Download Our Star: The Sun

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The Sun
Structure
Atmosphere
Variability and Activity
Interactions with Earth
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AKHENATON
(1353-1335 BC)
THE HERETIC PHARAOH
“LE DIEU SOLEIL’’
ATON The Supreme SUN God
Monotheistic religion with a good natured
God, the disc of life giving Sun
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AMONG THE WORSHIPERS OF THE SUN:
Pharaoh Akhenaton (1353-1335 BC) “Dieu Soleil”
Roman Emperor Constantin (274-337) “Sol Invictus”
King Louis XIV (1643-1715) “Roi Soleil”
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Solar flare affects communications, disruptions possible
Thursday, September 8, 2005; Posted: 7:36 a.m. EDT (11:36 GMT)
The solar flare is fourth largest in the last 15 years, a solar forecaster said.
• NOAA Space Environment Center
WASHINGTON (AP) -- A large solar flare was reported Wednesday and forecasters
warned of potential electrical and communications disruptions.
The flare was reported by the National Oceanic and Atmospheric Administration's
Space Environment Center in Boulder, Colorado.
Significant solar eruptions are possible in the coming days and there could be
disruptions in spacecraft operations, electric power systems, high frequency
communications and low-frequency navigation systems, the agency said.
"This flare, the fourth largest in the last 15 years, erupted just as the ... sunspot cluster
was rotating onto the visible disk of the sun," said Larry Combs, solar forecaster at the
center.
The flare has affected some high-frequency communications on the sunlit side of
Earth, NOAA reported.
Copyright 2005 The Associated Press
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The Sun
 The sun is a huge ball of fire.
 A million Earths can fit inside the sun.
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 The sun is a normal star.
 There are two hundred billion stars in the
Milky Way galaxy.
 We observe BILLIONS of galaxies in the
universe.
Basic Solar Information
 The sun is a gaseous fire ball with:
 Mass: 1.991033 gm
 Radius: 6.961010 cm
 Mean Density: 1.41 gm/cm3
 Surface Temperature: 5780 K
 Rotational Period: 25 days (at equator)
 Luminosity: 3.851033 erg/sec
 Distance from Earth: 1.496108 km
 The sun is a Main Sequence star.
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Birth of the Sun and Solar System
 The sun was
formed 5 billion
years ago by the
gravitational
collapse of an
interstellar cloud.
 Debris left behind
formed the planets,
satellites, and
asteroids.
The Solar System
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Solar-Earth Interaction
 The sun is continuously active with
storms and flares.
 These greatly affect the Earth and its
atmosphere.
Evolution of the Sun
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The Core
 The core of the sun is the place where nuclear
fusion reactions power the sun.
 It is approximately 15106 K.
 The sun has been burning for 5 billion years
and theoretically should continue burning for
another 4 to 5 billion.
 Should the core stop burning the star’s
luminous life would be at an end.
The Proton-Proton Chain
Reaction
 Three steps complete this fusion reaction:
1H
+ 1H
 2H + e+ + 
2H
+ 1H
 3He + energy
3He
+ 3He  4He + 1H + 1H + energy
 Net effect reaction:
4(1H)
 4He + energy
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The CNO Cycle
 Six steps complete this fusion reaction:
12C
13N
+ 1H  13N + 
 13C + e+ + 
13C
+ 1H  14N + 
14N
+ 1H  15O + 
15O
15N
 15N + e+ + 
+ 1H  12C + 4He
Solar Interior
 Radiative zone:
 Energy is
transported by
electromagnetic
radiation
 Convection zone:
 Energy carried
by convection
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Photosphere
 This is the visible layer of the sun.
 It has a density low enough to allow light to
escape.
 The photosphere is
gaseous and very
thin ~ 500 km, and
is covered by
granules and
supergranules
(boiling bubbles).
Granulation
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Granulation
 Granules cover the surface of the photosphere,
and are surrounded by darker boundary regions.
 The granules are rising gas that is hotter than the
sinking gas of the boundaries.
 They are about 1000 km (the size of Texas) and
each lasts several minutes.
 Supergranules measure about 30000 km across
and are believed to be caused by large, deep
convective cells under the photosphere.
Chromosphere
 Very faint layer above the photosphere, which is
about 10000 km thick.
 Only visible during a total solar eclipse.
 Spicules fire up through the chromosphere, these
originate along the edges of supergranules.
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Heliosiesmology
 This is the study of
the vibrations of the
sun using the Doppler
Effect.
 We are able to
estimate the interior
of the sun this way.
 Analogous to
measuring seismic
waves in an
Earthquake.
