An epic display of glowing clouds occurred overnight on June 4.
The phenomenon was reported widely across Europe.
Rare high-altitude polar noctilucent cloud display dazzles Europe
An epic display of glowing clouds occurred overnight on June 4.
The phenomenon was reported widely across Europe.
The clouds were bright enough for casual members of the public to notice and wonder what they were.
Noctilucent clouds consist of ice crystals that grow on meteorite dust.
They exist at around 83 km above the Earth in the mesosphere, the third layer above the stratosphere and troposphere.
Typical clouds only reach up to the tropopause where the temperature increases with height and the stratosphere begins, at around 12 km.
"Noctilucent" is Latin for "night glowing".
The clouds appear to be illuminated at night because they are so high, that the sun is still able to shine on them overnight at the peak of summer, where the sun doesn’t go far below the horizon.
It is not clear why they have become increasingly common since being first spotted in the 1800s, however, one of the causes is believed to be global warming.