Solar coronal loops. Coloured ultraviolet TRACE image of coronal loops on the Sun. The Earth has been superimposed for scale. The bases of the loops are the hottest areas (white). These raise the temperature of the solar corona (atmosphere) thousands of times above that of the Sun's surface (dark, lower frame). The loops comprise electrically-charged gases (plasma) at millions of degrees Celsius. Gas is heated as it is ejected from the surface, and follows the path of magnetic field lines before crashing back down at over 100 kilometres per second. TRACE (Transition Region & Coronal Explorer) is an observatory launched in 1998 to study the Sun at ultraviolet wavelengths.