Before expanding the Great Crusade to the stars beyond Sol the Emperor ordered the construction of the Astronomican on Earth. Huge number of Tech-Priests were brought from Mars to oversee the project and the majority of the Terran population were drafted to construct the towering machine-building.
At the time the Astronomican was the single largest construct on Earth, but more amazing than this fact was that the entire device was merely a focus through which the Emperor could direct his fathomless psychic energies.
The psychic navigational beam from the Astronomican cuts through the Warp and those attuned to its unique frequencies and modulations, the Navigators, are able to use it as a point of reference when calculating journeys therein. Using this beacon they can plot a course that last days rather than weeks or months rather than years.
The Emperor had realised a means by which interstellar travel was a practical proposition again.[/b]