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The Sun and The Stars
• All stars are suns
• Our Sun is a star
• At any given night, we can see about 2,000 stars
• Within a year, we will see over 6,000 stars
• With the use of telescopes, you see thousands
more
• The total amount of stars in our galaxy are in the
billions
• For example, if our sun was the dot over this “i”, the
nearest star would be ten miles away
• For these great distances, miles are no longer
practical, we use: ‘Light Years’
• the distance it takes light to travel in one year
moving at 186,000 miles per second or
about 6 million million miles (6 trillion miles)
• At this scale, the nearest star is 4.3 light years
away
• SIRIUS: the brightest star is 8.8 light years away
• Another interesting fact is that in the year 2000, it
is known that 30 stars have planets orbiting them.
One star (Andromedae) has three planets orbiting
around it.
• The only way we can truly see and study stars and
every thing else in space for that matter, is with the
use of telescopes.
TELESCOPES
•Invented in 1609 by Galileo Galilei
• Today, we have two types of telescopes:
1) Refracting
• These are great for viewing objects that have
a lot of light (planets and stars)
2) Reflecting
• this is better to look at fainter objects (Galaxies)
• the largest refracting telescope has a forty (40)
inch lens ( located in Yerkes Observatory in
Wisconsin )
• the largest reflecting telescope is 200 inches
• this can photograph stars 6 million times than the
faintest stars we see.
Name the type of telescope?
The Sun is the nearest star to Earth. The sun is just an
ordinary star. The next brightest star to us is called Alpha
Centauri. Light from Alpha Centauri takes 4.3 years to get to
us. Light from our sun only takes 8 minutes. Alpha Centauri
are really three stars all orbiting each other. One of these stars
Proxima Centauri is the closest star to Earth next to our sun.
There are many kinds of stars, big and small, close and far,
bright and dim, some even change in brightness in a matter of
hours (these are called pulsating stars).
When most stars get old they bloat and become ‘red giants’.
Our sun will eventually run out of fuel and become a red giant.
As it gets larger it will engulf the inner planets, possibly the
earth as well. It may explode or go ‘Super Nova’. Some times
a red giant just runs out of fuel, dims and grows smaller.
These type of stars are called ‘White dwarfs’.
The Herzspring-Russel (H-R) diagram illustrates the history of
a star. Generally the older the star the greater the luminosity.
The sun is an average middle age star. The youngest stars are
found in the bottom right called ‘Red Dwarfs, the oldest are the
‘Blue Giants’. Temperature generally increases with age.
Sometimes a massive star explodes and may form a black
hole. A black hole comes into being when the gravity of the
exploding star is so strong that it squeezes the ‘ash’ of the
explosion completely out of existence. It is a hole in space. It
is like a trash can, everything nearby is attracted into the
black hole never to be seen again, even light is absorbed by
the black hole.
A Nebulae
A Super Nova
A Black Hole
• The largest cluster of stars are called ‘Galaxies”. They
are literally cities of stars.
• To the unaided eye they look like faint blurs in the sky,
but a telescope reveals that they are made up of
thousands of millions of stars.
• A typical galaxy contains 100 000 stars. There are
about 1 000 000 galaxies in the Universe. The galaxy
that our solar system is in is of course the Milky Way.
Elliptical Galaxy
Irregular Galaxy
Spiral Galaxy
A Star is Born…
The space in between stars is not always empty. It
can be made of gas (mostly Hydrogen) and dust.
Some of this gas and dust even glows, this is called
a ‘Nebulae’. Stars are born deep inside nebulae and
dust clouds in space. Gravity pulls the thin gas of the
nebula into balls of denser gas. Perhaps the process
starts when, quite by chance, a swirl of gas forms
that is denser than neighboring gas. The gravity of
the dense swirl in turn attracts nearby gas and so a
ball of gas forms.
The ball shrinks, pulled inward by its own gravity.
