What causes an aurora to occur at the Earth?s magnetic poles?
An aurora occurs when charged particles in the solar wind incite electrons of atmospheric atoms through collisions and when the electrons return to their original energy levels, the atoms send out photons of visible light to create the colors displayed. Read more: http://www.webexhibits.org/causesofcolor/4B.html and http://science.howstuffworks.com/nature/climate-weather/atmospheric/aurora2.htm.
The Earth has a magnetic shield around it protecting it. But in the poles,there's an opening for the suns solar waves to poke thru.