I would warn you that almost everything he's doing is simple, though time consuming. The volumetric clouds are large groups of particles in a sort of voxel system designed to imitate real clouds. The land is less impressive. However the stars and planets are interesting.

Inifinity uses a similar system with strange attractors and coloring algorithms to make nebulae. Also, volumetric fog is created in a very interesting way, using a shader casting a ray through a "fog sphere" to lend the volumetric effect. Try reading a few of his development journals for inspiration.