Above the silhouettes of mountains to the north, below the twinkling stars, a ribbon of sky glowed emerald-green.
It was a hauntingly beautiful scene at Hauser Lake in Eastern Washington on Monday night. Similar otherworldly sights were visible throughout the Inland Northwest and the northernmost reaches of the contiguous United States. People had a rare chance to see one of the night sky's most incredible displays: aurora borealis.
And it was all thanks to explosions that happened three days before, 93 million miles away, on the surface of the Sun.
"It takes a special event on the sun for us to be able to see it," said John Whitmer, an astronomy instructor at Spokane Falls Community College.
Alaskans are the only Americans who can see aurora borealis, or the Northern Lights, on a regular basis. The light show is typically restricted to Earth's north and south poles.
But on Saturday, huge explosions on the Sun sent gusts of solar wind hurtling toward Earth.
Whitmer explained that the Sun constantly creates solar winds, made up of electrons and protons. Normally those winds blow across the 93 million miles between the Sun and the Earth — the trip takes three days — hit our magnetic field and get funneled to the two poles.
Those solar winds are what create aurora borealis. The electrons and protons from the Sun slam into atoms in our atmosphere 100 miles above Earth's surface. Those tiny collisions excite the electrons within the oxygen and nitrogen atoms in the sky.
When the electrons get excited, they rapidly jump up in energy level, then quickly jump back down in energy level, Whitmer explained. Those fluctuations give off energy — light — which shows up in the night sky.
Above Hauser Lake on Monday night, the sky happened to look green. Aurora borealis can be different colors though, Whitmer said. Oxygen molecules tend to glow green, while nitrogen molecules can glow red. Whitmer said it all depends on how excited the gases get.
But Inland Northwest residents don't typically get to see aurora borealis. We're generally too far south.
The natural marvel appeared in the night sky Monday because the explosions on the Sun's surface Saturday, and the resulting solar winds, were more powerful than normal.
Whitmer explained that Saturday's coronal mass ejections on the Sun created especially strong blasts of solar wind. When the stronger winds hit the Earth's magnetic field they created cracks in that planetary armor, Whitmer said.
Breaking through the armor allowed electrons and protons to push farther south, as opposed to remaining exclusively at the poles. The aurora borealis was, in general, increasingly brilliant farther to the north, Whitmer said.
In this instance, the Pacific Northwest was at the southernmost latitude where the aurora borealis was visible. There are times when solar events are strong enough that people around the world can see an aurora borealis.
Whitmer said it's rare for the Inland Northwest to have a chance to see an aurora borealis. He said he hasn't seen one here in several years. The likelihood of an aurora here ebbs and flows depending on where the Sun's at in its 11-year magnetic cycle.
Unfortunately for anyone who missed the spectacle Monday, the night sky isn't likely to glow green Wednesday, Thursday or Friday night.
For one, Whitmer said that the aurora, even if it's visible, won't be as brilliant as it was Monday.
"The gust is pretty sudden and it blows by Earth and once it's gone, it's gone," he said.
And even if it was visible, the forecast isn't favorable.
Ken Daniel, a meteorologist with the National Weather Service in Spokane, said it looked like showers and clouds would roll in Wednesday night. Without clear skies, the aurora won't be showing up, although Daniel said there's a chance skies will be clear during the wee hours Thursday morning.
Whitmer said he doesn't worry much about people fully understanding the science that makes an aurora borealis possible. The astronomy teacher said it's more important that people simply enjoy the Northern Lights on the rare occasions they make an appearance in the Pacific Northwest.
"It's just another way for people to kind of connect with the universe and realize it really is a gorgeous place."
