Getting up before dawn to go to work, Stéphane saw a noctilucent cloud in Sainte-Ode (province of Luxembourg) around 3am. A luminous night cloud, how does it happen?
A cloud that can be observed in the middle of the night, does it exist? Stéphane began his day on Thursday by observing shiny golden, blue or silver filaments in the sky, almost resembling lightning, making you want to dream. However, they are not really clouds. They are sets of particles that form in the atmosphere and can usually be observed during deep twilight.
These so-called “noctilucent” clouds are located between 75 and 85 km altitude (the highest in the Earth’s atmosphere) and are lit by the sun. They are lit, but the ground is no longer, after dark. The sun has therefore passed below the horizon line for the observer, but not for the particles. That’s why noctilucent clouds look so shiny.
But what are these particles made of? According to Wikipedia, it has been proposed in the past, as an explanation for this phenomenon, that noctilucent clouds are actually composed of volcanic ash or meteorite dust. It has been demonstrated more recently that these clouds are mainly composed of ice, which condenses on the freezing cores formed by these dusts, or spontaneously, which has been confirmed by the UARS satellite. It appears that these clouds are a relatively recent phenomenon, first reported in 1883, shortly after the eruption of the Krakatoa volcano. For several years, it has been established that the water vapor released by space launchers contributes to the formation of noctilucent clouds at an altitude of 100-110 km.
For insomniacs who wandered near their windows, or for early risers like Stéphane, who could see this phenomenon: you are lucky! They are mainly present in the polar regions in summer.
Another person sent us a similar photo earlier this week, also at sunrise: