Deneb

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.

## Contents

* 1 Nomenclature
* 2 Observation
* 2.1 Pole star
* 3 Physical characteristics
* 3.1 Evolutionary state
* 3.2 Variable star
* 3.3 Possible spectroscopic companion
* 4 Etymology and cultural significance
* 4.1 Namesakes
* 5 References

## Nomenclature

Deneb is the brighest star in the constellation of Cygnus (top)

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".[1] 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.[2]

Denebadigege was used in the Alfonsine Tables,[3] other variants include Deneb Adige, Denebedigege and Arided. This latter name was derived from Al Ridhādh, a name for the constellation. Johann Bayer called it Arrioph, derived from Aridf and Al Ridf, 'the hindmost' or Gallina. German poet and author Philippus Caesius termed it Os rosae, or Rosemund in German, or Uropygium – the parson's nose.[1] The names Arided and Aridif have fallen out of use.

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'.[4]

## Observation

The Summer Triangle

The 19th brightest star in the night sky, Deneb culminates each year on October 23 at 6 PM and September 7 at 9 PM,[5] corresponding to summer evenings in the Northern Hemisphere.[6] It never dips below the horizon at or above 45° north latitude, just grazing the northern horizon at its lowest point at such locations as Minneapolis, Montréal and Turin. In the Southern Hemisphere, Deneb is not visible south of 45° parallel south, so it just barely rises above the horizon in South Africa, southern Australia, and northern New Zealand during the southern winter.

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.[6] 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.[7][8] This outline of stars is the approximate shape of a right triangle, with Deneb located at one of the acute angles.

The spectrum of Alpha Cygni has been observed by astronomers since at least 1888, and by 1910 the variable radial velocity had become apparent. This led to the early suggestion by E. B. Frost that this is a binary star system.[9] In 1935, the work of G. F. Paddock and others had established that this star was variable in luminosity with a dominant period of 11.7 days and possibly with other, lower amplitude periods.[10] By 1954, closer examination of the star's calcium H and K lines showed a stationary core, which indicated the variable velocity was instead being caused by motion of the star's atmosphere. This variation ranged from +6 to −9 km/s around the star's mean radial velocity.[11] Other, similar supergiants were found to have variable velocities, with this star being a typical member.[10]

### Pole star

Due to the Earth's axial precession, Deneb will be an approximate pole star (7° off of the north celestial pole) at around 9800 AD.[12] The north pole of Mars points to the midpoint of the line connecting Deneb and the star Alderamin.[13]

Preceded by  | Pole Star  | Succeeded by

|
|

Alderamin | 8700 AD to 11000 AD  | Delta Cygni

## Physical characteristics

Wide-field view of the Summer Triangle and the Milky Way. Deneb is at the far left centre of the picture, at the end of the darker lane within the Milky Way.

Deneb is a bluish-white star of spectral type A2Ia, classifying it as a blue supergiant star.[14] Since 1943, its spectrum has served as one of the stable references by which other stars are classified.[15] Its mass is estimated at 19 M☉. Stellar wind causes matter to be lost at an average rate of 8±3×10−7 M☉ per year, 100,000 times the Sun's rate of mass loss or equivalent to about one Earth mass per 500 years.[16]

Deneb's distance from the Earth is uncertain. One estimate gives 802 parsecs (2,620 ly) assuming Deneb is a member of the Cygnus OB7 association.[17] The original derivation of a parallax using measurements from the astrometric satellite Hipparcos gave an uncertain result of 1.01±0.57 mas[18][19] that was consistent with this distance. However, the 2007 re-analysis gives a much larger parallax resulting in a distance of 433±60 pc, or 1,410±196 ly.[20] The controversy over whether the direct Hipparcos measurements can be ignored in favour of a wide range of indirect stellar models and interstellar distance scales is similar to the better known situation with the Pleiades.[20]

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☉.[21][22] By the distance from Hipparcos parallax, Deneb has a luminosity of 55,000 L☉.[23]

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.[24] 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;[23] 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.

