Custom Starscapes

[Treewyrm]

It's a model actually with large texture(s) on it. Some starscapes are just simple spheres with texture on it and polygons facing in. Other starcrapes are more complex, have asteroid belts and planes with big stars/etc. You can check them with HardCMP by opening starcrape models. I suppose you can use cubic or any other form if you want. Though sphere produces best effect and less visible seams but a bit harder to paint for.

Generally those things are called "skyboxes", a term appeared around unreal engine and it's dynamic sky.