The summer sun has long since set. The first stars appear. Night falls. Nevertheless, on some summer evenings you can see bluish-white, finely structured clouds to the north. These are the so-called noctilucent clouds. Normally, clouds form in the troposphere at altitudes of up to about 10 km. The noctilucent clouds have their realm in much higher areas of the earth's atmosphere, in the so-called mesopause – at an altitude of well over 80 km. Why clouds form at all at this enormous altitude has not really been clarified so far. "Condensation nuclei" are needed to form clouds, and where they come from at this altitude is still unknown – they could come from burned-up meteors. Because the clouds are so high, they are illuminated by the sun long after sunset until well into the night, showing us the unreal spectacle of light in the sky.
If you want to know more about this phenomenon, you can find more information about this phenomenon here:
