IC 4665 is a beautiful star cluster in the constellation Ophiuchus, ready for summertime observers to enjoy it.
To begin, this is a peculiar star cluster. It’s a prominent object viewable with binoculars from the suburbs, but it doesn’t belong to the Messier or NGC list. According to some sources, perhaps Messier felt the stars were too spread out to deem the object worthy of his list.
Regarding IC 4665’s structure, some observers call it the “Hi” cluster since the inner stars make out the letters H and I. Seeing this salutation will depend on one’s imagination, and the letters may be reversed depending on one’s telescope. For example, look at the cluster’s photo above; you’ll see the “Hi” reversed.
For me, IC 4665’s brilliance comes from its large diameter (spread out nearly the size of two full moons) and its vibrant blue-white stars of similar magnitude. Around 30 stars make up IC 4665, and most are white or blue-white, which indicates it’s a younger star cluster. We would see more reds and yellows if it was older.
Historically speaking, the Swiss astronomer Philippe Loys de Chéseaux first recorded IC 4665 in 1745. However, he didn’t publish his findings, so Johann Elert Bode “rediscovered” it around 1782, and then Caroline Herschel logged it on July 31, 1783. 1
My Observations
| Date | June 30, 2022 |
| Time | 10:35 p.m. |
| Location | Seattle, WA |
| Magnification | 64x |
| Scope | Meade 8″ SCT |
| Eyepiece | 32mm |
| Seeing | Average |
| Transparency | Average |
This is the best open cluster I’ve seen without a Messier or NGC label. What a delightful group of stars filling the wide-field view of my 32mm eyepiece! The stars are bright and a lot alike! So many are blue-white burning hot and bright like a welder’s torch.
a turn at the scope.
Wow. After a minute of observing IC 4665, a dark foot-long animal approached me from the left. I heard the rustle in the grass, pulled back, and noticed the dark shadow out of the corner of my eye. I froze; the moving target froze. I immediately stepped back from the scope, squinting my eyes to see through the shadows.
I started stomping my foot and, with teeth clenched, made a “psssssss” sound. Nothing. Thinking it may be a small raccoon approaching, I clapped my hands and stomped again with more muscle. With that, the critter bolted away.
Right then, I realized my backyard guest—the black cat from next door! I think we scared each other. It’s now taking my heart a few minutes to calm down. Ha. I don’t hear any rustling around back in the bushes ten feet from my scope; she must have run off back home for now.
As I view IC 4665 again, I’m calmed by its bright array of pristine stars filling my field of view.
Key Stats
| Constellation | Ophiuchus |
| Best Viewing | Summer |
| Visual Magnitude | +4.2 |
| Absolute Visual Magnitude | -3.5 |
| Distance from Earth | 1,300 ly |
| Milky Way Location | Orion Spur |
| My Viewing Grade | A |
Sources and Notes
- The banner photo of IC 4665 is a screenshot by Roberto Mura from Stellarium. This file is licensed under the Creative Commons Attribution-Share Alike 3.0 Unported license.
- Photo of the black cat by Colleen Martin. This file is licensed under the Creative Commons Attribution 3.0 Unported license.
- 1 IC 4665 – SEDS Messier Database. https://www.messier.seds.org/xtra/ngc/i4665.html.
- Sketch by Wayne McGraw
- AKA: Collinder 349, Melotte 179
The Garden Astronomer 
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