Why is the Big Dipper only an asterism while the big bear is a constellation?

An asterism is a collection of stars, but not a constellation. There are 88 constellations but there could be countless asterisms. The big Dipper (asterism) is part of Ursa Major (constellation).Why is the Big Dipper only an asterism while the big bear is a constellation?Simple, the Big Dipper is not considered a constellation because it is already part of a greater constellation known as Ursa Major, or the big bear.Why is the Big Dipper only an asterism while the big bear is a constellation?Because the IAU says so.