The Astronomican is a psychic beacon which the Navigators use to pilot the spaceships of the Imperium through the otherwise unnavigable chaos of Warp-space. As the beam generated is psychic it exists within the psychic universe of the Warp. It is the duty of the Adeptus Astronomica to maintain all aspects of the Astronomican, including training those who will power it.
The Astronomican was originally constructed in M30 in preparation for the Great Crusade. The Emperor brought in large numbers of Tech-Priests and drafted much of Terra's population for the gargantuan task of constructing the Chamber of the Astronomican at the Forbidden Fortress. At the time of its construction, the Astronomican was the single largest structure on Terra, though this would later be surpassed by the Imperial Palace. In the days of the Great Crusade, the Astronomican was powered by the Emperor's own psychic might directly. Without the beacon of the Astronomican to guide their ships through the Warp, Imperial armies would not have been to have waged the Great Crusade.
After the Heresy, the Emperor became interred within the Golden Throne and required increasing numbers of Psyker sacrifices to maintain the Astronomican. Today, the Astronomican is powered by ten thousand psykers trained by the Adeptus Astronomica. The omnipotent will of the Emperor constantly directs this energy across around fifty thousand light years of the galaxy. Although the Emperor does not provide the energy of the beacon, only he has the psychic power to handle such immense energy and direct it across the galaxy. The psykers who power the Astronomican are recruited into the organisation through the Adeptus Astra Telepathica. They are initiated into the Adeptus Astronomica as Acolytes, and taught how to use their powers, philosophy, the meaning of their lives, and the Lore of the Astronomican. Some achieve a mystic state, gaining the status of Chosen. It is these Chosen who are eventually called to serve in the Chamber of the Astronomican. Here they fuel the Astronomican beacon with their psychic energies; as their powers are drained the Chosen slowly fade and die. Up to one hundred Psykers die each day powering the Astronomnican.
However, the psychic power they generate through their sacrifice is directed by the mind of the Emperor across about fifty thousand light years of the galaxy. Because Terra is situated in the galactic west, the Astronomican does not cover the extreme eastern part of the galaxy. Warp travel beyond the Astronomican's reach is severely limited - this creates the effective borders of the Imperium. Because of this, destroying the Astronomican would most likely halt all Imperial Warp travel within the galaxy, effectively bringing the Imperium to its knees.[Needs Citation]Navigators, as well as other psykers, can sense the Astronomican. It is described as a sensation of silvery light and a chorus of many heavenly voices, beginning first with a solitary voice and progressively growing into an angelic choir. It is suggested that "pious marines" who can hear the Astronomican can fall into a meditative trance when they focus on it. Space Marine Captain Gabriel Angelos occasionally entered a sort of battle trance when he heard the Astronomican while fighting, improving his prowess in combat for the duration.
Right after the 13th Black Crusade and the appearing of a Great Rift, the Astronomican went out causing unrest and horror throughout the Imperium. This period, later called the Days of Blinding, varied wildly. On some worlds there were mere a days of blindnes, on others months. It is presumed that some of the Imperial planets are still depraved of the Emperor's Light. On Terra the blindness lasted thirty-three days.
- 1: Warhammer 40,000: Rogue Trader, pg. 140
- 2: Codex: Tyranids (5th Edition), pg. 28
- 3: Warhammer 40,000 6th Edition Rulebook, pg. 168
- 4: The Horus Heresy Book One - Betrayal, pg. 21
- 5: Dawn of War (Novel Series), [Needs Citation]
- 6: Watchers of the Throne: The Emperor's Legion (Novel), Chapter Five, Tieron
- Warhammer 40,000: Rogue Trader, pgs. 25-26
- Warhammer 40,000 3rd Edition Rulebook
- White Dwarf 140 (UK), Jervis Johnson, Andy Jones, Simon Forrest & Rick Priestley