1. Chapter 19
Section 3 Galaxies
Bellringer
Look at the photograph of a spiral galaxy (pg. 596).
Describe the evidence that indicates that the galaxy is rotating.
What other objects have you seen look similar to a spiral galaxy? Do they rotate?

2. Chapter 19 Objectives Identify three types of galaxies.
Section 3 Galaxies
Objectives
Identify three types of galaxies.
Describe the contents and characteristics of galaxies.
Explain why looking at distant galaxies reveals what young galaxies looked like..

3. Chapter 19
Section 3 Galaxies
A galaxy is a collection of stars, dust, and gas held together by gravity.
Edwin Hubble, the astronomer for whom the Hubble Space Telescope is named, began to classify galaxies, mostly by their shapes, in the 1920s.
Astronomers still use the galaxy classification that Hubble developed.
The Milky Way Astronomers think that our solar system is in a spiral galaxy.

4. Chapter 19 Types of Galaxies
Section 3 Galaxies
Types of Galaxies
Spiral Galaxies have a bulge at the center and spiral arms.
Elliptical Galaxies About one-third of all galaxies are simply massive blobs of stars. These are called elliptical galaxies.
Irregular Galaxies Galaxies that do not fit into any other class are called irregular galaxies.

5. Chapter 19
Section 3 Galaxies

6. Chapter 19
Section 3 Galaxies

7. Chapter 19 Contents of Galaxies
Section 3 Galaxies
Contents of Galaxies
Gas Clouds A large clouds of gas and dust in interstellar space is called a nebula.
Star Clusters A globular cluster is a tight group of stars that looks like a ball and contains up to 1 million stars.
An open cluster is a group of stars that are close together relative to surrounding stars.

8. Chapter 19
Section 3 Galaxies

9. Chapter 19 Origin of the Galaxies
Section 3 Galaxies
Origin of the Galaxies
Because it takes light time to travel through space, looking at distant galaxies reveals what early galaxies looked like.
Quasars A very luminous, starlike object that generates energy at a high rate is called a quasar. Some scientists think that quasars may be the core of young galaxies that are in the process of forming.