How an Explosion (Not Aliens) Turned New York's Night Sky an Electric Blue

By Friday morning, it was as if nothing had happened.

The power was back on for those who had lost it. Flights were operating as expected at La Guardia Airport, which was forced to ground all flights after its lights went out. And the No. 7 subway line, which was delayed after the incident, was operating with “good service.”

The sky was back to its appropriate hue.

Still, even if the aqua glow didn’t linger for long, the questions did. Among them: Did the accident leave any pollution or contamination? (Authorities said no.)

At the same time, countless people who saw the so-called Astoria Borealis — IRL or on social media — were left asking: Just why was the sky so blue?

— First, we should ask why it happened

The bizarre illumination was sparked by an “electric arc flash” tied to faulty equipment at a Con Edison substation, a spokesman for the utility, Bob McGee, said early Friday.

The equipment, about 20 feet above the ground, contained cables that transmit 138,000 volts of electricity — a staggering amount compared to the 120 volts supplied to American households.

An arc produced by equipment of that magnitude often looks similar to a thunder and lightning event, McGee said.

While initial reports Thursday traced the glow to a transformer explosion or a fire, McGee said there was no fire, and there were no transformers involved. There were also no injuries in connection with the fault, though Con Ed said one employee reported eye irritation from the flash.

The precise cause of the malfunction was still unknown Friday, but Con Ed said in a statement that the flawed equipment was associated with voltage monitoring. The utility was still investigating the incident Friday.

Con Edison employees who work at the substation thought the incident was a “one-off event” that was not caused by any larger issue, said John Melia, a spokesman for Local 1-2 of the Utility Workers Union of America, which represents Con Ed workers.

The Police Department said in an email that it did not believe there was “any criminality involved” in the explosion.

— So why was the sky that color?

When an electrical current moves through air in an electrical arc, it alters the molecules in the air, charging them with energy, splitting them into atoms and ionizing them. Electrons, excited by the extra energy, get separated from their atoms. The result is a plasma, or charged gas.

When the electrons and ions in a plasma recombine, the atoms glow and emit visible light. The same process is behind fluorescent light bulbs, neon signs and lightning. In all those cases, the color of the light is characteristic of the elements and atoms involved.

On Thursday, when the electrical arc ripped apart oxygen and nitrogen molecules in the air, the light was a surreal blue. (Da ba dee, da ba da.)

The flash continued for as long as there was power to supply it. Once the faulty equipment stopped emitting an electrical current, New York’s brief close encounter ended.

— What about the sound?

Some people who saw the electrical arc flash and its aftermath reported hearing a loud hum. Others described hearing loud bangs.

Lucy Paul, who works at a diner near the Con Ed facility but lives about 1 mile away from it, said she heard a loud boom that made her think a plane had crashed at La Guardia.

Her co-worker Serafina Santos, who lives one avenue away from the substation, described the sound as an electrical noise. “You heard the surge,” she said Friday.

That noise was created when the arc struck the ground, McGee said. Again, like thunder and lightning, he said.

Joe Sanchez, 48, who lives seven blocks away from the substation, estimated that the light-and-sound episode lasted about three minutes.

“You could smell the electricity in the air,” Sanchez said Friday. “The whole area felt charged.”

— And we’re sure it wasn’t aliens?

We’re pretty sure. So are Con Edison and the Police Department.

— Will there be any long-term effects?

Until Con Ed finishes investigating, it won’t know the extent of the damage to the substation, or the cost or time required to repair it, officials said. But electricity outages caused by the incident were resolved by Friday morning.

Melia said the utility workers’ union did not believe there was any reason to be concerned about the safety of the facility.

In connection with the incident, about 3 gallons of dielectric fluid, which cools electrical equipment, were released, a Con Ed spokesman said Friday. But the fluid, which is not hazardous, was contained within the substation, and the spokesman said the company did not expect there to be a major environmental impact.

— So where did ‘Astoria Borealis’ come from?

Well, Twitter, of course.

More than a few variations on the same jokes circulated on social media Thursday night, and references to the northern lights were among them.

So, too, were “Ghostbusters” references, “Transformers” jokes and mentions of superpowers.

This article originally appeared in The New York Times.