Open Star Clusters M35 and NGC 2158. Open star cluster M35 consists of several hundred stars (of which Wallenquist has counted 120 brighter than mag 13) scattered over the area covered by the full Moon (30'). At its distance of 2,800 light years (Sky Catalogue 2000.0), this corresponds to a linear diameter of about 24 light years; its central density is about 6.21 stars per cubic parsec. Some authors have estimated a larger diameter of up to 46' (H. Shapley in 1930). With about 100 million years, it is of intermediate age, and contains some post-main sequence stars (including several yellow and orange giants of spectral type late G to early K). Its hottest main sequence star is given as of spectral class B3 (Sky Catalogue 2000.0). It is approaching us at 5 km/sec.