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Hercules Cluster of Galaxies

Galaxies are found in a hierarchy of structures in the Universe: from rare isolated galaxies, to huge clusters of thousands of galaxies.  Located 470 million light-years away, Abell 2151 is a large cluster that provides a showcase for the main types of galaxies: elipticals, spirals, and irregulars.  As the galaxies move on their orbits within the dense cluster environment, close encounters are frequent.  Near the center of this image, such an event is caught in progress.