How large are typical open clusters?
Most of the brightest stars are older yellow stars, but a few young blue stars are also visible. This picture is a composite of three images taken by the Hubble Space Telescope.
Open clusters vary significantly in size, with linear diameters typically ranging from 5 to 75 light-years. While some sources note that many clusters have diameters between 2 and 20 light-yearsâwith the majority measuring less than 5 light-years acrossâit is increasingly recognized that many clusters possess large, extended halos of members that can increase these dimensions severalfold.12
Regarding their stellar population, about half of all known open clusters contain fewer than 100 stars, though the richest clusters can contain 1,000 or more. In terms of mass, most open clusters are relatively small, typically on the order of 50 solar masses. Due to their loose gravitational binding, these clusters are susceptible to tidal forces within the Galaxy, which eventually lead to their disintegration over time.12