This wellknown open cluster, situated very close to famous M35 (NGC 2168), was considered as a globular by Rosino (1954), see also Sawyer Hogg (1959). Despite this, its nature as an old Galactic open cluster is established with certainty; its age has been estimated at about 1.05 billion years.
The image in this page has been obtained with the Burell-Schmidt Telescope
of Kitt Peak National Observatory near Tucson, Arizona. It has been cropped
from a
larger image of NGC 2158 together with its more prominent neighbor M35.
Credit: NOAO/AURA/NSF
NGC 2158 had been discovered by William Herschel and cataloged as H VI.17.
References: