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"I am what remains of the Song of Salvation. I am His will rendered in silent light, sent forth to guide a billion vessels home. I am what remains of the Emperor now that His body is dead and His mind is dying. It is a death that may take an eternity, but it will come. And then I will fall silent with His final thought. [...] I stare into eternity and witness the dance of daemons. I sing forever into the endless night, adding my melody to the Great Game. I am Imperious, the Avatar of the Astronomican."

— Imperious, Avatar of the Astronomican

The great dome of the sphere that is the Astronomican sitting atop the Hollow Mountain on Terra.

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 and utilise 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.

The Imperium could not survive as an interstellar society in the absence of a functioning Astronomican. Long-range Warp travel would be rendered impossible as starships would be restricted to cogitator-calculated Warp jumps of no more than 4-5 light years at a time.

During the Age of Technology, before the Astronomican existed, its functions were fulfilled by a strange xenos techno-arcana device known as a Pharos which was later determined to have been built by the ancient Necrons. These devices projected a stable Warp-beacon for the Navigators to use as a reference point when doing their calculations.

It was theorised by savants of the Imperium that there had once existed an entire network of these devices across multiple worlds in the Human-dominated part of the galaxy to facilitate Warp travel, but over time, many were lost or forgotten in the Age of Strife that swallowed the first Human interstellar civilisation.

One such device, a xenos construct known as the Pharos, was later discovered by the Ultramarines Legion on the ancient world of Sotha beneath Mount Pharos.


Adeptus Astronomica Symbol

Icon of the Adeptus Astronomica.

At the very start of the Great Crusade in ca. 798.M30, the planets closest to Terra were easily reached by blind jumps through the Immaterium. The Empyrean of that time had only recently calmed after the great turbulence of the Age of Strife following the birth of the Chaos God Slaanesh.

However, it soon became clear that to travel further from Terra, the Imperium's Navigators would require a stable astronavigational reference point within the Immaterium to triangulate their current location against if longer Warp jumps were to be attempted with any hope of success.

Following the successful conclusion of the Unification Wars, the Emperor first ordered the construction of the Astronomican on Terra, which would enable His forces to expand the Great Crusade to the stars beyond Sol. Huge numbers of Tech-priests were brought from Mars to oversee the project and the majority of the Terran population was drafted to construct the towering machine-buildings needed to support this labour.

At the time the Astronomican was the single largest artifice on Terra, and the entire device was merely a focus through which the Emperor could direct His fathomless psychic energies to generate a partly self-sustaining telepathic signal through the Empyrean (although few were aware of this fact).

The psychic navigational beam the Astronomican generated was able to propagate through the Warp and those attuned to its unique frequencies and modulations, the Navigators, were able to use it as a beacon and pole star when plotting journeys through the Immaterium. By this beacon the Warp could be travelled at speeds and with a margin of safety that had been unprecedented, although the risk could, of course, never be fully mitigated.

The Astronomican was an incalculable boon to both the Great Crusade and the fledgling interstellar domain of Mankind that it was creating. In a similar way, the Emperor was able to shut down the Astronomican or interrupt the beam at will.

Only a handful of individuals knew that the great signal was actually powered by the Emperor's psychic powers, and they lived in fear that should He be disabled or killed, the galaxy would be plunged into a new Age of Strife. Such was the Astronomican's effect that even in that distant age of the Imperium's first founding some referred to it as the "Divine Light," or the "Emperor's Light," often without fully realising the literal truth of those words.

With His Imperial Webway Project only in its planning stages, the Emperor resorted to powering such a reference point Himself, using the focus chamber He had built earlier beneath the Imperial Palace to project a beam of unimaginable psychic power and range through the Warp. So colossal was the Emperor's psychic might that in the early days of the Great Crusade in the late 30th Millennium He could power the Astronomican while He was off-world, leading the Imperial war effort personally at the head of the Principia Imperialis expeditionary fleet.

For all His might, however, the Emperor still had limitations, and the task of powering the Astronomican so that its beacon was perceptible over the whole of the territory of the growing Imperium of Man became more and more taxing, weakening Him to the point He was nearly choked to death by a powerful Ork Warlord on the world of Gorro, only to be saved in the nick of time by His Primarch son Horus.

The ever-growing demand of projecting the Astronomican upon the Emperor was one of the reasons He handed command of the Great Crusade over to the Warmaster Horus after the victorious Ullanor Crusade against the Orks and returned to Terra to complete His Webway Project, an initiative intended to make the Astronomican all but unnecessary.

