Giant fountains of fast-moving, multimillion-degree gas in the outermost atmosphere of the Sun have revealed an important clue to a long-standing mystery -- the location of the heating mechanism that makes the corona 300 times hotter than the Sun's visible surface. Scientists discovered an important clue while observing immense coils of hot, electrified gas, known as coronal loops. These fiery, arching fountains now appear in unprecedented detail with NASA's Transition Region and Coronal explorer (TRACE) spacecraft. Scientists are interested in the corona, which appears as a halo of light seen by the unaided eye during a total solar eclipse, because eruptive events in this region can disrupt high-technology systems on Earth. Astronomers also hope to use the solar corona studies to better understand other stars.