1. Galaxies

2. Galaxies Galaxies – large groupings of stars in space
Contain more than a trillion stars (estimation based on size and brightness)

3. Types of Galaxies Spiral galaxies Elliptical galaxies
Irregular galaxies

4. Spiral galaxies Bulge at the center and very distinctive spiral arms
When the center has a bar shape, its a barrel spiral
Milky Way galaxy is thought to be a spiral galaxy, similar to the nearest galaxy, Andromeda
Our solar system is located on the outer edge

6. Elliptical galaxies Very bright centers and very little dust and gas
Contain very old stars, no new stars forming

7. Irregular galaxies Galaxies that don't fit into any other class
EX: Large Magellanic Cloud, companion to a large spiral galaxy whose gravity may be distorting the shape of their smaller neighbor

8. Contents of Galaxies Gas clouds – nebula
Open clusters – groups of stars that form when large amounts of gas and dust came together
located along spiral disk of a galaxy
Newly formed open clusters have many bright blue stars
Globular clusters – groups of older stars that formed from a large gas cloud
Looks like a ball of stars
Located in the spherical halo that surrounds spiral galaxies

9. Origin of galaxies
Galaxies form from collapsing clouds of gas and dust
If stars form slowly, the cloud collapses into a disk and forms a spiral galaxy
If stars form quickly, the cloud becomes an elliptical galaxy

10. Back in time
Looking through a telescope is like looking back in time because it takes time for light to travel through space
Quasars – star like source of light/radio waves that is extremely far away