The Astronomican is a psychic navigational beacon located on Terra that is ultimately calibrated and projected by the Emperor of Mankind from within the Golden Throne through a massive apparatus located in the Chamber of the Astronomican beneath the fortress called the Hollow Mountain in the Himalazian mountain range. It is powered by the life forces of 10,000 specially-selected psykers called “the Chosen,” up to 1,000 of which die every solar day.

The Emperor projects this astropathic beam 70,000 light years across the Milky Way Galaxy which Human Navigators can detect to triangulate a course for the starships of the Imperium of Man through the otherwise unnavigable chaos of Warpspace. As the signal generated is psychic in nature, it exists within the immaterial universe of the Warp.

The beacon can be psychically detected from almost anywhere in Warpspace and is vital for faster-than-light travel since the mutant Human Navigators use it as their only fixed reference point when calculating an accurate course through the Warp. Without it, long journeys through the Warp would be impossible and no Human starship would ever reach its intended destination.

Without the Astronomican, the Imperium could not survive as an interstellar society. Long-range Warp travel would be rendered impossible as starships would be restricted to smaller cogitator-calculated Warp jumps.