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Our 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
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.
• The sun is made up of some interesting components:
a) The Photosphere and Sun Spots: the outer 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.
b) Chromoshpere and Solar Flares: The part just above the
photosphere is called the chromosphere. It is this sphere that
gives the sun the redish colour. The chromopshere is the sun’s
atmosphere. Sometimes this atmosphere erupts into violent
stomrs sending part of the chromsphere 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.
c) The Corona: The sun also has an outer atmosphere called
the corona. The extreme brightness of the sun hinds the
corona. It can only be seen during a Solar Eclipse, which we
will talk about when we study the moon.
d) 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.
• The Sun converts 4 million tonnes of mass to energy every
second. The sun has enough fuel to burn for another 5 000
million years.
• The Sun’s energy production is enough to supply the
electrical needs of the USA for 50 million years.
Sunlight
• Sunlight is a mixture of colours.
• When you pass sunlight through a glass prism the light is
refracted (bent) into these mixture of colours called ‘The Spectrum’
• Red
Orange
Yellow
Green
Blue
Violet
(bent the least)
(bent the most)
(long wave lengths)
(short wave lengths)
• If the spectrum has dark lines running vertical, it tells us that
some of the light has been absorbed. These dark lines are called
Fraunhofer lines.
• If you study these lines you can tell what materials an object, like
a planed, is made up of. Later in this course you will see how the
study of the spectrum is important to Remote Sensing!
• 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.
• In northern latitudes the atmosphere is so thin that few gasses
exist (almost a vacuum). The sun’s rays light up the sky and create
the Northern lights or the Aurora Borealis. Northern lights occur
after highly charged particles from a recent solar flare or sunspot
excite the thin atmosphere.
• 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”