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THE SUN
Structure & Function
STRUCTURE OF THE SUN
Our Nearest Star
THE SUN’S INTERIOR

Core
Comprises about 25%
of sun’s interior
 site of nuclear fusion


Radiative Zone


Energy produced in
the core is carried
outward by photons
over LONG periods of
time
Convective Zone

Energy is carried
outward by convection
It takes photons produced through fusion from 100,000 to 1,000,000
years to move from the core to the edge of the convective zone
THE SUN’S ATMOSPHERE
THE SUN’S ATMOSPHERE: THE PHOTOSPHERE



Lower atmosphere or
“surface” of the sun
The only part of the sun we
can normally see
Granulation
 “Blotchy” appearance
 Granules are convection
cells in the photosphere
 Brighter areas are hotter
SOLAR GRANULATION ON PHOTOSPHERE
THE SUN’S ATMOSPHERE: THE CHROMOSPHERE



Visible during a solar
eclipse or with the use of
filters
Appears pink because
the gas here only emits
certain wavelengths of
light, mostly red
“spiky” surface due to
jets of gas that surge
upward
THE SUN’S ATMOSPHERE: THE CORONA


Extremely hot
temperature and low
density
Only seen using special
filters (or during an
eclipse)
THE HELIOSPHERE


The immense
electromagnetic bubble
containing our solar
system, solar wind, and
the entire solar magnetic
field.
It extends well beyond
the orbit of Pluto, but
within the Oort cloud.
SOLAR PHENOMEMA
SOLAR WIND


High-speed charged
particles (mostly
electrons and
protons) constantly
blowing off the Sun.
May be viewed as an
extension of the outer
atmosphere of the
Sun (the corona) into
interplanetary space.
Computer
image
SUNSPOTS



Can be seen on the
granular photosphere
Sunspots are cooler than
the photosphere at about
3800 K
Indicate magnetic
disturbances on the sun.


Sunspots reach a
maximum about
every 11 years
By tracking
sunspots,
astronomers have
determined that it
takes the Sun 27
days to rotate at the
equator, but 31
days at the poles


large regions of
very dense ionized
gas ejected from
the photosphere
and held in place
by the sun’s
magnetic fields
Return back to the
surface of the sun
along magnetic
field lines

Prominences may
stretch 150,000
Km or more along
the sun’s surface
(10x the size of
the Earth)
SOLAR FLARES
SOLAR FLARES
short-term outbursts on the sun, caused by the
sudden release of energy stored in twisted
magnetic fields in the solar atmosphere.
 release up to 1025 joules of energy—the energy
equivalent of ten million volcanic eruptions.
 They can last just a few minutes or up to
several hours.

EFFECTS OF SOLAR FLARES



Tremendous amounts of
energy flung into space,
including high-energy
particles and electromagnetic
radiation
When the radiation and
particles reach the Earth's
magnetic field, they interact
with it to produce auroras.
Solar flares can also disrupt
communications, satellites,
navigation systems and
power grids.
THE AURORA BOREALIS (NORTHERN LIGHTS)


This is an photograph of
the Big Dipper shining
through green-colored
aurora in the skies above
Washington State.
http://news.nationalgeographic.
com/news/stunning-time-lapsereveals-auroras-and-earth-fromspace/
CORONAL MASS EJECTION (CME)



Coronal mass ejections
can carry up to 10 billion
tons of plasma traveling at
speeds as high as 2000
km/s.
Near solar maximum we
observe an average of 2 to
3 CMEs per day
Thought to arise when the
sun’s magnetic fields
suddenly rearrange,
releasing an enormous
bubble of matter
NUCLEAR FUSION
Converting mass to energy
NUCLEAR FUSION ACTIVITY


Complete activity modeling nuclear fusion
Watch this video:


https://www.youtube.com/watch?v=Ux33-5k8cjg
Answer the questions on your wkst
NUCLEAR FUSION

The luminosity of a star is powered by nuclear
fusion taking place in the centre of the star
 The
temperature and density are sufficient to allow
nuclear fusion to occur.
 Stars are primarily composed of hydrogen, with
small amounts of helium.
 They are so hot that the electrons are stripped from
the atomic nuclei.
 This ionized gas is called a plasma.
THE PROTON-PROTON CHAIN

At temperatures above 4 million Kelvin
hydrogen nuclei fuse into helium
RUNNING OUT OF HYDROGEN
The star is kept in a delicate balance between
gravity trying to collapse it and radiation
pushing it outwards.
 As the hydrogen runs out, the energy released
from fusion decreases and the gravity causes
the star to collapse.
 If the star is massive enough the core
temperature increases until helium fusion
starts.

HELIUM BURNING

At temperatures above 100 million Kelvin
helium can be fused to produce carbon. This
reaction is called the “Triple Alpha process”
HEAVIER ELEMENTS

Helium is fused with carbon to make heavier
elements:
 oxygen,
neon, magnesium, silicon, sulphur, argon,
calcium, titanium, chromium and iron

It’s impossible to make elements heavier than
iron through nuclear fusion without putting in
more energy.
RUNNING OUT OF HELIUM
Eventually the helium is exhausted, and the
star collapses again.
 If it is massive enough, then the temperature
increases enough to allow carbon fusion.
 The cycle repeats, fusing heavier elements
each time, until the core temperature cannot
rise any higher.
 At this point, the star “dies”.
