The images shown are produced by the STEREO Extreme Ultraviolet Imaging Telescopes (EUVI). These show the Sun's super-hot atmosphere in ultraviolet wavelengths of light invisible to the human eyes and unobtainable from the Earth's surface. This hot, ionized material is shaped by the sun's magnetic fields so that observing the Sun's atmosphere in ultraviolet light allows us to study its magnetic field.
The Sun's atmosphere, the corona, is shaped by the Sun's complex and dynamic magnetic field. All the structures you see in these 3D movies are the result of that field. The magnetic field is also the source of solar activity. Complex magnetic fields rearrange and reconnect to form simpler magnetic structures and in the process release energy in the forms of flares and coronal mass ejections.
With STEREO we want to get 3D information about what is occurring on the Sun, which is 150 million km (93 million miles) away. Thus we need "eyes" which are much farther apart. At the time these images were taken in late March 2007 the two STEREO spacecraft were about 10 million km apart. This is far enough to give each spacecraft a distinct point of view of the structures in the Sun's lower atmosphere and makes 3D images of the Sun possible for the first time.