NGC 6940: An Open Cluster with a Cherry on Top

In the constellation Vulpecula lies the star cluster NGC 6940, which was first discovered by William Herschel in 1784. It is situated 2,500 light-years away from us and best viewed in the summertime or early autumn.

Several hundred stars, scattered across a patch of sky nearly the diameter of the moon, make up NGC 6940. Surrounding the cluster is a rich sea of dim “background” stars, which initially can make locating NGC 6940 a challenge.¹

One can identify the cluster by its abundant collection of red giant stars. Also, a variable red giant called VG Vulpeculae sits near the middle with its magnitude moving between 9 to 9.5 every 80 days.

My Observations

I notice a faint cloud of stars filling the eyepiece. This cluster is larger and more scattered than I expected. Although the stars are mostly dim, NGC 6940 is an attractive target because the stars exhibit a range of colors. In particular, an orange/red star lies near the middle and shines out like a small ruby gem in a trunk of other jewels. As I research on my phone, I realize the red star is a red giant variable star named VG Vulpeculae.

Also observed on September 30, 2021, at 8:15 P.M. No additional notes were taken.

Key Stats

Constellation	Vulpecula
Best Viewing	Fall
Visual Magnitude	+6.3
Absolute Magnitude	-3.1
Distance from Earth	2,500 ly
Diameter	18.3 ly
Apparent Size	25 arcmin
Milky Way Location	Orion Spur
My Viewing Grade	B

Sources

Photo of NGC 6940 by Roberto Mura and is licensed under the Creative Commons Attribution-Share Alike 3.0 Unported license.

¹Brecher, Ron. “NGC 6940 – Astrodoc: Astrophotography by Ron Brecher.” Astrodoc, 7 Sept. 2020, astrodoc.ca/ngc-6940/.

Sketch by Wayne McGraw