The objects, M35 (NGC 2168) and NGC 2158 are open clusters and are both seen in the constellation of Gemini, though they are not physically related. An open cluster is a group of up to a few thousand stars that were formed from the same giant molecular cloud and have roughly the same age.

M35 is the only Messier object in Gemini and consists of several hundred stars, of which 120 are brighter than magnitude 13. The age of M35 is about 110 million years with the hottest main sequence stars in the cluster having a spectral classification B3. M35 also contains more evolved stars, including several orange and yellow giants. The cluster is approaching us at 5 km/s. M35 was first discovered in 1745 by a Swiss astronomer called Jean-Philippe Loys de Cheseaux, but John Bevis, an English astronomer, found the cluster independently before 1750. NGC 2158 was discovered by William Herschel on November 16, 1784 and catalogued as H VI.17.