Epoch J2000 Equinox J2000
|Right ascension||19h 44m 58.47854s|
|Declination||+45° 07′ 50.9161″|
|Apparent magnitude (V)||2.87|
|Spectral type||B9 III + F1 V|
|U−B color index||–0.10|
|B−V color index||–0.02|
|Radial velocity (Rv)||–20.1 km/s|
|Proper motion (μ)||RA: +44.07 mas/yr
Dec.: +48.66 mas/yr
|Parallax (π)||19.77 ± 0.48 mas|
|Distance||165 ± 4 ly
(51 ± 1 pc)
|Surface gravity (log g)||3.49 cgs|
|Rotational velocity (v sin i)||135 km/s|
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. Consequently, δ Cygni itself is known as 天津二 (Tiān Jīn èr, English: the Second Star of Celestial Ford.)
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, 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. 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.
The other seven stars are
- Tau Herculis (of Hercules),
- Vega (of Lyra),
- Alpha Cephei (of Cepheus),
- Gamma Cephei (of Cepheus),
- Polaris (of Ursa Minor),
- Kappa Draconis (of Draco), and
- Alpha Draconis (of Draco).
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