Images of coronal mass ejections such as this one, obtained using the Soft X-ray Telescope aboard the Yohkoh spacecraft, are helping to explain how such sudden explosions occur. These events, which come about when plasma and magnetic fields are transiently ejected from the Sun's corona — the outermost region of the solar atmosphere — produce intense shock waves, accelerating vast quantities of energetic particles. When directed at the Earth, coronal mass ejections can cause strong geomagnetic storms, disrupting communications. Magnetic changes that occur before this energy release may act as a warning of imminent ejections. More on this and many other aspects of the Sun can be found in The Cambridge Encyclopedia of the Sun by Kenneth R. Lang (Cambridge University Press, £29.95, $49.95).