Rare red aurora borealis observed in northern Japan

A red aurora borealis is seen in the night sky from Bihoro, Hokkaido, at around 8:30 p.m. on Dec. 1, 2023, in this photo provided by planetarium video creator Kagaya.

A red aurora borealis was observed in the town of Bihoro and other areas in the northernmost Japanese prefecture of Hokkaido on Dec. 1, giving the night sky an otherworldly hue.

The aurora was so vivid that it could be seen with the naked eye. It is believed to have been caused by a solar flare on the morning of Nov. 29 (Japan Standard Time). Plasma emitted from the sun took about two and a half days to reach the Earth and collided with our planet’s geomagnetic field, generating a magnetic storm and causing a luminous phenomenon in the sky.

The northern lights are often thought of as green, but according to Ryuho Kataoka, an associate professor of space physics at the National Institute of Polar Research, the uppermost part of an aurora, at an altitude of some 250 to 400 kilometers, is red. From low-latitude areas such as Hokkaido, only the northern lights’ upper reaches are visible over the horizon, resulting in a red aurora.

“It’s rare for an aurora to be visible to the naked eye in Hokkaido,” Kataoka said. “It’s very interesting that we were able to see this much even though the scale of the magnetic storm wasn’t large”.

In Japan, northern lights were observed three times in 2015 from the town of Rikubetsu and the city of Nayoro, among other areas in Hokkaido.