Editing Cygnus (constellation) (section)

=== Star clusters ===
The rich background of stars of Cygnus can make it difficult to make out [[open cluster]].<ref name="thompson07" />

[[Messier 39|M39]] (NGC 7092) is an open cluster 950 light-years from Earth that are visible to the unaided eye under dark skies. It is loose, with about 30 stars arranged over a wide area; their conformation appears triangular. The brightest stars of M39 are of the 7th magnitude.{{sfn|Ridpath|Tirion|2001|pp=134–137}} Another open cluster in Cygnus is [[NGC 6910]], also called the Rocking Horse Cluster, possessing 16 stars with a diameter of 5 arcminutes visible in a small amateur instrument; it is of magnitude 7.4. The brightest of these are two gold-hued stars, which represent the bottom of the toy it is named for. A larger amateur instrument reveals 8 more stars, nebulosity to the east and west of the cluster, and a diameter of 9 arcminutes. The nebulosity in this region is part of the [[Gamma Cygni Nebula]]. The other stars, approximately 3700 light-years from Earth, are mostly blue-white and very hot.<ref name="S&T" />

Other open clusters in Cygnus include [[Dolidze 9]], [[Collinder 421]], [[Dolidze 11]], and [[Berkeley 90]]. Dolidze 9, 2800 light-years from Earth and relatively young at 20 million light-years old, is a faint open cluster with up to 22 stars visible in small and medium-sized amateur telescopes. Nebulosity is visible to the north and east of the cluster, which is 7 arcminutes in diameter. The brightest star appears in the eastern part of the cluster and is of the 7th magnitude; another bright star has a yellow hue. Dolidze 11 is an open cluster 400 million years old, farthest away of the three at 3700 light-years. More than 10 stars are visible in an amateur instrument in this cluster, of similar size to Dolidze 9 at 7 arcminutes in diameter, whose brightest star is of magnitude 7.5. It, too, has nebulosity in the east. Collinder 421 is a particularly old open cluster at an age of approximately 1 billion years; it is of magnitude 10.1. 3100 light-years from Earth, more than 30 stars are visible in a diameter of 8 arcseconds. The prominent star in the north of the cluster has a golden color, whereas the stars in the south of the cluster appear orange. Collinder 421 appears to be embedded in nebulosity, which extends past the cluster's borders to its west. Berkeley 90 is a smaller open cluster, with a diameter of 5 arcminutes. More than 16 members appear in an amateur telescope.<ref name="S&T">{{cite journal |title=Guide Me, Cygnus |last=French |first=Sue |pages=58–60 |journal=Sky and Telescope |date=September 2012|volume=124 |issue=3 |bibcode=2012S&T...124c..58F }}</ref>