I’ve drafted a section on the astrography to take up one page of a new Flat Black players’ brief. Please let me know whether you think this is adequate and clear, and whether the material deserves so much as a page.
The setting of Flat Black is a sphere approximately 175 light-years in radius, centred on Sol. This is a tiny fraction of the Galaxy, wholly embedded in the thickness of the Galactic disk. It contains over forty thousand stars: about one seven-millionth of the Galaxy. Scattered through that volume are one thousand worlds inhabited by humans.
Earth has no oceans or atmosphere any more; it was wrecked in AD 2353 (606 years ago) by a catalytic thermonuclear explosion originating at Buenos Aires. Earth is uninhabitable, but for political and symbolic reasons the Empire built several important space habitats in orbit around the ruins of Earth—including the Imperial capital.
640 colonies were established from Earth before its destruction, of which 625 survived. These “primary colonies” are all within 146 light-years of Sol. The colonies nearest Earth were established first, and received immigrants and supplies from Earth for up to 250 years before Earth was destroyed. Further out the colonies are younger and had less wherewithal to establish a population and industrial base before being cut off. Beyond the primary colonies there are 375 secondary colonies that have been established within the last fifty years, settled by pioneers and migrants from the primary colonies. These are mostly 140–175 light-years from Sol.
People speak of the “Core” (consisting roughly of worlds within 65 or 75 light-years of Sol), of the “Periphery” (consisting of primary colonies outside the Core), and the “Fringe” (consisting of recent, secondary colonies). The Core is supposed to be rich and politically advantaged, though in fact it has some miserably undeveloped worlds in it. The Periphery is supposed to be backward, politically neglected, and under-served by interstellar transportation—which is an over-simplification at best. The Fringe is new enough to have no place in the common concept of the universe, and is often treated as a bit of a joke.
The average distance of a colony from its nearest neighbour is 14.8 light-years, a journey of 5.4 days at typical interstellar liner speeds. Even though interstellar fares and freight rates are modest, the large cost in time means that few people travel and very few travel often. Interstellar visitors are rare, cultural influences are slight, and the worlds are socially isolated.
The median distance of a colony from the Imperial capital is 133 light-years (51 days). It takes over four months to cross the sphere of habitation or send a message from the frontier to the Capital and receive a reply. Because of slow response times, the Empire established nineteen “Sector HQs” in a shell about 100–120 light-years from Sol, to serve as reinforcement depots for its scattered contingents. Each inhabited world is assigned to a sector corresponding to the nearest SHQ, or to Central Sector if Sol is nearest. Despite this, the average distance of a primary colony from its SHQ is 41.8 light-years (fifteen days), and the furthest (Stockbrook at Zeta Cygni) is 73.5 light-years (26.8 days) from its SHQ (Andromeda SHQ in Gliese 9830). Imperial operations are five to 27 days each way from reinforcement and senior officers.
The sectors are named for the astronomical constellation that their HQs are in: Andromeda, Aquarius, Cassiopeia, Centaurus, Cetus, Corona Australis, Draco, Eridanus, Gemini, Hercules, Hydra, Leo, Libra, Pisces, Puppis, Reticulum, Sextans, Ursa Major, Virgo. Note that in the case of a sprawling constellation such as Eridanus, not every star in the constellation is necessarily in the corresponding sector.
Central Sector is somewhat smaller than the Core, containing no colonies further from Sol than 57 light-years.
Previous discussion of this topic may be found in the following linked topic: