Space.

This is a horrible picture, but oh well, you will get the idea.  I made a ton of stars on white paper, and had the kids decorate them.  I also had the kids make glow in the dark stars and planets using Elmer's glue and glow in the dark paint.  They made thick blobs of the mixture onto wax paper, so you could peel it off, then backed the blobs onto paper, and hung them up.  I also had the kids make rockets and paint white circles to look like planets.  Hanging in front of the wall from the ceiling I made stars.  I used cardboard star shapes and covered them in foil, hole punched them and hung them at different lengths.  Again sorry for the picture.