What was the mysterious cloud that appeared over Attica and Crete

A solitary cloud that appeared to be moving across the sky on Tuesday evening (11/8) caught the attention and interest of beachgoers in southeastern Attica.

In Saronida, shortly before sunset, the luminous formation seemed to be moving alone across the sky, with no other clouds around it. Similar images were recorded in other areas as well, with several reports coming from Crete.

Its unusual appearance was enough to spark questions and even comments about… UFOs. The reality, however, is very different — and much more earthly.

Meteorologist Thodoris Kolydas explained in a post on X that such luminous formations can be created by gases and rocket-propellant residue at very high altitudes, a phenomenon that has repeatedly been observed during SpaceX Falcon 9 rocket flights.

According to him, at very high altitudes the density of the atmosphere is extremely low. Therefore, when the upper stage of a rocket releases gases or propellant residue, they behave very differently from the exhaust fumes left behind by an aircraft lower in the atmosphere.

The gases expand rapidly and can spread across a very large area.

If, at the same time, the rocket’s upper stage is rotating or carrying out manoeuvres to change its orientation, the outflow of gases can take on a characteristic circular or spiral shape.

From the ground, the result can be spectacular: a huge glowing disc, cone or spiral appearing where just a few seconds earlier the sky had seemed completely clear.

 

Thodoris Kolydas’ post in full

“The spectacular spiral formations that suddenly appear in the night sky and can easily raise questions or even fuel theories about UFOs have a much more earthly — though extremely impressive — explanation. They are a known optical phenomenon that can be created by gases and rocket-propellant residue at very high altitudes, as has repeatedly been observed during SpaceX Falcon 9 rocket flights.

At these altitudes, the atmosphere is extremely thin. So, 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. They expand very rapidly and can cover an enormous area.

If, at the same time, the upper stage is rotating or changing orientation, the outflow of gases takes on a distinctive geometry. As the cloud continues to expand, it can appear from the ground as an almost perfect spiral or circular formation.

But why does it glow?

This is perhaps the most beautiful part of the phenomenon. While it may already be dark for an observer on the ground, at an altitude of hundreds of kilometres the cloud may still be illuminated by the Sun because it lies above the Earth’s shadow. The light is scattered and reflected by the particles and gases in the cloud, making it stand out vividly against the dark sky.

This is the so-called twilight effect, a phenomenon that has been observed many times during or after rocket launches. This is why the formations can appear white, bluish or slightly coloured and can seem enormous in size.

Therefore, such a luminous formation is not in itself evidence of an unidentified flying object. On the contrary, it is a striking example of how rocket technology, the physics of the upper atmosphere, the movement of gases at very low densities and sunlight combine.

And there is a beautiful contradiction: we are already surrounded by night, but hundreds of kilometres above us, the Sun is still illuminating the traces left behind by a rocket.

That is how these strange glowing spirals are created — formations that, for a few minutes, can truly make the sky look… extraterrestrial.”