Deep-sky tour
We explore objects in Cygnus, from the Swan’s body to the tip of its western wing
1 NGC 6888
We begin with an unusual favourite, the Crescent Nebula, NGC 6888. This mag. +7.5 object sits 2.7˚ southwest of Sadr (Gamma (g) Cygni). A 250mm scope reveals the brightest section to resemble a weak light arc between the brightest and dimmest members of a mag. +7.2, +7.5 and +8.5 star triangle. Larger apertures extend the arc to the north of the western triangle star, WR 136. NGC 6888 represents the interaction between the fast stellar wind from WR 136 catching up with slower moving material ejected when the star became a red giant over a quarter of a million years ago. SEEN IT
2 Collinder 419
Return to Sadr in order to locate our next target, a complex area of sky full of faint stars and weak nebulosity. Collinder 419 is a mag. +7.6 open cluster which lies 0.9˚ from Sadr, a fraction south of the line joining Sadr to the western tip of Cygnus’s wing marked by Rukh (Delta (d) Cygni) – so more or less northwest of Sadr. The cluster is tricky to see at first because it’s dominated by the double star Struve 2666. It’s best to centre on Struve 2666 and then increase power; magnifications of 100x to 150x should reveal the faint powdering of stars that is Collinder 419. SEEN IT
3 NGC 6910
Sadr can also be used for our next target, open cluster NGC 6910, which is located a fraction over half a degree to its north-northeast. With an integrated magnitude of +6.6, NGC 6910 should be easy to find in any size of instrument, but watch out for the rich star background, as it can make it a little harder than normal to pick open clusters out of the background. This is a nice cluster, bookended by a pair of brighter stars shining at mag. +7.3 to the northwest and +7.0 to the southeast. A 150mm scope shows about a dozen fainter stars running between the brighter pair. A 250mm scope almost doubles the star count, the fainter members remaining confined to a linear arrangement running between the bookending pair. SEEN IT
4 NGC 6866
Next is open cluster NGC 6866, located 0.9˚ northeast of the mid-point along the line between
Sadr and Rukh. It’s a mag. +7.6 cluster, around 7 arcminutes in size. NGC 6866 appears to contain around 20 stars through a 150mm instrument. The main concentration of the cluster appears stretched in a north to south direction. A 250mm scope doubles the star count to around 40 members, with more fainter stars on view. The fainter stars to the east and west of the main body appear like the wings of a bird, the main part of the cluster forming the body; could this be a mini-Cygnus? SEEN IT
5 NGC 6811
Our penultimate target is another cluster, but with a twist. NGC 6811 is a mag. +6.8 object measuring 15 arcminutes across. A small scope resolves it, revealing around 50 members, including a lot of white stars along with some striking red ones. The core of NGC 6811 is quite underpopulated and if you increase magnification it gives the impression that the inner portion is dark, almost as if it has a hole inside it. This has given it the informal title of ‘The Hole in the Cluster’. Estimated to be around 700 million years old, NGC 6811 lies about 3,600 lightyears from Earth. It sits against a bright portion of the Milky Way but, thanks to its rich star count, manages to stand out well. SEEN IT
6 NGC 6826
Our final target is a planetary nebula known as NGC 6826, which lies 5.4˚ due north of Rukh on the northern (trailing) edge of Cygnus’s western wing. The nebula has an integrated magnitude of +8.8, spread into an oval 27x24 arcseconds across. NGC 6826’s central star is mag. +10.7 and bright enough to interfere with the view. So, if you look directly at this star using a small instrument the nebula disappears, whereas if you use averted vision the nebula pops back into view. Although this effect is not completely unique to NGC 6826, it has become known informally as the Blinking Nebula. Thanks to ESA’s Gaia mission we know it is 5,136 lightyears away. SEEN IT