They appear as shimmering arcs and waves of light, often blue or green in colour, which seem to sweep their way across the dark skies. During the darkest months of the year, the northern lights, or aurora borealis, are visible in the night sky all across northern Sweden. Until you see the light displays yourself, it’s hard to describe the spectacle in mere words – try to imagine, though, someone waving a fantastically coloured curtain through the air and you’ve pretty much got the idea.

What makes the northern lights so elusive is that it’s impossible to predict when they’re going to make an appearance. The displays are caused by solar wind, or streams of particles charged by the sun, hitting the Earth’s atmosphere. Different elements produce different colours, blue for nitrogen, for example, and yellow-green for oxygen.

The best place to view these mystical performances is north of the Arctic Circle, where temperatures are well below freezing and the sky is often at its clearest – two conditions that are believed to produce some of the most spectacular sightings.

For the quintessential northern lights experience, pack a couple of open sandwiches topped with smoked reindeer meat and a thermos of hot coffee to keep out the chill, then take a snow-scooter tour deep into the forests of Lapland – Kiruna, Sweden’s northernmost city, is the best base. Park up beside a frozen lake and train your eyes on the sky. Try this between mid-December and mid-January, when there’s 24-hour darkness north of the Arctic Circle, and the chances are you won’t have to wait too long for your celestial fix.