An Etymological Dictionary of Astronomy and Astrophysics

The vast, three-dimensional region of space around the Sun filled with the → solar wind and the remnant of the → solar magnetic field
carried in it. It is bounded by the → heliopause, which is estimated to be 100 → astronomical units or more from the Sun. The radius of the heliosphere is expected to vary with the → solar cycle. The heliosphere may be very elongated owing to the presence of an interstellar wind of neutral hydrogen flowing from the direction of the Galactic center.

Etymology (EN): From → helio- + → sphere.