Space is a vacuum: the only song capturing the verbatim resonance of space is John Cage’s perfectly silent “4'33".” Any artist purporting to embody the acoustics of the cosmos is projecting a myth. That myth, however, is collective and widely understood. Space has no sound, but certain sounds are “spacey.” Part of this is due to “Space Oddity”; another part comes from cinema, particularly the soundtrack to 2001 (the epic power of classical music by Richard Strauss and György Ligeti). Still another factor is the consistent application of specific instruments, like the ondes martenot (a keyboard that vaguely simulates a human voice, used most famously in the theme to the TV show Star Trek). The shared assumptions about what makes music extraterrestrial are now so accepted that we tend to ignore how strange it is that we all agree on something impossible.

The application of these clichés is most readily seen in the dawn of heavy metal. The 1970 Black Sabbath song “Planet Caravan” processed Ozzy Osbourne’s vocals through a Hammond organ to create a sprawling sense of ethereal distance. Deep Purple’s 1972 “Space Truckin’” used ring modulation to simulate a colossal spacecraft traveling at high speed. The lyrical content of Led Zeppelin’s “No Quarter” is built on Norse mythology, but the dreamlike drone of John Paul Jones’s mellotron and Jimmy Page’s ultra-compressed guitar mirrored the sensation of exploring an alien landscape. Unsurprisingly, the ambiance of these tracks merged with psychedelic tendencies. The idea of “music about space” became shorthand for “music about drugs,” and sometimes for “music to play when you are taking drugs and thinking about space.” And this, at a base level, is the most accurate definition of the genre we now called space rock.

More ideologically intertwined with ’60s prog than ’70s metal, the qualities of space rock are delineated by the mood they manufacture: hypnotic song structures, punctuated by distortion that’s heavier than the riffs. The lyrics tend to be low in the mix and not particularly essential, but the focus on the galactic is overt: Hawkwind’s 1973 live album Space Ritual featured voice narration from sci-fi poet Robert Calvert. Because space rock songs tended to be long, meandering, and performatively trippy, they weren’t much played on commercial radio, with one notable exception: Pink Floyd. That exception, much like Bowie’s “Space Oddity,” culturally dwarfs the totality of its competition.

When rock was new, space was new—and it seemed so far beyond us. Anything was possible.

Dark Side of the Moon, Pink Floyd’s eighth studio album, is the most durably popular rock album ever recorded, selling nearly 50 million copies and remaining in the Billboard Top 200 for 917 weeks after its release in 1973. It’s a concept album, and it’s not about the moon. It does, however, allow a teenager lying in a dark room to feel as though that is where he’s going. The apotheosis of all the fake audio signifiers for interstellar displacement, Dark Side of the Moon (and its 1975 follow-up Wish You Were Here) perfected the synthesizer, defining it as the musical vehicle for soundtracking the future. Originally conceived as a way to replicate analog instruments, first-generation synthesizers saw their limitations become their paradoxical utility: though incapable of credibly simulating a real guitar, they could create an unreal guitar tone that was innovative and warmly inhuman. It didn’t have anything to do with actual astronomy, but it seemed to connote both the wonder and terror of an infinite universe. By now, describing pop music as “spacey” usually just means it sounds a little like Pink Floyd.

If America’s obsession with the space race during the 1960s explains the rise of space rock in the ’70s, it follows that waning public interest in NASA (post-Apollo) led to a decline in space-related music in the ’80s and ’90s. Tunes like “Space Age Love Song” by Flock of Seagulls or “Space Is the Place” by Spacehog did not seem inspired by anything unworldly; they just seemed to use the word “space” as a meaningless monosyllabic placeholder. Soundgarden’s “Black Hole Sun” derived not from an interest in the sky but from a misheard TV report. Even the most serious attempts contained elements of kitsch and caricature: the UK outfit Spacemen 3 was maybe the best of the bunch, but the group’s music was overshadowed by their comedic self-awareness. The last major rock album that felt like music from space was arguably Radiohead’s OK Computer, but the connection was ancillary. The band was simply using the instruments, tunings, and tempos that have become associated with space-age pop. The audience felt the correlation more than the artist.

What has happened, it seems, is that our primitive question about the moon’s philosophical proximity to Earth has been incrementally resolved. What once seemed distant has microscoped to nothingness. When rock music was new, space was new—and it seemed so far beyond us. Anything was possible. It was a creative dreamscape. But you know what? We eventually got there. We went to space so often that people got bored. The two Voyager craft had already drifted past Pluto before Nirvana released Nevermind in 1991. You can see a picture of a black hole in the New York Times. The notion that outer space is vast and unknowable has been replaced by the notion that space is exactly as it should be, remarkable as it is anodyne. In 1997, one of the former members of Spaceman 3, Jason Pierce, made an album with his new band, Spiritualized, titled Ladies and Gentlemen, We Are Floating in Space. That title was a reference to a Norwegian novel, but it accidentally illustrated precisely how much perception had changed. Space was no longer somewhere to go. Space was where we already were, all the time, and we were just floating along for the ride.

Chuck Klosterman is an author and essayist whose books include Fargo Rock City and But What If We’re Wrong?