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Galaxies
Three types of galaxies--all have billions of stars.
Spiral Galaxy
Our Milky Way is one.
Has bulge at center and spiral arms.
Our Sun is close to the edge of galaxy.
Elliptical Galaxy
Round or oval.
Can contain trillions of stars.
Has older stars.
Irregular Galaxy
No definite shape.
Which type of galaxy?
Star clusters
Nebulas--Gas clouds where stars are born.
Star clusters
Globular cluster--can have almost 1 million
stars.
Open cluster--100 to 1,000 stars.
Big Bang
14 billion years ago, all the matter in universe
was packed into the size smaller than an atom.
The matter exploded rapidly and created the
elements and forces of the universe.
The galaxies and everything in the universe is
still expanding and moving rapidly.
If the universe keeps expanding forever, stars
will die and it will become a cold & dark place.
Gravity controls the size and shape of the
universe.