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NASA
The Sun and the Solar Atmosphere
What are the "parts" of the Sun? The photosphere is the visible "surface" of the Sun. The three regions of the solar interior are the core, the radiative zone, and the uppermost convective zone. The solar atmosphere includes the chromosphere and the corona. The Sun's atmosphere, in the form of the solar wind and the Interplanetary Magnetic Field (IMF), extends outward into interplanetary space. In a sense, the Sun's atmosphere actually fills the heliosphere, the vast "bubble" in space extending well beyond Pluto.
What features and events can we see on the Sun? Regions of intertwined magnetic fields form in the solar interior and give rise to active regions, sunspots, and coronal holes at the Sun's visible surface. Fountains of electrified plasma shoot forth from the photosphere and give rise to prominences, helmet streamers, and spicules. Tremendous explosions on the Sun, solar flares and Coronal Mass Ejections (CME), hurl radiation and energized subatomic particles outward into space.
The solar wind is an extension of the Sun's atmosphere into space. This supersonic flow of plasma carries matter and energy outward. The IMF, embedded within the solar wind, carries the Sun's magnetic force field outward through the Solar System. Interactions between the solar wind and the magnetospheres, atmospheres, and sometimes the surfaces of planets affect the evolution of planets and their atmospheres.
The Sun changes over time. Vast explosions, flares and CMEs, alter the Sun's radiation and solar wind over time scales from minutes to hours to days. The 11-year sunspot cycle spans a much longer time scale. Studies of Sun-like stars of various ages have helped us learn about our Sun's wild youth and the changes in activity to expect throughout a star's lifetime.
