EDIT: Hey everyone, I really wasn't expecting so much attention and admiration to this piece lol
Just to fill you in on the "hows". Writing a tutorial for this would probably be around a novel in size. So Ill just put some ideas down for you.
1) Start off with a white blank canvas (any size, the bigger the better though) and choose a BIG soft brush. Draw the basic outline of you nebula (in only one color) MAKE SURE THAT YOU LEAVE HARD EDGES. Then create another layer, fill it with black or white, and add some "fibres" under the 'render' menu. Then change the transparency to 'multiply' and set the opacity to anything below 50. This should give you a 'streaky' cloud. Take a small soft brush, and delete any feathering around the hard edges of your gas cloud.
2) Duplicate your base layer and change the Hue...do this step as many time as you like, with different hue's. Keep your base's transparency 'normal', but the other layers, just go crazy with different transparencies.
3) Duplicate you base layer, and add some Gaussian blur and move it above your base, and change the transparency to linear dodge.
4) this should leave you with a massively colored piece. You could merge layers if you have many (personally, i like to leave layers separate, because some elements (like stars and planets) need a layer above the object, so add some 'luminosity' to it - to make it fit in, to its surroundings.
5) What you do next, is COMPLETELY up to your creative skills. On some of the duplicates you made earlier, add some effects to it...like liquify, and pretty much all of the functions under the "distort" menu. Move layers above and below others and PLAY AROUND. Add some cloud layers (under the render menu), and invert it, once again play around.
6)My photoshop document was 7000px across and contained roughly 170 layers and was 1.7gigs. So dont be shy on your document size - if it gets tooooo big, simply save it as a PSB file (photshop PSD only handles up 2 gig).
The best way to learn your way around is 'trial and error'. This is my 4th Spacescape, so I still have sooo much more room for improvement. Study nebula's, read about them. I watch a lot of space documentaries, so thats pretty much where i get my inspiration from. And take your time designing, dont rush it.
I hope this little bit helps you with your nebula...I have already started with my next one, so hopefully it will be up in the next month or so.
May I use this as a room for my friend's site? We can either have you add your signature or I can add it for you. The site would be willows.chatlands.com .
I love this, it is absolutely gorgeous and has the misty/fuzzy cloud look with the stardust. I love the contrast between the bright colors and the patches of pure highlight/shadow, it really brings out the things I like most in this piece.
Its an amazing picture.