Cygnus (constellation)

Cygnus

Constellation
List of stars in Cygnus
Abbreviation	Cyg
Genitive	Cygni
Pronunciation	/ˈsɪɡnəs/, genitive /ˈsɪɡnaɪ/
Symbolism	the Swan or The Northern Cross
Right ascension	20.62 h
Declination	+42.03°
Quadrant	NQ4
Area	804 sq. deg. (16th)
Main stars	9
Bayer/Flamsteed stars	84
Stars with planets	60
Stars brighter than 3.00m	4
Stars within 10.00 pc (32.62 ly)	1
Brightest star	Deneb (α Cyg) (1.25m)
Nearest star	61 Cyg (11.36 ly, 3.48 pc)
Messier objects	2
Meteor showers	October Cygnids Kappa Cygnids
Bordering constellations	Cepheus Draco Lyra Vulpecula Pegasus Lacerta
Visible at latitudes between +90° and −40°. Best visible at 21:00 (9 p.m.) during the month of September.

Cygnus (pron.: /ˈsɪɡnəs/) is a northern constellation lying on the plane of the Milky Way. Its name is the Latinized Hellenic (Greek) word for swan. One of the most recognizable constellations of the northern summer and autumn, it features a prominent asterism known as the Northern Cross (in contrast to the Southern Cross). Cygnus was among the 48 constellations listed by the 2nd century astronomer Ptolemy, and it remains one of the 88 modern constellations.

History and mythology

Cygnus as depicted in Urania's Mirror, a set of constellation cards published in London c.1825. Surrounding it are Lacerta, Vulpecula and Lyra.

In Greek mythology, Cygnus has been identified with several different legendary swans. Zeus disguised himself as a swan to seduce Leda, Spartan king Tyndareus's wife, who gave birth to the Gemini, Helen of Troy and Clytemnestra;Orpheus was transformed into a swan after his murder, and was said to have been placed in the sky next to his lyre (Lyra); and the King Cycnus was transformed into a swan.

In Ovid's Metamorphoses, there are three people named Cygnus, all of whom are transformed into swans. Alongside Cycnus, noted above, he mentions a boy from Tempe who commits suicide when Phyllius refuses to give him a tamed bull that he demands, but is transformed into a swan and flies away. He also mentions a son of Neptune who is an invulnerable warrior in the Trojan War who is eventually defeated by Achilles, but Neptune saves him by transforming him into a swan.

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

In non-western astronomy

In Polynesia, Cygnus was often recognized as a separate constellation. In the Society Islands it was called Pirae-tea, in Tonga it was called Tuula-lupe, and in the Tuamotus it was calledFanui-tai. Deneb was also often given a name. In New Zealand it was called Mara-tea, in the Society Islands it was called Pirae-tea or Taurua-i-te-haapa-raa-manu, and in the Tuamotus it was called Fanui-raro. Beta Cygni was named in New Zealand; it was likely called Whetu-kaupo. Gamma Cygni was called Fanui-runga in the Tuamotus.

Characteristics

Normally, Cygnus is depicted with Delta and Epsilon Cygni as its wings, Deneb as its tail, and Albireo as the tip of its beak.

Notable features

The constellation Cygnus as it can be seen by the naked eye.

Stars

See also: List of stars in Cygnus

There are several bright stars in Cygnus. Alpha Cygni, called Deneb, is the brightest star in Cygnus. It is a blue-white hued supergiant star of magnitude 1.3, about 3200 light-years away. The traditional name of Alpha Cygni means "tail" and refers to its position in the constellation. Albireo, designated Beta Cygni, is a celebrated binary star among amateur astronomers for its contrasting hues. The primary is an orange-hued giant star of magnitude 3.1 and the secondary is a blue-green hued star of magnitude 5.1. The system is 380 light-years away and is divisible in large binoculars and all amateur telescopes. Gamma Cygni, traditionally named Sadr, is a yellow-tinged supergiant star of magnitude 2.2, 1500 light-years away. Its traditional name means "breast" and refers to its position in the constellation. Delta Cygni is another bright binary star in Cygnus, 171 light-years with a period of 800 years. The primary is a blue-white hued giant star of magnitude 2.9, and the secondary is a star of magnitude 6.6. The two components are divisible in a medium-sized amateur telescope. The fifth star in Cygnus above magnitude 3 is Gienah, designated Epsilon Cygni. It is an orange-hued giant star of magnitude 2.5, 72 light-years from Earth.

