| http://digfir-published.macmillanusa.com/astro_interactive_exercise/ie_hertzsprung-russel_diagrams.html |
Chapter
1. Hertzsprung-Russell Diagrams
| 51406ccbb11c0fc20c000000 |
| http://digfir-published.macmillanusa.com/astro_interactive_exercise/ie_hertzsprung-russel_diagrams_dlap.xml | DLAP questions | 51406ccbb11c0fc20c000000 |