With an Imperial extension into the Aeldari Webway, the starships of Mankind would be able to cross the galaxy in the blink of an eye without having to deal with the deadly dangers of the Warp. Alas, such a dream was not to be, and the Webway Project was destroyed by the machinations of Chaos during the Horus Heresy.

Astra Telepathica

Astra Telepathica Icon

Ancient icon of the Astra Telepathica during the Great Crusade.

In addition to this invisible beacon amongst the stars, the forging of the Imperium would not have been possible without the creation and continuation of the Astra Telepathica. This special corps of interstellar communicators was created by the Emperor during the final months of the conquest of Terra, as the Emperor had foreseen their absolute future need.

For the most part, the Emperor did not favour the use of psychic talents in others. As a psyker Himself, albeit one of unprecedented power and control, He was well aware of the dangers inherent with Human contact with the Warp.

Furthermore, the Age of Strife on Old Earth had its own "witch-kings" and possessed psykers to attest to those dangers, some of whom the Emperor had personally slain.

However, He was able to identify those strong enough in will to maintain control of their abilities and aid their self-control through the ritual of soul-binding, and so with some prudence certain psykers were employed in a variety of special roles in the Imperium, and the astropaths of the Astra Telepathica were to be such an exception.

Horus Heresy

During the Age of Technology before the Astronomican existed, its functions were fulfilled by a techno-arcana device known as a Pharos. One of these xenos devices, later determined to be of Necron origin, was discovered beneath Mount Pharos on the world of Sotha by the Ultramarines Legion during the opening days of the Horus Heresy.

The Pharos was part of an ancient interstellar navigation system, both a Warp beacon and route-finder, and it also permitted instantaneous communication across unimaginable distances.

Unlike Imperial Warp-Drive technology that used the Immaterium to by-pass realspace, the quantum function of the Pharos once allowed for site-to-site teleportation, perhaps through a network of gateways. Its fundamental function lay not in the utilisation of psychic energy, but with empathic power.

It was believed that other devices like the Pharos still existed as way stations, or once did, on other worlds throughout the galaxy. Yet the Pharos technology did not act as a single beacon visible across the galaxy like the Astronomican.

It was theorised that the Pharos and other stations like it were once used to create a network of navigational pathways between the stars, as opposed to a single, range-finding point like the Astronomican. In that sense, the Pharos was more a lantern than a beacon. The Pharos could be tuned and pointed, illuminating a site or location for the benefit of range-finding.

Following the Battle of Calth, Erebus of the traitorous Word Bearers Legion had managed to complete a blasphemous ritual on Calth's surface, which summoned a Ruinstorm to the galaxy's Eastern Fringe -- a monstrous Warp Storm larger and more destructive than anything space-faring Humanity had witnessed since the days of the Age of Strife. It split the void asunder, dividing the galaxy in two and potentially rendering vast tracts of the Imperium impassable for centuries.

Utilising the strange abilities of the Pharos, the Ultramarines were able to illuminate Macragge, lighting it up as a psychic bright spot that was visible throughout realspace and the Warp. Despite the effects of the Ruinstorm, the Pharos provided a directional beacon for Warp navigation in the absence of the Astronomican.

Though Primarch Roboute Guilliman was loathe to use xenos technology, Ultramar had to be held together, and to rebuild the Five Hundred Worlds, the Loyalists had to restore communication and travel links by piercing and banishing the age of darkness initiated by the Traitors.

Just before the outbreak of the Horus Heresy in the early 31st Millennium, the Emperor of Mankind's Imperial Webway Project had required more and more of the Emperor's psychic might as He sought to penetrate the corridors of the Aeldari's Webway and claim it for Mankind, a task that dangerously weakened the Astronomican's signal across the galaxy.

Malcador the Sigillite suggested a compromise: the beacon would still be guided by the Emperor Himself, but a large part of the required energy would be provided instead by the psychic and life energies of 10,000 sacrificial psykers, allowing the Emperor to pour His own psychic might into finishing His great project.

The Emperor approved the notion only with the greatest of reluctance, and also made it clear that it would be only a temporary solution, for He had no intention of claiming the lives of thousands of innocent men and women on a regular basis, indefinitely.

