In 1947, Kenneth Arnold was flying his CallAir A-2 between Chehalis and Yakima, Washington, when he took a detour to search for a downed Marine Corps aircraft. There was a reward for anyone who could find the plane, and who couldn’t use $5,000?

Arnold flew around searching for a while, and accidentally found something else—something much stranger than what he’d actually been looking for. As he watched, rapt, nine objects flew through the air in formation.

Courtesy of Pegasus Books Excerpted from They Are Already Here by Sarah Scoles. Buy on Amazon.

That’s nothing crazy, really. You’d call it a fleet and go on with your day. But the craft appeared to be traveling much faster than the jets of the time. Arnold allegedly clocked them, as they flew between Mount Rainier and Mount Adams, at significantly more than 1,000 miles per hour. When he landed back on the ground, he—he claimed later—told an East Oregonian reporter that the objects skipped like saucers on water, referring to their motion and not their shape. The reporter wrote, however, that the craft appeared “saucer-like.” That line soon rushed out on the AP wire. The term “flying saucer” showed up a day later—the first time of many times to come—when the Chicago Sun ran the headline “Supersonic Flying Saucers Sighted by Idaho Pilot.” The actual path of the saucer description, from Arnold’s mouth to our modern ears, is more complicated: The reporter held fast to the transcription, and as a National Aviation Reporting Center on Anomalous Phenomena analysis notes, Arnold had plenty of opportunities to correct the record earlier.

“It seems impossible, but there it is,” the article ended, quoting Arnold.

Arnold’s sighting marks the origin point of modern UFO lore and terminology. His story contains several archetypal characteristics (which it would, of course, itself being the archetype): lights in the sky, spotted by a pilot who knows the sky and what should be in it (what insiders call “a reliable observer”), moving fast and with erratic, intelligent-seeming choreography. You could almost swap Arnold with the pilots in the videos from the Pentagon’s Advanced Aerospace Threat Identification Program, which ran secretly from around 2007 to 2012, and the military personnel who have come forward since, saying (probably honestly!) that they have seen quick, creepy, inexplicable things up there. Their status as hardened fighter jocks is what lends their stories credibility and unnerves the softer and less experienced rest of us.

For talking about his story, Arnold got more—and different—attention than he would have liked: People didn’t believe him. It was only a reflection on the glass, a meteor. He had made it all up. In his own book, Coming of the Saucers, Arnold wrote, “I have been subjected to ridicule, much loss of time and money, newspaper notoriety, magazine stories, reflections on my honesty, my character, my business dealings.” He was not happy about it, and according to the 1975 book The UFO Controversy in America, Arnold said: “If I saw a 10-story building flying through the air, I would never say a word about it.” (This statement, though, remains hard to reconcile with the fact that he published his own book, today’s edition complete with pulpy cover art showing bathing-suit-clad women holding pictures of outer space up for some saucer pilots to see.)

Arnold’s sighting, however he felt about it, began an epidemic. Soon, other people around the US started to see their saucers. The night sky opened up, kicking off a ufological period insiders refer to as a “flap”: a period of increased sightings. The term also has the contextual tinge of the word’s other definition, “an increased state of agitation.” Edward Ruppelt, an Air Force officer who would go on to be part of governmental UFO investigations, wrote that “in Air Force terminology a ‘flap’ is a condition, or situation, or state of being of a group of people characterized by an advanced degree of confusion that has not quite yet reached panic proportions.” In this case, the people were not yet panicking about strange sights in the sky.