Inside the shrinking gas balls - called protostars - the
pressure and temperature rise. This happens
because all gases get hotter as they are squeezed
into a smaller space. Eventually the temperature
reaches 10 million degrees centigrade and that starts
a nuclear fusion reaction with Hydrogen. A star is
born. Some nebulae can even be the remnants of a
star that has exploded.
Our Sun
• The Sun is a giant nuclear furnace. The nuclear reaction
that occurs inside the sun is called fusion (atoms are
combined), the opposite of fission which is the splitting of
atoms. Humans have harnessed fission, but not yet fusion.
• Hydrogen and helium are the main gases in the Sun’s
furnace.
• The reason why the sun doesn’t just blow up like a
hydrogen bomb is that as the gases expand from the
nuclear reaction, gravity takes over and pulls the gases back
in. These gases have cooled by now and as they come back
in they are reheated and the nuclear reactions occurs again
(convection currents). The Sun is a balanced nuclear
furnace.
Parts of the Sun
1) The Photosphere and Sun Spots: the surface of
the sun is called the photosphere. It has a temperature of
5 500 degrees Celsius. There are darker patches called
sunspots. These are not truly black; they are just cooler
areas and by contrast appear to be black.
Parts of the Sun
2) Chromoshpere and Solar Flares: The part just outside
the photosphere is called the chromosphere. It is this sphere
that gives the sun the reddish colour. The chromopshere is
the sun’s atmosphere. Sometimes this atmosphere erupts
into violent storms sending part of the chromosphere into
space. These fire balls are called prominences or solar
flares. A prominence is usually U shaped and falls back to
the sun. A solar flare shoots out into space.
Parts of the Sun
3) The Corona: The sun also has an outer atmosphere
called the corona. The extreme brightness of the sun hides
the corona. It can only be seen during a solar eclipse,
which is discussed when we study the moon.
Parts of the Sun
4) Solar wind: The sun gives off electrically-charged
particles called solar wind. It is this solar wind that creates
the famous tail on a comet. These particles take 4-5 days to
reach the earth.
•The earth is protected from the effects of too much solar
wind by the magnetosphere. Think of the earth as a giant
magnet with a magnet field extending thousands of
kilometres out into space.
http://science.nasa.gov/ssl/pad/sppb/edu/magnetosphere/mag1.html
This magnetic
field, however, is
deformed by the
solar wind.
The solar wind is also responsible for the Aurora
Borealis or Northern Lights (and the Aurora Australis or
Southern Lights). As the solar wind approaches the earth,
it gets caught in the earth’s magnet field, the
magnetosphere, some of the particles, especially after a
massive solar storm, get funneled along the lines of the
earth’s magnet field down toward the magnetic poles. As
the particles get closer to the earth, they pass through an
upper layer of the atmosphere called the ionosphere,
which is a very thin layer of ionized gases. The electrical
particles from the Sun cause these gases to glow, just like
the gases glow in a neon tube.
http://community.webshots.com/album/177837
These storms can cause communication and science
satellites to fail. They can also cause damage to electric
power systems on the surface of the Earth.
Sunlight
Sunlight is a mixture of colours.
• When you pass sunlight through a glass prism the visible light
is refracted (bent) into these mixture of colours called ‘the
spectrum’
• Red
Orange
(bent the least)
(long wave lengths)
Yellow
Green
Blue
Violet
(bent the most)
(short wave lengths)
• If the spectrum has dark lines running vertical, it tells us that
some of the light has been absorbed. We can tell what material
has done the absorbing by the location of the lines and the
wavelengths of this lines. These dark lines are called
Fraunhofer lines.
• A rainbow is the spectrum created by water droplets in the
sky.
• As the sun’s light passes through the atmosphere some of
the light is refracted or bent or scattered. Blue rays are
scattered the most - that is why the sky is blue. Yellow is
scattered the least - that is why the sun looks yellow.
•During certain sunsets and sunrises the sun’s rays are very
slanted and can literally bounce off the atmosphere and
project an image of the sun higher in the sky. The sun will
look distorted and huge and usually very red. “Red sky at
night - sailors delight”
THE END!