LUCY FLYBY OF EARTH TODAY: NASA's Lucy spacecraft will slingshot past Earth today, Dec. 12th, for a gravity assist en route to the asteroid belt. At closest approach, the spacecraft will fly just 220 miles above the Pacific Ocean. NASA says that astronomers may be able to see the spacecraft at sunset in Hawaii (6:14 p.m. HST) with additional sighting opportunities in Africa and South America a bit later. Full Story.
POLAR STRATOSPHERIC CLOUDS: Arctic skies are filling with color--but it's not the aurora borealis. A rare outbreak of polar stratospheric clouds (PSCs) is underway. Even Nilsen photographed the display from Troms, Norway:
"My favorite clouds appeared this morning," says Nilsen. "It's the earliest in December I have seen them here in Northern Norway. Fantastic sight!"
Polar stratospheric clouds are a sign of extreme cold. Normally, the stratosphere has no clouds at all. PSCs form when the temperature drops to a staggeringly-low -85 C. Then, and only then, can widely-spaced water molecules in the stratosphere coalesce into tiny ice crystals. When sunlight hits these crystals, they blossom with intense iridescent color.
Sky watchers in Sweden are seeing them, too. Aurora tour guide Oliver Wright was leading a group for Lights over Lapland when the clouds appeared over Abisko:
"It looked like the deer was farting rainbows," said an onlooker. Fact check: That's not how PSCs are formed.
There are actually two types of PSCs. The ones we're seeing now are harmless Type II clouds, made of pure clean water ice crystals. Type I PSCs are not so harmless. Containing both water-ice and nitric acid, they are associated with the destruction of ozone and can even presage the opening of an ozone hole. The two are easy to distinguish: Type II PSCs are very colorful, while Type I clouds tend to be wan and pale.
In most winters, the Arctic stratosphere is not cold enough for Type II PSCs until January. Seeing them in mid-December is unusual, and could herald a busy season to come. Arctic photographers, submit your images here.
more images: from Fredrik Broms of Kvaløya, Norway; from Anja of Alta, Norwegen
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