Arp 172 / IC 1178 & 1181
| Designation(s) | Arp 172, IC 1178, IC 1181 |
| Object Type(s) | Galaxy, Galaxy Cluster |
| Relevant Catalog(s) | All (Chron), Arp, IC |
| Arp Category | Galaxies with diffuse counter-tails |
| Obs. Lat/Long | 42° 17', 073° 57' |
| Constellation | Hercules |
| Date and Time Observed | 2025-07-15 23:50:00 |
| Instrument | EdgeHD 8" w/f7 reducer-1,422mm FL |
| Camera | Player One Apollo-M Mini |
| Image Details | Up is 175.9 degrees E of N. Transparency: Fair. Seeing: Good. Total integration time was 26m 30s. Exposures 15s@300g - no cut filter. Dithered and recentered in SharpCap. No guiding. |
| Description | We're reaching the end of "galaxy season" and essentially all of the Arp galaxies are already past the meridian when it's dark enough to capture them. So I had no particular reason to capture Arp 172 except it was higher in the sky than most. This observation was cut short by clouds. It was also notable as the first time I'd used my Apollo-M camera without an IR/cut filter. I think it helped: I thought the capture was remarkably fast given the conditions. From what I can see, this is a fun depiction of two galaxies in a dance of attraction. Of course, Arp rarely attributed what he saw to a merger; he categorized what he saw, but often not why. But to me, this looks like two galaxies which were orbiting each other, now in the throes of a deep gravitational attraction. The stars facing the other galaxy are moving largely as a group, but some stars on the far side get left behind. So the curvature of the tidal flows is tracing the final path of what will likely be a full merger (in a few hundred million years). Also notable for being located on one of the "great" Hercules Galaxy Cluster, aka Abell 2151. Two other Arp Peculiar Galaxies are in the FOV: Arp 71 and 272. |
| Related Observations | Arp071 (2) Arp272 (2) |
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