'Secret island' on sun sparks surprise solar storm and stunning auroras across the US (photos)

Aurora chasers around the world were treated to dazzling shows after a "secret" island within a coronal hole triggered an unexpected strong (G3) level geomagnetic storm overnight on Sunday (Sept. 14-15).

The outburst sent auroras spilling far beyond their usual range, thrilling aurora chasers across the U.S.

Space weather physicist Tamitha Skov explained in her latest aurora forecast on YouTube that the true culprit wasn't the big eruptions everyone was watching, but something hidden in plain sight. "The source of the big solar storm is due to this coronal hole right here, which is a really noteworthy coronal hole for a number of reasons," Skov said.

What made this coronal hole so unusual was a subtle, but influential magnetic twist. The coronal hole had a negative polarity that wasn't supposed to give us big geomagnetic storms or subsequent auroras, Skov explained. But as it moved across the sun's disk, something changed. An "island" of positive polarity appeared in the middle of the coronal hole. "That positive polarity is what ended up giving us about 6 hours worth of really intense storming," Skov explained.

The result was a stunning aurora show. "Little things like this can really make a big difference and change a nothingburger into a G3-level solar storm," Skov said.

Forecasts underestimated the storm

Just days earlier, forecasters had warned of possible G1 (minor) to G2 (moderate) geomagnetic storms from the same butterfly-shaped coronal hole. But when the solar wind arrived, the hidden polarity island turned what was expected to be a moderate event into a full G3 solar storm, surprising scientists and delighting skywatchers worldwide.

Geomagnetic storms are classified using a G-scale, which ranks their intensity from G1 (minor) to G5 (extreme). Auroras occur when solar wind interacts with Earth's magnetic field. The charged particles from the sun collide with gases in the upper atmosphere, such as oxygen and nitrogen, transferring energy to them. This energy is released as light, producing the colorful displays seen in the night sky. The stronger the solar wind, the more dynamic and widespread the auroras can become.

Northern lights across the US (photos & videos)

The surprise solar storm delivered mesmerizing northern lights shows across the U.S.

Photographer Ross Harried captured the stunning northern lights display in the sky above Monroe, Wisconsin, U.S., on Sept. 14.

(Image credit: Photo by Ross Harried/NurPhoto via Getty Images)

(Image credit: Photo by Ross Harried/NurPhoto via Getty Images)

(Image credit: Photo by Ross Harried/NurPhoto via Getty Images)

(Image credit: Photo by Ross Harried/NurPhoto via Getty Images)

Harried enjoyed a colorful green and purple display with vast pillars reaching high into the sky, as well as a subtle green glow as activity began to wane.

Auroras also danced above Anchorage, Alaska, U.S., on Sept. 15 during the geomagnetic storm. Photographer Hasan Akbas captured this lovely green display alongside the nearly half-lit moon.

Many aurora chasers took to X to share their stunning aurora photos during the recent geomagnetic storm.

Photographer Andrew Towne saw a vibrant northern lights display above Casper, Wyoming, U.S. As well as capturing a stunning shot of the Milky Way.

Tony Rodriguez captured striking red and green aurora pillars above Seneca Lake, New York, U.S.

"Spectacular #aurora on the southern shore of Seneca Lake in NY! The structures were visible to the naked eye. It was quite a show!" Rodriguez wrote in a post on X.

Aurora chaser Joshua Grisewood also enjoyed the surprise aurora show from Pavilion, New York, U.S.

"Awesome surprise Aurora here in New York! Generally I am on top of these but tonight caught me off guard for sure," Grisewood wrote in a post on X.

Photographer Blake Brown managed to capture the show as far south as Texas.

"Northern lights made an appearance down to Texas tonight! With a lightning cameo as well," Brown wrote in a post on X.

Gabe Zago captured a truly remarkable show as auroras competed against lightning to take center stage.

"Bro this day will be impossible to beat forever," Zago wrote in a post on X.

Latest forecast

For the latest space weather outlook, and a deeper dive into what caused this surprise G3 storm, check out Skov's full space weather forecast, available below and also on her YouTube channel.