Corona
Solar Outermost Thin Atmosphere
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Corona
Solar Outermost Thin Atmosphere
 The corona is much hotter (2 million Kelvin) than
the surface of the sun and has a density much
lower than the photosphere. It is normally seen
during a total solar eclipse.
 It is believed the magnetic field of the sun carries
energy from the photosphere to the corona, thus
heating it.
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Corona
Solar Outermost Thin Atmosphere
 It changes size and shape according to the stage
of the solar cycle.
 Occasionally releases magnetic energy into the
solar wind, which interacts with the Earth’s upper
atmosphere, causing auroras, and the possibility
of triggering a magnetic storm causing strong
electrical currents to run through the earth.
Coronal Mass Ejections
Earth Is Shown For
Size Comparison
Earth
Magnetic Cloud
Coronal
Mass
Ejection
SUN
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Solar Wind
 Hot gases and EM radiation escape from the
corona constantly and are unleashed into the
solar system.
 The matter in the corona is constantly
replaced by matter from the underlying layers.
 This wind interacts with Earth’s own magnetic
field.
Sunspots
 These are dark “spots” on the sun’s photosphere
which are about a few times the size of Earth.
 They often occur in groups and they vary in
duration lasting anywhere from a few days to a
few months.
 At any one time dozens of sunspots to none at all
can be seen on the sun.
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Sunspots
 The darker appearance is because sunspots are
cooler (4500 K) than the surrounding photosphere.
 The center of the sunspot is known as the umbra,
and the outer region is the penumbra.
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The Sunspot Cycle
 Sunspots are associated with strong
magnetic fields and are probably
magnetically interconnected below the
photosphere.
 Every 11 years the number of sunspots
hits a maximum then declines, this cycle
has been known for 100’s of years.
The Sunspot Cycle
1850 1860
1870
1880 1890
1900 1910
1920
1930 1940
1950 1960 1970
1980 1990
2000
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The Maunder Minimum
Magnetic Field and Sunspots
 The magnetic field in sunspots has been
measured to be 1000 times stronger than the
surrounding photosphere.
 Sunspots are caused by localized magnetic
enhancements through the photosphere.
 Sunspots are polarized with respect to which
hemisphere they occupy. The northern
hemisphere sunspots are oppositely polarized
from those in the southern hemisphere.
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The Solar Cycle
 A full solar cycle is 22 years in duration.
 Every 11 years the magnetic polarity of the
sun reverses.
 Thus for a full cycle to complete two
polarity reverses must occur.
Prominences
 These arch-shaped explosions of hot
ionized gas stem from groups of sunspots.
 They are thought to be caused by
magnetic instabilities around the sunspots.
 Eruptive prominences may shoot up to
500,000 km in a few hours.
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Prominences
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Solar Flares
 Flares are eruptions on
the surface of the sun
which seem similar to
prominences.
 Solar flares may only last
minutes or hours, and
releases enormous
amounts of energy.
Solar Flares
 The energy equivalent of that released by solar
flares is comparable to millions of 100 megaton
hydrogen bombs exploding at the same time.
 Flares almost always occur near sunspots, thus
linking them to magnetic field activity.
 A large fraction of radiation from flares escapes
the sun and some interacts with Earth.
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The Sun-Earth Relationship
 The sun affects many facets of life on Earth.
 Even small permanent changes in solar weather
would destroy much of life on Earth.
 Space weather can disrupt communications,
the power grid, and cause variations of the
Earth’s atmosphere.
Climate and Weather
 Surface temperatures, cloud cover, drought,
rainfall, tropical cyclones, and forest fires all
mutually compare to the sunspot cycle.
 Coronal ejections into the solar wind are the
cause of auroras often seen in the Northern
latitudes.
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Technology
 Coronal mass ejections increase the ionization in Earth’s
ionosphere which interferes with shortwave radio signals.
 Coronal ejections also are the cause of electrical ground
currents running through the earth, historically burning
telegram wires and starting fires. These currents can
greatly disrupt power grids causing blackouts to millions at
great cost.
 Recent strong solar flares have caused complete failure of
electronic systems on several artificial satellites.
Radiation
 Normally, the radiation received from the sun
is thought as inconsequential, this is ignoring
abnormally prolonged exposures.
 However, astronauts and airline crews, with
their higher altitude careers are exposed to
more radiation than the average person on the
ground, and this amount of radiation is
increased when solar flares erupt.
 Enhanced solar radiation reaching the Earth is
harmful to life and could be fatal.
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The Sun
 Arguably the sun is the
most important energy
source for life.
 Understanding the activities
of the sun better will allow
for predictions of potentially
damaging flares and bursts
that may even threaten life
on Earth.
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