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 2.6[2] M
Radius 2.8[2] R
Luminosity 76[2] L
Surface gravity (log g) 3.95[2] cgs
Temperature 10,120 ± 160[2] K
Rotational velocity (v sin i) 135[6] km/s
Other designations
18 Cygni, 18 Cyg, BD+44 3234, HD 186882, HIP 97165, HR 7528, SAO 48796.

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.,[7] 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.[8] Consequently, δ Cygni itself is known as 天津二 (Tiān Jīn èr, English: the Second Star of Celestial Ford.)[9]


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 9,800 kelvins. It is nearing the end of its main-sequence life stage with a luminosity 180 times that of the Sun, a radius of 4.7 solar radii, and a mass approximately 3.15 solar masses. 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:0708.1752free to read, Bibcode:2007A&A...474..653V, doi:10.1051/0004-6361:20078357 
  2. ^ a b c d e f 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. ^ 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 
  7. ^ 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. 
  8. ^ (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.
  9. ^ (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]