For example, I was surprised by the incandescent moons around Planemos. These are tidally heated moons that are so hot (over 700°C) that they emit a red light that illuminates the other objects in the system, which would otherwise be in total darkness. This provides a reason to go visit planemos and get some nice pictures!

Another thing (possibly? Not sure if this is deliberate) is the central region of the Arp 148 galaxy (a galactic collision site) seems to be unusually rich in nebulae - it looks like there are a lot more in the background too:

Has anyone else come across something that emerged from the procedural generation like this?