Sirius was a star system in the Alpha Quadrant. Located less than 20 light years from Sol, this system consisted of binary companion stars, Sirius A and Sirius B. This system had at least nine planets, including Sirius IX.
The location of Sirius in the Milky Way Galaxy was depicted on a Federation star chart in 2293. (TAS: "Mudd's Passion"; Star Trek VI: The Undiscovered Country, production art; TNG: "The Naked Now", display graphic)
In 2364, on several occasions that year, viewscreen readouts aboard the USS Enterprise-D showed the location of Sirius A and B stars, in the form of charts from the Enterprise library computer. (TNG: "The Naked Now", "The Last Outpost", "Conspiracy")
Behind the Scenes
The Sirius group was mentioned in Gene Roddenberry's original Star Trek pitch in one of the suggested story lines. In the storyline "Kentucky, Kentucky," the Sirius group was home to an Earth colony for fifty years. This colony was attacked by viking-like savages and reduced to a "frontier" log-fort life. They were regrouped and led by Captain Robert April when the SS Yorktown visited the colony.
This chart naming stars within 20 light years of Sol was drawn by Rick Sternbach for the Star Trek Spaceflight Chronology in the late 1970s. Found on page 77, this chart showed Earth commercial and exploration routes after the use of warp drive began. Sirius A was a destination on an exploration route.
The Explored Galaxy
"The Explored Galaxy" was a map of charted space in the Alpha Quadrant. Sirius was located between the Tholian Assembly and Romulus. Both locations were identified in DS9: "The Search, Part II", "Call to Arms" as being located in this quadrant. This chart was also seen in several Star Trek: The Next Generation and Star Trek: Deep Space Nine episodes set in the 24th century, from the year 2364 to 2370. These were: TNG: "Conspiracy", "The Measure Of A Man", "The Emissary", "The Mind's Eye", "The Game" and DS9: "In the Hands of the Prophets", "Cardassians".
Sirius (or Alpha Canaris Majoris) was located in or near Federation space, in the Beta Quadrant. This was a binary star system. Sirius A was an A-class star with a magnitude was +1, which was a hundred times brighter than Sol. Sirius B was an A-class star. (Pgs. 45)