More Auroras Due Friday Night After Largest Solar Flare in 12 Years

The northern lights near Tromsoe, Norway, on October 21, 2014. Jan Morten Bjoernbakk/AFP/Getty Images

Watching the famed northern lights flicker across a night sky is a rare treat for Americans outside of Alaska. But another large solar flare on September 6 could mean more auroras for the northern U.S. and Europe, which were also treated to the spectacle on Wednesday and Thursday nights.

The flare that caused auroras on Wednesday was classified as an M5 flare, whereas the more recent flare was an X9.3. Flares are ranked on a scale of five letter groups (M is the second largest, and X flares are 10 times larger); the number afterward represents subclasses of strength. The September 6 flare is the largest seen since 2005.

The flares themselves can interfere with GPS and communications satellites and even certain radio frequencies. But they are also associated with coronal mass ejections, which are spurts of the hot, charged particles called plasma that make up the sun.

When that plasma reaches Earth's atmosphere, it collides with air molecules, passing energy along to them accompanied by a burst of light. Although the transfer happens between 50 and 300 miles above the surface of the Earth, it's visible on clear dark nights.

This was about half an hour ago at Portobello Beach #Edinburgh #aurora

— Created Eye Photos (@CreatedEye) September 8, 2017

Typically, auroras are limited to a band circling the poles—in the Northern Hemisphere, at about the latitude of Alaska and Scandinavia. This week's coronal mass ejections, however, have made auroras occur much further south, including Edinburgh in the U.K. and Maine.

The auroras are due to continue Friday night, with some more northerly locations seeing a 90 percent likelihood of northern lights.

NOAA's aurora predictions for Friday night at 11 p.m. Eastern Time. NOAA's Space Weather Prediction Center

The sun's activity typically rises and falls over an 11-year cycle governed by the flipping of the sun's magnetic field (the solar equivalent of the North and South poles trading places every decade).

As the magnetic field roils and flips over the course of its cycle, it knots the sun's plasma into tangled storms called sunspots, which are the source of flares and coronal mass ejections. The magnetic activity blocks heat from rising to the sun's surface in that particular location, causing a cold splotch that looks dark from Earth.

Solar flare
A huge solar flare, recorded by NASA on September 6. NASA/GSFC/SDO

If you still have your solar-viewing glasses from August's eclipse, you can use them during the day to see the sunspot that caused the flare.

Or wait until the sun sets and see if you can catch an aurora. You'll need a dark sky, away from the city lights and free from cloud cover. The northern lights come and go in spurts of about half an hour, and it's impossible to predict where and when precisely they'll show up. So be prepared to be patient. If you do catch a glimpse, it will be worth the wait.