http://digfir-published.macmillanusa.com/astro_interactive_exercise/ie_some_properties_of_galaxies.html\t
Chapter
1. Some Properties of Galaxies
\t51413917b11c0f181b000000
http://digfir-published.macmillanusa.com/astro_interactive_exercise/ie_some_properties_of_galaxies_dlap.xml\tDLAP questions\t51413917b11c0f181b000000