Decoding the Astronomican in Warhammer 40K.
The Astronomican is a psychic beacon that allows Navigators to pilot spaceships through the Warp-space in Warhammer 40K. The Adeptus Astronomica maintains the Astronomican and trains psykers to power it. The psykers are initiated as Acolytes and eventually become Chosen, who serve in the Chamber of the Astronomican until their powers are drained and they die. The Astronomican is what draws the Tyranid Hive Fleets to threaten the Imperium, and its temporary outage caused unrest and horror throughout the Imperium.