As requested, here is some tutorial stuff from "The Art of Greg Martin" on how to make wicked planets and starfields/novas using Photoshop. You can check out his website http://www.artofgregmartin.com to see some of his kick-ass work that you can ahieve follwing the tutorials here.
Here is a really quick example of what you can make following the planets tutorial:
You can get the planets tutorial here:
http://dodownload.filefront.com/1003017 ... 7fc04e2552
Here is the starfield stuff...
http://dodownload.filefront.com/1003019 ... 7fc04e2552
Hope you find them helpful