Tragically, the Emperor would never resume His former role as the active ruler of the Imperium because of the mortal wounds He suffered at the hands of Horus during the Horus Heresy's climactic Siege of Terra. Although His mind would continue to calibrate the psychic beam's frequency following His physical internment in the Golden Throne, the Emperor was never able to resume powering the beacon solely by Himself, and the once-temporary measure of having the Astronomican powered by the regular sacrifice of thousands of psykers became permanent.

At the present time, in the 41st Millennium, the Astronomican is a complex piece of machinery powered by 10,000 specially-trained psykers, whose life-forces are exhausted in a matter of solar months maintaining the beacon. Their ranks must therefore be constantly replenished with fresh recruits drawn from the tithe of psykers brought by the Black Ships to Terra to be used by the Adeptus Astronomica.

Noctis Aeterna

The Noctis Aeterna, also known as the "Blackness" or the "Days of Blinding" in Low Gothic, was a catastrophic event which consumed the Milky Way Galaxy and the Imperium of Man beginning in ca. 999.M41.

The Blackness began following the fall of Cadia at the climax of the 13th Black Crusade and the eruption of the Great Rift that cut the Imperium in half, and was marked by the loss of access to the Astronomican for FTL navigation and a disruption in all astrotelepathic communications.

Beyond the Great Rift, in the half of the galaxy cut off from Terra by the great Warp rift known as the Imperium Nihilus, the Astronomican was no longer detectable by psykers and Navigators and the Blackness persisted indefinitely.

These disruptions endured for variable times across the galaxy, lasting for only thirty-three solar days on Terra itself, but for solar decades or even standard centuries elsewhere. This period saw more devastating events consume the increasingly isolated worlds of the Human-settled galaxy than at any time since the Age of Strife.

Such was the turmoil during the creation of the Great Rift and the period following it that there could be no reliable accounts of what transpired. As limited communications returned, Historitors and Chronotechs struggled to understand incoming reports.

With the influx of Warp energies into such vast regions of realspace, time passed strangely, speeding up in some sectors, slowing in others compared to the sidereal time experienced on Terra, at the heart of the Imperium.

These effects on the Warp from the birth of the Great Rift faded with the passage of time in the Imperium Sanctus, allowing for the reestablishment of interstellar communications with some regions and somewhat more reliable Warp travel. This restoration of stability, combined with the onset of the Imperial counteroffensive known as the Indomitus Crusade, eventually restored the grip of the Emperor over the Imperium Sanctus. But the Imperium Nihilus still remained beyond the Emperor's light.

However, the price paid proved steep. Slightly less than half of the one thousand Space Marine Chapters known to operate across the galaxy remained unaccounted for, and no less than twelve Space Marine Chapter homeworlds were reported as destroyed during the Noctis Aeterna and the equally bitter campaigns that followed.

Adeptus Astronomica

Emperors Thirst

Imperial psykers being herded to their inevitable fate -- to power the galactic beacon known as the Astronomican.

It is the duty of the portion of the Adeptus Terra called the Adeptus Astronomica to maintain all aspects of the Astronomican, including training those Sanctioned Psykers who will power it. The "psychic light" of the Astronomican is beamed from Terra, from the Chamber of the Astronomican buried deep beneath the Himalazian (Himalayan) Mountains.

The Astronomican is powered by the psykers trained by the adepta, though it is the omnipotent will of the Emperor Himself that constantly directs this psychic energy across the depths of approximately 70,000 light years of galactic space.

Although the Emperor does not provide the psychic energy of the beacon, only He has the psychic control required to handle such immense amounts of psychic energy and direct it across the galaxy.

The psykers who power the Astronomican are recruited into the Adeptus Astronomica through the division of the Adeptus Terra called the Adeptus Astra Telepathica. They are initiated into the Adeptus Astronomica as acolytes, and are taught how to use their powers as well as the philosophy of the adepta and the pivotal role it plays in the continued existence of the Imperium.

Astronomica acolytes learn the lore and technical arcana of the Astronomican. Some achieve a mystic state, gaining the status of "Chosen." It is these Chosen of the Astronomican who are eventually called to serve in the Chamber of the Astronomican.

Here they fuel the Astronomican's beacon with their psychic energies; as their powers are drained by the Emperor to fuel the beacon, the life forces of the Chosen slowly fade and they die, their lives a necessary sacrifice for the continued good of the Imperium and the existence of Mankind in a hostile galaxy.

