An Etymological Dictionary of Astronomy and Astrophysics

The point where the → stellar wind makes a transition from → subsonic to → supersonic flow. In the particular case of a spherically symmetric wind (thus with no magnetic field), the distance from star, at which the sonic point occurs, is given by: r_s = (GM)/2c_s², where G is the → gravitational constant, M is the stellar mass, and c_s the → sound speed at the sonic point.

See also: → sonic; → point.