1. Lecture 32- Properties of the Milky Way (cont)
Spiral patterns and rotation curves

2. Spiral Patterns Does the Milky Way have spiral arms? What causes them?
M81 (binocular object in Ursa Major)

3. Spiral Arms in the Milky Way
Measure distances to large number of objects (HII regions, star clusters, etc) and map them up
Transparency

4. What are the spiral patterns?
Not beads on a wire
It is a wave propagating through the gas of the galactic disk
Slinky model
Molecular clouds, young stars, star formation regions tend to be concentrated in spiral arms

5. All large disk galaxies have spiral structure to some degree

6. Next topic: rotation curves.
How is mass distributed in a galaxy?
What is a galaxy made of?