Deneb
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 Cygnus, the constellation in which Deneb is located. |
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| Observation data Epoch J2000 |
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|---|---|
| Constellation (pronunciation) |
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: 1.56 mas/yr Dec.: 1.55 mas/yr |
| Parallax (π) | 1.01 ± 0.57 mas |
| Distance | approx. 3000 ly (approx. 1000 pc) |
| Absolute magnitude (MV) | −8.73 |
| Other designations | |
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 white supergiant, Deneb is also one of the most luminous stars known. It is, or has been, known by a number of other traditional names, including Arided and Aridif, but today these are almost entirely forgotten.
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[edit] Distance and physical characteristics
Deneb's absolute magnitude is about −8.5, placing it among the most luminous stars known.
Deneb's exact distance from the Earth is uncertain. The most likely distance is 3,200 light-years, but the parallax uncertainties do not rule out a distance as close as 2,100 light-years or as far as 7,400 light-years. This distance uncertainty makes determining many of Deneb's other properties similarly imprecise. Deneb is a blue-white colored star.
Deneb is the farthest first-magnitude star from Earth.
Estimates for Deneb's luminosity range from about 60,000 times the brightness of our Sun (if Deneb is 1600 light-years away) to 250,000 times the Sun's brightness (if 3,200 light-years away).[2]
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 to 300 times that of the Sun; if placed at the center of our Solar System, Deneb would extend to the orbit of the Earth.[3] It is one of the largest stars known and the most powerful class A star identified.
A star of spectral type A2Ia, Deneb has a surface temperature of 8,400 kelvins. Deneb 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 to 25 solar masses.[4][3] As a white supergiant, its high mass and temperature mean that the star will have a short lifespan and will probably become a supernova within a few million years. It has already stopped fusing hydrogen in its core.
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.[3]
[edit] Etymology and cultural significance
The name Deneb is derived from dhaneb, the Arabic for "tail", from the phrase ذنب الدجاجة Dhanab ad-Dajājah, or "tail of the hen".[5] 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.[5]
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 across the bridge of magpies.
