The Coalsack was a galactic nebula located in the southernmost part of the Milky Way Galaxy. The planet Cheron was located near the Coalsack. By the late 2260s, the region surrounding the Coalsack had not yet been charted by the United Federation of Planets.
In 2269, the USS Enterprise was commandeered by Bele of the planet Cheron, who attempted to divert the Enterprise on course 403-mark-7 from their position near Ariannus. Chekov remarked that the course would have taken them straight to the Coalsack. (TOS: "Let That Be Your Last Battlefield")