The Crab Nebula was an interstellar gas cloud. In a 2365 attempt at an amusing anecdote with the aim of entertaining Captain Picard and Lwaxana Troi, Lieutenant Commander Data explained how he was able to precisely calculate the distance between the Crab Nebula and the Omicron system. He accomplished this by multiplying the square root of pi with nine to the third power. (TNG: "Manhunt" )