Extraordinary weather phenomenon: noctilucent clouds

In June, it is the time when you can observe bluish clouds which sparkle in the night: these are noctilucent clouds, or noctiluques, cloud formations resulting from icy meteorite dust.

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The arrival of summer marks the beginning of the period of observation of the sky nocturnal : if the appearances ofshooting Stars and planets are always fascinating phenomena to observe, there is another phenomenon less known but which deserves a lookeye. The noctilucent clouds are not at all similar to clouds clouds that are made up of water droplets and ice: these very special clouds appear as blue filaments that shine in the night sky, with a slight movement. They are in fact the only clouds perfectly visible in the middle of the night, without light artificial. The term “noctilucent” means “that shines in the night” in Latin. They are also called noctilucent clouds or mesospheric polar clouds.

Ice dust that sparkles in the dark

This almost astronomical phenomenon is visible around the period of the summer solstice because it was at this time that the mesosphere is the coldest: the noctilucent clouds are indeed made up of very fine dust of meteorites, even perhaps sometimes volcanic, coated with ice, and culminate between 75 and 90 km of altitude. Remember that in comparison, the highest classical clouds, such as storm clouds, peak at 12 or even 15 km. Ice would represent the major part of the formation, in the form of freezing nuclei around very fine dust. But the formation of this phenomenon still retains its share of mystery, and scientists continue to study the reasons for its formation. It would also seem that some rocketslike the launchers spatial, also contribute to or trigger their formation. Since it is not about ” real clouds “, they obviously do not give any precipitation and have no effect on the conditions weather report.

Polar clouds also observable in France

Noctilucent clouds are observable with the naked eye between 6 and 12° below the horizon, in clear skies, two hours after sunset. Sun (around midnight in June), or two hours before sunrise, in the Northern Hemisphere. It is indeed the reflection of sunlight that makes them visible to the observer. Without sunlight, these clouds, which are not, are too faint to be seen from the Earth. Regarding thesouthern hemispherethe only countries where it is possible to observe them sometimes are Argentina, Chile andAntarcticwhich are at the right latitudes to be able to admire them.

Timelapse of noctilucent clouds. © Maciej Winiarczyk

In France, this phenomenon is seen every summer in the four corners of the country, including above the capital. The period from mid-June to the end of June remains the best to observe them, but it is possible to see them globally from the end of May to the beginning of August. Contrary to northern Lights whose appearance can be predicted several days in advance thanks to observation satellites, noctilucent clouds are difficult to predict, but some organizations manage to issue forecasts a few hours in advance. Seeing them is above all a matter of luck…

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