Bow shock
The first observations were made in the 1980s and 90s as several spacecraft flew by comets which were 21P/Giacobini–Zinner, Halley's Comet, and 26P/Grigg–Skjellerup. It was then found that the bow shocks at comets are wider and more gradual than the sharp planetary bow shocks seen at for example Earth. These observations were all made near perihelion when the bow shocks already were fully developed.