This psychic power is then directed by the mind of the Emperor across the width of the approximately 70,000 light year range of the beacon. Because Terra is situated in the galactic west, the Astronomican does not cover the extreme Eastern Fringe of the galaxy. Warp travel beyond the Astronomican's reach is severely limited -- thus, it is the Astronomican's reach that effectively determines the true borders of the Imperium.

Destroying the Astronomican would most likely halt or badly cripple all Imperial Warp travel within the galaxy, effectively bringing the Imperium of Man to its knees, both economically and militarily.

The mutant Navigators, as well as other psykers of any intelligent species, 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 Space Marines" who can "hear" the Astronomican possess the ability to fall into a meditative trance when they focus on it, perhaps as a result of their genetic descent from the Emperor through the gene-seed of their primarchs.

Captain Gabriel Angelos of the Blood Ravens Chapter of Astartes was known to occasionally enter a sort of battle trance when he "heard" the Astronomican while in battle, improving his prowess in combat for the duration of the trance.

Astronomican Operation


Inside the Chamber of the Astronomican.

The Chamber of the Astronomican is located deep beneath the Himalazian (Himalayan) Mountains of Terra. The original purpose of the device which would become known as the Astronomican has been lost to time; what is known is that it was built by the Emperor of Mankind Himself as a focus for His fathomless psychic power.

Because of its vital role in the maintenance of the Imperium, the Astronomican has great religious significance for believers in the creed of the Imperial Cult and the Emperor's divinity and it is also sometimes metaphorically referred to as "the Light of the Emperor," "the Ray of Hope" or "the Golden Path."

Limitations of the Astronomican

Warp Storm activity can affect the overall range of the Astronomican but it generally had a range of approximately 70,000 light years before the birth of the Great Rift.

As the galaxy is about 100,000 light years in diameter and Terra is approximately 25,000 light years towards the galactic southwest, the Astronomican barely penetrates the Eastern Fringe of the galaxy; even less so in the wake of the arrival of the Warp-smothering Tyranid hive fleets.

Tyranid Attraction

The Astronomican's potent psychic beacon is what is drawing the Tyranids like moths to a candle flame to threaten the Milky Way Galaxy after they were alerted to its location by the Pharos' activation during the Battle of Sotha in the Horus Heresy.

It is now also drawing the hive fleets, inexorably and irresistibly, towards Terra itself.


See Also


  • Codex Adeptus Astartes - Space Marines (8th Edition), pp. 18-20, 45, 56, 98
  • Codex: Tyranids (5th Edition), pg. 28
  • Dark Heresy: Core Rulebook (RPG), pp. 6, 158, 221, 225, 247, 255, 279
  • Deathwatch: Core Rulebook (RPG), pp. 7, 181, 285, 287, 290-291
  • Horus Heresy: Collected Visions, pp. 9, 38, 188, 190, 252, 260, 351
  • Rogue Trader: Core Rulebook (RPG), pp. 7, 19, 48, 61, 155-156, 176, 183, 306, 310-311, 320
  • The Horus Heresy: Betrayal - Book One (Forge World Series) by Alan Bligh, pg. 21
  • Warhammer 40,000: Rulebook (3rd Edition), pg. 100
  • Warhammer 40,000: Rulebook (4th Edition), pp. 122-123
  • Warhammer 40,000: Rulebook (6th Edition), pp. 139, 146, 160, 169, 173, 197, 215, 403
  • Warhammer 40,000: Rulebook (8th Edition), pp. 27-28, 30-31, 35, 39, 41, 43, 48-53, 91, 152, 164, 278
  • Warhammer 40,000: Rogue Trader (1st Edition), pp. 25-26, 139-140
  • White Dwarf 140 (UK), "Space Fleet: Astronomican" Jervis Johnson, Andy Jones, Simon Forrest & Rick Priestley
  • Blood Ravens: The Dawn of War Omnibus (Novel) by C.S. Goto
  • The Talon of Horus (Novel) by Aaron Dembski-Bowden
  • Watchers of the Throne: The Emperor's Legion (Novel) by Chris Wraight, Cover Image, Ch. 5, Tieron
  • Belisarius Cawl: The Great Work (Novel) by Guy Haley, Chs. 8, 9, 23, 26
  • Vaults of Terra: The Hollow Mountain (Novel) by Chris Wraight, Chs. 16, 18-20
  • The Unremembered Empire (Novel) by Dan Abnett, pp. 30-45
  • Pharos (Novel) by Guy Haley, Epilogue
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