The aurora before midnight was soft-edged and billowy. When this photo was taken shortly before 3 a.m. today, the entire northern sky undulated with tall rays. Credit: Bob King
The blast of solar wind that raked over Earth’s protective magnetic bubble overnight has subsided for the moment, but there’s still a possibility for more auroras tonight. Be on the lookout at the end of evening twilight until around midnight.
A wispy, comet-like aurora high in the southern sky next to the Square of Pegasus around 2 a.m. Credit: Bob King
Speaking of which, there wasn’t much time for sleep last night. I tried to wind it up, but couldn’t resist checking in on the aurora one more time. Before I knew it, it was 3 a.m. By then undulating rays stretched to the zenith.
That’s how the aurora nails you. It begins slowly then ups the ante. Just when you think a display’s beginning to subside it rages and paints the whole sky. What’s a human to do but look up with mouth agape?
Separate “pieces” of aurora like these red and green patches in the constellation Cetus appeared off by themselves far away from the main display around 10:30 p.m. last night. Credit: Bob King
Early this morning geomagnetic activity reached the G2 moderate storm level on the NOAA scale that ranges from G1 (minor storm) to G5 (major storm). G2 storms are accompanied by auroras visible as far south as New York and fading of shortwave communications. Long-duration G2s can even cause damage to power transformers at high latitudes.
This large, north-south filament tens of thousands of miles long was responsible for last night’s auroral storm. Credit: Big Bear Solar Observatory
There’s no doubt where all this came from: the sun. Last week the sun grew an enormous dark moustache called a filament. Filaments are long troughs of cool, dense hydrogen gas held aloft in the sun’s atmosphere by solar magnetic fields. Against the sun, they’re dark and seen in silhouette, but as the sun rotates, filaments eventually reach the edge of the disk and stick out as brilliant red flames called prominences against the blackness of space. They’re what makes that beautiful red fringe around the sun during a total solar eclipse.
Now-you-see, now-you-don’t. By Sunday evening the shattered bits of the filament were gone , headed toward Earth and acrossthe solar system. Credit: Big Bear Solar Observatory
Filaments normally hang out like tourists in hammocks along a beach front, but every so often those magnetic fields become unstable and either eject the filament or it simply collapses. A portion can “rain” back down to the sun’s atmosphere and reform as a new filament, but sometimes they get shot straight into space or collapse, hurling a coronal mass ejection toward Earth.
Filament eruption caught by the Solar Heliospheric Observatory on Sunday evening Sept. 29 around 6:30 p.m. CDT. Credit: NASA/ESA
That’s what happened Saturday evening Sept. 29 CDT. What had been a peaceful filament minding its own business suddenly got the magnetic boot. The eruption sent bits of pieces of the hot solar gas at hundreds of miles a second across the solar system. Some of that material – what once rested quietly in the sun’s atmosphere – bee-lined into Earth’s upper atmosphere and set off an auroral storm. Pretty cool.
A bright, pale green arc gathers strength low in the northern sky around 11 p.m. last night. Credit: Bob King
I hope some of you got to see it. If you didn’t, the space weather experts predict more for tonight. Despite the U.S. government shutdown, the Space Weather Prediction Center remains open. Click the link to get the latest synopsis and forecast. Good luck!
(Update 10 p.m. CDT: Auroras kicked up again during late afternoon and early evening hours Oct. 2 across the Americas. Observers in Europe, where it was dark, likely had a nice show.)