For the third day in a row, #Arctic #sky watchers are reporting a widespread outbreak of #polar #stratospheric #clouds. "The colors are spectacular," says Ramune Sapailaite, who photographed the display over Gran, #Norway:

"The clouds were visible in the sky all day, but the #colors really exploded just before #sunset," says Sapailaite. "I took these pictures using my cellphone."

Widely considered to be the most beautiful clouds on Earth, polar stratospheric clouds (PSCs) are rare. Earth's stratosphere is very dry and, normally, it has no clouds at all. PSCs form when the temperature in the Arctic stratosphere drops to a staggeringly-low -85 C. Then, and only then, can widely-spaced water molecules begin to coalesce into tiny ice crystals. High-altitude sunlight shining through the crystals creates intense iridescent colors that rival auroras.

During a typical Arctic winter, PSCs appear no more than a handful of times, and the first sightings usually come in January. This week's apparition marks an early start, and may herald many more PSCs to come.
spaceweather.com