It is never made absolutely clear in the series, though the subject has been alluded to.The following is from the BSG Role Playing Game, which is an official product:"The Twelve Colonies spun around a single star on elliptical orbits. Closest to the sun was sweltering, volcanic Canceron, the greatest source of tylium in the system.
Next came a Trojan orbit of planets -- three worlds following the same orbital path, seperated by roughly the same distance (one-sixth the orbit's diameter).
In order, these planets were Aquaria, Caprica, and Virgon. They were centers of art, culture, and system-wide trade.
Two gas giants followed, each in its own elliptical path and each itself orbited by a number of moons.
The first of these behemoths was Zeus, named after the king of the gods, and it's moons were Leonis, Picon, and Scorpia.
Another large planet named Aerelon shared Zeus' orbit, positioned exactly opposite the giant.
The second gas giant was Hera and her charges were Gemenon and Libris, with Sagittaron likewise spinning opposite.
These giants and their moons were the heart of the system. This real estate was the most heavily contested during the colonies' many civil wars.
At the outermost edge of the system dwelled Tauron, followed by a third gas giant named Ragnar.
Tauron was the first world settled after the fall of Kobol. It was the springboard for all expansion in the system."However, in the TV movie Battlestar Galactica: The Plan (2009) (which is obviously higher canon than a role-playing game), the Cylon Hybrid is talking about twelve targets around three stars as the Cylons are about to launch their attack on the Colonies. This suggests that the Colonies are in a trinary star system.http://galactica.wikia.com/wiki/File:Twelve_Colonies_Map.jpgScriptwriter Jane Espensen, who was a prominent writer and producer for both Battlestar Galactica and its spin-off Caprica, helped to develop a map of the 12 Colonies, that was situated in a quadruple star system called Cyrannus. Espensen has stated that this newer map was "quasi-canon" and was created mainly for production purposes and was subject to future revision.http://en.battlestarwiki.org/wiki/Battlestar_Galactica_Map_of_the_12_Colonies