The New General Catalogue of Nebulae and Clusters of Stars (abbreviated as NGC) is a catalogue of deep-sky objects compiled by John Louis Emil Dreyer in 1888. The NGC contains 7,840 objects, known as the NGC objects. It is one of the largest comprehensive catalogues, as it includes all types of deep space objects, including galaxies, star clusters, emission nebulae and absorption nebulae.
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NGC 6819
NGC 6819 is an open cluster (commonly known as an "open star cluster") located 7,200 light years away in the Cygnus constellation. It was discovered by Caroline Herschel on 12 May 1784. Situated on the boundary of Cygnus and Lyra, NGC 6819 contains roughly two dozen stars of magnitude 10 to 12, with many more lower magnitude members. The age of NGC 6819 is estimated here to be ~ 2.5 ± 0.5 Gyr. Its distance is calculated to be 2.16 ± 0.57 kpc.
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Wikipedia Page: NGC 6819
NGC 6819 at In-The-Sky website