Milky Way Galaxy
The Milky Way Galaxy (otherwise known as Galaxias or Dakhaseri) is the name given to the SB(bc)-type barred-spiral galaxy in which the stars of Charted Space reside. It is but one of the 2 trillion galaxies in the observable universe.
Galaxias is approximately 30 kiloparsecs in diameter and is estimated to be between 300 and 600 parsecs thick in the region of the galactic disk, thickening to at least 1,000 to 1,500 parsecs toward the galactic center. The density of stars generally drops off exponentially with distance both in the direction of the galactic core to the galactic rim, as well as in thickness from the mean galactic plane to the outer surfaces of the disk. Approximately 95% of the disk stars lie within the 300pc thick region of the disk.
While Galaxias is almost as old as the universe itself (its oldest stars date to less than a billion years after the beginning of time), the majority of its stars are middle-aged and range between 6 and 10 billion years of age, and number between 200 to 400 billion star systems in total. Most of its stars have planetary systems with habitable zones capable of producing and supporting life.
Sol System and Charted Space
The Sol Star System within Charted Space is located within the galactic disk, about 8,150 pc from the Galactic Center, on the inner edge of one of the spiral-shaped concentrations of gas and dust called the "Local Arm" (or occasionally the "Orion-Cygnus Spur" of the Sagittarius-Carina Arm), about 6pc North of the mean galactic plane. 
The stars within the central 1500 pc radius form a spheroidal bulge and one or more "bars" that radiate from the bulge. These elongated bar-shaped structures have a stellar density of over 50,000 stars per cubic parsec. At the very center of the core of Galaxias is a super-massive black hole named Sagittarius A* that masses approximately 4.3 x 106 MSol. Approximately 10 million stars orbit within 1.0 lightyear of this object.
Based on observations, Galaxias appears to have two "major" (higher-density) spiral arms (the Perseus and Scutum-Centaurus Arms) as traced by old stars, and four "minor" (lower-density) spiral arms (the Norma/Outer, Sagittarius-Carina, and the Near and Far 3kpc arms) as traced by gas and both old and young stars. Outside of the major spiral arms is the Monoceros Ring (or Outer Ring), a ring of gas and stars torn from other galaxies billions of years ago. Galaxias's stellar disk does not have a sharp edge beyond which there are no stars; rather, the concentration of stars decreases exponentially with distance from the center of Galaxias. For reasons that are not understood, beyond a radius of roughly 13 kpc from the center, the number of stars per cubic parsec drops much faster with radius.
The spaces between the galactic arms are somewhat less dense in stars, but have comparatively less gas and dust than the spiral arms themselves, and are thus not generally regions of active star formation. As a result, most stars here tend to be cooler older stars and stellar remnants. The spiral arms themselves are thus largely an "optical" phenomenon, as the abundance of very young hot bright stars in the star-forming regions of the "arms" causes these regions to "stand out" visually compared to the regions populated by older and cooler stars that permeate the majority of the galactic disk.
Surrounding the galactic disk is a sparse spherical Galactic Halo of old stars and globular clusters that extends further than the galactic disk but is limited in size by the orbits of Galaxias's two satellite galaxies, the Large and Small Magellanic Clouds. Approximately 90% of globular clusters lie within 30 kpc of the Galactic Center, of which 40% are on retrograde orbits relative to the rotation of the galactic disk.
- See list at Universe
Galaxias has a number of satellite galaxies (including the Large and Small Magellanic Clouds, the Sagittarius Dwarf Galaxy the Virgo Stellar Stream, and the Canis Major Dwarf Galaxy) and is part of a cluster of galaxies known as the Local Group, which is itself a component of the Virgo Supercluster, which is a component of the Laniakea Supercluster. Galaxias is the second largest galaxy in the Local Group, the Andromeda Galaxy (M31) being larger.
Galactic Mapping and Coordinates
Positions of objects in Galaxias are specified by six primary directions nominally labelled Coreward (toward the galactic core), Rimward (diametrically opposite the direction of the galactic core), Spinward (in the direction of galactic rotation), Trailing (opposite the direction of galactic rotation), North (above the galactic plane), and South (below the galactic plane).
Modern Imperial astrogational coordinates and directions within Galaxias are specified both by the latitudinal distance from the galactic core and longitudinal angle from a meridian that extends from the galactic core through a reference point defined by the central star of the star system known as Reference. Please see Galactic Directions and the appropriate section in the article Astrography for details.
The old Solomani system of spherical galactic coordinates is based on a meridian-line running between the star Sol and Sagittarius A*, with Sol at the origin of the coordinate system. Due Coreward is defined as bearing 000o longitude, due Spinward is defined as bearing 090o longitude, due Rimward is defined as bearing 180o longitude, and due Trailing is defined as bearing 270o longitude. Spherical coordinate latitude angles are defined as a bearing angle +/- 90o above (i.e. North of) or below (i.e. South of) the galactic plane.
Galaxias is home to Humaniti and hundreds, perhaps thousands, of other sapient non-human species. In some of Galaxias's systems, life has come and gone, and their worlds bear the marks of long-dead civilizations. In other systems, life has not yet arisen, though some day it may. But in many systems, worlds have produced intelligent life, known as NILs, with cultures and societies almost too strange to understand.
Vilani Galaxy Appellation
The Vilani name for the Milky Way Galaxy is Dakhaseri, after an ancient Vilani story that tells of meritorious souls allowed to watch the events of the world; their discussions (and futile attempts to intervene) are the basis of many Vilani myths.
|This page uses content from Wikipedia. The original article was at Milky_Way. The list of authors can be seen in the page history. The text of Wikipedia is available under the Commons Attribution-ShareAlike 3.0 Unported License.|