Deneb

Deneb^[1]

Cygnus, the constellation in which Deneb is located.
Observation data Epoch J2000      Equinox J2000
Constellation	Cygnus
Right ascension	20h 41m 25.9s
Declination	+45° 16' 49"
Apparent magnitude (V)	1.25
Characteristics
Spectral type	A2 Ia
U-B color index	−0.24
B-V color index	+0.09
Variable type	Alpha Cyg
Astrometry
Radial velocity (Rv)	−4.5 km/s
Proper motion (μ)	RA: 1.99 mas/yr Dec.: 1.95 mas/yr
Parallax (π)	2.29 ± 0.32 mas
Distance	approx. 1400 ly (approx. 440 pc)
Absolute magnitude (MV)	−6.95
Details
Mass	~20 M☉
Radius	108 to 114 R☉
Luminosity	~54.400 L☉
Temperature	8,525 K
Rotational velocity (v sin i)	-4.5 km/s
Other designations
α Cygni, Alpha Cyg, 50 Cyg, Arided, Aridif, Gallina, Arrioph, HR 7924, BD +44°3541, HD 197345, SAO 49941, FK5: 777, HIP 102098.

Deneb (α Cyg / α Cygni / Alpha Cygni) is the brightest star in the constellation Cygnus and one of the vertices of the Summer Triangle. It is the 19th brightest star in the night sky, with an apparent magnitude of 1.25. A blue-white supergiant, Deneb is also one of the most luminous nearby stars. It is, or has been, known by a number of other traditional names, including Arided and Aridif, but today these have fallen out of use.

Distance and physical characteristics

Deneb's absolute magnitude is about −7, placing it among the most luminous stars known, with an estimated luminosity 60,000 times that of our Sun.^[2]

Deneb's exact distance from the Earth is uncertain, which makes determining many of Deneb's other properties similarly imprecise. However, the uncertainty has been dramatically reduced upon analysis of the New Hipparcos Data Reduction in 2007. One 2008 study puts the most likely distance at approximately 1,550 light-years, and the reduced parallax uncertainties do not rule out a distance as close as 1,340 light-years or as far as 1,840 light-years ^[3] It is the farthest first-magnitude star from Earth.

Estimates for Deneb's radius range from 200 to 300 times that of the Sun. This is the approximate size of the Sun (right) relative to Deneb.

Based on its temperature and luminosity and also on direct measurements of its tiny angular diameter (a mere 0.002 second of arc), Deneb appears to have a diameter about 200 times that of the Sun; if placed at the center of our Solar System, Deneb would extend to the orbit of the Earth.^[4] It is one of the largest white stars known.

Deneb is a blue-white colored star of spectral type A2Ia, with a surface temperature of 8,400 Kelvin. It is the prototype of a class of variable stars known as Alpha Cygni variables. Its surface undergoes non-radial fluctuations which cause its brightness and spectral type to change slightly.

Deneb's mass is estimated at 20 solar masses.^[5][4] As a blue-white supergiant, its high mass and temperature mean that the star will have a short lifespan and will probably go supernova within a few million years. It has already stopped fusing hydrogen in its core. The star was probably an O class star during its main sequence lifetime and is now likely expanding into a red supergiant like Mu Cephei. As it expands, it will go through the F, G, K and M spectral types.

Deneb's solar wind causes it to lose mass at a rate of 0.8 millionth of a solar mass per year, a hundred thousand times the flow rate from the Sun.^[4]

Etymology and cultural significance

The name Deneb is derived from dhaneb, the Arabic for "tail", from the phrase ذنب الدجاجة Dhanab ad-Dajāja^h, or "tail of the hen".^[6] Similar names were given to at least seven different stars, most notably Deneb Kaitos, the brightest star in the constellation Cetus, and Denebola, the second brightest star in Leo.

Less contracted names include Deneb Adige, Denebadigege, and Denebedigege. Arided was used in the Alfonsine Tables, this latter name derived from Al Ridhādh, a name for the constellation. Johann Bayer called it Arrioph, derived from Aridf and Al Ridf, 'the hindmost' or Gallina. Caesius termed it Os rosae, or Rosemund in German, or Uropygium – the parson's nose.^[6]

It is known as 天津四 (the Fourth Star of the Celestial Ford) in Chinese. 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.

See also

• Deneb in fiction

References

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