Discovered by William Herschel on November 16, 1784.

NGC 2158 is a dense open cluster of stars situated in the constellation Gemini. The cluster is only about one quarter of a degree to the southwest, but much more distant, to its better known cousin, M35.  NGC 2158 is very compact for an open cluster and was considered a globular cluster by the italian astronomer Leonida Rosino.  The current classification maintained by most astronomers is that of a very old Galactic Open Cluster.  The age of the cluster is estimated to be approximately 1.05 billion years.  The cluster consists primarily of old stars giving it a decidedly yellow color.  NGC 2158 is estimated to be approximately 11,000 light-years from the Earth.

¹http://spider.seds.org/spider/MWGC/n2158.html