Noctilucent clouds

Noctilucent clouds

Noctilucent clouds (luminous night clouds) Type of clouds, occurring at 80–85 km altitude, near the upper limit of the stratosphere, characterized by a blue to yellow hue, and similar in appearance to cirrostratus. The clouds are seen on summer nights at latitudes between about 50° and 65° in both northern and southern hemispheres, they move rapidly, at speeds up to 300 knots, often in a wave formation.