Heliosphere

The heliosphere is the vast bubble of space dominated by the solar wind and the magnetic field it carries, extending from the Sun to the termination shock where the wind finally surrenders to the pressure of the interstellar medium. It is not merely a region but a dynamical structure shaped by the continuous outflow of plasma from the solar corona — a boundary layer between the Sun's domain and the galaxy beyond. The heliosphere's size fluctuates with solar activity, compressing during solar maximum and expanding during solar minimum, making it a breathing membrane rather than a fixed shell.

The heliosphere is the Sun's atmosphere in the largest sense — not a passive container but an active shield that modulates the flux of cosmic radiation reaching the planets.