The Sun
By James Harkin
How do we know what the Sun is
made of?
We know what the Sun is made of because we know that atoms will absorb
very definite wave lengths and therefore very definite colours. When atoms are
excited each different type gives off very definite wave lengths and therefore
very definite colours; because we know this we know what elements are in the
Sun.
To see what visible light is emitted and absorbed from atoms we use a
spectroscope. If you look at white light through a spectroscope then you will
see all of the spectrum with different colours representing different wave
lengths. The full spectrum from white light is continuous and has no black lines
in it. This is called a continuous spectrum.
How do we know what the Sun is
made of?
Another type of spectrum is called an emission spectrum. In this
type of spectrum you look at an excited element through a
spectroscope. When you look through you will see coloured lines
on a black background. The coloured lines are the different
colours of light that the element gives off, with each colour
representing a certain wave length.
Here is the emission spectrum for hydrogen with the wave
lengths underneath.
How do we know what the Sun is
made of?
The last type of spectrum is the absorption spectrum. In this
spectrum you pass white light through a gas, and when it comes
out of the other side if you look at it through a spectroscope you
will see a spectrum with black lines in it. Because elements
absorb and emit the same wave lengths where the colour was in
the emission spectrum there will be black in the absorption
spectrum and where there was black in the emission spectrum
there will be colour in the absorption spectrum.
Here are the emission and absorption spectra for
hydrogen (the absorption spectrum is underneath).
How do we know what the Sun is
made of?
Now if you wanted to you could run a emission or an absorption spectrum on the Sun
and because each element gives out a different type of light you could see what
elements were in the Sun. Here is an absorption spectrum for the Sun.
On it there are thousands of different element absorption lines. The darker and wider the
line the more of the element that corresponds to it. For example the darkest widest lines
correspond to hydrogen the most common element in the Sun. The second most
common element in the sun is helium. In 1870 when an absorption spectrum was run
one set of lines in the yellow part didn’t correspond to any known element, so Lockyer
the man who had run the test named it Helium after the Greek Sun god Helios. 25 years
later Helium was discovered on Earth.
hydrogen
helium
helium
hydrogen
What is the Sun made of?
The Sun, as you know from the previous slide, is at the moment mainly
made up of hydrogen with quite a lot of helium. The composition of the
Sun is:
74% hydrogen (the must common element in the universe),
25% helium,
Carbon, nitrogen and oxygen make up just less than 1%,
The rest is made of many other elements such as neon, iron, silicon,
magnesium and sulphur.
Where does the Sun’s energy
th
from?
come people thought the Sun was powered by
In the early 19 century some very clever
coal. The only problem with this was that the Sun would burn itself out in a few
thousand years. The Sun actually gets its energy from a process called nuclear fusion.
In nuclear fusion nuclei of small atoms fuse together to form larger nuclei but in the
Sun’s case hydrogen is converted into helium; this is why the composition of the Sun is
always changing. Basically mass is converted into energy.
The conversion of hydrogen to helium can only happen under tremendous
pressure and heat because the nuclei must hit each other at tremendous speed. The
conversion happens in three stages; the first stage is when two hydrogen protons fuse
to make heavy hydrogen. Next a heavy hydrogen fuses with a hydrogen proton to
make unstable helium. Finally two unstable heliums fuse to form stable helium and
two hydrogen protons.
How does nuclear fusion convert
energy?
The reason why nuclear fusion creates energy is because the mass of the
products formed are slightly less than the starting mass. The mass that is not
there any more is converted into energy. To work out how much you must
understand Einstein's theory E=MC2 (energy=mass times the speed of light
times the speed of light). So the average mass lost per second is 4x1011g and
the speed of light is 3x108 m/s therefore the power output =4x1011x(3x108)2=
3.6x1028 watts. From working this out we know that the Sun’s energy output
which varies by about 0.1% is about 3.6x1028. Also, even though the Sun
looses 400,000 tons per second the Sun will keep going for another 5 billion
years. Of course people have tried to make energy by nuclear fusion but
present day results take up more energy than is made. However, if we could
harness the Sun’s power output for 1 second it would keep us going with
enough energy for the next million years.
Suns layers!
There are 7 layers in the Sun; the core (the centre of the Sun), the radiative
envelope, the convective envelope, the sub surface flows, the photosphere, the
chromosphere and the corona (the outer atmosphere of the sun). The core is
where nuclear fusion takes place and is about 15,000,000° C. The core also
has a very high pressure at 250 billion atmospheres; because of the pressure
light travels at less than 1 mm per second. This means the heat and light
produced in the centre of the sun takes 200,000million years to reach the
surface, but just another 8 minutes for it to reach the Earth. The core makes up
over half of the Sun’s mass, but occupies less than 2% of its volume.
