The Northern Lights are also known as the aurora borealis. It is caused by a large amount of charged particles in the sky. These are caused by solar flares as they disappear in the immense universe.
The magnetic field surrounding our planet deflects these charged particles. Bringing them close to the North (and South) Pole at high speed. Subsequently, the charged particles clash with the oxygen and nitrogen atoms that creates the colour-changing effect. And that what the Northern Lights actually are.
The best places to see the Northern Lights are: Northern Norway, Iceland, Finnish Laplan, Greenland, Canada, Alaska (USA) and Russia.