Observations from NASA's twin Solar Terrestrial Relations Observatory (STEREO) spacecraft allowed scientists, for the first time, to reveal the true size and shape of solar explosions known as coronal mass ejections, or CMEs, in three dimensions. Note: Dr. Angelos Vourlidas, the Project Scientist for STEREO's Sun Earth Connection Coronal and Heliospheric Investivation (SECCHI) instrument, explains how the STEREO satellites have been able to observe the true size, shape, and three-dimensional structure of a coronal mass ejection for the first time. For complete transcript, click here. Animator: Walt Feimer (HTSI). Producer: Chris Smith (UMBC). Scientist: Angelos Vourlidas (NRL). Platforms/Sensors/Data Sets: STEREO.