Milky Way Galaxy
Age: 13 billion years
Diameter: 100,000 light years
The Milky Way galaxy is an unremarkable medium sized barred spiral galaxy and the home of a large number of sentient species and innumerable non-sentient ones. It is about 100,000 light years in diameter and 1,000 light-years thick along the arms - thicker towards the core. There are about 2.5 x 1011 stars in the Milky Way, not including brown dwarfs. As many as 1.2 percent of all stars may have been capable of supporting complex life at some point in the history of the galaxy.
The Milky Way Core has a thickness of 15,000 light years. It is generally more hostile to the development of life, with disruptive gravitational forces, higher levels of radiationand frequent supernova detonations, although the rapid formation rate of planets at the galaxy's core serves to outweigh these negative effects to a large extent.
The Milky Way Halo is the sparse area surrounding the disk of the Milky Way, consisting of globular clusters, dark matter and several tidal streams. The huge, outer halo is thinly populated with some 500 million stars all more than ten million years old, with less than 10% metal content of main sequence stars. Terrestrial planets are rare, but where they do exist, they can be very, very old.
Somewhat more metal rich than the outer halo, the inner halo and thick disk populations of stars present a more crowded, younger star-scape, making up about 10% of the Milky Way’s total star population. Like the outer halo, though, there is about a 10 billion-year jumpstart, but, again, with fewer terrestrial planets in the heavy-element deficient halo and thick-disk stars.
- Main article: Quadrant
The disk of the Milky Way is divided into a number of overlaying regional classification systems. The most large scale is the division of the entire galaxy into four basic quadrants; Alpha Quadrant, Beta Quadrant, Gamma Quadrant and Delta Quadrant. This classification is entirely arbitrary and simply used to establish general reference points among different civilizations.
Slightly less arbitrarily, the Galaxy can also be divided into "Rims" around the Galactic Core; regions in this system include the Inner Core, Outer Core, Inner Rim and Outer Rim. This system has its benefits, but again, is largely useless without further details.
The third system involves the mapping of the Galaxy's various spiral arms. In the Milky Way galaxy, the spiral arms are the Norma, Scutum-Crux, Orion-Cygnus, Perseus, Outer and New Outer Arms.
This concention has its merits, but can prove inaccurate as there are no strict borders to spiral arms, which are not in fact cohesive entities.
Other ways to establish galactic location is the use of local landmarks, gravitational associations, and arbitrarily defined sectors, as well as counting the distance from the Galactic centerpoint. Most often, all of these systems are used together for optimal accuracy, for an example for the Ta'mag system, the galactic location is "Triangle of Ret, Outer Rim, Delta Quadrant".