HAPPY SOLSTICE! Today is the shortest day of the year in the northern hemisphere, and the longest day in the south--that is, it's the "December solstice." The exact moment of the solstice is Thursday, Dec. 21st, at 10:27 p.m. EST, when the sun stops moving south and starts moving north again. This event marks the beginning of winter in the north and summer in the south.
PSCs SPILL OUT OF THE ARCTIC: Normally, polar stratospheric clouds (PSCs) are confined inside the Arctic Circle. Only above the poles can the stratosphere become cold enough to create these rare clouds. However, during this week's outbreak of PSCs, the clouds have spilled out of the Arctic to places they are seldom seen. This morning, Ian Carstairs photographed them over Harleston, Norfolk, UK:
"The display has spread south all the way to +52N," says Nock. That's more than 14 degrees below the Arctic Circle.
Widely considered to be the most beautiful clouds on Earth, polar stratospheric clouds are a sign of extreme cold. 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 in the dry stratosphere coalesce into tiny ice crystals. High-altitude sunlight shining through the crystals creates intense iridescent colors that rival auroras.
Something new: For the rest of this northern winter season, we will publish daily predictions of temperatures in the Arctic stratosphere. This will help sky watchers know when to look for these rare clouds. The predictions are right here.
more images: from Shaun Greenwell of Newcastle upon Tyne, UK; from Alan C Tough of Elgin, Moray, Scotland; from Lesley Robertson of Black Isle, Scotland; from Sheri Karl of Aberdeen, Scotland; from Jamie McBean of Herne Bay, Kent, UK; from Tomas of Perthshire, Scotland; from Gordon Ward of Hightown Castleford UK; from Les Brooks of East Shore Village, County Durham, UK; from Michael Horne of Luncarty, Scotland; from Steve Brown of North Yorkshire, UK; from Stu Nock of Manchester, UK
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BIG SUNSPOT ALERT: Sunspot AR3529 is still growing, quadrupling in size since Tuesday. This 48-hour movie from NASA's Solar Dynamics Observatory shows its rapid development:
With two primary dark cores twice the size of Earth, AR3529 is an easy target for solar filtered telescopes. You can even see it through eclipse glasses--no magnification required.
Of greater interest is the sunspot's 'delta-class' magnetic field. Within the sunspot + and - magnetic polarities are pressing together. Magnetic reconnection could produce an X-class solar flare. Any eruptions today will be Earth-directed, as the sunspot is almost directly facing Earth. Solar flare alerts: SMS Text
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CHRISTMAS GIFTS FROM THE EDGE OF SPACE: Are you looking for a far-out Christmas gift? Check out the Earth to Sky Store. It's filled with unique items that have flown to the edge of space onboard cosmic ray research balloons.
Carried aloft by giant helium balloons, these unique gifts have flown above 99.7% of Earth's atmosphere, experiencing space-like blasts of cosmic rays, extreme cold, and a wild ride parachuting back to Earth after the balloon explodes. Even Amazon doesn't carry items this far out.
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