For Todd Slatt, a.k.a the "Aurora Hunter" photographing the northern lights is nothing out of the ordinary, but last Saturday, he witnessed something emerging from the darkness of the night sky that shocked and inspired him.

A spiral of pale blue light began to form in the distance, growing ever larger and coming ever closer to the man holding his camera and his breath.

Eventually, it completely passed over his viewing spot in Delta Junction, Alaska, leaving the expert photographer mystified.

"It was a beautiful piece of art in the sky," Slatt told Anchorage News Daily. "I would say this was maybe the most bizarre thing I've ever seen in my life."

Residents farther north, who are used to wild weather phenomenon, also saw the spiral and wondered what it was.

Like many others that night, Slatt did some research and soon appeared on his Facebook with a stunning image of the spiral and a surprising explanation for its origin.

"After doing some online research, this phenomenon appears to be rocket engine exhaust from a SpaceX Transporter-7 mission that launched on the Falcon 9 about three hours earlier in California," he wrote.

"Water vapor in the exhaust (or jettisoned fuel causing it to spiral?) from the second stage engine freezes and catches high-altitude sunlight, effectively glowing and creating this spiral-galaxy-looking display of light."

The beauty of the aurora is augmented no end by the blue spiral atop it, and serves to make the sky look somewhat like a national flag.

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