection
• Can alter the Suns magnetic field
• Often associated with solar flares
• Image from SOHO using coronagraph

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Coronal mass ejections

• Another Image of a CME from SOHO using
  coronagraph

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Effect on Earth

• Some coronal mass ejections, solar flares, and
  prominences head toward Earth
• Takes 8 minutes for radiation to arrive
• Takes a few days for particles to arrive
• Can produce aurora
• Can disrupt communications

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Maunder Minimum

• There are irregularities in the cycles
• Sometimes one pole reverses before the other
• Sometimes no sunspots for decades (as from
  1645-1715, Maunder Minimum)

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Solar cycle predictions

• From SCIENCE VOL 311 10 MARCH 2006
• Researchers at the National Center for
  Atmospheric Research (NCAR) predict that the next
  peak in sunspots will come a little late but will
  be far bigger than the last peakbigger, in fact,
  than all but one of the 12 solar maxima since
  1880.

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Solar cycle predictions

• They found that it takes a good 20 years for the
  magnetic remnants of past sunspots to recirculate
  deep into the interior, where the twisting action
  of the suns rotation amplifies them, and to rise
  back to the surface near the equator as the next
  cycles sunspots.

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Solar cycle predictions

• The model did an impressively accurate job
  hindcasting the size and timing of past cycles.
  
• That track record made researchers confident that
  the next solar cycle will be 30 to 50 stronger
  than the last solar cycle.
• The next cycle will begin 6 to 12 month later
  than average

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Where does the Suns energy come from?

• We see hot gas, intense magnetic fields, and the
  many features of both the quiet and active sun
• Where does the energy come from?
• Cant come from the hot gas or magnetic fields
  they have no mechanism to create energy

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Where does the Suns energy come from?

• In 1905, Einstein showed that mass can be
  converted into energy Emc2
• In 1920s, Eddington proposed that temperatures
  in the core of the sun are high enough to fuse H
  to He.
• In this reaction, a tiny amount of mass is lost.
• This mass is transformed into a very large amount
  of energy the energy of the Sun

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Thermonuclear fusion

• Mass of 4 H atoms 6.693 x 10-27 kg
• - Mass of 1 He atom 6.645 x 10-27 kg
• Mass lost 0.048 x 10-27 kg
• E mc2
• E (0.048 x 10-27 kg)(3x 108 m/s)2
• E 4.3 x 10-12 Joules
• 4H ? He neutrinos gamma rays

88
Sources of the Suns energy

• The energy generated by hydrogen fusion is the
  Suns core eventually escapers through the
  photosphere into space
• That energy makes the sun shine

89
Where does the Suns energy come from?

• There are 2 ways stars convert H to He
• Proton-proton chain
• CNO cycle
• Both yield the same results
• 4H ? He energy

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Where does the Suns energy come from?

• For stars with masses not greater than the Suns,
  the core temperature does not exceed 16 million
  K, so the proton-proton chain dominates
• For stars more massive than the sun, the core
  temperature is greater than 16 million K, and
  hydrogen burning occurs mainly via the CNO cycle

91
Sources of the Suns energy

• 98.5 of the Suns energy comes from the p-p
  chain
• 1.5 of the energy comes from the CNO cycle

92
Proton-proton chain

• Hydrogen fusion - converts hydrogen to helium
• Possible because of high temperature and pressure
  in the Suns core
• Mass of 4 H gt Mass of 1 He
• Results in 4H He neutrinos gamma rays
• The gamma rays balance inward force of gravity

93
Proton-proton chain

• There are 4 branches of the proton-proton chain
• The one below produces 85 of the Suns energy
• In the other 3 branches, the 3He nucleus follows
  a different fate
• Neutrinos are produced by all branches
• Physicists want to study these neutrinos

94
CNO cycle

• The initial reaction involves a carbon nucleus
  (with 6 protons) and a hydrogen nucleus
  (1 proton)
• Because of the large electrical charge of the
  carbon nucleus, there is a stronger electrical
  repulsion
• Therefore a higher temperature is needed in
  order for the reaction to take place

95
CNO cycle

• Since the CNO cycle recovers the original C
  nucleus, the carbon, nitrogen, and oxygen are
  unaffected, in net, by the reactions
• So it could start anywhere in the cycle with the
  addition of one proton to any of the carbon or
  nitrogen nuclei

96
CNO cycle

• Consequently, this cycle is often called the CN
  cycle (as They Might Be Giants call it!)

