A surprise storm rocking Earth’s magnetic field brought a rare display of the northern lights to parts of the northern United States early Wednesday, sending skywatchers staring upward at pastel hues. There’s a chance that observers could be treated once again Wednesday night as the display potentially continues courtesy of energetic particles striking the planet’s upper atmosphere.

The northern lights were sighted in Alaska and Minnesota, as well as across Canada and into parts of Europe and the United Kingdom. Their southern counterparts also made an appearance in New Zealand.

Forecasters at the National Weather Service’s Space Weather Prediction Center noted the geomagnetic storm reached a level 3 on a 1-to-5 scale; level 3 storming can easily send the lights dancing south into the Lower 48, but this time around, the most dramatic storming occurred during the daylight hours on Wednesday.

The storm was originally anticipated to peak at level 1 status, which would relegate any aurora sightings to places such as Canada and Alaska. Instead, a more direct impact of energy arriving from the sun occurred. A level 3 geomagnetic storm is considered “strong” by the Space Weather Prediction Center, and occurs on average of 130 days per 11-year solar cycle.

Will the aurora be visible Wednesday night?

It’s unclear whether the Earth’s upper atmosphere will continue feeling the effects of the geomagnetic storm Wednesday night, but it’s possible that the lights are still visible. G3 storms can sometimes produce faint auroral displays all the way to Boston, Chicago, Seattle, the northern Plains and northern parts of the Corn Belt.

For most, any display would appear as a milky-white arc on the horizon, akin to distant city lights. A few might witness playful pillars, gently shimmering like a curtain fluttering in a gentle breeze.

There’s a better chance of the lights lingering in Canada and Alaska, though far northern regions will be contending with near total daylight. In Utqiagvik, Alaska, formerly known as Barrow, the sun won’t dip below the horizon until Aug. 2.

Parts of northwest Europe, where nightfall will descend earlier than in North America, have elevated viewing prospects if and where cloud cover breaks.

It’s also worth remembering that many photographers use long exposures to capture the northern lights, meaning pictures will reveal brighter and more vibrant features than are visible with the naked eye. Still, it’s worth glancing northward if you live in northern parts of the United States; sometimes, events such as this can bring surprises.

The science of the lights

The northern lights stem from energy streaming off the sun and into space. High-energy particles make up the “solar wind.” The speed, density and magnetic characteristics of those particles determine how they will interact with Earth’s magnetosphere, or magnetic field.

Earth’s magnetosphere transforms the potentially hazardous electromagnetic energy into curtains of visible light that we see as the aurora. The more intense the disturbance, the farther away from the poles the lights will extend.

Usually, the solar wind is meager enough that only the high latitudes are treated to auroral displays. But when conditions line up just right, even those at the mid-latitudes can get in on the show.

The frequency and intensity of the northern lights are often tied to an 11-year cycle on the sun that describes the number of “sunspots” that are visible. Sunspots are localized cool spots on the surface of the solar disk that bubble up and pulsate with magnetic energy. They are most frequent every 11 years at the peak of a “solar cycle.” The sun has been relatively quiet in the last few years as solar cycle 24 concluded and solar cycle 25 began; Wednesday’s storm is the strongest geomagnetic storm to date of cycle 25.

Strong solar storms are born when sunspots produce eruptions of energy that can, on occasion, target Earth. Solar flares, which emanate from sunspots, are explosions of light that accelerate high-energy particles toward Earth in minutes and can cause radio blackouts.

Coronal mass ejections (CME), meanwhile, are explosions that launch solar material in a given direction. When pointed at Earth, they usually take a couple days to arrive. Scientists are concerned about the potential for particularly intense strong coronal mass ejections, which could disturb the electrical power grid and damage spacecraft electronics.

“The flare is like the muzzle flash, which can be seen anywhere in the vicinity,” NASA wrote. “The [coronal mass ejection] is like the cannonball, propelled forward in a single, preferential direction.”

The coronal mass ejection that reached Earth very early Wednesday wasn’t moving fast by CME standards — the solar wind speed only ticked up to about 280 miles per second when it arrived, compared with ordinary values of 186 to 217 miles per second.

During the fiercest solar storms, the solar wind can reach speeds of 373 miles per second or greater. Despite its unremarkable field, Wednesday’s event packed quite a punch.

Wednesday morning’s light show over Canada was captured by the Suomi-NPP satellite, operated by the National Oceanic and Atmospheric Administration and NASA, which has a day-night band that can sense the luminous emissions of the aurora. Cities such as Chicago, Minneapolis and Detroit are visible on the bottom of the images, while swirls of the aurora ebb and flow over Canada.