  The study of open star clusters makes us understand a lot about the
composition and construction of the Milky Way Galaxy. Thanks to the Gaia DR2
database that helps us to get the genetic members of star clusters using their
proper motions and parallaxes, estimating their physical properties in a very
accurate way. This study aims to detect the reasons that make proper motions
value of a cluster is completely separated from the background field stars and
not melted in. We studied a large sample of open stellar clusters taken from
Dias catalog and drawing the vector point diagrams using the astrometric data
of Gaia DR2. Marking the separated clusters and melted ones and study their
mean parameters in each galactic quadrant.
