Epsilon Cygni (ε Cygni, abbreviated Epsilon Cyg, ε Cyg) is multiple star system in the constellation of Cygnus. With an

apparent visual magnitude Apparent magnitude () is a measure of the brightness of a star or other astronomical object observed from Earth. An object's apparent magnitude depends on its intrinsic luminosity, its distance from Earth, and any extinction of the object's lig ...

of 2.48, it is readily visible to the naked eye at night as one of the brighter members of Cygnus. Based upon parallax measurement, Epsilon Cygni is about 73 light-years from the

Sun The Sun is the star at the center of the Solar System. It is a nearly perfect ball of hot plasma, heated to incandescence by nuclear fusion reactions in its core. The Sun radiates this energy mainly as light, ultraviolet, and infrared radi ...

. The system has three constituents: a spectroscopic binary (designated Epsilon Cygni A); an

optical companion In observational astronomy, a double star or visual double is a pair of stars that appear close to each other as viewed from Earth, especially with the aid of optical telescopes. This occurs because the pair either forms a binary star (i.e. a ...

(B) and a single star (C). A's two components are themselves designated Epsilon Cygni Aa (officially named Aljanah ) and Ab.

Nomenclature

''ε Cygni'' ( Latinised to ''Epsilon Cygni'') is the system's Bayer designation. The designations of the three constituents as ''Epsilon Cygni A'', ''B'' and ''C'', and those of ''A's'' components - ''Epsilon Cygni Aa'' and ''Ab'' - derive from the convention used by the Washington Multiplicity Catalog (WMC) for multiple star systems, and adopted by the

International Astronomical Union The International Astronomical Union (IAU; french: link=yes, Union astronomique internationale, UAI) is a nongovernmental organisation with the objective of advancing astronomy in all aspects, including promoting astronomical research, outreac ...

(IAU). Epsilon Cygni bore the traditional name ''Gienah'' from the

Arabic Arabic (, ' ; , ' or ) is a Semitic language spoken primarily across the Arab world.Semitic languages: an international handbook / edited by Stefan Weninger; in collaboration with Geoffrey Khan, Michael P. Streck, Janet C. E.Watson; Walter ...

''al janāħ'' ( ar, جناح) meaning "the

wing A wing is a type of fin that produces lift while moving through air or some other fluid. Accordingly, wings have streamlined cross-sections that are subject to aerodynamic forces and act as airfoils. A wing's aerodynamic efficiency is e ...

". However that name was more usually applied to

Gamma Corvi Gamma Corvi (γ Corvi, abbreviated Gamma Crv, γ Crv) is a binary star and the brightest star in the southern constellation of Corvus, having an apparent visual magnitude of 2.59. The system's two components are designated Gamma Corvi A (of ...

. For reasons of disambiguation it was sometimes called Gienah Cygni. In 2016, the IAU organized a

Working Group on Star Names The International Astronomical Union (IAU) established a Working Group on Star Names (WGSN) in May 2016 to catalog and standardize proper names for stars for the international astronomical community. It operates under Division C – Education ...

(WGSN) to catalog and standardize proper names for stars. The WGSN decided to attribute proper names to individual stars rather than entire multiple systems. It approved the name ''Aljanah'' for the component Epsilon Cygni Aa on 30 June 2017. It had previously approved the name ''Gienah'' for Gamma Corvi A on 6 November 2016. Both are now so included in the List of IAU-approved Star Names. In

Chinese astronomy Astronomy in China has a long history stretching from the Shang dynasty, being refined over a period of more than 3,000 years. The ancient Chinese people have identified stars from 1300 BCE, as Chinese star names later categorized in the twe ...

, the " Celestial Ford" () refers to an asterism consisting of Epsilon Cygni,

Gamma Cygni Gamma Cygni (γ Cygni, abbreviated Gamma Cyg, γ Cyg), officially named Sadr , is a star in the northern constellation of Cygnus, forming the intersection of an asterism of five stars called the Northern Cross. Based upon parallax mea ...

Delta Cygni Delta Cygni (δ Cygni, abbreviated Delta Cyg, δ Cyg) is a binary star of a combined third-magnitude in the constellation of Cygnus. It is also part of the Northern Cross asterism whose brightest star is Deneb. Based upon paralla ...

30 Cygni 30 Cygni is a class A5III (white giant) star in the constellation Cygnus. Its apparent magnitude is 4.83 and it is approximately 610 light years away based on parallax. The Bayer letter ο (omicron) has been variously applied to two or ...

Alpha Cygni Deneb () is a first-magnitude star in the constellation of Cygnus, the swan. Deneb is one of the vertices of the asterism known as the Summer Triangle and the "head" of the Northern Cross. It is the brightest star in Cygnus and th ...

