A smaller group of stars within a constellation is called an asterism.

Here's the difference:

* Constellation: A large, recognized pattern of stars that covers a large area of the sky. These are often based on mythological figures or animals.

* Asterism: A smaller, recognizable pattern of stars within a constellation. These are often named for their appearance or shape.

Here are some examples:

* The Big Dipper: An asterism within the constellation Ursa Major (Great Bear).

* The Little Dipper: An asterism within the constellation Ursa Minor (Little Bear).

* Orion's Belt: An asterism within the constellation Orion.

While a constellation is a larger, official grouping of stars, an asterism is a smaller, more informal grouping within a constellation.