Delta Cygni

From Wikipedia, the free encyclopedia

**Delta Cygni**
Observation data Equinox J2000
Constellation	Cygnus
Right ascension	19^h 44^m 58.5^s
Declination	+45° 7′ 51″
Apparent magnitude (V)	2.86
Characteristics
Spectral type	B9.5IV+F1V
U-B color index	0.49
B-V color index	0.582
Variable type	no
Astrometry
Proper motion (μ)	RA: 0.053 mas/yr Dec.: 0.047 mas/yr
Parallax (π)	19.07 ± 0.45 mas
Distance	171 ± 4 ly (52 ± 1 pc)
Absolute magnitude (M_V)	-0.74
Details
Mass	3.15 M_☉
Radius	4.7 R_☉
Luminosity	180 L_☉
Temperature	9,800 K
Metallicity	?
Rotation	135 km/s.
Age	? years
Other designations
Rukh, Urakhga, Al Fawaris, 18 Cyg, HR 7528, HD 186882, SAO 48796, BD +44 3234, FK5 000, HIP 97165.

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

1 Naming
2 Features
3 'North star'
4 External links

[edit] Naming

This star has carried the now obsolete proper names Ruc (Rukh) and Urakhga, both of which refer to the Roc, a mythical flying bird of enormous size and strength. The names رخ Rukh and Urakhga are Persian and Akkadian, respectively. Ancient Mesopotamians, as well as Persians and Arabians of antiquity, portrayed the constellation Cygnus as the Roc flying in mid-air with its wings stretched out.

Another name is Al Fawaris (الفوارس), meaning "The Riders"; named after an ancient Arabic asterism in Cygnus that included Delta Cygni.

[edit] Features

Delta Cygni is prominent in a great constellation, and is a triple star. This system lies at a distance of 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 B9.5, 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. It's 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.

[edit] 'North star'

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

The other seven stars are