My first tutorial, yaaaay!
I worked with a 500x300 image the whole time for the sky, hahaa. Sorry it's a big picture.
Um. I assumed you knew how to switch brushes and make new layers, since... Uh.. You wouldn't need a tutorial like this if you never used photoshop before. e_e;
I used Photoshop CS3, but it should work with most versions...
This would work for backgrounds, or shots of space, or... Whatever. You could pretty much stop after rendering the clouds, the rest just makes it pretty. XD
If you make a picture using my tutorial, link me in a comment, I want to seeee!