Alaskan locals were baffled in the early morning of April 16 as they looked up to the sky to see a light blue spiral resembling a galaxy.
You can rule out northern lights — along with aliens or a portal to the far reaches of the universe.
The cause of the spiral was surprisingly simple.
It was excess fuel that had been released from a SpaceX rocket that launched from California about three hours before the spiral appeared, according to space physicist Don Hampton.
Professor Hampton, from the University of Alaska Fairbanks Geophysical Institute, said rockets sometimes had fuel that needed to be jettisoned.
“When they do that at high altitudes, that fuel turns into ice,” he said.
“And if it happens to be in the sunlight, when you’re in the darkness on the ground, you can see it as a sort of big cloud, and sometimes it’s swirly.”
The appearance of the swirl was captured in time lapse footage on the Geophysical Institute’s all-sky camera and shared widely.
A rare sight, but not an extraterrestrial one
While not a common sight, Professor Hampton said he had seen such occurrences about three times.
“It created a bit of an internet storm with that spiral,” he said.
The SpaceX rocket, Falcon 9, took off from Vandenberg Space Force Base in California on the night of April 15.
It was a polar launch, which made it visible over a large swathe of Alaska.
“The timing was right. They had done some sort of fuel dump at that time, and we got that really cool-looking spiral thing,” he said.
And while it looked like a galaxy passing over Alaska, he promised it was not.
“I can tell you it’s not a galaxy,” he said.
“It’s just water vapour reflecting sunlight.”
AP