English: Arcs rise above an active region on the surface of the Sun in this series of images taken by the STEREO (Behind) spacecraft. The arcs are plasma, superheated matter made up of moving charged particles (electrons and ions). Just as iron filings arc from one end of a magnet to another, the plasma is sliding in an arc along magnetic field lines. Most coronal mass ejections are more bulbous and wide: this one is quite narrow and contained. Nonetheless, NASA solar scientists agree that its speed and characteristics suggest that it was indeed a non-typical coronal mass ejection.