A mysterious large glowing spiral in the night sky on Monday was likely caused by a SpaceX rocket launch in the U.S.

According to the Met Office, the shape was likely generated by a frozen plume of fuel from the rocket’s exhaust. This plume reflected off of the sunlight and appeared to spin in the atmosphere.

Spinning Sky Spiral

The unusual shape, which resembled a cloud, was visible for several minutes in the night sky above the U.K. and other parts of Europe. This strange sky phenomenon took place after the Falcon 9 rocket from Elon Musk’s space company lifted off at around 13:50 local time in Florida (17:50 GMT) on a classified US government mission.

The launch of the reusable rocket involves two distinct parts or stages. The first part takes the payload into space while the second part ejects leftover fuel. Due to the altitude and movement as this part of the rocket falls back to Earth, the fuel freezes and forms a spiral pattern.

Astronomer Allan Trow spotted the mysterious spiral above Wales’s Bannau Brycheiniog National Park at around 20:00 GMT. He also recalls seeing a similar phenomenon approximately four years ago.

“But these are pretty rare,” he told the BBC and agreed the rocket was its likely source.

Stockport-based Sonia was already out with her telescope when she saw “a swirling galaxy that was moving across the sky”.

People living around 200 miles away also spotted the phenomenon. Steven Hall, for example, was taking out the trash in Suffolk when he reported seeing what looked like “a huge Catherine wheel which appeared to have its own atmosphere around it.”

SpaceX and the Kennedy Space Center stated on X that the launch was carried out on behalf of the U.S. government National Reconnaissance Office mission.