Thanks by Julie

NPR reports that scientists have finally confirmed the source of the Northern Lights:

An article published in the journal Nature Communications this week suggests that the natural light show starts when disturbances on the sun pull on Earth’s magnetic field. That creates cosmic undulations known as Alfvén waves that launch electrons at high speeds into Earth’s atmosphere where they create the aurora.

“It was sort of theorized that that’s where the energy exchange is occurring,” said Gregory Howes, associate professor of physics and astronomy at the University of Iowa. “But no one had ever come up with a definitive demonstration that the Alfvén waves actually accelerate these electrons under the appropriate conditions that you have in space above the aurora.”

The sun is volatile, and violent events there such as geomagnetic storms can echo out into the universe. In some cases, the sun’s disturbances are so strong that they yank on the Earth’s magnetic field like a rubber band, pulling it away from our planet.

But, like a taut rubber band when it’s released, the magnetic field snaps back, and the force of that recoil creates powerful ripples known as Alfvén waves about 80,000 miles from the ground. As those waves get closer to Earth, they move even faster thanks to the planet’s magnetic pull.

…”Think about surfing,” said Jim Schroeder, an assistant physics professor at Wheaton College and the article’s lead author. “In order to surf, you need to paddle up to the right speed for an ocean wave to pick you up and accelerate you, and we found that electrons were surfing. If they were moving with the right speed relative to the wave, they would get picked up and accelerated.”

When the electrons reach Earth’s thin upper atmosphere, they collide with nitrogen and oxygen molecules, sending them into an excited state. The excited electrons eventually calm down and release light, which is what we see as the aurora.

More at NPR.

Julie took this celebratory photo back in March. See more in her massive Michigan gallery on Flickr & keep your eyes on the skies!!

More Northern Lights on Michigan in Pictures.