From Lexicanum

A Galaxy is a massive, gravitationally bound system consisting of stars, an interstellar medium of gas and dust, and dark matter. Most galaxies are several thousand to several hundred thousand light years in diameter and are usually separated from one another by distances on the order of millions of light years.

The Imperium exists within the Milky Way galaxy, a large spiral with a total mass of about 200-400 billion stars. The Imperial worlds are scattered throughout most of this galaxy, although it counts only a tiny fraction of the galaxy's stars as its territory. Even with new worlds constantly being discovered by the Imperium, there is no possibility of humanity or aliens exploring or settling all the worlds of the galaxy.

The distances between galaxies are so vast as to make intergalactic travel unfeasible even with advanced Warp jump.

Contents 1 Galactic Statistics 2 Notable regions of the Galaxy 3 Maps 4 Sources

Galactic Statistics

The galaxy is approximately 100,000 light years in diameter, and 15,000 light years thick at its center. Terra (Earth) is approximately 30,000 light years from the galactic core in the main western spiral arm

Notable regions of the Galaxy

• Spiral Arms - comprise recent stars and gas clouds, most of the galaxy's inhabited worlds are here
• Galactic Core - consists of older and cooler stars and a large nucleus of hydrogen and other gases, there are few inhabitable worlds here
• Halo Stars - the halo of very old stars surrounding the galactic disc
• The Eastern Fringe - beyond the reach of the Astronomican and outside the easy reach of the Imperium. It is known to contain human and alien planets, both advanced and primitive
• Wilderness Space - any part of the galaxy which is unexplored or unreachable to the Imperium
• The Homeworlds - the Homeworlds lie on the edges of the galactic hub and represent the remnants of one of the first areas of human exploration. When human explorers first began to study this area they found unique and valuable minerals in these ancient stars and on their dead planets
• Segmentae Majoris
  • Segmentum Solar
  • Ultima Segmentum
  • Segmentum Tempestus
  • Segmentum Pacificus
  • Segmentum Obscurus
• List of all known worlds in the galaxy

Maps

This is a map of the Warhammer 40.000 galaxy:

• Warhammer 40.000 Galaxy @ 640x640 pixel
• Warhammer 40.000 Galaxy @ 1000x1000 pixel

Map of Warhammer 40.000 galaxy at Black Reach:

Areas of influence of all races:

Sources

• Wikipedia on Galaxy
• Codex Imperialis