Science fiction fandom other groups including LGBT communities, libertarians, neo-pagans, and space activist groups like the L5 Society, among many others. Some groups exist almost entirely within fandom but are distinct and cohesive subcultures in their own rights, such as filkers, costumers, and convention runners (sometimes called "SMOFs"). Fandom encompasses subsets of fans that are principally interested in a single writer or subgenre, such as Tolkien fandom, and ("Trekkies"). Even short-lived television series may have dedicated followings, such as the fans of Joss Whedon's "Firefly" television series and movie "Serenity", known as Browncoats. Participation in science fiction fandom often overlaps with other similar
Television show November. British shows have tended toward shorter series in recent years. For example, the first series of long-running science fiction show "Doctor Who" in 1963 featured forty-two 25‑minute episodes, this dropped to twenty-five by 1970 to accommodate changes in production and continued to 1984. For 1985 fewer but longer episodes were shown, but even after a return to shorter episodes in 1986, lack of support within the BBC meant fewer episodes were commissioned leading to only fourteen 25‑minute episodes up to those in 1989 after which it was cancelled. The revival of "Doctor Who" from 2005 has comprised thirteen 45‑minute