Three types of galaxies--all have billions of stars.
Our Milky Way is one.
Has bulge at center and spiral arms.
Our Sun is close to the edge of galaxy.
Round or oval.
Can contain trillions of stars.
Has older stars.
No definite shape.
Which type of galaxy?
Nebulas--Gas clouds where stars are born.
Globular cluster--can have almost 1 million
Open cluster--100 to 1,000 stars.
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