The universe is estimated to be made up of one hundred billion galaxies (100,000,000,000). Most of these galaxies are formed in clusters. The galaxy cluster to which our galaxy belongs is termed the Local Group, and consists of about 30 galaxies, lying on the edge of the Virgo supercluster. The most prominent galaxies within the Local Group are the Triangulum Galaxy, Andromeda Galaxy and our Milky Way Galaxy. Within the universe, the space between individual galaxies is known as Void Space or simply as The Void. The only living beings known to have crossed such a void are the Tyranid Invasion fleets.
The Milky Way Galaxy
The Milky Way Galaxy is a disc shaped spiral galaxy containing atleast two hundred billion stars.(200,000,000,000) The Solar System is located within one of the spiral arms of the galaxy. The Milky Way has a width of approximately 80,000 light years. Therefore, based on the above calculations, we can roughly estimate that our universe is host to approximately 20,000,000,000,000,000,000,000 star systems. A figure and size far beyond the imagination of most humans who live in the Imperium. One can only imagine if there are more universes in the cosmos of not.
The Emperor of Man had been walking the earth for thousands of years, leading, directing and gently focussing human destiny. By the time the Eldar race decimated itself by allowing the birth of the Great Chaos God Slaanesh, the emperor was ready. Although the Primarch capsules had been scattered by the chaos gods, the space marine legions, the mighty Adeptus Astartes, were ready to be unleashed on the galaxy, when the warp storms abated following the birth of Slaanesh. The space marine legions went to the four corners of our galaxy, conquering all before them and the Imperium of Man was established.
The galaxy was divided in to five administrative segments, the Segmentae Majoris, each with its own Segmentum Fortresses. Each segmentum has its own merchant and battle fleet commanded by a Lord High Admirals. The segmentae and their Fortresses are shown in the map below. To see more details of each segmentae, click on the name tags below.
All human inhabited space is further broken down in to sectors, cubes of space 200 light years to each side. Each sector has its own battle fleet, commanded by a Lord Admiral and is the largest naval organisation in that sector. The battlefleet is generally broken down in to a loose organisation of battle groups which can be altered according to necessity. Each sector may be sub-divided in to sub-sectors centered around populated systems or navigational junctions, spanning 10-20 light years in diameter.