Nacreous or “mother of pearl” clouds are made of microscopic ice crystals floating in the stratosphere 9 to 16 miles high. These clouds gather when the temperature in the polar stratosphere drops below -85 C. Because of that numbing threshold, they tend to appear only during winter over cold places such as Scandinavia, Alaska and Iceland.

Nacreous clouds are supposed to be rare, yet sky watchers in Scandinavia has spotted them frequently during the past two weeks. Could this be a “nacreous storm”? A similar, mysterious abundance of nacreous clouds occurred in January 2008; it could be happening again. High-latitude sky watchers should be alert for mother of pearl during the twilight hours after sunset or before sunrise.

Photos taken by:
Ivar Marthinusen in Trondheim, Norway
Sauli Koski in Kittila Finland
Kalinka Irina Martín Iglesias in Tunhovdfjorden, Buskerud, Norway
Johannes Lillegaard Frøyen, in Bogstad, Oslo, Norway

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