Our sun is always sending out a stream of tiny particles into space. Scientists call this the 'solar wind'. Most of the time, the Earth's invisible magnetic field protects us from it - the particles whoosh past us into outer space.
But near the North and South Poles, the magnetic field dips down and lets some of those particles in. As they smash into the air, they make the gas glow - a bit like a giant neon sign in the sky. Different gases glow different colours. Oxygen makes green and red. Nitrogen makes pink and purple.
The aurora doesn't just sit there - it moves. Curtains of light ripple, swirl and shimmer across the sky. Sometimes they fade in seconds, sometimes they dance for hours. People stand outside in the freezing cold just to watch.
Long before scientists understood the aurora, Sami people in northern Norway told their children to stay quiet and respectful when it appeared. Some stories said the lights were the spirits of friends and ancestors, dancing in the sky. Different cultures around the Arctic told different stories about what the lights might be.