(…)it is useful for beginners and pros alike to see how other artists achieve certain results. These tutorials are only intended to be guides as you work through new processes and challenges. Upon these building blocks, you must add experimentation and a great deal of practice(…)
Solar Voyager hosts what in my opinion is the net’s best collection of tutorials on crafting realistic space scenes by means of 2D techniques. Most of them are focused on different approaches to rendering planets of all sorts, but fortunately there are several other articles which cover a broad field of subjects, from nebulae to asteroids to truly impressive star fields. As you’ll soon realize, following the articles will be a lot easier if you have Photoshop, since that´s the tool of choice in most of them; however, I’m sure that there’s no effect that you can’t achieve by using other programs, so that shouldn’t be a problem.
Besides from the tutorials, you should pay some to time to visit the rest of Solar Voyager, which covers all branches of space art: you´ll surely be surprised by the quantity and quality of many of the works shown!