Swan (constellation)

History

This constellation is associated with several legendary birds of the Greek Mythologie:

according to one of the legends, the god Zeus had been disguised in swan to allure Léda, of which it had as a child the Gemini and Helen of Troy.
It could also represent Orphée, metamorphosed in swan after its assassination and placed in the skies beside its quadrant.
Lastly, one says that an young man named Cygnus was the lover of the unhappy Phaéton. After this one had been crushed by leading the horses of the Sun, Cygnus started to hopelessly seek its body in the river Éridan where it fell. Cygnus plunged as well once in the river as Zeus had pity of him and changed it into the water bird which carries since its name.

Indexed by the Greek Astronomer S , this constellation was then indicated under the name of the Bird . It was also indicated under the name of Croix of Grey waxbill by Julius Schiller in 1627 at one time of massive christianization of the sky (the constellation of the Cross of the south in is contemporary).

In the Chinese Mythology, the constellation of the Swan once lodges per annum the bridge which connects the lovers Niu Lang and Zhi Nu.

Observation of stars

; location of the constellation The star α Cygni (Deneb) mark one of the angles of the Triangle of summer, visible as soon as the night fell (mag 1). Of three stars of the Triangle of summer, Deneb is the least brilliant.

When the conditions of visibility are better (mag 3), the swan recognizes itself easily by its shape of very characteristic cross.

; Form constellation The " Cross of Nord" what draws principal stars of the Swan is very clear and very regular; it is used as reference mark for the close constellations. The Swan has a long neck and wings placed on the back, the two figures are thus opposite one of the other: the " tete" cross is thus the " queue" swan, and the " tête" swan forms the " pied" cross.

The most brilliant star (mag 1) is Deneb, with the " tête" cross (and tail of the Swan bases it). Three aligned stars of the " bras" are appreciably of the same glare (mag 2), and are of Is in West ε Cyg, γ Cyg (shoulders, in the axis of the body), and δ Cyg. When the arm starts to be visible, one prolongs the body in the axis Deneb - γ Cyg, to fall 15° further on β Cyg (Albireo), which marks the foot of the cross (and thus the head of the Swan).

When the conditions are very good (mag 6) one can trace the whole of the shape of the Swan, with its entirely spread wings.

Between the shoulders and the " tête" swan, an alignment of three small intermediate stars marks the neck. They are η, χ (variable) and φ Cyg.

The axis of the wings bends towards the back on both sides, and reached ζ Cyg South-eastern side, and in the North-West, the pair of stars ι and κ Cyg.

In exceptional weather, one can follow the alignment back of the wings, which forms a second arc passing by Deneb, and bordered of small stars external (which can be detached warp ends or legs, according to imagination of the observer).

; Location of the vicinity The Petit Fox is located immediately at the South of the Swan. It borders all the constellation, but its two identifiable stars are located under the head of the Swan: in fact the two average stars form a East-West alignment, one with 5° of the head towards the South, and the other with 7° in South-east (opposed to Véga). Beyond the Petit Fox one rather easily recognizes the form of the Flèche if the visibility allows it.

The Northern wing of the Swan points roughly in direction of the head of the Dragon (according to whether one takes the right wing or the left, one fall on the level from ξ Dra, the point of the lozange, or on the level of the " two yeux"). This alignment passes by the heart of the Dragon (η Dra), Thuban (α Dra) and the interior edge of the " casserole" (δ and γ UMa).

In the other direction, the wing of the Swan points on a rather obscure zone where alignment passes by the feet of PEGASE, the center of the Sagittarius, and comes to finish on Fomalhaut after a crossing of almost 60°.

There is no alignment very convainquant in the axis of the Swan. The head of the Swan points in the direction of the Aigle and the Serpentaire, while the tail is directed towards Céphée.

Principal stars

α Cygni (Deneb)

α Cygni (Deneb) is the most brilliant star of the constellation of the Swan and the 19th the most brilliant star vault of heaven with a Magnitude connects of 1,25. Deneb, from which the name comes from an Arab word meaning the Tail and referring to the position of star in the constellation, one of the visible stars most remote since is however located between 1.800 and 3.200 light-years of the Ground (at this distance, the uncertainty of measurements of Parallaxe is very important), of a absolute Magnitude thus reaching approximately -8,7.

Without surprise, Deneb is a Supergéante blue, 200 times larger than the Sun (placed at its place, it would extend well beyond the terrestrial orbit), one of largest than one knows. It will probably finish in Supernova from here a million years.

Deneb is one of the tops of the known Astérisme under the name of Triangle of summer with Véga (α Lyrae) and Altaïr (α Aquilae).

