A spiral of light illuminating the night sky captivated observers in Britain and much of Europe on Monday. Its cause: a SpaceX rocket, experts said, after the glowing spectacle ignited widespread curiosity and speculation about its origin.

The ethereal display, seen from England to Eastern Europe, resembled a glowing celestial whirlpool in images posted on social media, where users reported seeing it for several minutes before it faded.

The Met Office, Britain’s national weather service, said on social media late Monday: “We’ve received many reports of an illuminated swirl in the sky this evening. This is likely to be caused by the SpaceX Falcon 9 rocket, launched earlier today.”

Prof. Brian Cox, a physicist at the University of Manchester, also confirmed the source of the light: “For everyone asking about the strange spiral shape in the sky earlier — it was associated with this launch,” he said on social media, referencing another post that showed footage of the rocket.

The Falcon 9 rocket, from Elon Musk’s company SpaceX, was launched from Cape Canaveral, Fla., on Monday, carrying a classified U.S. government payload.

The striking spiral effect was caused by frozen fuel released from the rocket’s upper stage, which caught sunlight at high altitude and produced the luminous display.

Among those who recorded the event was Christian Medica, an avid sky watcher who has spent the past two years filming the sky in Croatia for his YouTube channel. Even with his experience, the sight left him stunned.

“This is the first time I’ve seen this,” he said. “At first glance, I literally thought it was some kind of wormhole from Star Trek.”

The sight left him excited but “shaking slightly,” he said.

Similar spirals have appeared in the sky before, often in connection with SpaceX. In March 2024, a comparable spiral appeared over Europe after another Falcon 9 mission.