The Sirius Sector is not the immediate sector around the Sirius Star (albeit it includes it), but the sector of the sky seen from the Earth when you look at the Sirius Star, if the star is in the middle of your view field. Thus, the Solar System can also be part of the Sirius Sector, but doesn't have to. Likewise, the Sirius Star isn't necessarily part of the game map -- it could be a number of light years behind it, or in front of it.