A group of stars that are gravitationally bound and formed in the same gas cloud. Open clusters are generally young (but not always) and can contain up to a few thousand stars.

The Pleiades (M45) is a famous bright open cluster visible from Earth.

M45 The Pleiades Open Cluster (NASA, ESA, and The Hubble Heritage Team (credit:- STScI/AURA))

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Sky Highlights - April 2017

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