Download STARS


Structure of the Sun

Starting at the center
and working
outward
 The Core
 The Radiative Zone
 The Convective Zone
 The Photosphere
 The Chromosphere
 TheCorona
Core
•Innermost
region of
the Sun
•Contains about 10%
of the Sun’s mass
•Nuclear Fusion
occurs here
•Nuclear Fusion- A
nuclear reaction in
which atomic nuclei
of low atomic
number fuse to form
a heavier nucleus
with the release of
energy.
Radiative
Zone
•Energy
is
transported away
from the core by
photons. A photon
is what carries light
over space
•Photons are
absorbed and
scattered in random
directions
•It takes them
100,000 years to
make its way
through the zone
Convective
Zone

In the region surrounding the
radiative zone, heat is
transferred by convection:




A blob of gas near the bottom of
the region is heated by photons
emerging from the radiative
zone
The blob expands, becomes
buoyant, and rises
Near the Sun’s surface, the blob
is surrounded by cooler gas, so
it releases it’s heat to its
surroundings
Cooled, the blob becomes more
compact, then sinks back down
where the cycle will begin again

Photosphere
The visible surface of
the Sun lies at the top of
the convection region
 The presence of the
convective blobs
reaching the surface
and cooling makes the
photosphere appear
splotchy or grainy.
This effect is called
granualtion.

Photosphere
Features of the Photosphere



The presence of strong
magnetic fields at the Sun’s
surface can divert away hot
blobs of gas convecting
towards the surface
This causes cool spots to
form, 4,00 Kelvin as opposed
to the normal temp of 6,000
Kelvin
These cool regions appear as
sunspots and are often wider
than the Earth

Chromosphere



It is a thin layer, about 10,000
km, above the photosphere
Temperature is 10,000 K. It is
hotter than the photosphere
and we believe it is caused by
the Sun’s magnetic field but
we are not exactly sure
Most light emanated from the
chromosphere is reddish due
to H-alpha emission.
H-alpha emission can be seen
when Hydrogen’s one
electron moves from the first
energy level to the second
Corona



The corona is a large, low
density envelope
surrounding the Sun.
It is heated by the Sun’s
magnetic field and its
temperature is roughly
1,000,000 K.
The corona is the origin of
solar X-ray emissions
Magnetic
Activity in the
Corona




Plasma in the corona often
becomes trapped in magnetic
field loops.
These arcs of hot glowing
ionized gas are called
prominences and can be very
large
Some loop-like prominences
are short-lived, lasting only a
few minutes. Others can be
more stable, lasting hours or
days
Plasma consists of a collection
of free moving electrons and
ions.
Solar
Flares



Magnetic field lines in the
corona can become kinked
and break. Eventually they
reconnect with A LOT of
energy that needs to be
released.
The release of energy appears
as a solar flare which is an
extremely bright region on
the sun
Strong flares can affect
satellite communications
disrupting TV’s and phones
Solar
Flares

The earth itself is strongly
protected by its magnetic
field. When there is a great
deal of solar activity we
experience this as a beautiful
display of Aurora Borealis
reaching out from the North
and Aurora Australis
reaching out from the south
Coronal Mass
Ejections


Coronal mass ejections occur
when massive solar
explosions blast through the
Sun's outer atmosphere and
plow toward Earth at speeds
of thousands of miles per
second
They occur during a solar
flare. Large amounts of
plasma are ejected from the
Sun
Coronal Mass
Ejections



If directed towards the Earth,
CME’s could interfere with
communications, satellites,
cause power outages,
damage electronics, and even
endanger the lives of
astronauts.
Extremely large CME’s could
severely damage power grids
world wide. It is possible that
we could be without power
for months or even years.
It is not an impossibility that
we could see this happen
Coronal Mass
Ejections

Normal Conditions:
Earth’s magnetic field
typically deflects the charged
particles streaming out from
the sun, carving out a
teardrop-shaped volume
known as the magnetosphere.
On the sun-facing side, the
boundary, or magnetopause,
is about 60,000 kilometers
from our planet. The field
also traps particles in a
doughnut-shaped region
known as the Van Allen belts.
Coronal Mass
Ejections
First Stages of Impact:
When the sun fires off a
coronal mass ejection
(CME), this bubble of
ionized gas greatly
compresses the
magnetosphere. In
extreme cases such as
superstorms, it can push
the magnetopause into
the Van Allen belts and
wipe them out.

Coronal Mass
Ejections
Magnetic Reconnection:
The solar gas has its own
magnetic field, and as it
streams past our planet,
it stirs up turbulence in
Earth’s magnetic field. If
this field points in the
opposite direction as
Earth’s, the two can link
up, or reconnect—
releasing magnetic
energy that accelerates
particles and thereby
creates bright auroras
and powerful electric
currents.
Solar
Cycle



Solar magnetic phenomena
like sunspots, prominences,
flares, and CME’s do not
happen at random intervals.
The magnetic field at the
surface of the Sun varies in
strength over time, reaching
peak strengths roughly every
11 years.
This cycle is due to the Sun’s
differential rotation-The Sun
rotates more quickly at the
equator than at the poles
Solar
Cycle



As the Surface of the Sun
rotates differentially, it
carries magnetic field lines
with it, warping them with
time.
After several years, the
warped field lines begin to
kink.
It is at these kinks that
sunspots, prominences, and
flares occur
Solar
Cycle
The Maunder
Minimum



From 1645 to 1715, almost no
sunspots were observed.
This period of time correlates
to the time known as the
“Little Ice Age” during which
temperatures in Europe and
North America reached
record lows- records that
have still not been broken.
Whether there is a casual
connection between the solar
cycle and climate on Earth is
still uncertain and debated.
The Maunder
Minimum



Roughly ever 11 years, the
magnetic activity reaches a
peak- the so called “solar
maximum.”
At this point the magnetic
field of the Sun has become
so twisted and messed up
that the entire polarity of the
Sun flips- the north pole
becomes the south pole and
vice versa.
Most of the kinked field lines
snap and reform in a simpler
configuration
The Maunder
Minimum


The Maunder Minimum is a
long period wherein sunspot
occurrence was noticeably very
low.
Data gathered by astronomers
reveal a 30-year duration within
the Maunder Minimum
wherein only 50 sunspots were
accounted for. Compare that to
the usual 40,000 to 50,000
recorded in more recent years