Earth's magnetic field is an invisible shield around our planet that protects us from the solar wind. The shape of Earth's magnetic field causes the aurora to form two ovals that sit like crowns over the North and South magnetic poles. This is why communities in the northern regions of Canada see the aurora regularly. However, during periods of intense solar activity, the northern auroral oval can stretch as far south as the southern United States and Mexico. When solar activity decreases, the oval returns to northern latitudes.
The solar wind buffets our magnetic field, compressing it into a teardrop shape. Sometimes the magnetic field lines reconnect on the side of the Earth opposite the Sun. They snap back like an elastic band, sending large amounts of energy back towards the Earth's poles. This phenomenon, called magnetic reconnection, creates stunning displays of aurora. Scientists are only beginning to understand how this happens. Canada is a partner in NASA's THEMIS mission to help solve this mystery.