Tromsø sits directly beneath the auroral oval, the ring of near-permanent Northern Lights that circles the magnetic pole, so on a dark, cloudless night the sky here can turn green even when the Sun is quiet. The city lies about 350 kilometres north of the Arctic Circle at almost 70° north, yet the Gulf Stream keeps its harbour ice-free — one of the few real cities set this deep in the Arctic. Its winter is genuinely dark: from late November to late January the Sun never rises above the horizon at all, a two-month blue twilight that locals call mørketid. The lights appear when charged particles from the Sun spiral down the planet's magnetic field and strike oxygen and nitrogen about a hundred kilometres up, firing the sky with green, violet and, on strong nights, deep red. The season runs from late September to late March, when the nights finally grow long enough to hold it.
Seeing the lights is an open-air hunt in the cold. Because city glow washes out faint aurora, guides drive to darker ground — the islands of Kvaløya and Ringvassøya, or a valley walled by snow-loaded peaks — and then everyone waits. A pale grey-green smudge shows low on the horizon; within minutes it can uncoil into ribbons that race across the sky, brighten, fold and fade. You might watch from a sled behind a team of huskies, on snowshoes out on a frozen lake, or from Storsteinen, the ledge 421 metres up that the Fjellheisen cable car reaches in four minutes. Nothing is promised — the aurora answers to the weather and the Sun, not a schedule — so most people give it three or four nights.