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“Almost mystical,” says Lotte de Groot from Enschede. On a winter holiday in the north of Norway she saw the northern lights. “For a while we saw a faint greenish haze, but suddenly it became very bright, and spread over the whole sky, dancing. It even reflected in the snow on the mountains ahead. Very spectacular.”

Where the Sami see their ancestors in the aurora, and Inuit in Greenland see spirits that came to steal children, for a Westerner the aurora is primarily an awe-inspiring natural phenomenon, mysterious but also explainable. And the chances of seeing it are higher now than they have been in years.

The sun is nearing the peak of its 11-year activity cycle, increasingly belching out rarefied bubbles of charged solar particles, which sometimes collide with Earth after a few days of travel and produce auroras, colored curtains of light against the northern sky. Usually they can only be seen in the far north (or just around Antarctica), but sometimes also in the Netherlands, although here the curtains are more of a glow. The chances are extra good around the equinoxes, in March and September.

That’s the big picture, but there’s still a lot we don’t understand, says Manuela Temmer, a solar physicist at the University of Graz in Austria. “It always turns out to be more complex. As soon as we find one door we can close, five doors will open somewhere else.”

Research is not only important for aurora hunters and tourists. The electrically charged particles can disrupt or even damage the electronics of satellites, and the particle bombardment can also heat and swell the upper atmosphere, causing satellites to slow down unexpectedly. In 2022, 40 newly launched satellites from space company SpaceX crashed. Astronauts on board the International Space Station have to take shelter from solar storms, which is why space organizations such as ESA have departments for space weather.

Even on Earth, the blazing sun can sometimes cause damage, as the Canadian electricity company Hydro Quebec experienced in 1989, when a solar storm led to a build-up of voltage across long high-voltage lines. Transformer fuses blew, and Canadians were left in the dark for nine hours.

And that wasn’t even the most powerful eruption: in 1859 the Carrington eruption occurred, the most intense solar storm in recorded history. Polar lights could be seen as far away as Mexico, the magnetic fields led to disruptions on the newly constructed telegraphy networks, with telegraph operators receiving shocks.

If something similar were to happen again, the consultancy Metatech warned in 2009 in an influential report from the US National Academies of Science, it would lead to smoldering transformers and a catastrophic blackout. Although Ad Lagendijk, consultant in the field of electromagnetic fields at engineering firm DNV, thinks this is alarmist nonsense. “Most high-voltage connections are not so long that tensions build up in them. And since these events, networks and transformers have also become much more secure.”

Continuously distorting tangles

“We understand the processes fairly well, but that does not mean that we can also make good predictions,” says solar physicist Temmer. The sun consists of hot plasma, electrically charged particles, mainly hydrogen. Currents in it generate magnetic fields, and the sun, like the Earth, has a magnetic north and south pole. The particles are stuck like beads on a string to the magnetic field lines, which swirl inside the sun in continuously distorting tangles.

Sometimes these tangles pierce the surface of the sun in loops. In those places a relatively cool patch of sun is created, visible from Earth as a sunspot. In 1843, German astronomer Heinrich Schwabe noticed how their numbers increase and decrease in an 11-year cycle. Last February, the sunspot number was 124.7, one of the highest yet. During the last solar minimum, at the end of 2019, it was 0.

That cycle is also only partly understood, says Temmer. Because the sun rotates faster at the solar equator than at the poles, the tangles of magnetic fields within are increasingly wound up, like elastic bands around a spinning axis. The higher the built-up tensions, the more often the loops protrude.

Until a maximum is reached. Then the north and south poles of the sun switch places and a new cycle begins. How this change works is largely unknown, and the intensity of the solar cycles is also difficult to predict. NASA predicted a weak cycle, but the current cycle, number 25, turns out to be very powerful.

The loops of magnetic fields protruding from sunspots, loaded with solar particles, can sometimes detach and create a CME (coronal mass ejection), a bubble of plasma that is thrown into the solar system.

Sometimes a CME happens to be heading exactly towards Earth. It has its own magnetic field, which works like a protective cocoon that keeps charged particles out. But under the force of a powerful incoming CME, that cocoon can dent, deform and start to leak, so that the solar particles still flow in: a solar storm.

At hundreds of kilometers above sea level, the particles collide with sparse air molecules, which light up like cosmic neon tubes: green for oxygen, purple, blue and pink for nitrogen. Intense auroras mainly occur where the field lines pierce the Earth in the ‘aurora oval’ around the magnetic north pole in Northern Canada. Only during heavy solar storms does that area extend into the Netherlands.

Where do the polar lights come from?

Like water around a stone

“We can now predict space weather in a few days,” says Temmer. “With satellites we can see the CMEs arriving and accurately predict their arrival in about twelve hours.” Only if the CME’s magnetic field points south is there a chance of a solar storm. Temmer: “You cannot read the magnetic field from a distance, we only see that when the CME passes the ACE satellites 1.5 million kilometers from Earth. That gives us about half an hour’s notice.”

The magnetosphere, the protective bubble that the Earth itself generates, does its job well at the front. When the oncoming particle cloud collides with it, it initially washes around it like water around a stone in the river. Only at the back of the Earth, downstream, is the elongated magnetosphere more porous and open to leaks.

The current cycle of solar activity has presented yet another mystery: Steve

There, if the CME field is southerly, ‘reconnection’ can take place: the magnetic field lines of the particle cloud and the magnetosphere, initially separate, flip their configuration and suddenly connect. This gives the particles a free path to the Earth, and also an extra swirl, after which they light up the high atmosphere around the poles. This mechanism was only fully elucidated during the previous cycle, which peaked around 2014.

And the current cycle, number 25, has presented yet another mystery. In 2015, Neil Zeller, an amateur aurora photographer from Canada, took a photo of a bright white band in the northern sky. When he showed it to investigators, they couldn’t explain it. A fellow aurora hunter suggested naming the phenomenon Steve, a reference to the animated film Over the Hedgein which animals are afraid of a mysterious hedge, until someone suggests they name it Steve.

Northern Lights over Mierlo in November 2023.

Photos: Rob Engelaar/Hollandse Hoogte/ANP

More photos from Steve followed, often a long, narrow arc of white and purple colors in wavelengths not found in ordinary aurora. Research provided the beginnings of an explanation: electrical particles much lower in the atmosphere, which do not come directly from CMEs, although there does seem to be a connection: Steve only occurs during solar storms. The humorous name was retroactively given a scientific abbreviation: Strong Thermal Emission Velocity Enhancement. In 2021, Steve was spotted for the first time in Europe, in the Shetland Islands above Scotland, and last November in Northumberland, England. Steve has not yet been seen in the Netherlands.

Temmer: “We understand more and more and have more and more data. But we are still far from the point where we can make predictions, or where scientists even agree on the processes. Space weather is actually still a very young research field.”

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