Nebula Fragments are a Hardmode post-Golem crafting material. It is one of the four Lunar Fragments, dropped from the Nebula Pillar during the Lunar Events. The Nebula Pillar drops 12-60 / 18-90 . These fragments can be used to craft a lategame armor set that benefits all types of magic weapons, and can be used to create its respectively themed Tools, Weapons, Wings, etc.
Crafting all of the Nebula armor, weapons, and tools requires 121 Nebula Fragments and 68 Luminite Bars (272 Luminite).