A bunch of movement or motion cluster is a loose group of stars that are not characterized by a spatial concentration around a cluster center, but by a common movement towards a distant convergence or vanishing point.
Although they have a common origin ( see star formation ) in an open cluster of stars but dissolves due to the low gravitational binding after a few galactic orbits. The transition to the type of open cluster or star association is rather blurred. A second hypothesis explains the origin of motion clusters by an orbital resonance with the spiral structure of the Milky Way. If a bunch of movement is very close to the solar system - such as the current Bears with 5 bright stars of the Big Dipper - you can no longer see directly, but only to the proper motions its context.
Well-known examples of movement clusters whose togetherness is immediately recognizable as a result of their greater distance, the Hyades in Taurus and the crib ( Praesepe ) in Cancer. On the other hand include the Pleiades star because of their concentration to the open cluster.