Movie: A Computer Model of a CME - from the Sun to Earth
Movie: Journey Beneath a Sunspot
Movie: Geomagnetic Substorm Triggered by CME from Sun
A movie of a coronal mass ejection in white light, courtesy of the High Altitude Observatory (180K MPEG) Movie credit
Movie: Aurora and THEMIS Satellite
Coronal Mass Ejections"Without warning, the relatively calm solar atmosphere can be torn asunder by sudden outbursts of a scale unknown on Earth. Catastrophic events of incredible energy...stretch up to halfway across the visible solar surface, suddenly and unpredictably open up and expel their contents, defying the Sun's enormous gravity." (Sun, Earth, and Sky by Kenneth R. Lang)
These catastrophic events that the author is speaking about are coronal mass ejections (CME's).
Coronal mass ejections are explosions in the Sun's corona that spew out solar particles. A lot of material is thrown out into the solar wind. Coronal mass ejections can be dangerous when they hit the Earth.
CME's can seriously disrupt the Earth's environment. Intense radiation from the Sun, which arrives only 8 minutes after being released, can alter the Earth's outer atmosphere, disrupting long-distance radio communications. Very energetic particles pushed along by the shock wave of the CME can endanger astronauts or fry satellite electronics. These energetic particles arrive at the Earth (or Moon) about an hour later. The actual coronal mass ejection arrives at the Earth one to four days after the initial eruption, resulting in strong geomagnetic storms, aurorae and electrical power blackouts.
Coronal mass ejections will become more and more frequent as we near solar maximum. CME's, not discovered until the 1970's, are difficult to detect. That is why we need satellites such as the ACE satellite which acts as a spaceweather station while in orbit. ACE can provide a one-hour advance warning of any geomagnetic storms that would affect the Earth.