Northern lights outshine a nearly full moon over Fairbanks as solar wind keeps the aurora active

The northern lights put on a show over Interior Alaska this week, bright enough over Fairbanks to outshine a nearly full moon.

The cause was fast solar wind streaming from a coronal hole, a patch of the sun's outer atmosphere where the wind escapes more easily. It kept Earth's magnetic field stirred up through much of the week.

"This was the best show of the season," Vincent Ledvina wrote on X on Thursday, after a clear night of aurora. Ledvina is a University of Alaska Fairbanks Geophysical Institute doctoral student who studies aurora and guides aurora tours.

The next night brought another display. The institute's sky camera at Poker Flat Research Range caught the aurora glowing shortly before 2 am Friday, with the moon washing out the top of the frame. Ledvina posted video of what he described as an unusual substorm, the sudden brightening and burst of motion that makes an aurora dance. He wrote that substorms typically start directly over Fairbanks, but this one began to the south, possibly over Gakona. The Geophysical Institute notes that in years near the peak of the sun's activity cycle, many substorms start south of Fairbanks. Ledvina also wrote that a guest proposed on one of his tours during the back-to-back clear nights, which he called the two best of the season.

Officially, the activity fell just short of a geomagnetic storm. NOAA measures disturbances to Earth's magnetic field on a scale of 0 to 9, and a minor storm starts at 5. This week's readings topped out at 4, overnight into Friday and again Friday evening. NOAA had put the odds of a minor storm at 25% for Friday.

The solar wind is now easing. NOAA expects quiet to unsettled conditions Sunday and mostly quiet conditions Monday, with the next more active stretch forecast for Oct. 4 through 8.

The Geophysical Institute puts the Fairbanks aurora season at roughly Aug. 21 through April 21. Its aurora forecast guidance says clear skies and a stay of at least three nights make seeing the lights highly likely, though never certain.