The sun is always sending out a stream of tiny particles. Most of the time, the Earth's magnetic field gently pushes them away, like a giant invisible shield. But near the top and bottom of the world, some particles slip through and smash into the air. The air glows green, pink and purple. That glow is the aurora.
In Lapland, the very north of Finland, the lights appear on around 200 nights every year. You need three things to see them: a dark sky, a clear sky (no clouds), and patience. People sit outside wrapped in blankets, watching and waiting. Sometimes the lights stay still for ages. Other times they suddenly start dancing.
Old Finnish stories explain the lights in beautiful ways. The Finnish word for the aurora is 'revontulet', which means 'fox fires'. According to one old story, a magical Arctic fox runs across the snow so fast that his tail sweeps sparks into the night sky.
Today, scientists know exactly what causes the lights, but the old stories are still loved. Across northern Finland, people set up cameras pointing at the sky all winter, sharing photos with the world. There are also apps that ping you when the aurora is about to start - so you can run outside and look up just in time.