[RadioAstronomer]

I'm picturing sort of filmy rubber bands here ...

Think of a train whistle and the Doppler effect. Light exhibits the same phenomena.

http://archive.ncsa.uiuc.edu/Cyberia/Bima/doppler.html

[Tax-chick]

a train whistle and the Doppler effect

That I understand. I could even do the equations, back in high school :-).