1. An external galaxy; a spiral like our own.

2. Which way does it rotate?

3. An external galaxy; a spiral like our own. How does it rotate? i.e. what is rotation curve?

4. An external galaxy; a spiral like our own. How does it rotate? i.e. what is rotation curve?

5. An external galaxy; a spiral like our own. How does it rotate? i.e. what is rotation curve?

6. An external galaxy; a spiral like our own. How does it rotate? i.e. what is rotation curve? WRONG!

7. An external galaxy; a spiral like our own. How does it rotate? i.e. what is rotation curve?

8. An external galaxy; a spiral like our own. How does it rotate? i.e. what is rotation curve?

9. An external galaxy; a spiral like our own. How does it rotate? i.e. what is rotation curve?

10. An external galaxy; a spiral like our own. How does it rotate? i.e. what is rotation curve?

11. An edge-on spiral; we can measure its rotation

12. An external galaxy; a spiral like our own. How does it rotate? i.e. what is rotation curve?

13. We believe that only 10% of the mass of this object is baryonic matter (in the form of stars, stellar remnants, interstellar gas, interstellar dust) and the other 90% is “dark matter”

14. Vera Rubin showed that 90 % of a typical galaxy’s mass is “ dar k matter ”

15. Except for the closest few galaxies, they are all moving away from us (fast!)

16. Last 4 lectures - cosmology monday wednesay friday monday 3/6