A star cluster designates a small star concentration in a relatively reduced space to the astronomical scale (a few dozens to a few hundreds parsecs), bounded together by gravitational forces.
A cluster is distinct from a galaxy by the number of stars into it (a few hundreds or thousands for a cluster, against a few hundreds of billions for a galaxy).
We found open clusters for which the star are disseminated but sufficiently close to be gravitationally bounded, and the globular clusters for which the stars are very close.
Matching words: Galaxy, Star
- Alastor series, by Jack Vance