The solar wind is a stream of charged particles that flow away from the Sun. The particles that encounter Earth become trapped between two regions beyond the atmosphere that are known as the Van Allen radiation belts. At times the Sun releases an intense outburst of charged particles, causing the Van Allen belts to overflow. This causes particles to cascade down into Earth’s upper atmosphere, where they excite molecules of atmospheric gas, causing them to emit visible radiation. This radiation is known as an auroral display. Most of this activity occurs in the skies near the poles. The display is called the Aurora Borealis in the north and the Aurora Australis in the south.