AURORAS FOR CHRISTMAS? Earth is about to enter a solar wind stream that could spark polar auroras from Dec. 20th through 25th. Geomagnetic storming is most likely on Dec. 21st and 22nd with peak storm levels near G2. Sky watchers around the Arctic Circle should be alert for Northern Lights.
The source of the solar wind is a gigantic hole in the sun's atmosphere, now directly facing Earth. Earlier today NASA's Solar Dynamics Observatory photographed the structure, which covers nearly 1/3rd of the solar disk:
This is a "coronal hole"--a region in the sun's atmosphere where the magnetic field opens up and allows solar wind to escape. We've actually seen this coronal hole before--at least twice. It is rotating around with the sun, strobing Earth like a lighthouse every ~27 days. The last two times we experienced its solar wind (Oct. 25-28 and Nov. 23-26), G1- and G2-class magnetic storms sparked bright polar auroras. A repeat performance is likely in the week ahead.
AURORAS, NO SUNSPOTS REQUIRED: For the second day in a row, the sun is blank--no sunspots. Fortunately, sunspots are not required for the aurora borealis. Last night the sunspot number was zero when Sarah Skinner of Abisko, Sweden, witnessed a spray of green lights "bursting out from the top of Mount Nuolja and spreading across the sky with bursts of speeds and energy." She took this picture from the shore of Lake Torneträsk:
"I was with a group of guests from Lights over Lapland when the clouds started to clear revealing the powerful aurora," she adds. "We all cheered with excitement!"
This display, and others like it happening nightly around the Arctic Circle, defy a popular misconception about the solar cycle. Many people believe that auroras vanish during periods of low sunspot number. In fact, polar auroras may be seen throughout the 11-year sunspot cycle. Last night, for example, it was not a flaring sunspot that sparked green lights over Abisko; instead, the job was done by a stream of solar wind gently buffeting Earth's magnetic field. Such streams occur throughout the solar cycle.
The sunspot number will likely hover near zero for the rest of the week. Nevertheless, the forecast calls for bright Arctic auroras as another significant stream of solar wind approaches Earth. Stay tuned for sightings.
A GREEN FLASH OVER DRY LAND: Seaside photographers have a special fondness for the sunset. It's the time of day for the green flash--a split-second pulse of verdant light that signals the disappearance of the sun beneath the ocean waves. But the sea is not always required. Yesterday in Treviso, Italy, Enrico Finotto was looking across dry land when he witnessed this magnificent green flash:
"It was a complete surprise," says Finotto.
Atmospheric optics expert Les Cowley explains what happened: "This is a mock-mirage green flash produced by light rays bending as they cross a temperature inversion layer. Such flashes can happen over land as well as the sea. We see more flashes over the sea because the sea horizon is not obscured by hills or buildings. But land flashes can be just as spectacular."
Moreover, dry land offers an advantage that the sea does not. "Over land you might also see a flash twice!" continues Cowley. "I saw once one from our garden, ran indoors and upstairs to see a repeat performance a few seconds later. Try this on a hill slope but be careful, it can be the stuff of heart attacks!"
Realtime Space Weather Photo Gallery
ORDER NOW FOR CHRISTMAS DELIVERY: It's out of this world: the Sirius Space Pendant. To raise money for their space weather ballooning program, the students of Earth to Sky Calculus have flown 3 dozen pendants to the edge of space–and you can have one for $79.95. The pendant comes with a greeting card showing the jewelry in flight and certifying that it has been to the stratosphere and back again.
The pendants flew to the edge of space on Nov. 20, 2016, alongside an array of cosmic radiation sensors. During the flight, the sensors measured the highest radiation levels in the history of our monitoring program. After the balloon exploded, the payload parachuted back to Earth, landing in the snowy San Antonio mountains north of Tonopah, Nevada, where a student team recovered it on Nov. 22nd.
The research of Earth to Sky Calculus is not supported by government grants or corporate donations. Instead, we are entirely crowd-funded. Proceeds from the sale of items like the Sirius Pendant go right back into cutting-edge student research. More edge of space Christmas gifts may be found in the Earth to Sky Store.
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