Deep Sky astrophotography is the traditional nebulas, galaxies and star clusters you might expect of Astrophotography. It is not the easiest, and may well be the hardest type of astrophotography to accomplish, but can be the most rewarding. I personally like galaxies the most, each their own collection of billions of stars with untold numbers of planets and unexplored worlds.
This page contains a small collection of my deep sky astrophotography.