For many people, seeing the northern lights is the ultimate bucket list item. Lately, experiencing them has gotten a whole lot easier.
I asked Washington State University astronomer Michael Allen what those dancing green and pink lights are.
He says that, along with its light, the sun emits charged particles—mostly protons and electrons. The ejected particles freely stream into space, where some of them encounter the Earth’s magnetic field.
That magnetic field captures the charged particles that drift off the sun and shuttles them toward the Earth’s poles, where the pull is the strongest.
As the charged particles zoom to the poles, they bang into atoms hanging out in the upper atmosphere—mostly oxygen and nitrogen. During those collisions, the atoms absorb the particles’ energy, swelling the electron clouds that surround each atom. Then the clouds relax again, burping out the surplus energy as light.
The light’s color depends on the kind of atom doing the burping. Oxygen and nitrogen give off green and pink light, so the northern lights, the aurora borealis, are mostly those colors.
It’s a phenomenon that’s usually visible at Earth’s poles.
“A charged particle—like a plus or a minus—is going to go wherever the pull is the strongest,” Allen says. “That’s why you see the lights at the poles and not the equator. The particle density is higher at the poles because they migrate there.”
But every 11.1 years, the sun becomes more active than normal. This is called a solar maximum, which we’re experiencing. During a solar maximum, there are enough charged particles hurtling toward Earth that collisions are no longer constrained to the poles. Instead, they creep toward the equator, delivering a light show to everyone in their path.
Dr. Universe is WSU’s staff science cat who’s always in the mew-d to connect curious kids with science and the university. Cougs and their kittens can send Dr. Universe STEM questions: dr.universe@wsu.edu. Or check out the Ask Dr. Universe podcast episode featuring Michael Allen.