### Evolutionary state

Deneb spent much of its early life as an O-type main-sequence star of about 23 M☉, but it has now exhausted the hydrogen in its core and expanded to become a supergiant.[17][25] Stars in the mass range of Deneb eventually expand to become the most luminous red supergiants, and within a few million years their cores will collapse producing a supernova explosion. It is now known that red supergiants up to a certain mass explode as the commonly seen type II-P supernovae, but more massive ones lose their outer layers to become hotter again. Depending on their initial masses and the rate of mass loss, they may explode as yellow hypergiants or luminous blue variables, or they may become Wolf-Rayet stars before exploding in a type Ib or Ic supernova. Identifying whether Deneb is currently evolving towards a red supergiant or is currently evolving bluewards again would place valuable constraints on the classes of stars that explode as red supergiants and those that explode as hotter stars.[25]

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.[25] 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.[17]

### Variable star

A visual band light curve for Deneb, adapted from Yüce and Adelman (2019)[26]

Deneb is the prototype of the Alpha Cygni (α Cygni) variable stars,[27][26] whose small amplitudes and irregular rapid pulsations can cause its magnitude to vary anywhere between 1.21 and 1.29.[28] Its variable velocity discovered by Lee in 1910,[9] 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.[29] 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.[30] A longer period of about 800 days probably also exists.[26]

### Possible spectroscopic companion

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.[30] Later investigations have found no evidence supporting the existence of a companion.[27]

## Etymology and cultural significance

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 Celestial Ford, refers to an asterism consisting of Deneb, Gamma Cygni, Delta Cygni, 30 Cygni, Nu Cygni, Tau Cygni, Upsilon Cygni, Zeta Cygni and Epsilon Cygni.[31] Consequently, the Chinese name for Deneb itself is 天津四 (Tiān Jīn sì, English: the Fourth Star of the Celestial Ford).[32]

In the Chinese love story of Qi Xi, Deneb marks the magpie bridge across the Milky Way, which allows the separated lovers Niu Lang (Altair) and Zhi Nü (Vega) to be reunited on one special night of the year in late summer. In other versions of the story, Deneb is a fairy who acts as chaperone when the lovers meet.

### Namesakes

USS Arided was a United States Navy Crater-class cargo ship named after the star. SS Deneb was an Italian merchant vessel that bore this name from 1951 until she was scrapped in 1966.

Deneb also lends its name to the Deneb Ceph cluster, a large-scale shared storage system operated by the STFC, providing approximately 5 PB of erasure-coded storage for scientific computing workloads.[33]

