Northern Lights enthusiasts were left “bewildered” after a baby blue-coloured spiral resembling a galaxy appeared amid the aroura in the skies of Alaska.

Although it might have looked like the sudden appearance of a portal, or the beginnings of an alien invasion, the sky spiral was caused by excess fuel released from a SpaceX rocket that launched from California about three hours earlier.

“Sometimes rockets have fuel that needs to be jettisoned (dropped from the aircraft). When they do that at high altitudes, that fuel turns into ice,” space physicist Don Hampton, a research associate professor at the University of Alaska Fairbanks Geophysical Institute explained.

“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 rocket took off from Vandenberg Space Force Base in California on Friday 14 April.

Such a rare occurrence, it was no surprise the appearance of the swirl caused an “internet storm” after being caught on time-lapse on the Geophysical Institute’s all-sky camera.

Professional photographer Todd Salat was also left amazed by – what he referred to as – the “really cool looking spiral thing”.

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“This all happened as it passed over Alaska during a beautiful aurora display, stunning many night-watchers including myself,” he said.

“Trust me, at first, I was totally bewildered. I now know it can be explained with rocket science, but during and immediately after the experience, I thoroughly enjoyed the mysterious feeling of the unknown.”

It was the timing of the fuel dump and the fact it was a polar launch which made the blue spiral visible over parts of Alaska.

It comes as this week, Elon Musk’s SpaceX will make a second attempt at launching the world’s most powerful rocket system after the first was scrapped after it suffered a glitch moments before take-off.

The launch will take place from southern Texas between 8.28am local time (2.28pm in the UK) and 9.30am (3.30pm in the UK), on Thursday 20 April.

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