Deneb

Deneb

Location of Deneb
Observation data Epoch J2000      Equinox J2000
Constellation	Cygnus
Pronunciation	/ˈdɛnɛb/, /ˈdɛnəb/[1]
Right ascension	20h 41m 25.9s[2]
Declination	+45° 16′ 49″[2]
Apparent magnitude (V)	1.25[3] (1.21–1.29[4])
Characteristics
Evolutionary stage	Blue supergiant
Spectral type	A2 Ia[5]
U−B color index	−0.23[3]
B−V color index	+0.09[3]
Variable type	Alpha Cygni[4]
Distance		1,410±196 or 2,615±215 ly (433±60[2] or 802±66[7] pc)
Absolute magnitude (MV)	−8.38[7]
Details
Myr
HR 7924, SAO 49941
Database references
SIMBAD	data

Deneb (/ˈdɛnɛb/) is a blue supergiant star in the constellation of Cygnus. It is the brightest star in the constellation and the 19th brightest in the night sky, with an apparent magnitude slightly varying between +1.21 and +1.29. Deneb is one of the vertices of the asterism known as the Summer Triangle and the "head" of the Northern Cross. Its Bayer designation is α Cygni, which is Latinised to Alpha Cygni, abbreviated to Alpha Cyg or α Cyg.

Deneb rivals Rigel, a closer blue supergiant, as the most luminous first-magnitude star. However, its distance, and hence luminosity, is poorly known; its luminosity is estimated to be between 55,000 and 196,000 times that of the Sun. Distance estimates range from 1,400 to 2,600 light-years; assuming its highest value, it is the farthest star with an apparent magnitude brighter than 2.50.

α Cygni (Latinised to Alpha Cygni) is the star's designation given by Johann Bayer in 1603. The traditional name Deneb is derived from the Arabic word for "tail", from the phrase ذنب الدجاجة Dhanab al-Dajājah, or "tail of the hen".^[12] The IAU Working Group on Star Names has recognised the name Deneb for this star, and it is entered in their Catalog of Star Names.^[13]

Denebadigege was used in the

An older traditional name is Arided /ˈærɪdɛd/, from the Arabic ar-ridf 'the one sitting behind the rider' (or just 'the follower'), perhaps referring to the other major stars of Cygnus, which were called al-fawāris 'the riders'.^[15]

The 19th

Deneb is located at the tip of the Northern Cross asterism made up of the brightest stars in Cygnus, the others being Albireo (Beta Cygni), Gamma Cygni, Delta Cygni, and Epsilon Cygni.^[17] It also lies at one vertex of the prominent and widely spaced asterism called the Summer Triangle, shared with the first-magnitude stars Vega in the constellation Lyra and Altair in Aquila.^[18][19] This outline of stars is the approximate shape of a right triangle, with Deneb located at one of the acute angles.

The

Deneb is a bluish-white star of

At its highest distance estimate, Deneb's absolute magnitude is estimated as −8.4, placing it among the visually brightest stars known, with an estimated luminosity of nearly 200,000 L_☉.^[29][30] By the distance from Hipparcos parallax, Deneb has a luminosity of 55,000 L_☉.^[9]

Deneb is one of the most luminous first magnitude stars, that is, stars with a brighter apparent magnitude than 1.5. Deneb is also the most distant of the 30 brightest stars.^[31] Based on its temperature and luminosity, and also on direct measurements of its tiny angular diameter (a mere 0.002 seconds of arc), Deneb appears to have a diameter about 100 – 200 times that of the Sun;^[32] if placed at the center of the Solar System, Deneb would extend to the orbit of Mercury or Earth. It is one of the largest white 'A' spectral type stars known.

Deneb spent much of its early life as an

Stars evolving red-wards for the first time are most likely fusing hydrogen in a shell around a helium core that has not yet grown hot enough to start fusion to carbon and oxygen. Convection has begun dredging up fusion products but these do not reach the surface. Post-red supergiant stars are expected to show those fusion products at the surface due to stronger convection during the red supergiant phase and due to loss of the obscuring outer layers of the star. Deneb is thought to be increasing its temperature after a period as a red supergiant, although current models do not exactly reproduce the surface elements showing in its spectrum.^[33] On the contrary, it is possible that Deneb has just left the main sequence and is evolving to a red supergiant phase, which is in agreement with estimates of its current mass, while its spectral composition can be explained by Deneb having been a rapidly rotating star during its main sequence phase.^[7]

Deneb is the prototype of the Alpha Cygni (α Cygni) variable stars,^[35][34] whose small irregular amplitudes and rapid pulsations can cause its magnitude to vary anywhere between 1.21 and 1.29.^[36] Its variable velocity discovered by Lee in 1910,^[20] but it was not formally placed as a unique class of variable stars until the 1985 4th edition of the General Catalogue of Variable Stars.^[37] The cause of the pulsations of Alpha Cygni variable stars are not fully understood, but their irregular nature seems to be due to beating of multiple pulsation periods. Analysis of radial velocities determined 16 different harmonic pulsation modes with periods ranging between 6.9 and 100.8 days.^[38] A longer period of about 800 days probably also exists.^[34]

Deneb has been reported as a possible single line spectroscopic binary with a period of about 850 days, where the spectral lines from the star suggest cyclical radial velocity changes.^[38] Later investigations have found no evidence supporting the existence of a companion.^[35]

Names similar to Deneb have been given to at least seven different stars, most notably Deneb Kaitos, the brightest star in the constellation of Cetus; Deneb Algedi, the brightest star in Capricornus; and Denebola, the second brightest star in Leo. All these stars are referring to the tail of the animals that their respective constellations represent.

In Chinese, 天津 (Tiān Jīn), meaning