NGC 6087
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NGC 6087, also referred to as Caldwell 89 or the S Normae Cluster, is an open star cluster consisting of 40 or more stars, located in the constellation Norma. The cluster is centred around the Cepheid variable star, S Normae, and is approximately 3,500 light-years away. It spans nearly a quarter of a degree in the sky, with stars ranging in brightness from magnitude 7 to 11, the brightest being S Normae at magnitude 6.5. The total visual magnitude of the cluster is around 5.4.
Spectral analysis of the radial velocities of the stars confirms that S Normae is indeed a member of the cluster. The distance to the cluster can be accurately measured using the period-luminosity relationship of Cepheid variable stars.