Sector measurement system - SUMMARY

In interstellar mapping, a sector is a volume of space measuring approximately twenty light-years across. A typical sector in United Federation of Planets space contains about six to ten star systems, although sectors toward the galactic core will often contain many more.

The Milky Way Galaxy is divided into hundreds of thousands of sectors, grouped into four quadrants.

Sectors are usually numbered, although in common usage they are often named for a major star or planet located in that sector. Earth's star system, for example, is Sol (the name of the sun).

The numbering system for sectors had been inconsistently used (and sometimes interchanged with quadrants) during Star Trek, especially in its early days, these being mainly confined to [TOS]. To deal with inconsistencies arising from that time, and thereby retain plausibility for reasons of 'suspense of disbelief', it is possible to assume that some sectors may retain older designations from previous mapping systems, in the same way that present-day astronomers still use NGC and Messier catalogue numbers.

Sector measurement system

(The following is explained by and illustrated by Geoffrey Mandel, Star Trek's star-mapper and author of source STSC, with minor additions or clarification by me.) The first digit (or letter) in the sector designation refers to the SUBQUADRANT, a wedge-shaped slice of the galactic disc 50,000 light years long, 3,600 light years high, and 8,727 light years wide at its widest point.

The second digit (0-9) refers to the SECTOR ZONE, a concentric circle 5,000 light years wide and 3,600 light years high centred on the galactic core.

above: sideways view

above and below: the thick orange line denotes the galactic meridian and the meeting point of the four Quadrants

above: dorsal view - part of the Milky Way Galaxy

Each intersection of a subquadrant and sector zone is a SECTOR GRID 5,000 light years long by 3,400 light years high (for instance, sector grid 15 is the intersetion of subquadrant 1 and sector zone 5). The width of a sector grid depends on its distance from the galactic core. Near the United Federation of Planets, a sector grid is approximately 4,500 light years wide at its widest point.

Sector grids are divided into 100 SECTOR QUADS of equal volume, which are number 00 through 99. These represent the third and fourth digits in the sector designation (prior to the mid-24th century, sector quads were commonly although mistakenly referred to as "quadrants"). Closer to the galactic centre, sector quads will resemble wedges rather than cubes, and the further from the centre of the Galaxy, the larger the volum of space contained in each sector quad.

Each sector quad is divided into 900 or more roughly cubical SECTOR BLOCKS (also known as "Sectors" with a capital "S"). The next three digits in the sector designation (000-999) represent the number of thie sector block. Near the United Federation of Planets, sector blocks are exactly 100 light years long by approximately 100 light years wide, with a height of exactly 80 light years.

Sector blocks are laid out in a 9 x 10 x 10 grid instead of a 10 x 10 x 10 grid so that the resulting sectors wil be as close to perfect 20 light year cubes as possible. Further out from the galactic centre, the width of a sector block increases from 9 sectors to 10 or more.

Finally, each sector block is divided into 100 sectors proper, each exactly 20 light years long by exactly 20 light years high by approximately 20 light years wide. The sector number (00-99) represents the final digits of the sector designation.

Near the United Federation of Planets, sectors resemble perfect cubes, 20 light years on each side, with the slight curvature all but invisible due to the Galaxy's immense size. Typically, a sector contains approximately 40 stars, about two-thirds of which are members of a binary, trinary or quadrinary system. However, in dense globular star clusters, a sector may contain as many as several thousand stars, and in the void between spiral arms, sectors may contain no stars at all.

Since the vast majority of explored sectors are contained in the sector grids bordering the United Federation of Planets, the sector grid designation (for instance, "15°") is often omitted. In fact, in common usage, it is not unusual to refer to a sector by its last five digits ("sector 07612"), or even its last two digits ("sector 12). Given this numbering system, the last five digits of a sector designation will always be unique for a distance of at least 800 light years in any direction, and the last two digits will always be unique for a distance of at least 80 light years.

In the illustration below, stars and star systems have been greatly enlarged for clarity. Distances above and below the galactic plane are shown approximately to scale.

The two views (top view shown above, side view shown below - see the two illustrations together) show the eight sectors nearest to Sol, as seen from above the galactic plane as well as in a cross-section view through the Alpha/Beta Quadrant border. Each angle tells only part of the story. An observer might assume that 61 Cygni is the closest star to Sol from this side view, while the top view shows that it is actually some 11.36 light years away.

By convention, SOL SECTOR is known as SECTOR 001. This designation has no relation to the overall sector designation system. It merely indicates that this was the first sector explored by manned space vessels. Nearby sectors are numbered in the order in which they were explored, beginning with Alpha Centauri sector (which is Sector 002).

Although the Sol system is located in the exact corner of the sector, and is thus divided equally among all eight sectors, it is considered to be Sector 001 for the purposes of celestial navigation. Similarly, while the Sol system is divided equally between the Alpha and Beta Quadrants, it is considered to be part of the Alpha Quadrant.

excerpt of star chart of Federation space, showing Sol at the centre or meeting point of the four Quadrants - the thick orange line is the galactic meridian; the curved thin orange lines represent the distance from Sol measured in 10 light year increments

On the next pages there follows a multi-page illustrated list of the sector numbers according to the Federation and Starfleet star-mapping standard and conventions, and their mentions in [Voyager] and other Star Trek.

NEXT PAGE: Sector 001