a sharp front formed in the solar wind ahead of the magnetosphere, marked by a sudden slowing-down of the flow near Earth. It is quite similar to the shock forming ahead of the wing of a supersonic airplane. After passing near Earth, the slowed-down flow gains speed again, to the same value as the surrounding solar wind.
The boundary between the undisturbed solar wind and the region being deflected around the planet or comet
A bow shock is a supersonic shock wave that is formed as the solar wind interacts with the outermost layer of a planet's magnetosphere (or a highly conducting ionosphere). At this boundary onthe sun-ward side, the solar wind plasma is deflected around the planet and is slowed to subsonic speed by the planet's magnetic field.
The shock wave that flanks the magnetosphere on the day side. It causes the solar wind flow to slow down and flow around the magnetosphere.
The outermost part of a planetary magnetosphere; the place where the supersonic flow of the solar wind is slowed to subsonic speed by the planetary magnetic field.
In a planetary magnetosphere, the bow shock is the boundary at which the solar wind abruptly drops as a result of its approach to the magnetopause. The best-studied example of a bow shock is that occurring where the solar wind encounters the Earth's magnetopause, although bow shocks occur around all planets. The Earth's bow shock is about 100-1000 km thick and located about 90,000 km from the Earth.