CHANCE OF STORMS: NOAA forecasters say there is a 35% chance of minor G1-class geomagnetic storms on Dec. 11th and 12th when a stream of solar wind reaches Earth. The gaseous material is flowing at speeds of ~500 km/s (1.1 million mph) from a canyon-like hole in the sun's atmosphere. Arctic sky watchers should be alert for auroras after local nightfall. Free: Aurora Alerts.
A ROCK COMET APPROACHES EARTH: You've heard of comets. But have you ever heard of a rock comet? They exist, and a big one is approaching Earth this week. 3200 Phaethon will fly past our planet on Dec. 16th only 10 million km away. Measuring 5 km in diameter, this strange object is large enough for amateur astronomers to photograph through backyard telescopes. A few nights ago, the Astronomy Club of the Sing Yin Secondary School in Hong Kong video-recorded 3200 Phaethon's approach using a 4-inch refractor:
"We observed 3200 Phaethon from the basketball court of our school campus," the club reports. "Our school is located close to the city center where the visual limiting magnitude is about 2 to 3. Despite the glare, we were able to record the motion of this object." (For others who wish to do this, Bob King of Sky & Telescope has written an excellent set of observing tips.)
3200 Phaethon is the source of the annual Gemini meteor shower, which is also coming this week. Sky watchers can see dozens of Geminids per hour on Dec. 13th and 14th as gravelly bits of the rock comet disintegrate in Earth's upper atmosphere. The best time to look is during the dark hours before sunrise when Gemini is high in the sky.
"This is 3200 Phaethon's closest encounter with Earth until December of 2093, when it will come to within 1.8 million miles," notes Bill Cooke of NASA's Meteoroid Environment Office. Despite the proximity of the rock comet, he doesn't expect to see any extra Geminids this year. "It would take at least another revolution around the sun before new material from this flyby could encounter Earth - probably longer."
A "rock comet" is an asteroid that comes very close to the sun--so close that solar heating scorches plumes of dust right off its stony surface. 3200 Phaethon comes extremely close to the sun, only 0.14 AU away, less than half the distance of Mercury, making it so hot that lead could flow like water across its sun-blasted surface. Astronomers believe that 3200 Phaethon might occasionally grow a comet-like tail of gravelly debris--raw material for the Geminid meteor shower. Indeed, NASA STEREO-A spacecraft may have seen this happening in 2010. There is much to learn about 32900 Phaethon, which is why NASA radars will be pinging it as it passes by. Stay tuned for updates.
Realtime Space Weather Photo Gallery
FAR OUT CHRISTMAS GIFTS: Helium doesn't pay for itself. That's why the students of Earth to Sky Calculus fly cool things to the edge of space onboard their cosmic ray balloons--so you can buy them in our Christmas Store:
Crystal balls, solar eclipse pendants, pyramids, pickles and much more: they've all been to the edge of space and back, and they all make great holiday gifts. Every dollar spent in the store supports STEM education and high-altitude space weather research. Shop now!
Far Out Gifts: Earth to Sky Store
All proceeds support hands-on STEM education
DIAMOND DUST SKI HALOS: Ski resorts are some of the best places to see sun halos--rings and pillars of light that surround the sun when ice crystals fill the air. The most sublime halos are caused by jewel-like crystals called "diamond dust." On Dec. 7th, Kameron Barge was skiing in Whitefish, Montana, when he saw these specimens:
"As we rode the chair down into the clouds today, we begin seeing all sorts of halos, and sundogs!" says Barge. "It was an unforgettable display."
Ordinary sun halos are caused by ice crystals floating in high cirrus clouds. "Ski halos," on the other hand, are formed by ice crystals near the ground, kicked into the air by the action of skis and snow-making machines. A close look at Barge's picture shows specks of light in the air. Those are the glittering crystals of diamond dust which make these halos so beautiful.
Barge documented a rare variety of forms: a 22-degree halo, sundogs, sub-sundogs, a sub-sun, a lower sun pillar, an upper tangent arc, a 46-degree halo, a circumzenithal arc, and a partial parhelic circle--all sculpted from sunlight by floating diamond dust.
If you're on the slopes this weekend, and the sun dips behind a cloud of ice, be alert for "ski halos." They can make your day.