A sector is one of the 25 equal partitions of the Milky Way galaxy, defined so that the general galactic location of a star or other object can be quickly understood. Since the Milky Way is shaped like a whirlpool, there are only six sectors on the periphery. Each sector is shaped like a perfect hexagon when viewed from the bottom, and extends up into a hexagon-shaped pillar. These interlocking sectors neatly partition the entire galaxy.
The sector that includes the center of the Milky Way is called the Zero Sector. The central point of the Zero Sector lies along a straight line that connects to the point at the center of the universe, or the point from which all galaxies are expanding. Other sectors are drawn in a whirlpool fashion radiating out from this line starting with the Alpha Sector, then the Beta, and so on. The center of the galaxy is much thicker than the surrounding areas, so the seven sectors from Zero to Zeta are also divided vertically, unlike the other sectors. In this case, the sectors above and below the central sectors have either a + (plus) or a - (minus) affixed to the end of each sector name, in order to differentiate them from the central sectors.
If these sectors are also included, the entire Milky Way is divided into a total of 39 sectors.