Deneb

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. Other names include Arided and Aridif, but these have fallen out of use.

Distance and physical characteristics

Deneb's absolute magnitude is approximately −7.0, placing it among the most luminous stars known, with an estimated luminosity nearly 60,000 times that of our Sun.^[3]

Deneb's exact distance from the Earth is uncertain, which makes determining many of Deneb's other properties similarly imprecise. However, the uncertainty was dramatically reduced upon analysis of the New Hipparcos Data Reduction in 2007. One 2008 study puts the most likely distance at 1,550 light-years, with an uncertainty of approximately 10%. 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.^[4] It is the farthest-known first-magnitude star from Earth.

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 of about 110 times that of the Sun; if placed at the center of our Solar System, Deneb would extend halfway out to the orbit of the Earth.^[2] It is one of the largest white stars known.

Deneb is a bluish-white 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.^[2][5] 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 probably 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.^[2]

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; Deneb Algedi, the brightest star in Capricornus; and Denebola, the second brightest star in Leo. All these stars are referring to the tail of the animals that their respective constellations represent.

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]

In Chinese, 天津 (Tiān Jīn), meaning Celestial Ford, refers to an asterism consisting of Deneb, γ Cygni, δ Cygni, 30 Cygni, ν Cygni, τ Cygni, υ Cygni, ζ Cygni and ε Cygni.^[7] Consequently, Deneb itself is known as 天津四 (Tiān Jīn sì, English: the Fourth Star of the Celestial Ford.).^[8]

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.

Deneb is the north pole star of Mars^[9].

Namesakes

USS Arided was a United States Navy Crater-class cargo ship named after the star.

See also

• Deneb in fiction

References

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