Nacreous Clouds over Sweden

Nacreous Clouds over Sweden

Image Credit &
Copyright:

Vojan Höfer

Explanation:

Vivid and lustrous,
wafting iridescent waves of color wash across this skyscape
from northern Sweden.

Known as nacreous
clouds or mother-of-pearl clouds, they are rare.

But their
unforgettable
appearance was captured in this snapshot on
January 12 with the Sun just below the local horizon.

A type of
polar stratospheric cloud,
they form when unusually cold temperatures in the usually cloudless
lower stratosphere form ice crystals.

Still sunlit at altitudes of around 15 to 25 kilometers, the clouds
diffract the sunlight even when the Sun itself is hidden from direct view.