## References

1. ↑ 1.0 1.1 Allen, Richard Hinckley (1963). Star Names: Their Lore and Meaning (Reprint ed.). Dover Publications. p. 195. ISBN 978-0-486-21079-7. https://archive.org/details/starnamestheirlo00alle/page/195.
2. ↑ "IAU Catalog of Star Names". http://www.pas.rochester.edu/~emamajek/WGSN/IAU-CSN.txt.
3. ↑ Kunitzsch, Paul (1986). "The Star Catalogue Commonly Appended to the Alfonsine Tables". Journal for the History of Astronomy 17 (49): 89–98. doi:10.1177/002182868601700202. Bibcode: 1986JHA....17...89K.
4. ↑ Kunitzsch, Paul; Smart, Tim (2006). A Dictionary of Modern star Names: A Short Guide to 254 Star Names and Their Derivations (2nd rev. ed.). Cambridge, Massachusetts: Sky Pub. ISBN 978-1-931559-44-7.
5. ↑ James, Andrew (2015-06-17). "The Constellations : Part 3 Culmination Times". http://www.southastrodel.com/Page20502.htm.
6. ↑ 6.0 6.1 Smith, C. E. (1937). "Stars of the Summer Sky". Astronomical Society of the Pacific Leaflets 3 (102): 23. Bibcode: 1937ASPL....3...23S.
7. ↑ Pasachoff, J. M. (2000). A Field Guide to Stars and Planets (4th ed.). Houghton Mifflin. ISBN 978-0-395-93431-9.
8. ↑ Upgren, A. R. (1998). Night Has a Thousand Eyes: A Naked-Eye Guide to the Sky, Its Science, and Lore. Basic Books. ISBN 978-0-306-45790-6.
9. ↑ 9.0 9.1 Lee, O. J. (March 1910). "Four stars having variable radial velocities". Astrophysical Journal 31: 176–179. doi:10.1086/141741. Bibcode: 1910ApJ....31..176L.
10. ↑ 10.0 10.1 Abt, Helmut A. (July 1957). "The Variability of Supergiants". Astrophysical Journal 126: 138. doi:10.1086/146379. Bibcode: 1957ApJ...126..138A.
11. ↑ Struve, Otto; Huang, S. S. (October 1954). "The Stationary Calcium Lines of Alpha Cygni". Publications of the Astronomical Society of the Pacific 66 (392): 251. doi:10.1086/126710. Bibcode: 1954PASP...66..251S.
12. ↑ Kaler, James B. (1998-06-19). "Deneb". http://stars.astro.illinois.edu/sow/deneb.html.
13. ↑ Barlow, N. G. (2008). Mars: An introduction to its interior, surface and atmosphere. Cambridge University Press. p. 21. ISBN 978-0-521-85226-5. https://archive.org/details/marsintroduction00barl_258.
14. ↑ Wagle, Gururaj A.; Ray, Alak; Raghu, Adarsh (2020-05-01). "Type IIP Supernova Progenitors III: Blue to Red Supergiant Ratio in Low Metallicity Models with Convective Overshoot". The Astrophysical Journal 894 (2): 118. doi:10.3847/1538-4357/ab8bd5. ISSN 0004-637X. Bibcode: 2020ApJ...894..118W.
15. ↑ Cite error: Invalid `<ref>` tag; no text was provided for refs named `baas25_1319`
16. ↑ Aufdenberg, J. P.; Hauschildt, P. H.; Baron, E.; Nordgren, T. E.; Burnley, A. W.; Howarth, I. D.; Gordon, K. D.; Stansberry, J. A. (2002). "The Spectral Energy Distribution and Mass-Loss Rate of the A-Type Supergiant Deneb". The Astrophysical Journal 570 (1): 344. doi:10.1086/339740. Bibcode: 2002ApJ...570..344A.
17. ↑ 17.0 17.1 17.2 Cite error: Invalid `<ref>` tag; no text was provided for refs named `schiller`
18. ↑ Perryman, M. A. C.; Lindegren, L.; Kovalevsky, J.; Hoeg, E.; Bastian, U.; Bernacca, P. L.; Crézé, M.; Donati, F. et al. (1997). "The Hipparcos Catalogue". Astronomy and Astrophysics 323: L49–L52. Bibcode: 1997A&A...323L..49P.
