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SLIM CHANCE OF FLARES: Sunspot AR1635 is crackling with low-level C-class solar flares. There is a slim chance of stronger flares: NOAA forecasters put the odds of an M-class eruption on Dec. 27th at 5%. Overall, solar activity is very low and is likely to remain so for the rest of the week. Solar flare alerts: text, voice.
VAN GOGH CLOUDS: On Christmas morning, Gene Hart of Jonesport, Maine, woke up early to enjoy the sunrise before opening presents. What he saw may have been the best gift of all. "There was a cloud formation showing a remarkable series of wave shapes," says Hart. "They were backlit by the rising sun over Moosabec Reach." He snapped this picture of the harbor using a 14-megapixel digital camera:
"I also took some 28x zoom images of the wave structure," says Hart. The close-ups are a must-see.
These clouds, sometimes called "billow clouds," are produced by the Kelvin-Helmholtz instability when horizontal layers of air brush by one another at different velocities. A better name might be van Gogh clouds: It is widely believed that these waves in the sky inspired the swirls in van Gogh's masterpiece The Starry Night.
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CHRISTMAS COVER-UP: When the sun went down on Christmas, a pair of bright lights rose in the east; Jupiter and the Moon were having a holiday conjunction. In Brazil, the pair were so close, the Moon completely covered Jupiter. Marcelo Domingues of Brasilia snapped this picture seconds before the occultation:
"It was a beautiful event," he says.
"What a perfect Christmas gift this was!" adds Gustavo Rojas of São Carlos. "I managed to capture the giant planet just as he started to disappear behind the lunar disk."
In case you missed it, there will be more lunar occultations of Jupiter in 2013. A complete list is available from the International Occultation Timing Association.
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ODD-RADIUS MOON HALOS: Many sky watchers have witnessed a halo around the moon--a ring of light that surrounds the lunar disk at a radius of 22 degrees. The phenomenon is caused by pencil-shaped ice crystals in cirrus clouds that bend moonlight. On Dec. 21st, Harald Edens of Magdalena, New Mexico, witnessed a rare double halo:
"Just after 7 PM local time I noticed a bright 22-degree halo around the moon," says Edens. "It was only when I started photographing that halo when I discovered a rare 9-degree halo inside the 22-degree halo."
The inner 9-degree halo is caused by ice crystals in the shape of pyramids. "Apart from the 9-degree circular halo, an 18-degree and perhaps a 35-degree circular halo were also present at times," he adds. All of these "odd-radius" halos are caused by icy pyramids.
The display quickly became even more varied. Edens saw at least a dozen different kinds of luminous rings and arcs, enumerated in his complete description of the event. "The display was highly transient," he notes. "Not only did the cirrus move fairly swiftly in the sky, but the halos - especially the odd-radius halos - appeared to come and go over the course of just a few minutes." But what a few minutes it was!
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