For the first ten billion kilometres of its radius, the solar wind travels at over a million kilometres per hour. It slows down before finally stopping altogether. The point where the solar wind slows down is the termination shock; the point where the interstellar medium and solar wind pressures balance is called the heliopause; the point where the interstellar medium, travelling in the opposite direction, slows down as it collides with the heliosphere is the bow shock. 