19. ↑ Perryman, M. (2010). The Making of History's Greatest Star Map (Submitted manuscript). Astronomers' Universe. Springer-Verlag. doi:10.1007/978-3-642-11602-5. ISBN 978-3-642-11601-8. Bibcode: 2010mhgs.book.....P. https://cds.cern.ch/record/1338896.
20. ↑ 20.0 20.1 Van Leeuwen, F. (2007). "Validation of the new Hipparcos reduction". Astronomy and Astrophysics 474 (2): 653–664. doi:10.1051/0004-6361:20078357. Bibcode: 2007A&A...474..653V.
21. ↑ van de Kamp, P. (1953). "The Twenty Brightest Stars". Publications of the Astronomical Society of the Pacific 65 (382): 30. doi:10.1086/126523. Bibcode: 1953PASP...65...30V.
22. ↑ Lamers, H. J. G. L. M.; Stalio, R.; Kondo, Y. (1978). "A study of mass loss from the mid-ultraviolet spectrum of α Cygni (A2 Ia), β Orionis (B8 Ia), and η Leonis (A0 Ib)". The Astrophysical Journal 223: 207. doi:10.1086/156252. Bibcode: 1978ApJ...223..207L.
23. ↑ 23.0 23.1 Chesneau, O.; Dessart, L.; Mourard, D.; Bério, Ph.; Buil, Ch.; Bonneau, D.; Borges Fernandes, M.; Clausse, J. M. et al. (2010). "Time, spatial, and spectral resolution of the Hα line-formation region of Deneb and Rigel with the VEGA/CHARA interferometer". Astronomy and Astrophysics 521: A5. doi:10.1051/0004-6361/201014509. Bibcode: 2010A&A...521A...5C. https://hal.archives-ouvertes.fr/hal-00501515.
24. ↑ Kaler, James B. (2017). "The 172 Brightest Stars". STARS. http://stars.astro.illinois.edu/sow/bright.html.
25. ↑ 25.0 25.1 25.2 Georgy, Cyril; Saio, Hideyuki; Meynet, Georges (2014). "The puzzle of the CNO abundances of α Cygni variables resolved by the Ledoux criterion". Monthly Notices of the Royal Astronomical Society: Letters 439 (1): L6–L10. doi:10.1093/mnrasl/slt165. Bibcode: 2014MNRAS.439L...6G.
26. ↑ 26.0 26.1 26.2 Yüce, K.; Adelman, S..J. (2019). "On the variability of the A0 supergiants 9 Per, HR 1035, 13 Mon, Deneb, and HR 8020 as seen in FCAPT Strömgren photometry". New Astronomy 66: 88–99. doi:10.1016/j.newast.2018.07.002. Bibcode: 2019NewA...66...88Y.
27. ↑ 27.0 27.1 Richardson, N. D.; Morrison, N. D.; Kryukova, E. E.; Adelman, S. J. (2011). "A Five-year Spectroscopic and Photometric Campaign on the Prototypical α Cygni Variable and A-type Supergiant Star Deneb". The Astronomical Journal 141 (1): 17. doi:10.1088/0004-6256/141/1/17. Bibcode: 2011AJ....141...17R.
28. ↑ "GCVS Query forms". http://www.sai.msu.su/gcvs/cgi-bin/search.cgi?search=alf+Cyg.
29. ↑ Kholopov, P. N.; Samus', N. N.; Frolov, M. S.; Goranskij, V. P.; Gorynya, N. A.; Kireeva, N. N.; Kukarkina, N. P.; Kurochkin, N. E. et al. (1996). "VizieR Online Data Catalog: General Catalog of Variable Stars, 4th Ed. (GCVS4) (/gcvs4Kholopov+ 1988)". VizieR On-line Data Catalog: II/139B. Originally Published in: Moscow: Nauka Publishing House (1985–1988) 2139: 0. Bibcode: 1996yCat.2139....0K.
30. ↑ 30.0 30.1 Lucy, L. B. (1976). "An analysis of the variable radial velocity of alpha Cygni". Astrophysical Journal 206: 499. doi:10.1086/154405. Bibcode: 1976ApJ...206..499L.
31. ↑ 陳久金 (2005). 中國星座神話. 五南圖書出版股份有限公司. ISBN 978-986-7332-25-7. https://books.google.com/books?id=0Vex0rYzdu8C.
32. ↑ "香港太空館 - 研究資源 - 亮星中英對照表"] (in zh). http://www.lcsd.gov.hk/CE/Museum/Space/Research/StarName/c_research_chinengstars_c_d.htm.
33. ↑ "Ceph at RAL". CERN Indico. https://indico.cern.ch/event/995485/contributions/4263422/attachments/2209923/3740064/CephAtRAL.pdf. Retrieved 23 December 2025.

