The Northern Lights — the aurora borealis — are curtains of coloured light that appear in the night sky at high latitudes. In Ruka, Finland, we see them dozens of nights each winter, and guests always ask the same first question: what actually causes them?
Here's the science in plain language, and why Ruka is one of the best places on Earth to witness it.
Where the light comes from
The Sun constantly streams charged particles into space — the solar wind. When those particles reach Earth, our planet's magnetic field funnels them toward the poles. High in the atmosphere (100–300 km up) they collide with oxygen and nitrogen atoms, and those atoms release energy as light. That glow is the aurora.
Why it's usually green
Colour depends on which gas is hit and how high. Oxygen at ~100–150 km glows the familiar green; oxygen much higher up glows red; nitrogen adds blue and violet edges. Green is most common because that oxygen layer is densest.
Why Ruka is ideal
The aurora forms in a ring around the magnetic pole called the auroral oval. Ruka and Kuusamo sit at ~66°N, right under that ring, so even quiet nights can produce visible light. Add dark rural skies and 200+ clear nights a year and you have near-perfect conditions.
How to see them
You need darkness, a clear sky, and a little geomagnetic activity. A guided aurora hunting tour maximises all three by chasing clear skies, or track our live aurora forecast and head somewhere dark facing north.