Albireo (β Cygni)

Albireo (β Cygni) is at the end of the nozzle of the Swan and its name comes from an Arab word meaning besides the Nozzle .

It is about the one of most beautiful the double stars of the sky, a gilded star (magnitude 3,08) which one can easily distinguish, in small a Télescope, of his/her blue companion (magnitude 5,11). They Orbite NT in 7.300 years and most brilliant is itself doubles, made up of a yellow giantess and a star of the principal sequence very close one to the other. The blue star turns quickly on itself and of this fact is surrounded by a gas disc coming from its own surface.

Ruchba (ω Cygni)

Ruchba (ω Cygni), the knee in Arabic, indicates actually two distinct stars in the same way standard (both are binary stars with eclipses of the type Algol and the spectral classes of stars in question are identical) that a coincidence reveals one beside different the sights of the Earth.

Most brilliant, ω¹ Cygni (31 Cygni in the Designation of Flamsteed), is magnitude 3,8, an orange supergéante eclipsed by a blue star during 63 days every 10,36 years.

ω ² Cygni (32 Cygni in the designation of Flamsteed) is magnitude 3,96 and every 3,143 years, the orange supergéante is eclipsed by the blue star which turns to him around.

This kind of stars with eclipses is a ground of investigation privileged for the study of their Chromosphère.

P Cygni

P Cygni is a blue star of which the current magnitude is of 4,81 in the visible one (5,135 in blue), but that was not always the case. In the past, this star is assembled until the 3rd magnitude. Spectral class B2pe

P Cygni is a supergéante, distant of approximately 6.000 years light (although at this distance, this value is difficult to estimate with precision), between 500.000 and 900.000 times more luminous than the Sun, very hot (its temperature of surface seems to border 19.000 K) and it are still largely darkened by interstellar dust. P Cygni saw its luminosity increasing abruptly when it expelled a gas shell on several occasions: in 1600, it was indexed like “Nova Cygni 1600” and another eruption occurred in 1654.

This star is surrounded by a nebula and continuous to lose mass uninterrupted, producing a stellar wind several million times more important than the solar wind.

It is estimated that P Cygni is 50 to 60 times more massive than the Sun. It is dedicated to finish in Hypernova and to crumble in Black hole.

Other stars

Sadir (γ Cygni), the second star of the constellation of the Swan by its glare, is a supergéante yellow/white, which is rather rare, very remote (probably around 1.500 years light). It would seem that it is about a double star, but his/her companion is not known.

δ Cygni, the only brilliant star of the constellation without proper name, is a triple system composed of two relatively close stars - distant from 84 to 230 ua - around of which orbit a third, definitely more distant.

ξ Cygni is a star Variable of the type Mira (in the constellation of the Baleine): it can reach magnitude 3,5 during 407 days period.

SS Cygni is one 50 days total period a variable star, changing luminosity in a rather irregular way, sometimes into two or three hours.

16 Cygni is a double star of class G, made up of two stars of 5th and 6th magnitude rather similar to the Sun, distant one of the other of 840 ua and orbiting in 17.000 years. What characterizes this system, it is that it is about the first double star in which one detected a planet extrasolaire. 1,5 times more massive than Jupiter, it orbits around 16 Cygni-B (the least brilliant of the pair) at an average distance from 1,7 ua, in 804 days, according to an eccentric orbit very .

Another interesting star, 61 Cygni, is certainly not very impressive for an occasional observer, but has an extremely fast own movement (108 km/s, five times faster than surrounding stars). It became thus the first star - after the Sun - of which the distance was measured thanks to its Parallaxe. It is besides among the stars closest to the Earth, distant of only 11,4 years light.

Gienah means Arab wing in and Gienah Cygni (ε Cygni) bears this complete name to differentiate it from Gienah Corvi, located in the constellation of the Corbeau.

A last star of the constellation has a name: Azelfafage (π¹ Cygni).

Celestial objects

Gràce with its position on the Milky Way, several stellar Cluster S and Nébuleuse S is in the Swan.

One can see the open Amas there S M29 and M39.

NGC 7000, the nebula of North America, is a little in the east of Deneb. Its resemblance to this continent is enough striking the photographs.

Close to Sadir Cygnus has (or 4C 40.40), one of the most powerful sources radio that one knows (see Désignation of the sources of waves radio). It is about a radiogalaxie, undergoing a massive explosion or a collision with another Galaxie, catalogued like Galaxie of Seyfert.

Lastly, the Swan contains the source of X-rays, Cygnus X-1 , which one regards as probable a Black hole.

See too

List of stars of the Swan

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