To help answer another question here What's the biggest expansion of the Empire of Man before the Horus Heresy?

I looked online to try and find the stated range of the Astronomican; however, in 3 different non-official places I have seen 3 stated ranges, 30,000 - 70,000 light years.

Has it been stated in any official GW source material how far the emperor’s lighthouse can be seen?

  • For what it is worth, Lexicanum claims it is 50,000 light-years. Their source is Rogue Trader and the Dawn of War novel. The Warhammer 40k claims it is 70,000 light-years and has a bunch sources for the article, but the source and the claim above are not precisely linked.
    – Taladris
    Feb 9, 2020 at 12:08

1 Answer 1


I don't think there was ever an official statement about it, as GW likes to be obscure and not fix information that is not required to be fixed. But we can calculate it.

Earth is around 26'000 light years from the centre of the milky way:

The black hole known as Sagittarius A* (Sgr A*) is situated in the middle of the Milky Way, just 26,000 light years from Earth, according to NASA. Scientists observing the black hole for four days in April and May of this year using the Keck II Telescope in Hawaii saw the event.

From this article

We know it does not reach the Ghoul Stars:

This region of space lies almost entirely beyond the light of the Astronomican, which is used by Imperial Navigators to guide vessels while travelling in the Warp.

but the T'au Empire is:

The Tau Empire borders the Imperium of Man, and lies within the reach of the Astronomican.

With that information, we can draw a map:


So, we know it reaches 60'000 light years but not 71'000 light years.

  • Seeing as the milky way is 50,000 light years it seems like Games Workshop has decided to expand the universe.
    – Richard C
    Feb 9, 2020 at 19:32
  • I seem to recall reading that the Tyranids are drawn to Terra because of the Astronomican, so it may be reaching beyond the galaxy. Granted, the Tyranids probably would have invaded our galaxy anyway, but maybe not as soon.
    – EvilSnack
    Feb 9, 2020 at 22:58
  • @EvilSnack Heard that too. But to the best of my knowledge, that is a rumour and has not been confirmed. I've also heard the thing that some SM activated a beacon the Tyranids waited for.
    – Shade
    Feb 10, 2020 at 7:23
  • 1
    The Tyranids where first called to our galaxy by the destruction of the Pharos engine. That is stated in the hours heresy book. Since then the Astronomicum has called them like a lightbulb calling a moth, now that raises a lot of questions as if they ever reached earth the psychic shadow would mean the warp would no longer threaten at eternity gate and the emperor would be free to do other things. Also if the emperor died he may ascend, or if his genetic material was repurposed by nids, Big E gets resurrected with 8 legs and his perfect anti chaos army.
    – Richard C
    Feb 10, 2020 at 9:00

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