NGC 2509

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NGC 2509 is an open star cluster in the southern constellation Puppis. It was discovered by William Herschel on December 3, 1783 and later described as bright, fairly rich, and slightly compressed.

The cluster is about 14 light-years across. Distances to NGC 2509 have varied widely: older estimates ranged from about 3,000 to 9,500 light-years, while the most recent Gaia-based analyses place it at roughly 2,500–3,000 parsecs away (about 8,000–10,000 light-years).

Its age estimates have also varied, from around 1.2 billion years to about 8 billion years. Current data continue to refine these values but do not yet provide a precise age.

Observation data: Right ascension 08h 00m 48s, Declination −19° 03′ 06″. Apparent magnitude about 9.3; apparent size about 2.5 by 0.5 arcminutes. Other names for the cluster include Cr 171, Mel 81, and OCl 630.