Mysterious blue spiral spotted over European skies. What was it? (photos)

Is it a plane? Is it a satellite? Is it a galaxy? Is it aliens? A strange blue spiral lit up the skies over Europe on Monday night (March 24), causing residents of the U.K. and other European countries like Croatia, Poland, and Hungary to flood social media with photos and videos, along with requests to identify this weird light. Some users even speculated that the spiral could be the work of aliens!

Space.com can reveal the identity of the object behind this spectacular event, and unfortunately (possibly reassuringly), rather than being the work of extraterrestrial visitors, it's a bit more down to Earth.

The cause of the strange blue spiral is actually a SpaceX Falcon 9 rocket that blasted off from Space Launch Complex 40 (SLC-40) at Cape Canaveral Space Force Station in Florida at 1:48 p.m. EDT (1748 GMT) on Monday. The rocket was carrying the secretive NROL-69 mission for the National Reconnaissance Office (NRO).

The spiral appeared over Europe at around 4 pm EDT (2000 GMT) and persisted in the sky for a few minutes. The X feed of Shanghai Daily shared a stunning timelapse video of the spiral appearing and expanding over the skies of Croatia.

As the above post indicates, the strange blue whirlpool, which to many social media users resembled a spiral galaxy, is an example of what some people call a "SpaceX spiral." These structures develop after the upper stage of a Falcon 9 rocket has separated from its first-stage booster.

As the upper stage continues towards space, the lower stage falls back to Earth. As this happens, the booster stage begins to spiral, simultaneously dumping what remains of its fuel. Due to the altitude at which this fuel is ditched, it freezes instantly, preserving a swirling pattern created by the booster's motion.

When light reflects from this structure, it creates these strange-looking manifestations in the sky.

X user Merlin Tomkins captured the wonder and mystery of this object in images posted to his X feed.

X user Shu from Wolverhampton in England was slightly more concerned about the spiral manifestation in the sky, writing on his X feed: "So it seems many of us across Europe (I am in Wolves UK) just witnessed an object in the sky, I thought it was the moon behind cloud at first until it started moving with spiraling light emanating from it... any ideas?"

Physicist and science communicator Brian Cox took to his X feed to reassure U.K. and European citizens like Merlin and Shu that the event they witnessed was associated with the SpaceX launch earlier that day.

Though the spiral has a terrestrial origin, that doesn't mean its manifestation in the sky is any less spectacular in appearance.

Daniel Puchalski posted images of the blue spiral in the Facebook group Smartphone Astrophotography, commenting: "Captured this stunning sight of a Falcon 9 fuel dump over Poland! Taken handheld with a Xiaomi 14 Ultra. An unforgettable view!"

He also shared the incredible photos with Space.com.

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SpaceX spiral seen over Poland on March 24

A mystery blue spiral captured by Daniel Puchalski in the sky over Poland on March 24

Astronomer Allan Trow caught the spiral with an icy white hue over the sky of Bannau Brycheiniog National Park in Wales. He shared the image via his @AlDarkSkyWales X account.

X user matts shared an incredible video of the SpaceX spiral gradually fading from the sky over the course of around 3 minutes.

SpaceX spirals like this one seen over the U.K. and Europe remain fairly rare, but with Falcon 9 and other rocket launches becoming more common, they are likely to soon become a more familiar sight.

Some people may be disappointed by the rational explanation for this spiral light in the night sky. The aforementioned Shu responded to a commentator discussing the spiral's true identity: "I wish it was an invasion; I could use the time off work."

We feel you Shu!