The Universe (season 4) - History Channel. A look at star clusters; how all stars within them are formed from the same material and are approximately the same age; a look at the two kinds of clusters -- "open clusters" which are young and exist in the spiral arms of the galaxy, and "globular clusters" which are old and exist in the outskirts of the galaxy and possibly as old as the universe itself.

The Universe (season 4) 2009 episodes:

1. Death Stars
2. The Day the Moon Was Gone
3. It Fell From Space
4. Biggest Blasts
5. The Hunt for Ringed Planets
6. 10 Ways to Destroy the Earth
7. The Search for Cosmic Clusters
8. Space Wars
9. Liquid Universe
10. Pulsars & Quasars
11. Science Fiction, Science Fact
12. Extreme Energy Less