Here's the difference:
* Constellations: Large and recognizable patterns of stars that are officially recognized by the International Astronomical Union (IAU). They can contain many stars, including those that don't form the recognizable pattern.
* Asterisms: Smaller, more easily recognizable patterns of stars within a constellation. They are not officially recognized by the IAU.
The Big Dipper is an asterism within the constellation Ursa Major (the Great Bear).