There are several other dimmer double and binary stars in Cygnus. Mu Cygni is a binary star with an optical tertiary component. The binary system has a period of 790 years and is 73 light-years from Earth. The primary and secondary, both white stars, are of magnitude 4.8 and 6.2, respectively. The unrelated tertiary component is of magnitude 6.9. Though the tertiary component is divisible in binoculars, the primary and secondary currently require a medium-sized amateur telescope to split, as they will through the year 2020. The two stars will be closest between 2043 and 2050, when they will require a telescope with larger aperture to split. Omicron Cygni is a contrasting double star similar to the brighter Albireo. The components, 30 Cygni and 31 Cygni, are divisible in binoculars. The primary, 31 Cygni, is an orange-hued star of magnitude 3.8, 1400 light-years from Earth. The secondary, 30 Cygni, is a blue-green hued star of magnitude 4.8, 720 light-years from Earth. 31 Cygni itself is a binary star; the tertiary component is a blue star of magnitude 7.0. Psi Cygni is a binary star divisible in small amateur telescopes, with two white components. The primary is of magnitude 5.0 and the secondary is of magnitude 7.5. 61 Cygni is a binary star divisible in large binoculars or a small amateur telescope. It is 11.4 light-years from Earth and has a period of 650 years. Both components are orange-hued dwarf (main sequence) stars; the primary is of magnitude 5.2 and the secondary is of magnitude 6.1. 61 Cygni is significant because Friedrich Wilhelm Bessel determined its parallax in 1838, the first star to have a known parallax. 16 Cygni is a binary star 70 light-years from Earth. Both components are white and of the 6th magnitude.

The constellation also contains 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. The system is located close to the star Eta Cygni on star charts.

Cygnus is also home to several variable stars. Chi Cygni is a red giant and the second-brightest Mira variable star at its maximum. Its maximum magnitude is 3.3 and its minimum magnitude is 14; it has a diameter of 300 solar diameters. Chi Cygni has a period of 400 days and is 350 light-years from Earth. P Cygni is a large, unstable blue supergiant that is evolving into a red supergiant. In 1600, it brightened suddenly to 3rd magnitude, though its normal magnitude is approximately 5. It began to brighten gradually in the 1700s and has continued to brighten to the present day; this is part of the process of stellar evolution. W Cygni is a semi-regular variable red giant star, 618 light-years from Earth. It has a maximum magnitude of 5 and a minimum magnitude 8; its period of 130 days.

There are several asterisms in Cygnus. Patchik 56 is one less prominent, a small asterism that measures 3.3 by 2.2 arcminutes. Named for its discoverer, Dana Patchik, an amateur astronomer, it appears in small amateur telescopes as a group of six stars described as resembling a dolphin.

The two component stars of Albireo are easily distinguished, even in a small telescope.

Deep-sky objects

Several star clusters and nebulae are found in Cygnus due to its position on the Milky Way.

M39 (NGC 7092) is an open cluster 950 light-years from Earth that is 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. 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.

This Hubble Space Telescope picture captures a brief but beautiful phase late in the life of a star in the constellation of Cygnus.

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.

NGC 6826, the Blinking Planetary Nebula, is a planetary nebula with a magnitude of 8.5, 3200 light-years from Earth. It appears to "blink" in the eyepiece of a telescope because its central star is unusually bright (10th magnitude). When an observer focuses on the star, the nebula appears to fade out. Less than one degree from the Blinking Planetary is the double star 16 Cygni.

The North America Nebula (NGC 7000) is one of the most well-known nebulae in Cygnus, because it is visible to the unaided eye under dark skies, as a bright patch in the Milky Way. 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. Illuminated by a hot embedded star of magnitude 6, NGC 7000 is 1500 light-years from Earth.

