Northern lights could dazzle Seattle sky this weekend

Seattle-area sky watchers could get a rare treat this weekend – a visit from the cosmic light show commonly known as the Northern Lights.

The brilliant display is normally only visible in the far northern and southern latitudes. But a huge solar flare known as an “X 1.6” that blasted off the sun Wednesday night is giving Earth’s atmosphere an extra spark, and sending the lights south.

“It could be a complete dud all the way to a spectacular show,” says University of Washington professor John Sahr, who chair’s the school’s Department of Electrical Engineering.

So what causes the phenomenon known as the aurora? Sahr says the solar material that hits the atmosphere causes large electric currents to flow up and down the earth’s magnetic field lines.

“Those electric currents make what are basically fluorescent lights. It’s electric current that’s zipping through a gas and causing the gas molecules to get excited and then emit light of a particular color,” he says.

They can be spectacular, shimmering lights of green, red or other colors that often dazzle in far northern reaches like Alaska or Norway. But at times they can stretch as far south as Texas, Sahr says.

If you want to go looking for the lights, Sahr says try and go where it’s as dark as possible, away from the city lights. The best chance is Friday night between 10:30 and 11:30 p.m., and again after midnight between approximately 12:30 and 2:30 a.m.

“That has to do with the detailed structure of the Earth’s magnetic field and interaction with the solar winds,” he says.

For a better idea of how much activity we can expect over the next couple of nights, Sahr suggests following NOAA’s online “Wing Kp” index, which he says is like a Richter Scale for the upper atmosphere. The higher the number, the brighter the lights.