Attached are two backgrounds that are great for evening or night scenes.
One is a picture that can be applied by Objects > Background > Surface Shaders > Create New Shader > Default Shader. From here, you open the shader details and click the folder icon to insert the .jpg into the "Colour image" and "Luminosity image" sections. Mess around with the "Diffuse colour" option to make it adequately visible.
The other is a clip file that needs to be applied by File > Insert Clip File. As the organization of nodes is pretty complex, I find it easier to edit in the node manager. I found this node cluster somewhere on this forum so if you find the original I'd be happy to edit it to include the author!
If the background doesnt show up, it most likely means that it's behind the background that was there previously. This means that you have to delete the other one in the Objects tab or the node manager.
Thumbs up to the clip file in particular. Fairly easy to tweak, which is nice, and helps create an appealing, understated, space scene.