1. “Globular” Clusters: M15: A globular cluster containing about 1 million (old) stars. distance = 10,000 pc radius  25 pc “turn-off age”  12 billion years

2. HR diagram for a cluster: (all stars formed at the same time). main sequence turnoff point

3. “Open” Clusters: stars tend to form in clusters. The “Pleiades”: An open cluster containing about 500 (young) stars distance = 135 pc diameter  4 pc “turn-off age”  10 8 years

4. M35 and NGC 2158: Two open clusters in the same field of view.

5. Interstellar Dust Extinction Curve: UV optical infrared

6. Globule GDC1 with an embedded protostar. A star is born! Bipolar outflow. Shock wave heating.

7. Massive Star-Forming Clouds: A stellar nursery of 100,000 new stars! Milky Way is currently forming stars at a global rate of about 5 M  per year. Orion nebula

8. Molecular Clouds: optical Sakamoto et al. 1994 Orion molecular clouds as traced by carbon monoxide (CO). H 2 is the dominant component, but difficult to observe directly. 1+1+ GHz J CO rotational ladder 2.6 mm

9. Hubble Space Telescope Plateau de Bure millimeter-wave interferometer (IRAM French Alps). Whirlpool Galaxy as observed in the 2.6 mm rotational line of carbon monoxide (CO) !

10. HII Regions : hydrogen ionized by radiation from central hot massive star. “Stromgren Sphere”

11. (HII) H + (HI) H 0 H2H2

12. Recombination Emission Line Radiation: (optical) (ultraviolet)

13. O 2+ Cooling Line Radiation:

14. Optical Emission Line Spectrum of an “HII Region”: hydrogen recombination lines plus “cooling” lines of heavy elements.

15. mass = 3 M  99% gas (H 2 ) 1% “ dust ” 0.1  m grains diameter = 0.4 light years H 2 density = 10 4 cm -3 (a million times lower than lab vacuums) temperature = 10 – 20 K Gravitational Instability and Star Formation: “ Bok Globule ” Barnard 68 (optical image)

16. “Globular” Clusters: M15: A globular cluster containing about 1 million (old) stars. distance = 10,000 pc radius  25 pc “turn-off age”  12 billion years

17. Period-Luminosity Relation of “Cephied” Variable Stars: Very important as standard candles. Measured period gives intrinsic luminosity L. Observed flux then gives distance f = L / 4  d 2 Can be used up to around 50 Mpc (1 Mpc = 10 6 pc).

18. Type Ia low-mass stars (around 1 M  ) mass transfer onto a degenerate white dwarf in a binary system: explosion of entire white dwarf. Supernovae as Standard Candles:

19. Supernovae “Light Curves”: Shape of light-curve determines peak luminosity.

20. Milky Way as Viewed from Earth:

21. Schematic Structure of the Milky Way Galaxy (our home): “Population I” in the disk (metal rich). “Population II” in the bulge and halo (metal poor).

23. Supermassive Black Hole in the Galactic Center: as traced by the orbital motions of individual stars (OB type and red giants). 0.2 arcseconds Result: Black Hole Mass = 4 x 10 6 M 

24. Schematic View from Above the Disk: “Spiral Density Waves”

25. The “Rotation Curve” of the Galaxy: Constant rotational velocity at large radii is dynamical evidence for a “dark matter” halo.

26. Schematic Structure of the Milky Way Galaxy (our home): dark halo

27. Andromeda Galaxy: distance = 800,000 pc as determined by Cepheid variables

28. Hubble Classification of Galaxies: “Ellipticals and Spirals”

29. distance = 9 Mpc type = SA

30. distance = 22 Mpc type = SB

31. Distance = 20 Mpc type = SA

32. The Elliptical Galaxy M87: distance = 17 Mpc type = E1

33. Virgo Cluster: tens of “big” galaxies plus hundreds of “dwarf galaxies”. distance = 17 Mpc

34. Coma Cluster: distance = 150 Mpc