“Most viewers seem to have little difficulty in staking out some fairly clear territory from which to start thinking about the science fiction film, and certainly are not much troubled by […] fundamental questions of generic boundary or definition – all concerns that are seemingly best left to critics and academics. Anyone who has watched even a few science fiction films, episodes of a Flash Gordon serial, or several episodes of the Star Trek or Babylon 5 television series, for example, would probably argue that he or she could, with little hesitation, decide if a certain work belongs within the science fiction category. That sense of certainty probably springs from the fact that the typical viewer easily recognizes particular hallmarks, visual icons that, over the course of many years, have helped constitute a common signature that cultural consensus or historical use has by now assigned to the genre. Included in this broad category are such things as character types, situations, clothing, lighting, tools or weaponry, settings – all those elements that have often been described as the “language” of the genre, and much of which has been long established in the popular consciousness thanks to the corresponding literary tradition and its reliance on illustration, on visualizing its “what if” scenarios.”
Telotte, J.P. “Introduction: The World of The Science Fiction Film, Chapter, Genre Determinations.” Science Fiction Film. Cambridge: Cambridge University Press, 2001. pp16-17.