A strange spiral appears amidst the Northern Lights in the Alaskan night sky

ANCHORAGE, Alaska (AP) — Aurora lovers got a surprise for the green bands of light dancing across the Alaskan sky: A bright blue galaxy-like spiral appeared in the middle of the aurora borealis for a few minutes.

The reason early Saturday morning was more mundane than an alien invasion or the appearance of a portal to the edge of the universe. It was excess fuel fired by a SpaceX rocket that launched from California about three hours before the spiral appeared.

Sometimes rockets contain fuel that needs to be disposed of, said astrophysicist Don Hampton, an associate research professor at the University of Alaska’s Fairbanks Institute of Geophysics.

“When they do it at high altitude, that fuel turns into ice,” he said. “And if it happens in sunlight, when you’re in the dark on Earth, you can see it as kind of a big cloud, and sometimes it just goes around.”

Although it is not common, Hampton said he has seen such events about three times.