This is an attempt to automate making a galaxy via GIMP. I'd seen a few excellent tutorials, but none that could be easily automated. One of the resulting pictures is attached to this page.
The galaxy can have any number of arms, and they can have varying degrees of curvature. Very high degrees of curvature will result in an elliptical galaxy rather than a spiral. Stars can be added, and the galaxy can be set to have any perspective or color.
This script uses the Outer Glow function from the layer effects script found elsewhere on this site. The Outer Glow script (and the sub procedures) have already been added to my galaxy script. Their names have been changed to make sure there are no conflicts with the original layer effects script, in case you also have that installed.
The script is under the "/Filters/SambrookJM/" menu in GIMP, although that can be changed by editing the last line of the script to put it wherever you want it to go.
As always, if you've got any suggestions, improvements, or comments (or if it's not working for you) go ahead and post them. One thing that can happen is that if the galaxy color is too bright, some of the other details can be washed out. Try to decrease the brightness of the top two layers to counteract this.
 Yeah, I screwed up. There were a couple of scripts that I didn't copy over from the layer effects script. I thought refreshing the scripts on my GIMP would flush them out of the memory after I removed that script file. It didn't. My fault, 100%. This new script should fix things.
gerard82, I think figured out what your problem was. The problem was in the (rand 4000000000) statement. For some reason, Linux versions of GIMP don't like the random number being that high. I lowered the maximum possible random number to 1000000000, which allowed me to run this script (and the brick wall one) on a Ubuntu 10.10, 64-bit build. Try this and the Brick Wall script (soon to be updated) and see if that works.