Messier 26 (NGC 6694): The Cluster with a Little Hole

Messier 26, also known as NGC 6694, is a star cluster in the constellation Scutum, which is best viewed in late summer.

Backyard suburban astronomers farther north, like myself, may struggle to find M26 since it lies deeper in the southern sky, and it’s a fainter cluster. It will be a challenge to find with binoculars, so you’ll want to use the scope with this one. Essentially, we are having to view these southern gems (for which there are many) through more atmosphere at an angle vs. looking straight up.

As for M26 itself, it is a rich cluster of around 30 dim stars between magnitude 11 and 13. Also, the object lies in a dense sea of Milky Way stars. Astrophotos of the area are stunning, but it’s not so hot for visual astronomers!

On an interesting note, a darker low-star density patch lies near the center. It seems to create a hole in the cluster. Some astronomers believe this conspicuous area is caused by interstellar matter blocking our view, while others argue it’s a different density in space. The answer to this “hole” remains unsolved. ¹

Historically speaking, Charles Messier discovered the cluster on June 20, 1764.

My Observations

I’ve had to double-check my coordinates to be sure I’m really looking at M26. Based on other sketches and my star app, I’ve been able to confirm I’m on target. While M26 is known as a rich cluster, it is not as impressive as many others—at least when viewing it under heavy light pollution. The dimmer stars just don’t come out. However, one blogger writes that M26 perhaps benefits from light pollution because it helps the cluster’s brighter stars stand out amongst the sea of Milky Way stars. This may be true, but I’ll have to view this cluster from dark skies to compare.

Key Stats

Constellation	Scutum
Best Viewing	Summer
Visual Magnitude	+8.1
Absolute Magnitude	-3.1
Distance from Earth	5,600 ly
Diameter	11 ly
Apparent Size	7 arcmin
Milky Way Location	Sagittarius Arm
My Viewing Grade	C
Designations	M 26, NGC 6694

Historical Observations

June 20, 1764, observation by Charles Messier

“A cluster near Eta and Omicron in Antinous [now Alpha and Delta Scuti], between which there is another one of more brightness: with a telescope of 3.5-foot [FL] one cannot distinguish them, one needs to employ a good instrument. This cluster contains no nebulosity.“

Sources and Notes

M26 banner photo created by Hillary Mathis, Vanessa Harvey, REU program/NOIRLab/NSF/AURA. Source file. The image file is licensed under the Creative Commons Attribution 4.0 International license.

¹ Merrifield, Michael (Oct 2, 2015). “M26 – Open Cluster”. Deep Sky Videos. University of Nottingham/University of Sheffield. Retrieved March 29, 2016.