The compressed wave that forms in front of a spacecraft or satellite as it moves rapidly through Earth’s atmosphere; more generally, any such wave that forms between an object and a fluid medium.

Imagine an object moving at super-sonic speed. This object, as it moves through a medium, causes the material in the medium to pile up, compress, and heat up. The result is a type of shock wave, known as a bow shock.

In astrophysics, a bow shock occurs when the magnetosphere of an astrophysical object interacts with the nearby flowing ambient plasma such as the solar wind. For Earth and other magnetised planets, it is the boundary at which the speed of the stellar wind abruptly drops as a result of its approach to the magnetopause