Telling humanity's story was, as team member Ann Druyan puts it in the phenomenal "Space" episode of Radiolab, "a sacred undertaking." She and Sagan and their group of, as she calls them, "half a dozen very flawed human beings" had taken it upon themselves to represent humanity as a culture and also as an aesthetic -- to explain to anything that might be out there who, and what, we're all about. They arrived at the idea during a meeting of the American Astronomical Society in January 1977; the Voyager probes would launch in late August and early September. Representing the entirety of human achievement in a single recording would have to be done quickly.

So the group, as humans are wont to do, divided the labor. Jon Lomberg was in charge of assembling pictures of Earth. Timothy Ferris selected the music. Druyan, the project's creative director (and later the co-writer, with Sagan, of Cosmos, and, as of 1981, Sagan's wife) oversaw the record's "Sounds of Earth" essay. Linda Salzman collected greetings from people around the world. Sagan served as the liaison with NASA. The team set about researching -- talking to historians and artists and ethnomusicologists. They reached out to political groups and documentarians. They recorded humans speaking -- among them, in perhaps the record's most iconic track, Sagan's young son saying, "Greetings from the children of planet Earth."

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The result was a time capsule that was (and still is, somewhere out there in space) much more suggestive than summative. Humanity's cosmic mix tape for, and about, itself. Included on the pair of Golden Records that blasted from Earth in 1977 are sounds of the planet, including surf and wind and thunder. The record shares the tweetings of birds, and the calls of humpback whales, and the hootings of chimpanzees. It includes, via Salzman's work, spoken greetings from earthlings rendered in 55 languages -- starting with Akkadian, spoken in Sumer about 6,000 years ago, and culminating with Wu, a modern Chinese dialect. There's music, 90 minutes' worth of it -- music that includes classic tunes from cultures around the globe, including the first two bars of Beethoven's String Quartet No. 13 in B Flat. Jimmy Carter sent a message of greeting on the record. So did U.N. Secretary General Waldheim.

And though the Golden Record does, indeed, adopt the form and the logic of a standard, late-'70s-era record, it's more accurately thought of as a kind of early CD: Its archive contains images from Earth (118 of them) as well as sound.

So how would a notional extraterrestrial, encountering this sweeping record of human existence, actually play it? Like you'd play any record. (NASA apparently assumed that alien civilizations, should they be sufficiently advanced, would be familiar with vinyl. Which is fair.) Each Golden Record is encased in a protective aluminum jacket, along with a cartridge and, yep, a needle. And both include instructions -- in the symbolic language you can see etched in the image above -- that both explain the origin of the Voyager crafts and indicate how the record is meant to be played. (Ideally, NASA explains, the record is played at 16-2/3 revolutions per minute.) The logic of all this is simple: It will be tens of thousands of years (if ever) before either Voyager can make a close approach to any planetary system that lies beyond our own. "The spacecraft," Carl Sagan put it, "will be encountered and the record played only if there are advanced spacefaring civilizations in interstellar space."