Gamma Cygni (γ Cygni, abbreviated Gamma Cyg, γ Cyg), officially named Sadr , is a

star A star is an astronomical object comprising a luminous spheroid of plasma (physics), plasma held together by its gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked ...

in the northern

constellation A constellation is an area on the celestial sphere in which a group of visible stars forms a perceived pattern or outline, typically representing an animal, mythological subject, or inanimate object. The origins of the earliest constellation ...

of Cygnus, forming the intersection of an asterism of five stars called the Northern Cross. Based upon

parallax Parallax is a displacement or difference in the apparent position of an object viewed along two different lines of sight and is measured by the angle or semi-angle of inclination between those two lines. Due to foreshortening, nearby object ...

measurements obtained during the

Hipparcos ''Hipparcos'' was a scientific satellite of the European Space Agency (ESA), launched in 1989 and operated until 1993. It was the first space experiment devoted to precision astrometry, the accurate measurement of the positions of celestial ob ...

mission, it is approximately 1,800

light-year A light-year, alternatively spelled light year, is a large unit of length used to express astronomical distance, astronomical distances and is equivalent to about 9.46 Orders of magnitude (numbers)#1012, trillion kilometers (), or 5.88 ...

s (560

parsec The parsec (symbol: pc) is a unit of length used to measure the large distances to astronomical objects outside the Solar System, approximately equal to or (au), i.e. . The parsec unit is obtained by the use of parallax and trigonometry, an ...

s) 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 ...

. It forms the primary or 'A' component of a

multiple star system A star system or stellar system is a small number of stars that orbit each other, bound by gravitational attraction. A large group of stars bound by gravitation is generally called a ''star cluster'' or ''galaxy'', although, broadly speaking ...

designated WDS J20222+4015 (the secondary or 'BC' component is CCDM J20222+4015BC, a close pair of stars 40" away from γ Cygni).

Nomenclature

''γ Cygni'' ( Latinised to ''Gamma Cygni'') is the star's

Bayer designation A Bayer designation is a stellar designation in which a specific star is identified by a Greek or Latin letter followed by the genitive form of its parent constellation's Latin name. The original list of Bayer designations contained 1,564 stars ...

. WDS J20222+4015A is its designation in the

Washington Double Star Catalog The Washington Double Star Catalog, or WDS, is a catalog of double stars, maintained at the United States Naval Observatory. The catalog contains positions, magnitudes, proper motions and spectral types and has entries for (as of June 2017) 141,7 ...

. It bore the traditional name ''Sadr'' (also rendered ''Sadir'' or ''Sador''), derived 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 ...

صدر ''ṣadr'' "chest", the same word which gave rise to the star Schedar ( Alpha Cassiopeiae). In 2016, 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 ...

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 catalogue 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 ''Sadr'' for this star (WDS J20222+4015A) on 21 August 2016 and it is now so included in the List of IAU-approved Star Names. In the catalogue of stars in the ''Calendarium'' of

Al Achsasi al Mouakket Muḥammad al-Akhṣāṣī al-Muwaqqit ( ar, محمد الاخصاصي الموقت) was an Egyptian astronomer whose and catalogue of stars, ('Pearls of brilliance upon the solar operations'), was written at Cairo about 1650. Al-Akhsasi was a s ...

, this star was designated ''Sadr al Dedjadjet'', (صدر الدجاجة / ''ṣadr al-dajājati''), which was translated into

Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through ...

as ''Pectus Gallinǣ'', meaning ''the hen's chest''. In Chinese, (), meaning '' Celestial Ford'', refers to an asterism consisting of Gamma Cygni, Delta Cygni,

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 the 1 ...

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 ...

, Zeta Cygni and Epsilon Cygni. 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 Gamma Cygni itself is (, en, the First 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.

Properties

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 2.23, Gamma Cygni is among the brighter stars visible in the night sky. The

stellar classification In astronomy, stellar classification is the classification of stars based on their spectral characteristics. Electromagnetic radiation from the star is analyzed by splitting it with a prism or diffraction grating into a spectrum exhibiting the ...

of this star is F8 Iab, indicating that it has reached the

supergiant Supergiants are among the most massive and most luminous stars. Supergiant stars occupy the top region of the Hertzsprung–Russell diagram with absolute visual magnitudes between about −3 and −8. The temperature range of supergiant stars spa ...

stage of its

stellar evolution Stellar evolution is the process by which a star changes over the course of time. Depending on the mass of the star, its lifetime can range from a few million years for the most massive to trillions of years for the least massive, which is cons ...

. 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 this star has served as one of the stable anchor points by which other stars are classified. Compared to the Sun this is an enormous star, with 12 times the

Sun's mass The solar mass () is a standard unit of mass in astronomy, equal to approximately . It is often used to indicate the masses of other stars, as well as stellar clusters, nebulae, galaxies and black holes. It is approximately equal to the mass of ...

and about 150 times the Sun's radius. It is emitting over 33,000 times as much energy as the Sun, at an

effective temperature The effective temperature of a body such as a star or planet is the temperature of a black body that would emit the same total amount of electromagnetic radiation. Effective temperature is often used as an estimate of a body's surface temperature ...

of 6,100 K in its outer envelope. This temperature is what gives the star the characteristic yellow-white hue of an

F-type star An F-type main-sequence star (F V) is a main-sequence, hydrogen-fusing star of spectral type F and luminosity class V. These stars have from 1.0 to 1.4 times the mass of the Sun and surface temperatures between 6,000 and 7,600 K.Tables VII ...

. Massive stars such as this consume their nuclear fuel much more rapidly than the Sun, so the estimated age of this star is only about 12 million years old. The

of this star shows some unusual dynamic features, including variations in

radial velocity The radial velocity or line-of-sight velocity, also known as radial speed or range rate, of a target with respect to an observer is the rate of change of the distance or range between the two points. It is equivalent to the vector projection ...

of up to , occurring on a time scale of 100 days or more. Indeed, on the

Hertzsprung–Russell diagram The Hertzsprung–Russell diagram, abbreviated as H–R diagram, HR diagram or HRD, is a scatter plot of stars showing the relationship between the stars' absolute magnitudes or luminosities versus their stellar classifications or effective te ...

, Gamma Cygni lies close to the instability strip and its spectrum is markedly like that of a

Cepheid variable A Cepheid variable () is a type of star that pulsates radially, varying in both diameter and temperature and producing changes in brightness with a well-defined stable period and amplitude. A strong direct relationship between a Cepheid vari ...

. This star is surrounded by a diffuse nebula called IC 1318, or the ''Gamma Cygni region''.

References

External links

Sadr
by Jim Kaler. * http://www.atlasoftheuniverse.com/nebulae/ic1318.html

NASA The National Aeronautics and Space Administration (NASA ) is an independent agency of the US federal government responsible for the civil space program, aeronautics research, and space research. NASA was established in 1958, succeedin ...

, July 9, 2013 {{Stars of Cygnus Cygni, Gamma Cygnus (constellation) F-type supergiants Sadr Cygni, 37 7796 194093 100453 Durchmusterung objects Suspected variables