To the south of Epsilon Cygni is the Veil Nebula (NGC 6960, 6962, 6979, 6992, and 6995), a 5,000-year-old supernova remnant covering approximately 3 degrees of the sky - it is over 50 light-years long. Because of its appearance, it is also called the Cygnus Loop. The Loop is only visible in long-exposure astrophotographs. However, the brightest portion, NGC 6992, is faintly visible in binoculars, and a dimmer portion, NGC 6960, is visible in wide-angle telescopes.

The Northern Coalsack Nebula, also called the Cygnus Rift, is a dark nebula located in the Cygnus Milky Way.

The Gamma Cygni Nebula (IC 1318) includes both bright and dark nebulae in an area of over 4 degrees. DWB 87 is another of the many bright emission nebulae in Cygnus, 7.8 by 4.3 arcminutes. It is in the Gamma Cygni area. Two other emission nebulae include Sharpless 2-112 and Sharpless 2-115. When viewed in an amateur telescope, Sharpless 2-112 appears to be in a teardrop shape. More of the nebula's eastern portion is visible with an O III (doubly ionized oxygen) filter. There is an orange star of magnitude 10 nearby and a star of magnitude 9 near the nebula's northwest edge. Further to the northwest, there is a dark rift and another bright patch. The whole nebula measures 15 arcminutes in diameter. Sharpless 2-115 is another emission nebula with a complex pattern of light and dark patches. Two pairs of stars appear in the nebula; it is larger near the southwestern pair. The open cluster Berkeley 90 is embedded in this large nebula, which measures 30 by 20 arcminutes.

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 recent years, amateur astronomers have made some notable Cygnus discoveries. The "Soap bubble nebula" (PN G75.5+1.7), near the Crescent nebula, was discovered on a digital image by Dave Jurasevich in 2007. 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.

A bubbling cauldron of star birth is highlighted in this image from NASA's Spitzer Space Telescope.

More supernovae have been seen in the Fireworks Galaxy (NGC 6946) than in any other galaxy.

Cygnus A is the first radio galaxy discovered; at a distance of 730 million light-years from Earth, it is the closest powerful radio galaxy. In the visible spectrum, it appears as an elliptical galaxy in a small cluster. It is classified as an active galaxy because the supermassive black hole at its nucleus is accreting matter, which produces two jets of matter from the poles. The jets' interaction with the interstellar medium creates radio lobes, one source of radio emissions.

Extrasolar planets

Several extrasolar planets including HAT-P-7b, HAT-P-11b, HD 185269 b, HD 187123 b and c, Gliese 777 b and c, and 16 Cygni Bb, have been discovered in Cygnus, but the most notable is Kepler 22b, which is believed to be the first "Earth-twin" planet ever discovered, with an estimated average surface temperature of 73 degrees Fahrenheit. In January 2010 the Kepler Mission announced the discovery of the additional planets Kepler-5b and Kepler-6b, which are expected to be the first of many discovered by the mission, which has a significant part of its field of view in Cygnus. Now with numerous planets discovered by Kepler, Cygnus contains more identified planet-hosting stars than any other constellation, it currently stands at 57.

See also

• Cygnus Loop
• John Birmingham (astronomer)
• Cygnus Bubble
• Cygnus (Chinese astronomy)
• Kronberger 61
• Orion can be confused with Cygnus by novice observers.

Bibliography

• Allen, R. H., (1963). Star Names: Their Lore and Meaning (Reprint ed.). New York, NY: Dover Publications Inc. ISBN 0-486-21079-0. 
• Levy, David H. (2005). Deep Sky Objects. Prometheus Books. ISBN 1-59102-361-0. 
• Makemson, Maud Worcester (1941). The Morning Star Rises: an account of Polynesian astronomy. Yale University Press. 
• Ridpath, Ian; Tirion, Wil (2001), Stars and Planets Guide, Princeton University Press, ISBN 0-691-08913-2 
• Ian Ridpath and Wil Tirion (2007). Stars and Planets Guide, Collins, London. ISBN 978-0-00-725120-9. Princeton University Press, Princeton. ISBN 978-0-691-13556-4.

External links

• The Deep Photographic Guide to the Constellations: Cygnus
• Northern Cygnus Mosaic Pan and Zoom In on deep sky objects in Cygnus.
• The clickable Cygnus
• Star Tales – Cygnus
• 4 Cygni Nebula