Noctilucent Cloud

Also found in: Dictionary, Thesaurus, Wikipedia.

noctilucent cloud

[¦näk·tə¦lü·sənt ′klau̇d]
A cloud of unknown composition which occurs at great heights and high altitudes; photometric measurements have located such clouds between 45 and 54 miles (75 and 90 kilometers); they resemble thin cirrus, but usually with a bluish or silverish color, although sometimes orange to red, standing out against a dark night sky.

Noctilucent Cloud


a type of luminous, transparent cloud that sometimes appears in the upper part of the mesosphere at altitudes of 70–90 km. The structure of noctilucent clouds is somewhat similar to that of light cirrus clouds. Noctilucent clouds consist of aggregations of particles 10-4–10-5 cm in size that scatter sunlight. Such particles may consist of ice crystals formed upon condensation of water vapor that has been borne upward to high altitudes, or they may be volcanic or cosmic (meteoric) dust. It is possible that ice crystals form only around dust particles.

Noctilucent clouds were first investigated by V. K. Tseraskii in 1885. They are observed in the northern hemisphere between the latitudes of 45° and 70° and in the southern hemisphere between the latitudes of 40° and 65°. They occur only during the warm part of the year—from May through August in the northern hemisphere, with a maximum number of occurrences in July. The annual number of recorded occurrences observed from a given point may be as high as 20 to 30. Noctilucent clouds exist for periods of several minutes to several hours. In appearance they assume four basic configurations: gauze, bands, combs, and whirls. For observations from the ground, the best visibility is during nautical twilight, when the sun is 6°-12° below the horizon. Noctilucent clouds can also be observed during daylight if the observation equipment is raised aloft to high altitudes. Observations of noctilucent clouds are used to obtain data on the winds prevailing at the altitude of formation.


Bronshten, V. A., and N. I. Grishin. Serebristye oblaka. Moscow, 1970.


References in periodicals archive ?
Prof Gary Thomas, of the University of Colorado's laboratory for atmospheric and space physics and a world expert on noctilucent clouds, said: "This is a big event.
The researchers contend that the massive amount of water vapor spewed into the atmosphere by the comet's icy nucleus was caught up in swirling eddies with tremendous energy by a process called two-dimensional turbulence, which explains why the noctilucent clouds formed a day later many thousands of miles away.
The Director has given talks about aurora and noctilucent clouds to several astronomical societies during 2010 '11.
The noctilucent clouds remain lit by the sun because of their great height, whereas weather clouds remain in silhouette against the twilit summer evening sky.
The thin wispy glowing clouds, known as 'night shining', or noctilucent clouds (NLCs), have been seen from Earth and photographed by astronauts aboard the International Space Station.
Since the late 1960s, the appearance of noctilucent clouds has increased, providing inspiration for those inclined towards photography, romance and prose.
Cloud experts have sighted beautiful noctilucent clouds, or silvery blue ice clouds, over Colorado--1,000 kilometers farther south than usual.
Noctilucent clouds develop in the mesosphere at an altitude of 85 kilometers.
Images include optical phenomena such as moon glitter on the ocean, a lunar corona, noctilucent clouds, mirages, supersuns, and underwater 3-D imaging.
June is also a good time to observe noctilucent clouds in the northern sky.
The eerie glow, which appeared to change colour and hang above the horizon, has been confirmed as a phenomenon known as noctilucent clouds - the highest clouds in the Earth's atmosphere at 50 miles above the ground.
Jay Brausch is a dedicated amateur observer of the aurora borealis and noctilucent clouds residing at Glen Ullin, North Dakota, USA, 46[degrees]48'N, 101[degrees]46'W.