Nu Cygni Nu Cygni, Latinized from ν Cygni, is a binary star system in the constellation Cygnus. Its apparent magnitude is 3.94 and it is approximately 374 light years away based on parallax. The brighter component is a magnitude 4.07 A-type g ...

Tau Cygni Tau Cygni, Latinised from τ Cygni, is a binary star system in the constellation Cygnus, approximately 69 light years away from Earth. This visual binary system has a period of 49.6 years. The main star, 4th magnitude GJ 822.1 A, is a ...

Upsilon Cygni Upsilon Cygni, Latinized from υ Cygni, is a star in the northern constellation of Cygnus. It is visible to the naked eye, having an apparent visual magnitude of 4.43. Based upon an annual parallax shift of , it lies at a distance of r ...

and

Zeta Cygni Zeta Cygni (ζ Cyg) is a binary star system in the northern constellation of Cygnus, the swan. It has an apparent visual magnitude of 3.26 and, based upon parallax measurements, is about away. The primary component, ζ Cyg A is a g ...

. ''中國星座神話'', written by 陳久金. Published by 台灣書房出版有限公司, 2005, . Consequently, the

Chinese name Chinese names or Chinese personal names are names used by individuals from Greater China and other parts of the Chinese-speaking world throughout East and Southeast Asia (ESEA). In addition, many names used in Japan, Korea and Vietnam are ofte ...

for Epsilon Cygni Cygni itself is "the Ninth Star of Celestial Ford" ().香港太空館 - 研究資源 - 亮星中英對照表
, Hong Kong Space Museum. Accessed on line November 23, 2010.

Companions

Epsilon Cygni A has an optical companion, Epsilon Cygni B, with which it is not physically associated, and a 13th magnitude candidate common proper motion companion, Epsilon Cygni C, at an angular separation of 78

arcseconds A minute of arc, arcminute (arcmin), arc minute, or minute arc, denoted by the symbol , is a unit of angular measurement equal to of one degree. Since one degree is of a turn (or complete rotation), one minute of arc is of a turn. The ...

. If the latter star is

gravitationally bound The gravitational binding energy of a system is the minimum energy which must be added to it in order for the system to cease being in a gravitationally bound state. A gravitationally bound system has a lower (''i.e.'', more negative) gravitati ...

to Epsilon Cygni A, then they are currently separated by 1700 AU or more, and have an

orbital period The orbital period (also revolution period) is the amount of time a given astronomical object takes to complete one orbit around another object. In astronomy, it usually applies to planets or asteroids orbiting the Sun, moons orbiting planets ...

of at least 50,000 years.

Properties

Epsilon Cygni A is a single-lined spectroscopic binary. Radial velocity observations suggest a possible companion with an orbital period of at least 15 years. It presents as a

giant star A giant star is a star with substantially larger radius and luminosity than a main-sequence (or ''dwarf'') star of the same surface temperature.Giant star, entry in ''Astronomy Encyclopedia'', ed. Patrick Moore, New York: Oxford University Press ...

with a stellar classification of K0 III. This indicates that the star has left the main sequence and has begun the final stages in its stellar evolution. The effective temperature of its photosphere is 4,710 K, giving an orange hue that is a characteristic of K-type stars. It has nearly 11 times the

solar radius Solar radius is a unit of distance used to express the size of stars in astronomy relative to the Sun. The solar radius is usually defined as the radius to the layer in the Sun's photosphere where the optical depth equals 2/3: :1\,R_ = 6.957\ ...

and is about 62 times the

luminosity of the Sun The solar luminosity (), is a unit of radiant flux ( power emitted in the form of photons) conventionally used by astronomers to measure the luminosity of stars, galaxies and other celestial objects in terms of the output of the Sun. One nominal ...

. Since 1943, the

spectrum A spectrum (plural ''spectra'' or ''spectrums'') is a condition that is not limited to a specific set of values but can vary, without gaps, across a continuum. The word was first used scientifically in optics to describe the rainbow of colors ...

of Epsilon Cygni A has served as one of the stable anchor points by which other stars are classified.

Veil Nebula

ε Cygni lies about three degrees north of the

Veil nebula The Veil Nebula is a cloud of heated and ionized gas and dust in the constellation Cygnus. It constitutes the visible portions of the Cygnus Loop, a supernova remnant, many portions of which have acquired their own individual names and ca ...

, a probable ancient

supernova remnant A supernova remnant (SNR) is the structure resulting from the explosion of a star in a supernova. The supernova remnant is bounded by an expanding shock wave, and consists of ejected material expanding from the explosion, and the interstellar mat ...

. The nebula is far more distant than the star.

References

External links

* http://www.pbase.com/mcrowle/image/81902791 {{Stars of Cygnus Cygni, Epsilon Cygnus (constellation) K-type giants Aljanah Cygni, 53 7949 197989 102488 BD+33 4018 0806.1 Multiple stars