1. The Milky Way in visible light

2. near-IR (2Mass)
1500 LY

3. near-IR (2Mass)
1500 LY
elliptical stellar
orbits in central
arcsecond

4. Active Galactic Nuclei

6. The Hertzsprung-Russel diagram
a.k.a. HR diagram
Vertical axis: L*
Horiz. axis: Ts*

7. The Hertzsprung-Russel diagram
a.k.a. HR diagram
Vertical axis: L*
Horiz. axis: Ts*

8. The Hertzsprung-Russel diagram
a.k.a. HR diagram
Vertical axis: L*
Horiz. axis: Ts*

9. The Hertzsprung-Russel diagram
a.k.a. HR diagram
Vertical axis: L*
Horiz. axis: Ts*

10. The Hertzsprung-Russel diagram
a.k.a. HR diagram
Vertical axis: L*
Horiz. axis: Ts*

11. The Hertzsprung-Russel diagram
a.k.a. HR diagram
Vertical axis: L*
Horiz. axis: Ts*

12. The Hertzsprung-Russel diagram
a.k.a. HR diagram
Vertical axis: L*
Horiz. axis: Ts*

13. A main sequence G2 star, like the Sun, makes a good standard candle
Certain types of giant stars, especially the so-called Cepheid variables, are also used as standard candles

14. Edwin Hubble found Cephieds in Andromeda galaxy - 1923

15. Another type of standard candle ; type 1a supernovae

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