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Galaxies |
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There are billions of Galaxies in the
Universe. Some are very small with only
a few million stars. While others could
have as many as 400 billion stars, or
even more. There are three kinds of
Galaxies, Spiral, Elliptical, and Irregular.
The only difference between the three
is what shape they are. |
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Spiral:
The most beautiful type
of galaxies are Spiral Galaxies.
Their long twisting arms
are areas where stars are
being formed.
Where do the spirals come
from?
Like ripples in a pond,
the spiral arms seen in
this kind of galaxy are
circling waves. These waves
cause new stars to form.
That's right; they are like
star farmers, planting star
seeds where ever they go.
What causes the waves
glow?
Some of the new stars created
in the wave are very large.
Because of their size these
large stars glow brighter
than their smaller cousins,
causing the nearby dust
clouds to glow brightly.
Thus any area near one of |
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these waves glows like a fluorescent
light. In other words you can't actually
see the waves, the spirals that we see
are the glowing clouds illuminated by
large, hot stars. As the waves move
on the clouds behind them dim down,
no longer glowing until another wave
passes through. |
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Why doesn't
the whole galaxy shine brightly?
The large bright stars created
in the waves don't live
very long. Their large size
makes them burn all their
fuel quickly. Usually they
die before they ever leave
the wave. Only the smaller
stars which do not glow
brightly survive to leave
the waves they formed in.
Elliptical:
The stars found in Elliptical
Galaxies are often very
old. This is because elliptical
galaxies don't actively
create new stars. The only
stars found with in them,
were created along time
ago. Although they are usually
smaller, this type of galaxy
can be large. Most have
only a few thousand |
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stars, but some can have billions of
stars. The stars in an elliptical galaxy
are often very close together making
the center look like one giant star.
If the Earth were inside an elliptical
galaxy it would be bright both day and
night. |
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Irregular:
Irregular Galaxies are simply
all the galaxies which are
not spiral, or elliptical.
They can look like anything
and have many different
characteristics. Many irregular
galaxies probably used to
be spiral or elliptical
until they had some kind
of accident which changed
them such as crashing with
another galaxy. Many other
irregular galaxies probably
were never spiral or elliptical;
they simply didn't evolve
that way. |
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