A small, named group of fixed stars

One word substitute is Constellation.

Galaxy: a system of millions or billions of stars, together with gas and dust, held together by gravitational attraction.
Cluster: a group of similar things or people positioned or occurring closely together.
Constellation: a group of stars forming a recognizable pattern that is traditionally named after its apparent form or identified with a mythological figure.
Congregation: a group of people assembled for religious worship.