How are the northern lights colors created?
MINNEAPOLIS — From Seattle in the Northwest, to across the world in Spain, and right back in Minnesota, the human collective looked north for a few nights as a massive light show performed for one of its largest audiences ever.
"This is the strongest storm that has been on record since at least 2003, if not longer than that," said Sally Brummel, the planetarium manager at the Bell Museum.
What causes the aurora borealis, also called the northern lights?
"The aurora is caused by the interaction of energetic particles that have erupted from the sun and collided with molecules in the earth's atmosphere," she said.
Those energetic particles from the sun, known as electrons, first hit the Earth's magnetic field. They then dive toward the Earth's poles in our atmosphere. They then interact with particles, like oxygen or nitrogen, exciting them, which causes an energy burst of light. It's bright enough for people to see when it happens on a massive scale.
"It's really kind of fun because looking at the colors tells you a bit about the height of the aurora as well as what type of particles you have in the atmosphere," said NASA researcher Alexa Halford. "At different altitudes, you're going to have those electrons hitting, interacting with those different types of atmospheric particles."
Oxygen gives off green colors, the most common. It also gives off red, but that color is harder to see.
"The people who could see the red, those are typically people who are farther south, more toward the equator," said Brummel.
Halford offered further explanation on why people near the equator saw red.
"They're looking further away from where all the action is happening. So, when they're looking up and towards the (North Pole), they're actually only able to see the top part of the aurora, so they might only see those reds," she said.
A mix of nitrogen and oxygen can produce purple or yellow. Nitrogen alone produces blue, the rarest color of them all.
"Minnesota happened to be effectively right under where most of the action was happening, so (they) get to see all the colors," Halford said.
No matter how rare the color, advancements in technology are unlocking these light shows' true potential. Even cellphones are now capturing highly-detailed images.
"It's an exciting time because cameras have never been this fast or this sensitive," Halford said.
Nor has the sun been this active. Halford said not to be surprised if another aurora borealis greets people in Minnesota or Wisconsin next month. She said the sunspot that produced the recent storm could return about four weeks later.
"Stay tuned, keep an eye on the sky, and enjoy the dancing lights," she said.
Several planets in the solar system experience auroras, but a few don't, like Venus and Mercury. That's because they're either missing an atmosphere or a magnetic field.