The Hercules Cluster, cataloged as ACO 2151, is a sprawling galaxy cluster in Hercules that spans roughly 5,300,000 light-years across an angular field of 0.6° (37′), making it a superb wide-field target for astrophotographers who want dozens of galaxies in a single frame. Its members present a photogenic mix, from the interacting pair Arp 272 (NGC 6054) to the barred spirals Arp 71 (NGC 6045), NGC 6040B, and NGC 6056 (IC 1176), plus Seyfert galaxies NGC 6034 and NGC 6061, all listed in the catalogs as separate, independent objects. Because most members shine faintly — NGC 6061 registers at about 15 mag with a surface brightness near 23.6 mag/arcsec², long integration times under dark skies are essential to pull out the sea of soft, elongated smudges. A moderate to long focal length paired with a well-sampled sensor rewards patient imagers, revealing tidal bridges, warped disks, and the subtle color differences between the cluster’s spiral and lenticular members.
Names and Catalog numbers
- Hercules Cluster
- ACO 2151 (Abell 2151)
- NGC 6041A (member object: NGC 6041A)
- PGC 56962 (member object: NGC 6041A)
- NGC 6054 (member object: Arp 272)
- Arp 272 (member object: Arp 272)
- NGC 6045 (member object: Arp 71)
- UGC 10177 (member object: Arp 71)
- PGC 57031 (member object: Arp 71)
- Arp 71 (member object: Arp 71)
- NGC 6034 (member object: NGC 6034)
- PGC 56877 (member object: NGC 6034)
- NGC 6040B (member object: NGC 6040B)
- UGC 10165 (member object: NGC 6040B)
- PGC 56932 (member object: NGC 6040B)
- NGC 6042 (member object: NGC 6042)
- PGC 56972 (member object: NGC 6042)
- NGC 6043 (member object: NGC 6043)
- PGC 57019 (member object: NGC 6043)
- NGC 6044 (member object: NGC 6044)
- PGC 57015 (member object: NGC 6044)
- NGC 6047 (member object: NGC 6047)
- PGC 57033 (member object: NGC 6047)
- NGC 6055 (member object: NGC 6055)
- UGC 10191 (member object: NGC 6055)
- PGC 57076 (member object: NGC 6055)
- NGC 6056 (member object: NGC 6056)
- PGC 57075 (member object: NGC 6056)
- IC 1176 (member object: NGC 6056)
- NGC 6057 (member object: NGC 6057)
- PGC 57090 (member object: NGC 6057)
- NGC 6061 (member object: NGC 6061)
- UGC 10199 (member object: NGC 6061)
- PGC 57137 (member object: NGC 6061)
Position and the cosmic neighborhood
Centered near right ascension 16h 05m 15s and declination +17° 44′ 55″ in Hercules, the Hercules Cluster gathers a dense knot of galaxies within a field only about 0.6° (37′) wide, so framing and plate-solving pay off when hunting the many faint members. Anchoring the crowded core are NGC 6047, NGC 6042, and the galaxy group NGC 6043, while the striking interacting duo Arp 272 (NGC 6054) and the edge-on barred spiral Arp 71 (NGC 6045) sit nearby for detail-rich close-ups. Slightly farther afield the frame collects NGC 6044, NGC 6041A, and the more distant NGC 6040B, along with the northern trio NGC 6055, NGC 6057, and NGC 6061; the Seyfert galaxy NGC 6034 lies off to the southwest. Each of these carries its own catalog designation and its own distance, ranging from around 422 million light-years for the group NGC 6043 out to roughly 601 million light-years for NGC 6040B, so the cluster’s apparent tidiness hides real depth along the line of sight.
Nice to Know
- The Hercules Cluster packs an enormous structure some 5,300,000 light-years across into an angular field of just 0.6° (37′), letting a single wide-field exposure capture many galaxies at once.
- It hosts the famous colliding pair Arp 272 (NGC 6054), a highlight for astrophotographers chasing tidal bridges and interaction-warped disks.
- Two of its members, NGC 6034 and NGC 6061, are active Seyfert galaxies, and NGC 6061 is the brightest listed member at about 15 mag.
- Though the members look clustered, their catalog distances span from roughly 422 million light-years (NGC 6043 and NGC 6044) to about 601 million light-years (NGC 6040B), revealing surprising depth in a compact frame.
Brightness, distance and size
It lies about 492.0 million light-years from Earth and spans roughly 5,300,000 light-years across. On the sky it appears about 0.6° (37′) in size.
