Milky Way

The Milky Way is the galaxy where the Humans and the Covenant reside. It is a barred spiral galaxy that lies with the Local Group of galaxies neighborhood of the Universe, visible from Earth as a band of light in the night sky. Although the Milky Way is one of billions of galaxies in the observable universe, the Galaxy has special significance to Humanity as it is the home galaxy of the planet Earth.

Structure
The Milky Way is estimated to contain 200 billion, or up to 400 billion, stars (if small-mass stars predominate). As a guide to the relative physical scale of the Milky Way, if it were reduced to 130 km (80 mi) in diameter, the Solar System would be a mere 2 mm (0.08 inches) in width. The Galactic Halo extends outward, but is limited in size by the orbits of the two Milky Way satellites, the Large and the Small Magellanic Clouds, whose perigalacticon is at ~180,000 light-years. New discoveries indicate that the disk extends much farther than previously thought.

The galactic disk, which bulges outward at the galactic center, has a diameter of between 70,000 and 100,000 light-years. The distance from the Sun to the galactic center is now estimated at 26,000 ± 1400 light-years, while older estimates could put the Sun as far as 35,000 light-years from the central bulge. The galactic center harbors a compact object of very large mass (named Sagittarius A*), strongly suspected to be a supermassive black hole. Most galaxies are believed to have a supermassive black hole at their center. The Galaxy's bar is thought to be about 27,000 light-years long, running through its center at a 44 ± 10 degree angle to the line between the Sun and the center of the Galaxy. It is composed primarily of red stars, believed to be ancient (see red dwarf, red giant). The bar is surrounded by a ring called the "5-kpc ring" that contains a large fraction of the molecular hydrogen present in the Galaxy, as well as most of the Milky Way's star formation activity

Each spiral arm describes a logarithmic spiral (as do the arms of all spiral galaxies) with a pitch of approximately 12 degrees. There are believed to be four major spiral arms which all start at the Galaxy's center. These are named as follows, according to the image at left: Outside of the major spiral arms is the Outer Ring or Monoceros Ring, a ring of stars around the Milky Way proposed by astronomers Brian Yanny and Heidi Jo Newberg, which consists of gas and stars torn from other galaxies billions of years ago.

Orion Arm
The Orion Arm is the place of origin for humanity, with at least 800 worlds colonised by the UNSC at one point. It is also the area of origin for the various races of the Covenant, with possibly even more worlds. It is assumed to be the place of origin for the Forerunners as well, but their mysterious nature and advanced technology means that it is not known exactly where they came from, or if they expanded further out through the galaxy.

The Orion Arm is the setting for the Human-Covenant War of the 26th Century, and the far more ancient Forerunner-Flood War, witnessing at least two massive wars. It is also the home to two Halo Installations and the Ark.

Solar System
The colonization of the Milky Way includes the early colonization attempts of the UN and the UNSC, beginning with the colonization of the Solar System during the 2100's. The first planet believed to be colonized is Mars, followed by the Jovian Moons. During 2160 - 2164, the Solar System was the site of the Interplanetary War, the most brutal conflict known to man since World War II. The war was fought between the UN naval and infantry forces, the Neo-Communist Koslovics (led by hardliner Vladimir Koslov), and the Frieden rebels (Jovian secessionists). Following the successful Marine deployments on Mars during the Argyre Planitia Campaign of 2163, the UN ultimately defeated both Koslovic and Frieden rebels throughout the Solar System, thus forming the United Nations Space Command.

Beyond
The development of the Shaw-Fujikawa Translight Engine in 2291 enabled the UNSC to explore and colonize planets beyond the confines of the Solar System, thus the Inner Colonies were born. By 2310, the first line of colony ships was made public by the Earth Government. On January 1, 2362, the Odyssey, the first colony ship capable of faster-than-light travel was launched. It was laden with troops and terraforming gear. This sparked the first wave of colonization in the inner colonies. By 2390, the colonization of the Inner Colonies was underway. There were 210 human-occupied worlds in various stages of terraforming, and the population burden across human-controlled space was largely stabilized.

Colonial expansion continued and by 2490, UNSC colonial space encompassed over 800 worlds, large and small in the Orion Arm. The success of colonization of the Outer Colonies made the Inner Colonies the primary stronghold, both military and economic, though they relied heavily on raw materials supplied by the Outer Colonies. During this period, the planet Reach (orbiting Epsilon Eridani, right on Earth's metaphorical doorstep) became the UNSC's primary Naval yard and training academy. Reach was a major producer of warships and colony vessels, as well as a training ground for covert operatives and Special Forces.

On April 20, 2525, contact with the Outer Colony, Harvest, was lost. After failing to re-establish contact with Harvest, the Colonial Military Administration sent a scout ship, the Argo, to investigate. Contact with the Argo was subsequently lost after the ship arrived in the Harvest system, plunging humanity into a deadly war with an alien race known as the "Covenant". Harvest was glassed from orbit, and marked the beginning of the war with the covenant. The war was named the Human-Covenant War.

Summary
Basically every combat engagement, large and small, between either Rebel factions, the UNSC or the Covenant takes place in the home galaxy of the Milky Way. The galaxy is home to both Humans and the Covenant, however, it has been confirmed that it is not the home galaxy to the Flood.

Trivia

 * The only known engagement or conflict to ever take place "outside" the Milky Way (considered the Outer Rim) is the Battle of Installation 00.

Related Articles

 * Humans
 * Solar System
 * Earth
 * Luna
 * Mars
 * Jovian Moons
 * UN
 * UNSC
 * Colonial Administration Authority
 * Colonial Military Administration
 * Covenant
 * Covenant Loyalists
 * Covenant Separatists