IC 4756 is an open cluster in the constellation of Serpens. It’s best viewed in summer through early fall. With a visual magnitude of +4.6, the cluster makes a fine object in binoculars. From a dark site, some may be able to pick out the cluster with the naked eye among a dense field of background stars.
Graff’s Cluster lies in a region (around Serpens and Ophiuchus) that hosts some brilliant globular and open star clusters. To get a good idea of different open star cluster sizes and designs, take a look at NGC 6633 and IC 4665 nearby. There are many more objects in the area, but these two make a good comparison while studying IC 4756.
On a historical note, early 20th-century astronomer Solon Bailey discovered the cluster, and Kasimir Graff independently discovered it in 1922.
My Observations
| Date | July 15, 2023 |
| Time | 11:15 p.m. |
| Location | Seattle, WA |
| Magnification | 85x |
| Scope | Meade 8″ SCT |
| Eyepiece | 24mm |
| Seeing | Average |
| Transparency | Average |
The star cluster is truly stunning. It’s amazing how it keeps reappearing in my summer observations, despite having seen it before in 2020 and 2022. There must be something truly special about it that draws me in every time. It’s a beautiful reminder that the wonders of the universe are always present, even in our own backyard.
| Date | July 1, 2022 |
| Time | 12:05 a.m. |
| Location | Seattle, WA |
| Magnification | 85x |
| Scope | Meade 8″ SCT |
| Eyepiece | 24mm |
| Seeing | Average |
| Transparency | Average |
This is my second time studying this cluster. I’m ending a great night with this one after taking my time through this region. I just finished looking at NGC 6633, and based on that observation, Graff’s Cluster is more spread out and fainter. Also, the stars appear around the same magnitude. At the moment, it looks like someone sprinkled salt on a black tablecloth.
| Date | October 5, 2020 |
| Time | 8:35 p.m. |
| Location | Seattle, WA |
| Magnification | 64x |
| Scope | Meade 8″ SCT |
| Eyepiece | 32mm |
| Seeing | Average |
| Transparency | Average |
At first, I thought I was only looking at a normal patch of the Milky Way. However, after pushing the scope from left to right, back and forth, I realize I am now centered on Graff’s Cluster. It is a bright and wide cluster, filling my 20mm eyepiece with similarily bright stars across the field of view.
Key Stats
| Constellation | Serpens |
| Best Viewing | Summer |
| Visual Magnitude | +4.6 |
| Absolute Magnitude | -3.8 |
| Distance from Earth | 1,600 ly |
| Diameter | 18 ly |
| Apparent Size | 39 arcmin |
| Milky Way Location | Orion Spur |
| My Viewing Grade | B |
Sources and Notes
Banner photo by Roberto Mura and is licensed under the Creative Commons Attribution-Share Alike 3.0 Unported license.
Sketch by Wayne McGraw
AKA: Secret Garden Cluster, Tweedledee Cluster
The Garden Astronomer 
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