The Northern Lights — or aurora borealis — are one of nature's greatest spectacles: shifting curtains of green, violet and red light that ripple across the Arctic night sky. But what actually causes them? Here is the science, explained simply.
How the aurora forms
The Sun constantly streams charged particles into space, known as the solar wind. When these particles reach Earth, most are deflected by our magnetic field — but near the magnetic poles they funnel down into the upper atmosphere. There, at 100–300 km altitude, they collide with gas atoms, which release energy as light. That glow is the aurora.
Why it moves and dances
The aurora isn't static. As the solar wind and Earth's magnetic field interact, the bands of light shift, fold and pulse — sometimes slowly over minutes, sometimes erupting into fast, dancing curtains during a geomagnetic storm.
Why the aurora appears in Rovaniemi
Auroras cluster in a ring around each magnetic pole called the auroral oval. Rovaniemi sits at 66.5°N, right on the Arctic Circle and directly beneath this oval — which is exactly why it's one of the most reliable places on Earth to see the lights. Read more in our why the aurora appears in Rovaniemi guide.
When can you see them?
You need three things: darkness, clear skies and solar activity. In Rovaniemi that means the season runs September to April — see our best time to see the Northern Lights guide for the month-by-month breakdown.