This is something that I've been wanting, but nobody else had the same idea... Or at the very least, nobody would share what they created with this idea.
So, I started up Universe Sandbox 2, made a custom galaxy, and took a few screenshots. With that done, I stitched them together using a skybox template, using a big screenshot of the Just Stars background from universe sandbox as the base so that everything looked good when I pasted the galaxy screenshots in, and now I have a working night time skybox with Spore style galaxies.
Final Side notes:
I don't know which of the primary categories this skybox fits in.
I believe it should work for most versions of Minecraft, but I am uncertain of if that's a matter of fact.
I am too lazy to test for compatibility, but it should in theory work fine so long as you have a working version of optifine.
