Starfleet Line Officers
Starfleet Line Officers represent the bulk of the members of Starfleet holding officer ranks, with responsibilities ranging from the command of starship to junior staff positions on minor outposts. Line officers are subordinate to flag officers and have authority over more junior line officers and all non-commissioned officers. There are eight line officer ranks.
Fleet Captain
Captain
Captain, is as the name suggests, the rank assigned to those officers fortunate enough to be granted the command of a starship. While lower ranking line officers do also hold commands of some smaller starships, the rank of captain carries with it additional prestige and authority, as well as greater access to sensitive information. Starfleet captains are also empowered as ambassadors for the United Federation of Planets, with the ability to negotiate on behalf of the Federation Council. Captains also command starbases and space stations, serve as aides to flag officers, and head up departments on large stations and starships. It is possible to reach this rank without commanding a starship at all, though for an engineer or physician to reach this rank, they would have to be extremely talented and have a long and exemplary service record. Most captains have served with Starfleet for at least twenty years before promotion, but there have been notable exceptions such as Tryla Scott and James T. Kirk over the decades.
Captain is also a title and is the correct way of addressing the commanding officer of a starship while they are onboard their own ship, regardless of their actual rank. This courtesy does not extend to the commanding officers of space stations.