Probing the Sun's hot atmosphere

The solar corona is an extremely hot (10(6) K), almost fully ionized plasma which extends from a few thousand km above the photosphere to where it fre ely expands into the solar system as the solar wind. The exact reason for i ts high temperature is still unknown, despite more than 50 years of researc h, but magnetic fields are certainly involved. This article reviews some re cent progress in our understanding using data from spacecraft (SOHO, Yohkoh , and TRACE) as well as ground-based eclipse experiments.