Close Encounters of the Third Kind, I wondered what made this such a phenomenon. The aliens are totally cloaked in incomprehensibility. Later, Spielberg would make the alien human in E.T., which makes the popularity understandable, but the complete mystery of Close Encounters must have tapped into a 70s zeitgeist. Perhaps piggybacking on Close Encounters, Omni Magazine, 1978, survived the era's surfeit of science magazines by including paranormal phenomena and treating them as seriously as science. But that era's acceptance of mystery had to have precedent.
In discussing aliens, Wikipedia notes the background events of Orson Wells' 1938 radioed Martian hoax on the public, 1947 Roswell, and subsequent proliferation of UFO religions. Literary precedents include H. P. Lovecraft's (~1920-1930s) inexplicable horrors and James Gunn's 1972 The Listeners, which is said to have inspired a number SETI scientists.
Lovecraft's focus, however, is the evocation of horror and Gunn's is the scientific progress needed to uncover communication with aliens. Close Encounters, meanwhile, touches on all of the above: government cover-up, horror, hoax, science, and perhaps most significantly an almost spiritual encounter with the other. Spielberg plays up the mystery of light, simple music, and visions of mountains reconstructed in mud, clay, charcoal, and most famously mashed potatoes. Not just the aliens behave inexplicably but those visited by aliens. Roy tears up his and his neighbor's yard to the spectacle of the neighborhood. Every time Roy tries to patch up things with his wife, his obsession with aliens intervenes. He asks, "What is it?" and "What's going on?" but there are no answers except MacGuffins like the mountains and light and sound.
Music of the film, the soundtrack of which went gold, plays a more integral part of the storytelling as the UFO's theme is revisited. Wikipedia states, "In 1998, Spielberg recut Close Encounters again for what would become the 'Collector's Edition' .... but omits the mothership interior scenes which Spielberg felt should have remained a mystery." And Roy volunteers to be taken away from his family into the bright unknown.
What a curious film, and how curious that it captured the imagination of so many, relying as it does on the impact of mystery.