Open stars clusters are collections of stars with similar ages,
chemical compositions, and distances from the Sun. These qualities
make open clusters important cosmic laboratories for studies of
fundamental astrophysics such as: the formation of stars, stellar
evolution, dynamical interactions between stars, and the chemical
and dynamical evolution and structure of the disk of our Galaxy.
Nearby open clusters play a key role in calibrating our measure
of cosmic distances.
Open clusters are strongly concentrated close to the galactic plane
where they form from cold dense clouds of molecular gas and dust.
There are over 1,000 known open clusters in our galaxy, but the
actual number may be up to ten times higher. The number of stars
in open clusters, typically from hundreds to a few thousands, make
them only loosly bound by gravity and thus vulnerable to dynamical
disruption in the dense traffic of the galactic disk. Accordingly,
most open clusters are younger than a few hundred million years,
and older clusters are preferentially found at greater distances
from the galactic center.
Web database for stars in open clusters (WEBDA)
WIYN Open Cluster Study (WOCS)
OPEN CLUSTERS AND GALACTIC STRUCTURE (Dias catalog)
The Star Clusters Young & Old Newsletter (SCYON)