Solar envelope
The Solar envelope is the second most inner layer and is made up of
two layers; the radiative envelope and convective envelope. In the
radiative envelope it is more efficient for heat and light to travel by
radiation so it does. By the time the energy reaches the convective
envelope it is more efficient for the energy to travel by convection so
it starts to travel in this way. The solar envelope puts pressure on
the core and maintains its temperature. The solar envelope contains
49% of the Sun’s mass but 90% of its volume. The solar envelope is
about 3900000°C.
The heat transfer in the solar envelope.
Photosphere
The photosphere is the surface of the Sun and is where the sunlight we see
is emitted. The photosphere is a very thin layer and is only about 6000°C
but still enough to vaporize solid rock. However, it still bubbles like a giant
bowl of porridge with bubbles 1000 miles across. Underneath the surface
of the Sun there is a complicated network of subsurface flows.
Sun spots
Sun spots are dark regions on the surface of the Sun about the size
of the Earth. They are of course only dark in comparison to the rest
of the Sun, but are still bright enough to blind you if you looked at
one. The spots are constantly moving. When observed the spots all
seem to move in the same direction, this showed the Sun is rotating
and other evidence showed it is faster at the equator than the poles.
Sun spots come and go in an 11/12 year cycle with sometimes their
being no sun spots at solar minimum and sometimes hundreds at
solar maximum. Sun spots also have an effect on our climate. For
70 years from 1645-1715 there were no sun spots on the surface of
the Sun.
This picture
shows how the
Sun changed
between 1991
and 1995.
Sun spots also have an effect on our climate.
For 70 years from 1645-1715 there were no sun
spots on the surface of the Sun. This correlated
almost exactly with the last period of prolonged
cold to strike the northern hemisphere. This is
sometimes referred to as the little ice age. In the
little ice age there wasn’t a huge dip in
temperatures; just a degree or two but it was
enough to have drastic effects. For example the
Viking colonies in Greenland were wiped out
and the population of Iceland fell by a half. Also
the Thames froze over which meant that fairs
were held on the ice. The cold wasn’t caused by
the solar output lessening, in fact no matter how
many sun spots there are the output never
changes.
If you look at the sunspots in the uv the sunspots
burn a bright white and through x-ray you can see
plumes of super heated gas erupting from the sun
spots. By placing a disc in front of the sun you can
simulate an eclipse. By doing this you will see solar
flares and coronal mass ejections which erupt from
the heart of sun spots.
The temperature in a solar flare is tens of
millions of degrees which means there is a
very dramatic change in temperature over
a short period of time. When they erupt
completely masses the same as Mount
Everest are flung out into the solar system.
Because there are fewer sun spots at solar minimum there
are therefore fewer flares and at solar maximum there are
more sun spots therefore more flares. The cause of these
explosions is not fusion but magnetism. The Sun is covered
in a complex network of magnetic fields. With the areas with
the strongest fields being the places where the Sun spots are.
At the sunspots the magnetism can be magnified 10,000
times. The sun spot magnetic fields are between 1000-3000
gauss which is roughly the same as a very strong household
magnet. The difference is that the sun spots are much bigger.
Sun spots are dark because strong magnetic fields prevent
some heat reaching the surface.
The magnetic fields can be seen using special equipment. This shows
they can arch 200000km high. If you were to add up the total energy
content of one of these loops it adds up to about 1021 joules of energy,
which is about 10 times the annual energy consumption of the USA, but
there are thousands of these loops. The loops are caused by the
twisting of the Sun’s basic magnetic field. This happens because when
the Sun rotates faster at the equator than the poles it drags and
stretches the fields. As the fields get more and more twisted they break
through the surface, until at solar max the whole surface is covered in
loops stretched to breaking point.
Solar flares are what happens when the strain gets too
much and the loops snap. When the loops snap all the
energy stored in the magnetic field is released at once
and billions of tons of plasma are fired into space at
huge speeds; this is the solar wind. If the plasma is
bound for Earth then it will take two days to reach us and
when it does the Earth’s magnetic field deflects most of
the blow. The auroras (more commonly known as the
Northern and Southern lights) are produced when the
solar wind gets through the magnetic field at the poles
and strikes the upper atmosphere. At Solar max the
auroras can be seen as far south as Athens. The
buffeting of the magnetic field causes migratory animals
that navigate using the magnetic field to lose their
bearings and fly or swim to the wrong place. The
disrupted magnetic fields can affect electronics and
sometimes the solar wind can even destroy satellites.
