A lonely, glowing formation spotted drifting across the evening sky triggered widespread fascination—and plenty of UFO rumors—among beachgoers and residents across several parts of Greece.
As sunseekers along Attica’s Saronida beach looked up, they witnessed a single, bright cloud gliding through an otherwise entirely clear, dusk-filled sky. With no other cloud cover in sight, photos and videos quickly flooded social media, sparking wild theories ranging from alien visits to secret atmospheric military tests. The sighting was also confirmed by people as far as Crete.
However, former director of Greece’s National Meteorological Service (EMY), Thodoris Kolydas, offered a much more grounded—yet equally breathtaking—explanation.
Rocket Exhaust in the Upper Atmosphere
According to Kolydas, the spectacular aerial phenomenon was not a natural cloud at all, but rather gas and propellant remnants released high in the atmosphere by a satellite launch rocket, such as a SpaceX Falcon 9.
“In the extreme upper atmosphere, the air is extraordinarily thin. When a rocket’s upper stage vents excess gas or propellants, they don’t behave like standard jet exhaust near the ground. Instead, they expand rapidly across vast distances,” Kolydas explained in a detailed post on X (formerly Twitter).
As the rocket rotates or maneuvers, this expanding exhaust trail twists into massive, near-perfect geometrical spirals or glowing halos.
The “Twilight Effect”: Glowing in the Dark
The most mesmerizing part of the spectacle was its intense luminosity against a darkening sky. While observers on the ground were already standing in twilight or full night, the cloud was floating hundreds of kilometers high—well above the curve of Earth’s shadow.
Still bathing in direct sunlight, the frozen particles and dispersed gases acted like a giant mirror, reflecting sunlight back down to observers on the dark surface below.
Known among scientists and space enthusiasts as the twilight effect, the phenomenon often leaves brilliant white, blue, or iridescent trails in its wake—turning an ordinary rocket launch into a surreal optical illusion.
“There is a beautiful paradox here,” Kolydas concluded. “We on the ground are enveloped in darkness, yet hundreds of kilometers above us, the Sun is still illuminating the footprints of human technology, making the night sky look briefly… extraterrestrial.”
Related: Is it a Cloud or a UFO? Video of Surreal Sight Goes Viral
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