Star Trek Expanded Universe

A depiction of our galaxy as seen in the Voyager Astrometrics Lab

The Milky Way Galaxy (translated from Latin Via Lactea, derived from the Greek Γαλαξίας (Galaxias), often referred to as simply "the galaxy", is a large barred spiral galaxy in the Local Group.

Age and structure[]

Approximately 13.6 billion years old (nearly as old as the universe itself), the Milky Way is roughly 100,000 light years in diameter, 250-300 thousand light years in circumference, and about 1,000 light years thick outside the galactic core. Between 200 and 400 billion stars comprise the galaxy. Although only one of billions of galaxies in the universe, the Milky Way has special significance to humanity as the home of the Sol system.

The galaxy is comprised of three major parts: the core, which contains a supermassive black hole called Sagittarius A; the disc, the ring of stars and interstellar dust that gives the galaxy its spiral shape; and the halo, which includes many older stars orbiting the core. Outside the disc, most stars are concentrated in massive globular clusters.

The Milky Way's disc is surrounded by a massive barrier of unknown origin, which can interfere with travel in and out of the galaxy. A similar force field called the Great Barrier surrounds the core, which is extremely difficult to penetrate. The Q Continuum created these fields in order to protect the galaxy from a gang of powerful malicious beings.

The galaxy is naturally subdivided into several arms, with the Federation and its neighbors occupying the Orion Arm. For the sake of standardized navigation, the Federation and other galactic powers recognize the galaxy as being partitioned into four equal segments, or quadrants: Alpha, Beta, Gamma and Delta, each comprising one-quarter of the galaxy.

By 2365, the Federation had charted only nineteen percent of the galaxy. Due to its immense span and the limited velocities available at warp drive, a number of races use subspace pathways to navigate the galaxy. Some are natural, such as those formerly controlled by the Vaadwaur, while others are artificial constructs, including Borg transwarp conduits, Iconian gateways and the Bajoran wormhole.

The development of quantum slipstream drive and the artificial wormhole network opened the galaxy to widespread exploration beginning in 2378. Combined with extragalactic probes, this led to the popularization of the term Galaxy Alpha, applied to the Milky Way by the mid-2380s. (Star Trek: Arcadia)

Arms of the Milky Way[]

(Radiating clockwise from the center)

  • 3 KPC Arm
  • Norma Arm
  • Crux Arm
  • Carina Arm
  • Orion Arm
  • Perseus Arm
  • Outer Arm
  • Scutum Arm
  • Sagittarius Arm


Thousands of races have existed and continue to exist in the Milky Way. According to Dr. Leonard McCoy, there is a mathematical probability of three million Earth-type (Class M) planets in the galaxy. (TOS: "Balance of Terror") An average of only one in every 43,000 planets in the galaxy supports intelligent lifeforms. Influential races and nations of the galaxy include the Federation, Klingons, Romulans, the Dominion and the Borg. Long ago, the Tkon Empire and the Iconians reputedly ruled large portions of the galaxy. For a complete list of races see races and cultures.

Many species have tried to destroy inhabitants of the Milky Way, including extragalactic parasites, Species 8472 and the Sphere Builders. A Kelvan expedition from the radiation-imperiled Andromeda Galaxy scouted the Milky Way for possible invasion in 2268.

Sargon's people may have been extragalactic, since he stated that his people colonized the galaxy some six million years ago. (TOS: "Return to Tomorrow")

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