 Stardates were established in order to keep the audience guessing as  to when the series takes place. A calendar year for the adventures  of the Enterprise crew is never given in any episode, and  Gene Roddenberry (qv) said the series could have taken place  anywhere from the 21st to the 31st Centuries. By the time of  _"Star Trek: The Next Generation" (1987)_ (qv), however, calendar  years for Trek adventures had been established and the official Star  Trek Chronology now indicates that the original "Star Trek" TV  series takes place between the years 2266 and 2269.