The atmosphere of the Sun, the corona is threaded by strong magnetic fields. These fields can trap gas into huge bubbles which are suddenly released and expand outward as a coronal mass ejection (CME). The buble can contain a billion tons of matter and can expand outward at millions of miles per hour. When this material reaches Earth it can effect space travellers, satellites and communication. Scientists are beginning to focus a lot of effort on understanding and predicting these effects. They call it space weather.
The movie above shows a coronal mass ejection as seen by the LASCO (Large Angle and Spectrometric COronagraph) instrument on the SOHO (Solar and Heliospheric Observatory) spacecraft. LASCO is an instrument called a coronagraph. It blocks the light coming from the solar disk, in order to be able to see the faint light from the solar corona.