In the Going Deep column in the July 2016 issue Sky & Telescope Contributing Editor Steve Gottlieb shared his expert knowledge, gathered through multiple observing sessions and outside research, of the Hercules Galaxy Cluster, cataloged as Abell 2151. The central 18' × 6' region, called Abell 2151C, is the richest region of the cluster and contains over 15 member galaxies from 14th- to 15th-magnitude. Steve first tackled the cluster in 1983, using a 13.1-inch reflector. More recently, he surveyed the region using his 18-inch f/4.3 reflector.
As Ken Crawford's image shows, Abell 2151 contains an abundant number of spiral galaxies (some 50% of the total) and includes a number of interacting pairs and trios. These galaxies are typically quite small, so Steve recommends using a magnification of 250x or higher if the seeing allows. The higher power will increase visibility and help to resolve the close pairs.
To aid your observing endeavor, Steve has provided an expanded table of galaxies, with their position angles, visual magnitudes, size, and positions. The table is available for download as an Excel file and as a PDF. The galaxies listed in boldface type are discussed in the July issue.