Cosmology - An Expanding Universe

The Doppler Effect and Sonic Booms

Cosmology resources

Some useful links:
Cambridge Cosmology
Cosmology - The Study of the Universe at NASA
The Cosmos: A Beginner's Guide - BBC and Open University site
Cosmology at The Official String Theory Web Site (some of this gets a bit complicated!)
Cosmology - New Scientist
A brief history of Cosmology