The Earth's magnetosphere on the sunward side extends to about 65 000 km, but stretches to many times this on the side away from the Sun. In June 2001, Cluster began to explore the extended magnetotail. It is in this region that storms of high energy particles are generated. When these arrive on Earth they can result in auroras on the nightside of Earth. Other less attractive consequences are power cuts, damage to satellites and disruptions in communications.