Here's why:

* Star groupings are based on specific criteria: Astronomers use terms like "constellation" (a pattern of stars recognized by humans), "galaxy" (a massive collection of stars, gas, and dust bound by gravity), and "cluster" (a group of stars that are physically close together).

* Numbers aren't the defining factor: Star groupings are named based on their characteristics, not just the number of stars they contain.

While there's no name for 1000 stars specifically, you could refer to it as:

* A "thousand-star cluster"

* A "collection of 1000 stars"

* A "group of 1000 stars"