Chasing the Northern Lights: Aurora Borealis Uncovered

In 1619, Galileo Galilei reached for a Latin phrase to describe the shifting glow he had read about in northern skies: aurora borealis, the “northern dawn”. He borrowed the first word from Aurora, the Roman goddess of the dawn who was said to race across the sky ahead of the sun, and the second from Boreas, the Greek god of the north wind. The name stuck, even though Galileo’s own explanation for the lights was wrong. It would take another three centuries, and a Norwegian scientist with a laboratory full of magnets, to work out what actually paints the polar sky green and crimson.

What the aurora actually is

The aurora begins ninety-three million miles away, at the surface of the sun. Our star constantly sheds a stream of charged particles — electrons and protons — known as the solar wind, and during solar storms it hurls out great gusts of them. When this charged material reaches Earth, most of it is deflected by the planet’s magnetic field, which acts as an invisible shield. But near the magnetic poles the field lines dip down towards the surface, funnelling some of those particles into the upper atmosphere.

There, roughly a hundred to three hundred kilometres up, the particles collide with atoms of oxygen and nitrogen. The collisions excite those atoms, nudging their electrons into higher energy states; when the electrons drop back down, they release the surplus energy as light. Oxygen produces the familiar green glow at lower altitudes and, more rarely, a deep red at greater heights. Nitrogen contributes blues and purples. The colour you see is therefore a direct readout of which gas was struck, and how high up — a piece of atmospheric chemistry written across the whole sky.

From gods to geophysics

Long before Galileo named it, the aurora was woven into the mythology of the peoples who lived beneath it. In Norse tradition, the shimmering lights were sometimes linked to the Valkyries, the warrior-maidens who chose the slain and guided fallen fighters to Valhalla; the glow was imagined as light glinting off their armour. Several Indigenous peoples of northern North America regarded the lights as the spirits of ancestors, and in parts of Scandinavia and among the Sámi there were cautions against whistling or waving at them, lest the lights take notice of you.

The scientific answer arrived through one obsessive figure: the Norwegian physicist Kristian Birkeland. Between 1899 and 1900 he led expeditions into the Arctic to measure the magnetic disturbances that accompanied auroral displays, and in his laboratory he built a “terrella” — a small magnetised sphere representing the Earth, which he bombarded with cathode rays inside a vacuum chamber. Glowing rings appeared around its magnetic poles, mimicking the aurora. From this, Birkeland argued in 1908 and 1913 that the lights were caused by charged particles from the sun channelled by the Earth’s magnetic field — essentially the modern explanation, decades before instruments in space could confirm it. He was so associated with the phenomenon that he is sometimes called the father of the aurora, and his portrait once appeared on the Norwegian 200-kroner banknote.

Reading the aurora forecast

The strength and frequency of auroral displays rise and fall with the sun’s own eleven-year cycle of activity. Near the peak of that cycle, sunspots are more numerous and the sun more prone to the eruptions that drive strong displays, which is why serious aurora-watchers pay attention to where the sun sits in its cycle. On a night-to-night basis, the key number is the Kp index, a scale from 0 to 9 that measures geomagnetic disturbance. A low Kp means the aurora hugs the poles; a high Kp pushes the visible oval further south, so that during major storms the lights can be seen far below their usual latitudes.

Occasionally the sun produces an event large enough to be seen almost everywhere. The Carrington Event of September 1859, the most intense geomagnetic storm on record, pushed the aurora as far as the Caribbean and set telegraph systems sparking. In May 2024, a severe solar storm produced displays visible across unusually low latitudes, including much of the United States and Europe — a reminder that the aurora is not solely a polar privilege, but a planet-wide phenomenon that simply favours the poles.

The camera as a second pair of eyes

One quirk that surprises first-time aurora hunters is that a camera often sees more than the naked eye does. Human night vision relies on the rod cells in the retina, which are highly sensitive to light but almost colour-blind; a faint aurora that reads as a pale grey smudge to your eyes can register as vivid green in a photograph, because the camera’s sensor accumulates light over a long exposure and records colour that your eyes cannot. This is why photographs of the aurora so often look more dramatic than people expect from their memory of the night — the camera is not lying, it is simply better equipped for the conditions.

Capturing it is a matter of a few settings rather than expensive gear, though a camera with manual control helps enormously. A sturdy tripod is non-negotiable, because exposures run from a couple of seconds to fifteen or more, far too long to hold steady by hand. A wide-angle lens with a fast aperture — something around f/2.8 or wider — lets in the most light and takes in a broad sweep of sky. A useful starting point is an aperture near f/2.8, an ISO of around 1600, and a shutter speed of five to fifteen seconds, then adjusting from what the first frames show. A remote release or a two-second timer avoids the tiny shake of pressing the shutter. And a warning worth heeding: batteries drain alarmingly fast in Arctic cold, so keep spares in an inside pocket where your body heat can keep them alive.

Where and when to go

Practically speaking, the reliable places to see the aurora are those sitting under the auroral oval with dark, clear skies. Tromsø in northern Norway, Abisko in Swedish Lapland, Rovaniemi in Finland, Reykjavík and the wider Icelandic interior, Fairbanks in Alaska, and Yellowknife in Canada’s Northwest Territories are among the best-known bases. Abisko is prized because a local microclimate, the so-called “blue hole”, often keeps its skies clearer than the surrounding region.

Timing matters as much as place. The aurora is present year-round, but you need darkness to see it, so the long nights from roughly late September to late March are the window in the far north; high summer, with its midnight sun, is hopeless. The equinox months of September and March tend to bring heightened geomagnetic activity, a genuine seasonal advantage. Beyond that, the rules are simple and unromantic: get away from town lights, keep an eye on the forecast, be prepared to move if cloud rolls in, and dress for cold that can be genuinely dangerous. Patience is the real equipment. Displays can flare suddenly after hours of nothing, brightening from a faint arc to a full curtain in minutes, and the people who see the best shows are usually the ones still outside at two in the morning long after their companions have given up and gone to bed.

Fun facts

• Galileo coined the term aurora borealis in 1619 — yet his own theory of what caused it, involving sunlight reflecting off the atmosphere, was mistaken.
• Kristian Birkeland reproduced the aurora in miniature using a magnetised sphere called a terrella, and later appeared on Norway’s 200-kroner banknote alongside it.
• The Carrington Event of 1859 pushed the aurora as far south as the Caribbean and caused telegraph lines to spark, in some cases operating with their power supplies disconnected.
• The southern equivalent, the aurora australis, occurs simultaneously and near-mirrors the northern display, but is seen by far fewer people because so little land sits under the southern auroral oval.
• Some Sámi and Scandinavian traditions warned against whistling at or waving to the lights, for fear of drawing their attention.

A closing reflection

There is a peculiar humility in standing beneath the aurora once you know what it is. The green ribbon overhead is not a symbol or a spirit but the visible edge of a collision between the sun and the shell of air we live inside — a shield doing its quiet work, made briefly luminous. Galileo gave it a beautiful, wrong name; Birkeland, in a cold laboratory with a glowing sphere, gave it the right explanation and none of the poetry. The remarkable thing is that both survive. We still call it the northern dawn, and we still stand out in the freezing dark to watch it, even armed with the physics. Understanding a thing, it turns out, rarely diminishes the wonder of seeing it — a lesson that carries over to the way orbiting instruments on the ISS reveal the polar lights from above, and to the fragile, crowded orbital environment those same instruments share with a growing hazard of space debris.