1. ASTR 1102-002 2008 Fall Semester Joel E. Tohline, Alumni Professor Office: 247 Nicholson Hall [Slides from Lecture18]

2. Chapter 23: Our Galaxy and Chapter 24: Galaxies

3. Typical Galaxy Large collection of stars (typically ~ 10 11 stars) held together by the mutual gravitational attraction of all the stars Gas & dust dispersed throughout space, between the stars (interstellar medium) Two typical geometric shapes –`Spiral’ Disk (with central, more spherical “bulge”) –Elliptical (much closer in shape to a sphere than to a disk)

15. Schematic Illustration of Our (Milky Way) Galaxy

21. Real ‘All Sky’ Images of Our (Milky Way) Galaxy

30. Stellar Populations Pop I Pop II Pop III