The base of this sensory box is what we call moon sand...This is a mixture of two ingredients: flour and baby oil. For a large batch of moon sand, mix 8 cups of flour and 1 cup of baby oil.
We also placed our galaxy playdough (http://workingmomwonders.blogspot.com/2013/09/galaxy-play-dough.html) in the box. It works very well to hold the rockets, flags, and people into place while he is playing. The green pebbles are glow-in-the-dark pebbles I found online. For a final touch, we placed planet and galaxy stickers around the bin.