1. The Galaxies

2. Description Size Number From 10^7 to 10^12 stars
From from 1000 to parsecs
1 parsec = 3,262 light years
Number
More than 10^11

3. History of observation
End of the 18th century : Messier - Herschel
1845 : Lord Rosse
1923 : Hubble

4. Spiral Barred spiral Elliptical Irregular
Types
Spiral
Barred spiral
Elliptical
Irregular

5. Dynamics and Activities
Interactions :
- Near misses
- Collision
- Merger
Starburst
Active galaxies

6. Formation and Evolution
- Just after big bang : rapid expansion of the universe
years after Big Bang : first structures
- 2 billion years after the Big Bang : protogalaxies
- 4 billion years after the Big Bang : mature galaxies

7. Larger and smaller scale structures