How would you do this kind of background?

How would one go about creating a background like this in terms of Unity? Specifically, the space scenes (not the city)? It has a depth to it and allows for a large map.

http://www.youtube.com/watch?v=wZX3ia4Ot68&hd=1

For the space scenes i would use a space skybox and particle effects for moving stars. you can adjust the speed and the direction to make it more "spacy"

that would do.