Open Cluster NGC 6791

Object Description

There are only a few bright deep sky objects in the Lyra constellation. Among the few is the open star cluster NGC 6791 at the eastern constellation border. Its distance is given as about 17'000 light years. The age is about 7.1 billion years, which makes NGC 6791 one of the older clusters. The oldest known star cluster is NGC 188 with about 11 billion years. Observational data on this cluster is quite sparse - Burnham is limited to a mirror image, the NGC only has the tenuous «vF». In more detail, the «Saguaro Astronomy Club» writes in its V6.0 database: «! vF, L vRi, *F», with which he is quite right - see below.

— 1997, Frank H. Leiter

NGC 6791
NGC 6791: Open cluster in Cygnus; 500 mm Cassegrain f=3625 mm f/7.2; SBIG STL11K; 70+30+30+30 min LRGB; Bernese Highlands; © 2011 Radek Chromik
NGC 6791
NGC 6791: Open cluster in Cygnus; Takahashi Mewlon 250 CR (f=2500 mm / f10), SBIG ST-8300; 24L x 600 sec 1×1, 15R, 15G, 15B 2×2 x 600 sec; Bernese Highlands; © 2016 Bernhard Blank, Dragan Mihajlovic
«Revised New General Catalogue and Index Catalogue» Dr. Wolfgang Steinicke, 2021 [277]
DesignationNGC 6791
TypeOCL (II3r)
Right Ascension19h 20m 52.7s
Declination+37° 46' 27"
Diameter10.00 arcmin
Visual magnitude9.5 mag
Dreyer DescriptionvF (Auw 45)
IdentificationOCL 142

Finder Chart

The open star cluster NGC 6791 lies 9 degrees east of Vega in the constellation Lyra. It is easier to find if you swing from the 4.4 mag bright star θ Lyrae one degree towards east. However, note the brightness and size of the cluster and choose the magnification on the telescope accordingly so that the sky background is already quite dark.

Chart NGC 6791
Chart created using SkySafari 6 Pro and STScI Digitized Sky Survey. [149, 160]

Visual Observation

200 mm aperture: One sees a few moderately bright stars in front of a large, round, faintly luminous area. These stars are probably foreground stars and therefore not part of the cluster. Up to about 100x magnification, this area appears foggy to granular - depending on the atmospheric transparency. It's not resolved properly. The cluster is strongly reminiscent of the globular cluster NGC 5053 in terms of stellar density and brightness.

— 1997, Frank H. Leiter

450 mm aperture: With a large aperture, it is fairly easy to miss the open star cluster. Here it is necessary to reduce the magnification a little. You can see the cluster very nicely broken up into many faint individual stars.

— 1997, Frank H. Leiter

References

149SkySafari 6 Pro, Simulation Curriculum; skysafariastronomy.com
160The STScI Digitized Sky Survey; archive.stsci.edu/cgi-bin/dss_form
277«Historische Deep-Sky Kataloge» von Dr. Wolfgang Steinicke; klima-luft.de/steinicke (2021-02-17)