A class 12 nebula was a type of astronomical phenomenon first discovered in the Delta Quadrant by Ensign Harry Kim of the USS Voyager in 2373, on stardate 50716.5. A class 12 nebula is stable in size, darker than other classes, and with stronger energy currents. The class 12 was the first new type of nebula to be classified by Federation science since the 22nd century (presumably when the first class 11 nebula was discovered). (VOY - Strange New Worlds I short story: "Monthuglu")