STOCKHOLM (AP) — A storm from the broiling sun turned the chilly northernmost skies of Earth into an ever-changing and awe-provoking art show of northern lights on Tuesday.

Even experienced stargazers were stunned by the intensity of the aurora borealis that swept across the night sky in northern Scandinavia after the biggest solar flare in six years.

“It has been absolutely incredible,” British astronomer John Mason cried from the deck of the MS Midnatsol, a cruise ship plying the fjord-fringed coast of northern Norway.

“I saw my first aurora 40 years ago, and this is one of the best,” Mason told The Associated Press, his voice nearly drowning in the cheers of awe-struck fellow passengers.

U.S. space weather experts from the National Oceanic and Atmospheric Administration said Tuesday evening that so far they had heard of no problems from the storm that triggered the auroras, which made it as far south as Wales, where the weather often doesn’t cooperate with good viewing.

It was part of the strongest solar storm in years, but the sun is likely to get even more active in the next few months and years, said physicist Doug Biesecker at the U.S. Space Weather Prediction Center in Boulder, Colorado.

“To me this was a wake up call. The sun is reminding us that solar max is approaching,” Biesecker said. “A lot worse is in store for us. We hope that you guys are paying attention. I would say we passed with flying colors.”

Even before particles from the solar storm reached the Earth on Tuesday, a different aurora Monday night was dancing across the sky as far south as Ireland and England, where people rarely get a chance to catch the stunning light show.

Those northern lights were likely just variations in normal background solar wind, not the solar storm that erupted Sunday, Biesecker said.

Tuesday’s colorful display may not have moved that far south, limiting its audience, but those who got to see it got brilliance in the sky that had not been around for years.

“It was the biggest northern lights I’ve seen in the five-six years that I’ve worked here,” said Andreas Hermansson, a tour guide at the Ice Hotel in the Swedish town of Jukkasjarvi, above the Arctic Circle.

He was leading a group of tourists on a bus tour in the area when a green glow that had lingered in the sky for much of the evening virtually exploded into a spectacle of colors around 10:15 p.m.

“We stopped the bus. And suddenly it was just this gigantic display of dancing lights and Technicolor,” said Michele Cahill, an Irish psychologist, who was on the tour. “It was an absolutely awesome display. It went on for over an hour. Literally one would have to lie on the ground to capture it all.”

But in -30 degrees F (-35 C), that didn’t seem like a good idea.

An aurora appears when a magnetic solar wind slams into the Earth’s magnetic field, exciting electrons of oxygen and nitrogen.

The northern lights are sometimes seen from northern Scotland, but they were also visible Monday night from northeast England and Ireland, where such sightings are a rarity.