Coordinates:  20h 41m 25.9s, +45° 16′ 49″

* v
* t
* e

Constellation of Cygnus

* List of stars in Cygnus

Stars|

| Bayer|

* α (Deneb)
* β (Albireo)
* γ (Sadr)
* δ (Fawaris)
* ε (Aljanah)
* ζ
* η
* θ
* ι1
* ι2
* κ
* λ
* μ
* ν
* ξ
* π1 (Azelfafage)
* π2
* ρ
* σ
* τ
* υ
* φ
* χ
* ψ
* ω1
* ω2
* P
* Q

|

Flamsteed|

* 2
* 4
* 8
* 9
* 14
* 15
* 16 (c)
* 17
* 20 (d)
* 22
* 23
* 26 (e)
* 27 (b1)
* 28 (b2)
* 29 (b3)
* 30
* 31
* 32
* 33
* 35
* 39
* 41
* 47
* 52
* 55
* 56
* 57
* 59 (f1)
* 61
* 63 (f2)
* 68 (A)
* 71 (g)
* 72
* 74
* 75

Variable|

* R
* T
* W
* RW
* SS
* TT
* BC
* BI
* CH
* KY
* V404
* V476
* V1057
* V1143
* V1191
* V1489
* V1500
* V1668
* V1974
* V2513

HR|

* 7633
* 7912
* 8193

HD|

* 185269
* 185435
* 187123
* 188753
* 191806

Gliese|

* 777
* 806
* 1245

Kepler|

* 5
* 6
* 11
* 15
* 16
* 17
* 18
* 22
* 23
* 27
* 28
* 29
* 31
* 32
* 33
* 34
* 35
* 36
* 39
* 40
* 41
* 42
* 43
* 44
* 45
* 47
* 51
* 56
* 61
* 66
* 67
* 68
* 69
* 70
* 78
* 80
* 84
* 86
* 89
* 107
* 182
* 186
* 223
* 371
* 419
* 432
* 451
* 452
* 1229
* 1520
* 1625

Other|

* AFGL 2591
* BD+40° 4210
* BD+43 3654
* Cygnus OB2 #8A
* Cygnus OB2 #12
* Cygnus X-1
* Cygnus X-3
* G 208-44
* G 208-45
* HAT-P-7
* HAT-P-11
* HAT-P-17
* KELT-9
* KIC 8462852
* KIC 9832227
* KIC 11026764
* KOI-74
* KOI-81
* KOI-256
* KPD 1930+2752
* MWC 349
* N6946-BH1
* NML Cygni
* PH1
* PSR J2032+4127
* W75N(B)-VLA2
* WISE J2000+3629
* WR 134
* WR 135
* WR 136
* WR 137
* WR 140
* WR 142
* WR 147
* WR 148

Former|

* 3

Star
clusters|

| Association|

* Cygnus OB2
* Cygnus OB7

|

Open|

* DR 6
* IC 5146
* Messier 29
* Messier 39
* NGC 6811
* NGC 6819
* NGC 6834
* NGC 6866
* NGC 6871
* NGC 6910

Molecular
clouds|

* Cygnus X (including DR 21)

Nebulae|

| Dark|

* Barnard 146
* Barnard 147
* IC 5146
* L1014

|

H II|

* NGC 6914
* North America Nebula
* Pelican Nebula
* Sadr Region
* Sh2-101
* Sh2-106

Planetary|

* Abell 78
* Egg Nebula
* IRAS 19475+3119
* Kronberger 61
* M1-92
* NGC 6826
* NGC 6881
* NGC 6884
* NGC 7008
* NGC 7026
* NGC 7027
* NGC 7048
* Soap Bubble Nebula

WR|

* Crescent Nebula

SNR|

* Cygnus Loop (including Veil Nebula)

Galaxies|

| NGC|

* 6801
* 6946
* 7013

|

Other|

* 3C 438
* Cygnus A

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