Discussion
The Aurora Borealis, or Northern Lights, is caused by
Answer: A
Correct answer: Charged particles from the Sun interacting with gases in the upper atmosphere
Auroras occur when charged particles carried by the solar wind are funnelled by the Earth’s magnetic field towards the poles and collide with atoms in the upper atmosphere, exciting them so that they emit light as they return to their normal state. The colour identifies the gas and the altitude: oxygen gives the common green at around 100 to 300 km and a rarer red higher up, while nitrogen gives blue and purple. The magnetic field is what confines the display to two rings around the geomagnetic poles - the aurora borealis in the north and the aurora australis in the south, which often mirror each other almost exactly. Activity follows the eleven-year solar cycle, and a strong geomagnetic storm can push the aurora to much lower latitudes. The same storms can disrupt satellites, radio communication and power grids.
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