97

• The sun is large If the sun were hollow, a
  million Earths could fit inside. And yet, the sun
  is only a middle-sized star.
• The sun is far away About 93 million
  miles away, and that's why it looks so small.
  And even when it's out of sight The sun shines
  night and day The sun gives heat The sun gives
  light The sunlight that we see The sunlight
  comes from our own sun's Atomic energy
  Scientists have found that the sun is a huge
  atom-smashing machine. The heat and light of the
  sun come from the nuclear reactions of hydrogen,
  carbon, nitrogen, and helium. The sun is a mass
  of incandescent gas A gigantic nuclear furnace
  Where hydrogen is built into helium At a
  temperature of millions of degrees

• Why Does the Sun Shine?
• THEY MIGHT BE GIANTS
• The sun is a mass of incandescent gas A gigantic
  nuclear furnace Where hydrogen is built into
  helium At a temperature of millions of degrees
  Yo ho, it's hot, the sun is not A place where
  we could live But here on Earth there'd be no
  life Without the light it gives We need its
  light We need its heat We need its energy
  Without the sun, without a doubt There'd be no
  you and me The sun is a mass of incandescent
  gas A gigantic nuclear furnace Where hydrogen
  is built into helium At a temperature of
  millions of degrees The sun is hot It is so
  hot that everything on it is a gas iron, copper,
  aluminum, and many others.

p-p chain!
CN cycle!
98
Direct observation of nuclear processes in the Sun

• Since the sequence of events, the variety of
  reactions, and the number of assumptions are so
  numerous, direct verification of the postulated
  nuclear reaction is desirable
• The most promising observations would involve
  measuring the neutrinos emitted in the nuclear
  reactions
• Neutrinos can easily escape the Sun
• If astronomers could detect these neutrinos, they
  would have a means of probing the reactions
  occurring at Suns core.

99
Direct observation of nuclear processes in the Sun

• Early attempt by Ray Davis and colleagues
• Looked for neutrinos via
• 37Cl n 37Ar e-
• 37Ar is radioactive and decays emitting an x-ray
  which can be recorded

100
Missing neutrinos
The 37Cl neutrino detector is a tank containing
100,000 gallons of perchloroethylene in the
cavity 4,850 feet below ground in the Homestake
Mine in Lead, S.D
101
Missing neutrinos
But only 1/3 of the expected number of neutrinos
from the Sun were detected Maybe there are 3
kinds of neutrinos that can change into one
another If so, then Ray Davis detector would
only have detected 1/3 of the expected number of
neutrinos emitted by the Sun
102
Neutrino oscillations

• Changing from on type of neutrino to another is
  called neutrino oscillation
• If neutrinos oscillate, it implies neutrinos have
  mass

103
Super-Kamiokande

• Neutrinos can interact in water and give rise to
  Cherenkov light
• The Cherenkov light provides information about
  the neutrino energy, direction, and type
• This light can be detected by phototubes lining
  the inside of the Super-Kamiokande detector which
  is filled with water
• In 1998, Super-K determined that neutrinos
  produced in the atmosphere by cosmic rays do
  oscillate

Super-K
104
Neutrino detectors

• In 2001, evidence of oscillation of solar
  neutrinos was found in the combined data from
  Super-K and the Sudbury Neutrino Observatory
  (SNO)
• Since then, these oscillations have been
  confirmed using man-made neutrino beams

SNO
105
Missing neutrinos get 2002 Nobel Prize
"for pioneering contributions to astrophysics, in particular for the detection of cosmic neutrinos" "for pioneering contributions to astrophysics, which have led to the discovery of cosmic X-ray sources"
Raymond Davis Jr. Masatoshi Koshiba Riccardo Giacconi
  1/4 of the prize   1/4 of the prize   1/2 of the prize
USA Japan USA

University of Pennsylvania Philadelphia, PA, USA University of Tokyo Tokyo, Japan Associated Universities Inc. Washington, DC, USA
b. 1914 b. 1926 b. 1931(in Genoa, Italy)

