Transcript dtu7ech10sun - Fort Thomas Independent Schools

CHAPTER 10:
The Sun: Our
Extraordinary
Ordinary Star
What do you know about the
Sun?
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Brightest object in our Solar system
Center of our S.S.
Hot
Large (largest object in the solar system)
Star
Can cause blindness
Fusion at the core
Plasma state
Solar Wind
Has been worshipped as Ra
Gives us light
Planets orbit the Sun
Layered
Rotate
Average sized star
THE SUN
Overview
The Sun is a huge ball of hot gas
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Primary component is hydrogen
Secondary component is helium
tiny amounts of other elements are recognized by spectral
analysis of surface gases
Size
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100 Earths across in diameter
one million Earths would fit inside
Contains 99.85% of the mass in the solar system
If the Sun was as close to the Earth as the Moon, it would
consume 2/3 of the sky.
Age
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Estimated at 5 billion years old
It will be another 5 billion years until it begins to die
BIRTH
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Rotating nebular dusts and gases condense and
flatten, producing a protoplanetary disk and
protosun at the center.
Temperature of the protosun continues to rise as
more matter collapses inward.
If the temperature at the core of the protosun
rises above 10 million Kelvin, then fusion of
hydrogen into helium nuclei occurs.
The Sun becomes a star at this time.
ANATOMY OF THE SUN
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Internal Structure--The Sun has three
internal layers
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Deep, dense, hot core (+ 10 million Kelvin)
A radiative zone
A convective zone
THE SOLAR
INTERIOR
Internal Structure
Thermonuclear Core (25 % of radius)
 Radiative zone (55 % of radius)
 Convective zone (20% of radius)
 Photons created in the core take 170,000
years to make the journey through the
radiative zone.
 Hot gas rises and falls in the convective
zone, eventually reaching the surface of
the Sun.
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The Core
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Fusion at the core
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The crushing, immense weight of the outer
layers compresses the gas and increases its
temperature
When the temperature reaches 10 million
Kelvin, fusion of hydrogen into helium
begins
Fusion of hydrogen into helium releases
energy at the expense of mass
The Sun is powered by thermonuclear fusion,
which converts hydrogen into helium.
Radiative Zone
It takes about 170,000 years for the energy
released from the core to travel through the
radiative layer.
 Photons created at the core carry the energy
through this layer
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Convective Zone
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This energy heats up the gases in the this
zone and delivers its energy to the Sun’s
surface by convection (hot, less dense gases
rise and cooler, more dense gases sink)
Why does the Sun stay a
constant size?
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Outward pressure due to hydrogen fusion
is balanced by the inward pressure of the
overlying gases (hydrostatic equilibrium).
The Sun’s interior is held stable by a balance between
pressure forces and gravity, in a condition called
hydrostatic equilibrium.
Outer layers of the Sun
Photosphere (5800 K, low density, 0.01%
of air at sea level)
 Chromosphere (4000 K – 10,000 K, less
dense than photosphere)
 Corona (1 million K, extremely low
density—10 trillion times less than air at
sea level)
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Photosphere
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Light energy (mostly in the form of visible light,
and a smaller percentages of UV rays and
infrared light, x-rays, gamma rays, microwaves
and radio waves) is released from the Sun’s
surface, which is 5800 Kelvin in temperature.
The density of the photosphere (Sun’s surface)
is 0.01% of the air that we breathe.
Granulated surface represents the rising and
falling hot gases
Darker areas represent cooler temperatures
The bright visible surface of the Sun is
called the photosphere.
When looking at the Sun,
the edges appear orange
and darker than the
central yellow region.
This is known as limb
darkening.
Upon closer inspection, the Sun has a marbled pattern called
granulation, caused by the convection of gases just beneath the
photosphere.
During an eclipse, sometimes you can see the layers of the Sun’s
atmosphere just above the photosphere, which emits only certain
wavelengths of light, resulting in a reddish appearance. We call this the
sphere of color, or chromosphere.
The solar chromosphere is characterized by jets of gas
extending upward called spicules.
Corona
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Hot, ionized extremely thin gas up to 1 million
K
caused by the Sun’s complex magnetic fields
charged particles are moving so fast that they
can escape the gravitational pull of the Sun.
This is the solar wind.
Sun ejects about a million tons of matter per
second
matter travels fast (2.9 x 106 km/h)
5 particles per cc by time it reaches the Earth
(atm 6 x 1019 particles per cc)
THE SOLAR CORONA
This x-ray image shows the milliondegree gases.
Seen in visible light during an Bright areas are where the Sun’s magnetic field is so
eclipse.
strong that it trap the super heated gases of the
Corona. Darker areas represent coronal holes. This
is where the solar wind originates (700 km/s).
The temperature of the solar
gases increase with distance
from the solar surface.
Within the narrow transition
region between the
chromosphere and the
corona, the temperature
increases by 100 times.
Surface Features of the Sun
Sunspots
 Plages
 Filament (a top view of a prominence)
 Prominences
 Solar Flares
 Coronal Mass Ejections
 All are due to changes in solar magnetic
fields
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Sunspots are regions of intense magnetic fields
For sunspots to form, the magnetic field lines of the Sun become
intertwined after several rotations, creating regions of intense
magnetic fields. Sunspots are produced at distortions along
these field lines.
