A solitary, unusual cloud that appeared over Attica and Crete on Tuesday evening drew the attention of beachgoers and residents, with some even wondering whether they were seeing an unidentified flying object.
The formation was visible shortly before sunset from the beach at Saronida in southeastern Attica. With no other clouds visible in the sky at the time, the unusual sight prompted speculation about its origin.
The same phenomenon was reportedly seen from several other areas of Attica and Crete.
Meteorologist Theodoros Kolydas offered an explanation in a post on X, saying the phenomenon was linked to gases and propellant residue released by rockets at very high altitudes, as has repeatedly been observed during SpaceX Falcon 9 launches.
How the unusual formation forms
At such altitudes, the atmosphere is extremely thin. When gases or propellant residue are released from the upper stage of a rocket, they do not behave like aircraft exhaust in the denser lower atmosphere.
Instead, they expand very rapidly and can spread across a huge area.
If the rocket’s upper stage is rotating or changing its orientation, the gases can take on a distinctive geometric shape. As the cloud continues to expand, it can appear from the ground as an almost perfect spiral or circular formation.
Why does the cloud glow?
Kolydas said the most striking part of the phenomenon is the way the cloud can remain illuminated even after darkness has fallen on the ground.
At an altitude of hundreds of kilometers, the cloud can still be exposed to sunlight because it is above Earth’s shadow.
The sunlight scatters and reflects off particles and gases in the cloud, making the formation stand out against the dark sky. This is known as the twilight effect, a phenomenon that has been observed repeatedly during or after rocket launches.
As a result, these formations can appear white, bluish or slightly colored and can seem enormous when viewed from the ground.
From a UFO to a lesson in physics
According to Kolydas, a glowing formation of this kind is not, by itself, evidence of an unidentified flying object.
Instead, it illustrates the interaction between rocket technology, upper-atmosphere physics, the movement of gases in extremely low-density environments and sunlight.
As he put it, there is a striking contradiction at work: people on the ground may already be in darkness, while hundreds of kilometers above them, the Sun is still illuminating the trail left behind by a rocket.
For a few minutes, those conditions can create strange, glowing spirals that make the night sky appear almost otherworldly.