106
Missing neutrinos get 2002 Nobel Prize
Raymond Davis Jr constructed a completely new
detector, a gigantic tank filled with 600 tons of
perchloroethylene, which was placed in a mine.
When a neutrino hits a Cl atom, it can convert
one of its neutrons into a proton, creating a
radioactive atom of Ar. By measuring the amount
of Ar produced, one can infer how many neutrinos
were detected. Over a period of 30 years he
succeeded in capturing a total of 2,000 neutrinos
from the Sun and was thus able to prove that
fusion provided the energy from the Sun. With
another gigantic detector, called Kamiokande, a
group of researchers led by Masatoshi Koshiba was
able to confirm Daviss results.
107
Solar model

• How does the energy produced in the core of the
  Sun get to us?
• By combining theoretical modeling of the Suns
  interior with observations of the energy that the
  sun produces, astronomers have created the
  standard solar model
• This is a mathematically-based picture of the
  structure of the Sun.
• The model seeks to explain both the observable
  properties of the Sun and the properties of the
  unobservable interior

108
Solar model

• There are 3 methods of energy transport
• Conduction
• Convection
• Radiation

109
Solar model

• Experience tells us that energy always flows from
  hot regions to cooler ones
• The efficiency of this method, called conduction,
  varies significantly from one substance to
  another
• Conduction is not an efficient means of energy
  transport inside stars like the Sun
• It is important in compact stars like white
  dwarfs (later lecture)

110
Solar Model

• In the Sun, energy moves from the center to the
  surface by convection and radiative diffusion
• Convection zone
• Radiation zone

111
Solar Model

• Core
• At the very high temperatures of the core, all
  matter is completely ionized (stripped of its
  electrons).
• Photons move slowly out of the core into the next
  layer of the suns interior, the radiation zone

112
Solar Model

• Radiative zone
• Here the temperature is a bit lower, and the
  photons emitted from the core of the Sun interact
  continuously with the charged particles located
  there, being absorbed and re-emitted
• This is called radiative transport
• This occurs 80 of the way out to photosphere in
  the radiative zone

113
Solar Model

• Convection zone
• While the photons remain in the radiative zone,
  heating it and losing energy, some of the energy
  escapes into the convection zone.

114
Solar Model

• Convection zone
• Here hot gases rise to the photosphere and
  cooling gasses sink back into the convection zone
• Convection cells become smaller and smaller,
  eventually becoming visible as granules at the
  solar surface (photosphere).

115
Solar model

• At the Suns surface, a variety of processes give
  rise to the electromagnetic radiation that we
  detect from Earth. Atoms and molecules in the
  photosphere absorb some of the photons at
  particular wavelengths giving rise to the Suns
  absorption-line spectrum
• Given the temperature of the Sun, most of the
  radiation is emitted in the visible part of the
  spectrum, in agreement with the blackbody curve
  for a body at that temperature

116
Helioseismology

• The sun vibrates discovered in 1960
• Can study these vibrations to learn about the
  interior.
• Learned that the convective zone is twice as
  thick as first thought
• Below the convective zone, the Sun rotates as a
  rigid body (not differentially)

117
Helioseismology

• With a technique that uses ripples on the Sun's
  visible surface to probe its interior, SOHO
  scientists have, for the first time, imaged solar
  storm regions on the far side of the Sun, the
  side facing away from the Earth.
• The new technique, which uses the Michelson
  Doppler Imager (MDI) instrument on SOHO, gives a
  warning of storms by creating a window to the far
  side of the Sun.

118
The Sun's motion around the Galaxys
center

• Using the VLBA, astronomers plotted the motion of
  the Milky Way and found that the Sun is orbiting
  the Galaxy at about 135 miles per second.
• Used the motion of Sagittarius A relative to
  distant quasars

135 miles/sec
Sgr A
119
The Sun's motion around the Galaxys
center

• The spiral arms extend in a direction opposite to
  our motion
• At the moment, the motion of the Sun is toward
  the constellation of Hercules

135 miles/sec
Sgr A
120
The Sun's motion around the Galaxys
center

• It takes the Sun 226 million years to orbit the
  Galaxy
• The last time the Sun was at this spot of its
  Galactic orbit, dinosaurs ruled the world
• The period of time is called a cosmic year
• The Sun has orbited the Galaxy about 20 times
  during its 5 billion year lifetime

135 miles/sec
Sgr A