Delta Cygni

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Delta Cygni
Diagram showing star positions and boundaries of the Cygnus constellation and its surroundings
Cercle rouge 100%.svg

Location of δ Cygni (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Cygnus
Right ascension 19h 44m 58.47854s[1]
Declination +45° 07′ 50.9161″[1]
Apparent magnitude (V) 2.87[2]
Spectral type B9 III + F1 V[3]
U−B color index –0.10[4]
B−V color index –0.02[4]
Radial velocity (Rv) –20.1[5] km/s
Proper motion (μ) RA: +44.07[1] mas/yr
Dec.: +48.66[1] mas/yr
Parallax (π) 19.77 ± 0.48[1] mas
Distance 165 ± 4 ly
(51 ± 1 pc)
Mass 2.93 M
Radius 5.13 R
Luminosity 155 L
Surface gravity (log g) 3.49 cgs
Temperature 10,150 K
Rotational velocity (v sin i) 135[7] km/s
Other designations
18 Cygni, 18 Cyg, BD+44 3234, HD 186882, HIP 97165, HR 7528, SAO 48796.
Database references

Delta Cygni (δ Cygni, δ Cyg) is the third-magnitude star in the constellation Cygnus. It will be the "North Star" for at least four centuries around 11,250.

This star belonged to the Arabic asterism al-Fawāris (الفوارس), meaning "the Riders" in indigenous Arabic,[8] together with ζ, ε, and γ Cyg, the transverse of the Northern Cross.

In Chinese, 天津 (Tiān Jīn), meaning Celestial Ford, refers to an asterism consisting of δ Cygni, γ Cygni, 30 Cygni, α Cygni, ν Cygni, τ Cygni, υ Cygni, ζ Cygni and ε Cygni.[9] Consequently, δ Cygni itself is known as 天津二 (Tiān Jīn èr, English: the Second Star of Celestial Ford.)[10]


Delta Cygni is a triple star; the system lies at a distance of about 170 light years and consists of two stars quite close together and one much farther out. This sort of common configuration lends stability.

The bright naked-eye star is a blue-white giant of spectral class B9,[3] with a temperature of 10,500 K. It is nearing the end of its main-sequence life stage with a luminosity 155 times that of the Sun, a radius of 5.13 solar radii, and a mass approximately 2.93 solar masses.[6] Like many hot stars, it spins rapidly, at least 135 kilometers per second at the equator, about 60 times that of the Sun. Its close companion is a yellow-white class F of the sixth magnitude (6.33) with a luminosity about 6 times that of the sun, and a mass about 1.5 times that of the sun. The much more distant third companion is an orange (class K) twelfth magnitude star, being only 38% as luminous as the sun, and only 70% as massive as the sun. As seen from Earth, the entire triple star system of Delta Cygni shines at a combined apparent magnitude of 2.86.

'North star'[edit]

It is one of eight bright stars in the northern hemisphere that lay claim to the position of "North Star"[citation needed] over the course of Earth's 26,000-year precession cycle.

The other seven stars are

See also[edit]


  1. ^ a b c d e van Leeuwen, F. (November 2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics, 474 (2): 653–664, arXiv:0708.1752Freely accessible, Bibcode:2007A&A...474..653V, doi:10.1051/0004-6361:20078357 
  2. ^ Malagnini, M. L.; Morossi, C. (November 1990), "Accurate absolute luminosities, effective temperatures, radii, masses and surface gravities for a selected sample of field stars", Astronomy and Astrophysics Supplement Series, 85 (3): 1015–1019, Bibcode:1990A&AS...85.1015M 
  3. ^ a b Edwards, T. W. (April 1976), "MK classification for visual binary components", Astronomical Journal, 81: 245–249, Bibcode:1976AJ.....81..245E, doi:10.1086/111879 
  4. ^ a b Johnson, H. L.; et al. (1966), "UBVRIJKL photometry of the bright stars", Communications of the Lunar and Planetary Laboratory, 4 (99), Bibcode:1966CoLPL...4...99J 
  5. ^ Evans, D. S. (June 20–24, 1966), Batten, Alan Henry; Heard, John Frederick, eds., The Revision of the General Catalogue of Radial Velocities, University of Toronto: International Astronomical Union, Bibcode:1967IAUS...30...57E 
  6. ^ a b Challouf, M.; et al. (2014), "Improving the surface brightness-color relation for early-type stars using optical interferometry⋆", Astronomy & Astrophysics, 570: A104, arXiv:1409.1351Freely accessible, Bibcode:2014A&A...570A.104C, doi:10.1051/0004-6361/201423772. 
  7. ^ Abt, Helmut A.; Levato, Hugo; Grosso, Monica (July 2002), "Rotational Velocities of B Stars", The Astrophysical Journal, 573 (1): 359–365, Bibcode:2002ApJ...573..359A, doi:10.1086/340590 
  8. ^ Allen, R. H., (1963). Star Names: Their Lore and Meaning (Reprint ed.). New York, NY: Dover Publications Inc. pp. 193, 197. ISBN 0-486-21079-0. 
  9. ^ (Chinese) 中國星座神話, written by 陳久金. Published by 台灣書房出版有限公司, 2005, ISBN 978-986-7332-25-7.
  10. ^ (Chinese) AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 7 月 4 日

External links[edit]