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Cygnus


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Abbreviation:
Cyg
English name:
Swan (sometimes: Northern Cross)
Coordinates
see Stellar data
see Object data

Particulars:

General:

A conspicious constellation of the northern hemisphere. It belongs to the Hercules constellation family. The stars forming the swans body resemble a cross, so sometimes this constellation is refered as Northern Cross. The brightest star (spectraltype A2Iae; 1.25 mag), alpha Cyg, called Deneb (arab.: the tail), is among the 20 brightest stars in the sky.
The northern border of this constellation reaches as high as DECL=+60 degrees; to the south it extends down to about DECL=+28 degrees. From east to west it lies between RA=22h to RA=19h 10m (average).
See here how the stars form the swan.

Stars and other objects

When watching stars in Cygnus the binary beta Cyg, called Albireo (arab.: the bill), is a must. It is one of the most beautiful colored binaries, a real showpiece in the sky. Even a binocular reveals the reddish giant (3.08 mag) with its blue-white companion (5.11 mag). The brighter component is double itself: A K3II and a B0.5 main sequence star are seen as one star in amateur telescopes.
The star gamma Cyg (the 'breastbone' Sadr) seems to be a binary, too. But it is not an object for low power amateur instruments.
The double delta Cyg consists of B9.5 sub giant and a F1 main sequence star. The two stars have a orbital period of 300 years. The brightness of the two stars differ from each other about 5 mag.
Viewed with binoculars the 4th mag orange giant omicron 1 Cyg forms a nice wide double with 30 Cyg. Closer to omicron 1 Cyg lies the companion of this star, a blue star of 7th mag. With a period 10.5 years these two stars revolve and eclipse each other. Without additional help the variation in brightness cannot be seen because it is just about a few tenth of a mag.
61 Cyg became famous not only because it is an attractive and easily resolvable object for small telescopes, but because it lies in a distance of only 11.1 lightyears. Its the first star which distance was actually measured. The pair consists of two orange dwarf stars of 5th and 6th mag.
All 407 days the brightness of chi Cyg varies from 12th mag up to 4th or 5th mag.
P Cyg flared up to 3rd mag in the past. Usually this blue star shows a brightness of 4.81 mag. Physically this is explained that the star is throwing off shells of gas. When looking at the spectrum of this star, a curious profile of the absorbtion lines can be seen: Instead of of a more or less symmetric line profile a broad trough with an emission peak at the red side of the trough. Investigations with satellites showed that below 2000 Angstroem many O- and B supergaints have this kind of lines in their spectra. It is something so typical that P Cygni gave name to a subclass of stars, the P Cygni stars (yet the novalike flares are not typical for these stars; P Cygni is something special).
The variable star SS Cyg should be in the favour of every amateur. Within 50 days the brightness shows a strong de- and increase (on a somewhat irregular schedule). Sometimes the brightness changes significantly within two or three hours.
When looking at the planetary nebula NGC 6826 it seems to twinkle. When looking at it or away from it seems to blink on and off. This feature gave it the nickname the Blinking Nebula. The nebula is of 8th mag and it needs a telescope of at least 75 mm aperture to show the pale blue disk. It can be found near theta Cyg (to the east). Withing 1 degree of the nebula lies another easy double for small scopes, 16 Cyg.
The planetary nebula NGC 7072 show a somewhat irregular shape. Its four bright condensations make it interesting to observe.
The diffuse nebula NGC 6960 markes the wester half of a faint nebula, which is so some times called Wreath, sometimes Loop or Network. Best known is it under the name Veil Nebula. More than 50000 years ago a supernova exploded south of epsilon Cyg, close to southern border of Cygnus. Nowadays the afterglowing gas forms this large nebula which shows a circular shape. The eastern and brighter part of this nebula got its own NGC number, too: NGC 6992. It is a challange for binoculars. You need best conditions to observe it. Using a wide-angle telescope at low power will show NGC 6992. The complete nebula is too faint to observe; it can only be seen in total on long exposure photographs.
East of alpha Cyg lies the famous North Amerika Nebula, NGC 7000. Although it is quite large, it is a difficult object to observe because of its low surface brightness. In a clear and dark night one may be lucky to see it with binoculars.
Close to NGC 7000 lies the Pelican Nebula, I 5070. This nebula and its neighbour, I 5067, are extremely faint for telescopic observations. Long exposure photographs show that they are interesting objects, too.
When watching this area in a clear night one discovers that the Milky Way is divided into two parts. A lane of dust absorbes a good deal of the starlight. This lane is known as The Cygnus Rift or sometimes as the Northern Coalsack.
Near gamma Cyg lies the open star cluster M29. Its 50 member stars build a not too impressive stargroup.
About nine degrees east and a bit north of alpha Cyg is the open star cluster M39 located. Only about 50 stars belong to this quite large cluster which has therefore a somewhat loose appearance. More details about both Messier objects can be found in the Messier database.
Next to gamma Cyg one of the strongest radio sources astronomer know of is located, Cygnus A. This object is far beyond everything an amateur can reveal. It is a radio galaxy of 18th mag. On long exposure photographs a pair of fuzzy blobs a revealed. This galaxy is either undergoing an explosion or is colliding with another galaxy. For information and pictures see this site.
If black holes exist then Cygnus X-1 was the first one ever identified (it lies near eta Cyg). The existence of this star was discovered in 1972/73 due to its strong x-ray radiation. Gas falling into the star is heated so much that it radiates in the x-ray range of the spectrum. The signals of Cygnus X-1 show no periodicites. They are completely irregular and fluctuate within the 1000th part of a second. This indicates a very compact object. This and the fact that there was no hint of eclipsing in the spectrum, made it difficult to see whether or not this is a binary system. It took highly precise measurements to find the 13th mag star HDE 226868 at the position of the x-ray source. The spectrum of fhis star shows the typical Doppler shift of binaries. The two stars revolve each other each 5.6 days. This is of course not an amateur object. Some more information can be found in an article of the observatory of the Jagiellonian University in Krakow.
Between September 26th and October 10th the meteor shower October Cygnids seems to be active.
Quite long is the shower Kappa Cygnids active: from July 26th to September 1st. The maximum of the shower activity seems to occur on August 18th with an average rate of 6 meteor per hour. Detailed information and observing data can be found in Gary Kronk's database about meteor showers.

Mythological Background:

Cygnus, the swan, is one of the the two birds (Aquila, the eagle, is the second), which are hunted by Hercules. Yet it seems that the two birds were lucky and have escaped. It is assumed that these birds (together with a third one, the Vulture - nowadays the constellation Lyra) represent the Stymphalian Birds - one of the tasks of Hercules. (See: Peterson Field Guide to the Stars)



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C. Kronberg --- 97/07/05 --- smil (at) clell.de