The Oort cloud, (IPA: BrE /ɔːt klaʊd/, AmE /ɔɹt klaʊd/), alternatively termed the Öpik-Oort Cloud (/ˈøpik/-, like /ˈepik/ with a rounded /e/), is a postulated spherical cloud of comets situated about 50 to 50,000 AU from the Sun. This is approximately 1000 times the distance from the Sun to Pluto or nearly a light year. The outer extent of the Oort cloud places the boundary of our Solar System at nearly a quarter of the distance to Proxima Centauri, the nearest star to the Sun.
Although no confirmed direct observations of the Oort cloud have been made, astronomers believe it to be the source of all long period and Halley-type comets entering the inner solar system (some short-period comets, based on their orbits, may come from the Kuiper belt).