A loosely bound group of typically young, hot stars that formed together from the same molecular cloud, containing hundreds to thousands of members. These clusters gradually disperse over millions of years as their weak gravitational bonds are overcome by galactic tides.
The term 'open' contrasts with 'globular' clusters, referring to the loose, scattered appearance of these stellar groups. First systematically cataloged by Charles Messier in the 18th century, who noted their diffuse, non-spherical structure compared to globular clusters.
Open clusters are stellar nurseries caught in the act of breaking up! Most stars, including our Sun, were born in open clusters but have long since drifted apart, making these clusters snapshots of stellar families before they scatter across the galaxy forever.
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