1. What are Other Galaxies Like? Chapter 31.2

2. Remember that galaxies are groups of stars held together by gravity Remember that galaxies are groups of stars held together by gravity There are three basic galaxy shapes: There are three basic galaxy shapes: Spiral Spiral Elliptical Elliptical Irregular Irregular They are further classified according to other features They are further classified according to other features

4. Galaxies tend to group up. We call these “Clusters” Galaxies tend to group up. We call these “Clusters” Milky Way and Andromeda are part of the “Local Group” cluster Milky Way and Andromeda are part of the “Local Group” cluster Clusters of galaxies are also grouped. These are called “Super Clusters” Clusters of galaxies are also grouped. These are called “Super Clusters” By studying other galaxies, Hubble discovered that the universe was expanding. By studying other galaxies, Hubble discovered that the universe was expanding.

5. Some other objects are Active Galaxies and Quasars which are strong radio- emitters Some other objects are Active Galaxies and Quasars which are strong radio- emitters It turns out these are galaxies It turns out these are galaxies Since they are so far away, they are some of the first objects in the universe to form, and it seems that Active Galaxies turn into Quasars. Since they are so far away, they are some of the first objects in the universe to form, and it seems that Active Galaxies turn into Quasars.