Coronal loop of hot electrified gas
can be 300,000 miles high and
span 30 Earths.
It takes the Sun 25 days to rotate at its equator,
and 35 days to rotate at its poles. Its rotational
speed is roughly 2 km/s.
Sunspots
Overlapping
sunspots
Sunspots have two regions: the
inner, darker umbra and the outer
penumbra.
Darker regions of the Sun are
cooler than the brighter yellow
regions.
The number of sunspots on the photosphere varies
over an eleven-year cycle.
Sunspot Maximum
Sunspot Minimum
Sunspot max to min to max = 22 years
Sunspots
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Sunspot cycle is 11 years from sunspot
maximum to minimum (22 years for full cycle)
10,000 km across
A sunspot develops at a place where the
magnetic field pokes through the photosphere
A plage is a bright spot associated with an
emerging magnetic field that compresses and
heats up gases.
Differential rotation of the Sun leads to
overlapping magnetic fields which leads to
unstable conditions on the photosphere
Sunspots can be used
to determine the rate
of the sun’s rotation.
Prominances
Arched volumes of hot gas pushed up by
magnetic field.
 Upward of 50,000 K
 Almost always associated with sunspots
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Solar Flares
Violent, eruptive event
 Associated with sunspot activity
 Releases vast quantities of high energy
particles and x-ray and uv rays.
 Powerful, will leave Sun’s surface quaking
for an hour or more
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Coronal Mass Ejections
Largest ejection event
 8 minutes for light
 2-4 days for charged particles
 These ejections overwhelm the Van Allen
Belts (earth’s magnetic field) and lead to
dramatic aurorae and potential disruptions
of communications.
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Viewing the Sun with an H-Alpha filter reveals an
active chromosphere during a sunspot maximum
Ionized gases trapped by magnetic fields form prominences
that arc far above the solar surface.
Sometimes these gases are ejected into space.
Violent eruptions called
solar flares eject huge
amounts of solar gases
into space.
By following the trails of gases released during a
solar flare, we can map the Sun’s global magnetic
field.
Coronal Mass Ejections (CMEs) typically expel 2
trillion tons of matter at 400km per second.
An x-ray view of a
coronal mass ejection
It reaches Earth two to four days
later, and is fortunately deflected
by our magnetic field.
Changes in
Physical
Properties of
Solar Gases
from the Solar
Core to the
Photosphere
A mystery involving
undetected neutrinos
produced in the Sun’s core
prompted an investigation into
the fundamental nature of
these particles.
Subsequent experiments
showed that neutrinos can
change as they travel through
space.
During the sunspot cycle, the latitude at which sunspots
appear changes.
A plot of the latitude of appearing sunspots over time reveals
that early in the sunspot cycle, they appear away from the
equator, then slowly move toward the equator as the cycle
progresses.
DEATH OF THE SUN
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The Sun does not have enough mass to explode
as a supernova (low mass star).
It is to become a red giant that will alternately
expand and contract in response to variations in
inward and outward pressure.
At some point, the star will expand and then
slowly release its outer gas layer. Up to 80 %
mass loss.
The carbon-oxygen core cools and is called
white dwarf.
WHAT DID YOU THINK?
How does the mass of the Sun compare
with that of the rest of the solar system?
 The Sun contains 99.85% of the solar
system’s mass.
 Are there stars nearer the Earth than the
Sun?
 No, the Sun is our closest star.
 Does the Sun have a solid and liquid
interior like the Earth?
 No, the Sun is composed of hot gases.
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WHAT DID YOU THINK?
What is the surface of the Sun like?
 The Sun has no solid surface, and no solid
or liquids anywhere. The surface we see is
composed of hot, churning gases.
 Does the Sun rotate?
 The Sun’s surface rotates differentially;
once every 35 days near its poles, and
once every 25 days near its equator.
 What makes the Sun shine?
 Thermonuclear fusion in the Sun’s core
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Key Terms
Cerenkov radiation
chromosphere
convective zone
core (of the Sun)
corona
coronal hole
coronal mass ejection
filament
granule
helioseismology
hydrogen fusion
hydrostatic
equilibrium
limb (of the Sun)
limb darkening
magnetic dynamo
neutrino
photosphere
plage
plasma
positron
prominence
radiative zone
solar cycle
solar flare
solar luminosity
solar model
solar wind
spicule
sunspot
sunspot maximum
sunspot minimum
supergranule
thermonuclear
fusion
transition zone
Zeeman effect
You will discover…
•why the Sun is a typical star
•how today’s technology has led to a new
understanding of solar phenomena, from sunspots to
the powerful ejections of matter that sometimes enter
our atmosphere
•that some features of the Sun generated by its varying
magnetic field occur in cycles
•how the Sun generates the energy that makes it shine
•new insights into the nature of matter from solar
neutrinos
The Sun undergoes
differential rotation.
The rotation period of
the Sun’s gases varies
from 25 days in the
equatorial region to 35
days near the solar
poles.
WHAT DO YOU THINK?
How does the mass of the Sun compare
with that of the rest of the solar system?
 Are there stars nearer the Earth than the
Sun?
 Does the Sun have a solid and liquid
interior like the Earth?
 What is the surface of the Sun like?
 Does the Sun rotate?
 What makes the Sun shine?
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Coronal holes are conduits for gases to flow out from the Sun