1. Title: 30.1 Galaxies and The Universe
Stellar Populations in the Milky Way

2. Word of the Day
Nebula: A rotating cloud of interstellar dust and gas.

3. Stellar Populations in the Milky Way
Page 866
Milky Way can be divided into 2 components:
Round Part: The bulge and halo.
Contains old stars.
Traces of heavy elements (elements heavier than helium.)
Disk: Spiral arms.
Where most star formation takes place.
Contains younger stars.

5. Stellar Populations in the Milky Way
Page 866
Stars in regions of Milky Way can be divided into 2 classes:
Population I Stars: In spiral arms of disk (Sun is a population I star.)
Young stars.
Small amounts of heavy elements.

7. Stellar Populations in the Milky Way
Page 867
Population II Stars: In bulge and halo.
Old stars
Hardly any heavy elements.
Oldest known objects in the galaxy are globular clusters: Billion years old.

8. Formation and Evolution of the Milky Way
Page 867
Halo and bulge contain older stars.
Formed First
How?
Nebula: A rotating cloud of interstellar dust and gas collapsed under its own gravity.
Rotation caused cloud to flatten out into a disk shape.
Younger stars then formed in spiral arms.

9. The Orion Nebula