Cygnus is a northern constellation on the plane of the Milky Way, deriving its name from the Latinized Greek word for swan.

The constellation is also home to Cygnus X-1, a distant X-ray binary containing a supergiant and unseen massive companion that was the first object widely held to be a black hole.

Alongside Cygnus, noted above, he mentions a boy from Aetolia who throws himself off a cliff when his companion Phyllius refuses to give him a tamed bull that he demands, but he is transformed into a swan and flies away.

[10] Together with other avian constellations near the summer solstice, Vultur cadens and Aquila, Cygnus may be a significant part of the origin of the myth of the Stymphalian Birds, one of The Twelve Labours of Hercules.

[12] The official constellation boundaries, as set by Belgian astronomer Eugène Delporte in 1930, are defined as a polygon of 28 segments.

[13] Covering 804 square degrees and around 1.9% of the night sky, Cygnus ranks 16th of the 88 constellations in size.

[14] Cygnus culminates at midnight on 29 June, and is most visible in the evening from the early summer to mid-autumn in the Northern Hemisphere.

[15] There is an abundance of deep-sky objects, with many open clusters, nebulae of various types and supernova remnants found in Cygnus due to its position on the Milky Way.

The rift begins around the Northern Coalsack, and partially obscures the larger Cygnus molecular cloud complex behind it, which the North America Nebula is part of.

Albireo, designated β Cygni, is a celebrated binary star among amateur astronomers for its contrasting hues.

[21] γ Cygni, traditionally named Sadr, is a yellow-tinged supergiant star of magnitude 2.2, 1800 light-years away.

[22] δ Cygni (the proper name is Fawaris[23]) is another bright binary star in Cygnus, 166 light-years with a period of 800 years.

Though the tertiary component is visible in binoculars, the primary and secondary currently require a medium-sized amateur telescope to split, as they will through the year 2020.

[28][29] Located near η Cygni is the X-ray source Cygnus X-1, which is now thought to be caused by a black hole accreting matter in a binary star system.

[41] Cygnus X-2 is another X-ray binary, containing an A-type giant in orbit around a neutron star with a 9.8-day period.

The star's spectrum is unusual in that it contains very strong emission lines resulting from surrounding nebulosity.

[14] M39 (NGC 7092) is an open cluster 950 light-years from Earth that are visible to the unaided eye under dark skies.

A larger amateur instrument reveals 8 more stars, nebulosity to the east and west of the cluster, and a diameter of 9 arcminutes.

Collinder 421 appears to be embedded in nebulosity, which extends past the cluster's borders to its west.

It appears to "blink" in the eyepiece of a telescope because its central star is unusually bright[65] (10th magnitude).

However, its characteristic shape is only visible in long-exposure photographs – it is difficult to observe in telescopes because of its low surface brightness.

It has low surface brightness because it is so large; at its widest, the North America Nebula is 2 degrees across.

[4] To the south of Epsilon Cygni is the Veil Nebula (NGC 6960, 6979, 6992, and 6995), a 5,000-year-old supernova remnant covering approximately 3 degrees of the sky -[66] it is over 50 light-years long.

More of the nebula's eastern portion is visible with an O III (doubly ionized oxygen) filter.

[64] Also of note is the Crescent Nebula (NGC 6888), located between Gamma and Eta Cygni, which was formed by the Wolf–Rayet star HD 192163.

In 2011, Austrian amateur Matthias Kronberger discovered a planetary nebula (Kronberger 61, now nicknamed "The Soccer Ball") on old survey photos, confirmed recently in images by the Gemini Observatory; both of these are likely too faint to be detected by eye in a small amateur scope.

But a much more obscure and relatively 'tiny' object—one which is readily seen in dark skies by amateur telescopes, under good conditions—is the newly discovered nebula (likely reflection type) associated with the star 4 Cygni (HD 183056): an approximately fan-shaped glowing region of several arcminutes' diameter, to the south and west of the fifth-magnitude star.

It was first discovered visually near San Jose, California and publicly reported by amateur astronomer Stephen Waldee in 2007, and was confirmed photographically by Al Howard in 2010.

California amateur astronomer Dana Patchick also says he detected it on the Palomar Observatory survey photos in 2005 but had not published it for others to confirm and analyze at the time of Waldee's first official notices and later 2010 paper.

[66] Cygnus is also the apparent source of the WIMP-wind due to the orientation of the solar system's rotation through the galactic halo.