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The Northern Lights, or Aurora Borealis, are caused by charged gas particles – that flow away from the Sun as a “solar wind” – interacting with the Earth's magnetic field.
This solar wind has its own magnetic field, which can “drag away” the Earth's magnetic field lines, disconnecting them from our planet.
Eventually though, the field lines “snap back” into the continuous loop that exits one of the Earth's magnetic poles and re-enters at the other. This snapping back or “reconnection” means that particles that were in the solar wind are pushed into the Earth's atmosphere.
The charged particles “excite” gases in our atmosphere and make make them glow – just like gas in a fluorescent tube. The colours depend on the type of gas – a red or green glow is oxygen and the blue and purple colours are produced by nitrogen.
Northern lights
The spectacular Aurora Borealis are usually only visible in the far north
