Blue light illuminates the night sky over New York City after a transformer explosion.Melissa Coffey via Reuters

With a flash, the sky over New York City turned a mystical blue.

The spectacle, which appeared without warning on Thursday night, stunned observers. They sensed something was wrong—because, obviously, would you look at the freaking sky?—and quickly formulated some possible explanations. The theories leaned heavily on science fiction. Maybe the glow signaled the end of a massive battle between superheroes. Maybe it was an alien invasion. Maybe the apocalypse was nigh, and this, these eerie turquoise clouds over Queens, were the first sign that the end was near.

What people witnessed was much less dire: a quirk of electricity. Just after 9 p.m. local time, some equipment at an electrical power plant in the Astoria neighborhood short-circuited. (There was no explosion or fire, contrary to early reports.) According to the station’s operator, Con Edison, the malfunction produced something called an arc flash. A powerful electric current shot into the air and sent atoms of gas in the air into a state of excitement. When atoms become excited, they emit light, and different gases produce different colors. In this case, the atmospheric recipe resulted in a ghostly blue.

“No injuries, no fire, no evidence of extraterrestrial activity,” the New York Police Department tweeted, extinguishing most of the theories that had flooded social media.

It was a joy to watch the discussion of the blue light unfold online. This strange December night encapsulated so much of what makes the internet great: the dissemination of captivating photos and videos in real time, a shared sense of camaraderie that transcends state lines and borders, and some pretty funny jokes. But the evening also tapped into something much older and more primal. We human beings have long been intrigued by strange lights in the sky. Like the blue glow over New York, these sights have baffled, scared, and mesmerized us, even when we’ve known their source.

Perhaps the oldest example is the aurora borealis, the resplendent performance of dancing lights in the night sky. Today, we know the northern lights are the product of electrons from the sun interacting with different gases in Earth’s atmosphere. But centuries ago, observers, captivated by the wisps of colors, dreamed up their own explanations. In ancient China and Europe, the auroras were dragons and serpents, flitting around in the night. In Scandinavian folklore, they were the burning archway that allowed gods to move between heaven and Earth. During the American Civil War, soldiers thought the lights were a sign of disapproval from God to the Confederacy.

During at least one time in history, the sight of weird lights in the sky became a business opportunity. Starting in the early 1950s, during the height of the Cold War, the United States government detonated thousands of atomic bombs in the Nevada desert, illuminating the sky with bright flashes. The city of Las Vegas, located just 65 miles away, saw lucrative potential in the morbid spectacle, and decided to monetize the mushroom clouds. As Laura Bliss wrote in a 2014 CityLab story:

The Chamber of Commerce printed up calendars advertising detonation times and the best spots for watching. Casinos like Binion’s Horseshoe and the Desert Inn flaunted their north-facing vistas, offering special “atomic cocktails” and “Dawn Bomb Parties,” where crowds danced and quaffed until a flash lit the sky. Women decked out as mushroom clouds vied for the “Miss Atomic Energy” crown at the Sands. “The best thing to happen to Vegas was the Atomic Bomb,” one gambling magnate declared.

Spectators knew what they were looking at, but they were still astonished—excited and frightened at the same time. “People were fascinated by the clouds, by this idea of unlocking secrets of atom,” Allen Palmer, then the executive director of the National Atomic Testing Museum, told CityLab. “But there was absolutely an underlying fear—we were so close by.”

In other cases, a shroud of mystery can heighten those feelings. Around the same time tourists in Las Vegas were watching nuclear explosions bloom, Americans on the other side of the country were enthralled by a different kind of light in the sky. On a summer day in 1952, multiple people in the Washington, D.C., area reported spotting several unearthly points of light traveling over the landscape. One commercial pilot described them as “falling stars without tails.” When they approached the White House, the military summoned a pair of jets to intercept the unknown flyers, but no mystery invaders were found.

The next day, the news of the moving objects was all over the news. Headlines suggested, in capital letters, that the objects were extraterrestrial. Government officials, stumped themselves, didn’t exactly try to quash the rumors. According to The Washington Post, an unnamed Air Force source told reporters: “We have no evidence they are flying saucers. Conversely we have no evidence they are not flying saucers. We don’t know what they are.”

Unidentified flying objects have maintained this allure for decades. As recently as 2012, the Pentagon was operating a program to investigate reports of UFOs. When The New York Times broke the story in late 2017, it proved to be full of the hallmarks of a timeless mystery—surprise, suspense, wonder.

The blue lights over New York were a good mystery, too. The unnatural glow eventually dimmed and the sky returned to its usual evening hue. Con Edison resumed normal operations. People went on with their lives. But for a brief time, they were engaged in a long-standing tradition: trying to make sense, together, of something strange in the sky.

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