John Herschel discovered NGC 2645 = h3136 on 29 Dec 1834 and described a "close group or small cluster of 12 or 13 large and small stars; place of a double star, the chief one." This cluster is equivalent to Pismis 6 with the nearly central pair HD 73919/CoD-45 4352 at 08 39 04 -46 13.6 (2000). Paris Pismis reported the cluster as new in her 1959 list of clusters found on Tonantzintla Schmidt plate and commented, "Two pairs of doubles, including the brightest star."

RNGC classifies NGC 2645 as nonexistent (Type 7) and Lynga labels the cluster Pismis 6 without reference to NGC 2645.

300/350mm - 14" (4/5/16 - Coonabarabran, 145x and 178x): bright compact group with a dozen stars packed into a 2' region. Contains 4 very bright stars forming a right angle, including a striking pair of mag 9 stars (HJ 4122) at 11" separation. A third mag 9 star is 1' W of the pair and another mag 9.5 star is 1' SSE. The latter star is also a double with a mag 10.5 companion at 16" separation. This knot of bright stars is situated 15' ENE of mag 6.9 HD 73658.

Notes by Steve Gottlieb