Graph and global warming
As you can see from the graph there is a strong correlation between sun
spot numbers and the Earth’s surface temperature. However in recent
years when the temperature should have been falling with the sun spot
numbers it has increased. This increase has correlated with a recent surge
in carbon dioxide levels. However Carbon dioxide has only been recorded
accurately since 1958 so we can’t be sure whether this is the cause.
The atmosphere
The inner atmosphere is called the chromosphere and
is a red circle around the outside of the Sun. The
chromosphere is red because of an abundance of
hydrogen. Also strangely the temperature of the
chromosphere is higher than the photosphere ranging
from 6000°C to 50000°C.
The outer atmosphere is the corona. The corona
is hotter still ranging from 1000000°C to 2800000°C.The
corona is only visible during eclipses and is made of a
low density cloud of plasma which extends millions of
kilometers into space.
Life cycle of the sun
The universe started by with the big bang and has
been expanding at the speed of light ever since. The
Sun however was born in a nebulae. Nebulae are
huge clouds of hydrogen which can be hundreds of
light years across. They are some of the brightest
parts of the sky due to the intense light of newly
formed massive stars. The Sun’s life started in a cold,
dark cloud of gas which was very stable. These
clouds can stay stable for thousands of millions of
years before they do anything by being hit on one side
by a supernova blast wave.
A supernova blast wave is produced from a massive star
exploding at the end of its life. A supernova blast wave
is a very energetic compression wave, so when it hits the
cold, dark gas cloud it compresses it. The shock waves
knock the cloud off balance which causes localised
clumps of hydrogen to form. The clumps of hydrogen
are what new stars grow from and the increased gravity
of the clumps causes them to pull together. This part of
the process lasts for millions of years and as more
hydrogen is squeezed into the clumps the pressure and
temperature increases. As they get bigger and bigger
they start to spin. This throws out a disk of debris that
will in time form a solar system. This is the reason why
the planets all rotate in the same direction around the
Sun and that they are on the same flat sheet.
Finally the star lights up and because it produces so much energy in the first
fusion the process takes off. The star then begins its lifelong activity of making
other elements. Every atom in the universe was made in a star, therefore every
element was made from hydrogen. In about 5 million years the Sun will run out of
hydrogen. When it does it will become a red giant. The core will shrink because
of lack of fuel. This will generate so much heat that the outer layers will expand
into the solar system meaning the inner planets will be swept up; it may even
swallow up the Earth. The Earth is doomed anyway because the Sun will burn
2000 times hotter than it is now and will melt and seal the outer layers of the
planet. When the Sun finally stops burning its core will collapse and finally it will
blow its last shroud of gas into space.
How big the Sun will
become as a red
giant.
How large is the Sun compared to
other stars?
The Sun is huge (you could fit the Earth in it 1000000 times) but the Sun is
just an average star with many stars being much bigger than it. These
pictures show how big the Sun is compared to other stars.
The brightest star in the
sky The sun 1 pixel
Sites I have used
• The sun websites:
• http://intro.chem.okstate.edu/1314F00/Lecture/Chapter7/Lec11300.html
• http://www.efg2.com/Lab/ScienceAndEngineering/Spectra.htm
• http://www.astronomygcse.co.uk/AstroGCSE/Unit2/Unit2MoonandSun.htm
• http://staff.imsa.edu/science/astro/astrometry/spectra/sld010.htm
• http://www.solarnavigator.net/the_sun.htm
• http://coolcosmos.ipac.caltech.edu/cosmic_kids/AskKids/suncomp.shtml
• http://fusedweb.llnl.gov/CPEP/Chart_Pages/5.Plasmas/SunLayers.html
• http://www.co-intelligence.org/newsletter/comparisons.html
• http://www.sciencedaily.com/releases/2007/04/070416152726.htm
• http://www.northern-lights.no/english/contest/winner.shtml
• http://sunearth.gsfc.nasa.gov/sunearthday/media_viewer/flash.html
• http://solar.physics.montana.edu/YPOP/Spotlight/Tour/tour07.html
• http://en.wikipedia.org/wiki/Image:Solar-filament.gif
• http://www-istp.gsfc.nasa.gov/Education/wcorona.html
• http://www.outdoorsearch.co.za/images/Uploads/200610128237nebulae3.jpg
• http://www.solarviews.com/browse/ds/cloop.jpg
• http://www.lcsd.gov.hk/CE/Museum/Space/EducationResource/Universe/framed_e/lecture/ch15/ch15_cnt.html
• http://www.brighton73.freeserve.co.uk/gw/solar/temp_vs_spot_irradiance.gif