What are the Northern lights?
The Northern lights (or 'aurora') are caused by energetic particles that perpetually rain down onto the upper part of Earth's atmosphere - most of these particles stream from the sun in the 'solar wind', although some originate from deeper out in space. Many are guided along the Earth's magnetic field down deeper into our atmosphere, where they collide with atoms and molecules of air. In such a collision, the particle gives up some of its energy to the atom, which later gives off this energy in the form of light. So if the sun is active there's a strong solar wind, and many millions of these collisions occur high up in the atmosphere to produce the luminous glow that is the northern lights. The actual colour observed depends on what kind of atom or molecule is giving off the light, and how much energy has been given to it by the collision. The northern lights are emitted from a region from about 100-300km above the Earth's surface.