Our Star
KATHRINE CARRICK
Why does it shine?
o During the 19th century astronomers had a
theory called gravitational contraction which
suggests that the sun generates its energy by
slowly contracting in size.
o However later studies showed that
gravitational contraction could not be the way
the sun was generating its energy.
Formation
o The true answer to the suns generation of energy came with Einstein's theory of E- mc^2. This
equation showed that mass itself contains an enormous amount of potential energy. In the
1930s this idea led to the theory that the sun uses nuclear fusion to generate its energy.
Nuclear Fusion
o Nuclear fusion is the process of joining two
or more light weight small nuclei into a larger
one.
o This process occurs because the suns
temperature is so hot that the positively
charged nuclei move around at high speeds
until they collide with each other.
o However sticking positively charged nuclei
together is not easy but the strong force is
what binds a protons and neutrons together.
oThis process of nuclear fusion combines four
hydrogen nuclei into one helium nucleus,
releasing energy in the process.
Core
o Located in the center of the star is the suns
core. Here the temperature raises to about 15
million K. The density is 100 times the density
of water on earth and the pressure is 200
billion times that on the surface of the earth.
o The core is also where nuclear fusion occurs
transforming hydrogen into helium which will
take about a few hundred thousand years to
reach the surface.
Radiation Zone
o Located about a third of the way to the Suns
center, is what we call the Radiation Zone. In
this layer energy moves outward mostly in the
form of photons. Here, the temperatures rises
to nearly 10 million K and x rays are very
intense.
o Again, this picture shows where the Radiation
Zone in located within the sun.
Convection Zone
o The Convection Zone is the first layer of the
suns interior. This is where energy generated
from the suns core travels upward,
transported by the rising of hot gas and falling
of cool gas called convection.
o The diagram to the right depicts the different
layers of the Sun, showing the convection
occurring in this particular layer.
Atmosphere
o Solar Winds blow a stream of charged particles continually outward from the sun in all
directions
o The Suns atmosphere is defined as low density gas
o The Chromosphere is the first layer which is extremely hot, at about 1 million K, but has very
low density.
o The second layer, or Photosphere which is much cooler compared to the chromosphere, is also
considered the visible surface of the sun. However it may look like a surface, the photosphere is
comprised of gas less dense than the earths atmosphere. The temperature is slightly under 6000
k resulting in the effect of a boiling pot of water.
Sunspots
o Sun Spots are defined as dark splotches on the suns surface which can be larger than Earth.
They are regions of strong magnetic fields, which keep the sun spots cooler than the
surrounding photosphere.
o Sun spots appear darker because they are less bright than the surrounding photosphere
oThe sunspot cycle is when the number and location of the sunspots vary depending whether it
is at solar maximum or solar minimum. The number of sunspots rises during solar maximum.
Solar flares & Prominences
o Similar to sunspots, solar flares and
prominences are all considered solar activity.
Solar activity being defined as solar weather.
o Solar prominences occur when gas in the
chromosphere and corona becomes trapped in
these giant loops formed by magnetic field lines.
o When magnetic field lines that cause solar
prominences and solar flares undergo sudden
changes, it creates intense solar storms know as
solar flares. During these storms, bursts of X rays
and fast-moving charged particles are shot into
space.
o Again, similar to sunspots, solar flares and
prominences change with the solar cycle.
Coronal Mass Ejections
o As a result of solar storms, large numbers of highly energetic particles are ejected from the
suns corona forming huge bubbles referred to as coronal mass ejections.
o A coronal mass ejection can reach earth which results in a geomagnetic storm. These storms
can produce very strong aurora borealis but on the down side they can effect radio
communications, disrupt electrical power delivery, and damage the electronic components of
orbiting satellites.