Solar corona

The solar corona is the outermost atmosphere of the Sun, a halo of million-kelvin plasma extending millions of kilometers into space and visible during total solar eclipses as a pearly white glow. It is the birthplace of the solar wind and the site of coronal mass ejections, maintained at temperatures far hotter than the photosphere below through mechanisms involving magnetic reconnection and Alfvén wave heating that remain partially unexplained. The corona's extreme temperature inversion — hotter with distance from the surface — is one of astrophysics' oldest unsolved puzzles, and its solution likely involves the coupling between small-scale turbulence and large-scale magnetic topology.

The solar corona is the Sun's crown not in name alone: it is the furnace from which the heliosphere is forged, and its secrets are the secrets of the Sun's power over the solar system.