Tyllus III is the center of the campaign.
The planet provides home to 2 billion souls of the Imperium.
The world doesn’t have a proper spin; so only 70% of the world ever sees sunlight. There is a small portion of the world that never goes dark. The core of the planet is riddled with immense crystalline veins that are exposed to the sky and take the light from the sunny side and bleed it out on the dark side, providing a dusk-like atmosphere everywhere at night.
The world is a light industrial center that provides refinement to the resources from the surrounding worlds.