Alpha Draconis
 Location of Thuban (circled) |
|
| Observation data Epoch J2000 Equinox J2000 |
|
|---|---|
| Constellation | Draco |
| Right ascension | 14h 04m 23.3498s |
| Declination | 64° 22′ 33.062″ |
| Apparent magnitude (V) | 3.6452 |
| Characteristics | |
| Spectral type | A0III |
| U−B color index | -0.08 |
| B−V color index | -0.04 |
| Variable type | suspected Maia |
| Astrometry | |
| Radial velocity (Rv) | -13.0 km/s |
| Proper motion (μ) |
RA: -56.34 mas/yr Dec.: 17.21 mas/yr |
| Parallax (π) | 10.76 ± 0.17 mas |
| Distance | 303 ± 5 ly (93 ± 1 pc) |
| Absolute magnitude (MV) | −1.20 |
| Orbit | |
| Period (P) | 51.4167 days |
| Semi-major axis (a) | 0.46 AU |
| Eccentricity (e) | 0.4355 ± 0.0042 |
| Inclination (i) | 90° |
|
Semi-amplitude (K1) (primary) |
47.9340 ± 0.2990 km/s |
| Details | |
| α Dra A | |
| Mass | 2.8 M☉ |
| Radius | 3.4 R☉ |
| Luminosity | 479 L☉ |
| Surface gravity (log g) | 3.5 cgs |
| Temperature | 10,100 K |
| Metallicity | −0.20 |
| Rotation | 26.2 |
| α Dra B | |
| Mass | 2.6 M☉ |
| Luminosity | 40 L☉ |
| Other designations | |
| Database references | |
| SIMBAD | data |
Thuban, also designated Alpha Draconis (α Draconis, abbreviated Alpha Dra, α Dra), is a star (or star system) in the constellation of Draco. A relatively inconspicuous star in the night sky of the Northern Hemisphere, it is historically significant as having been the north pole star from the 4th to 2nd millennium BC.
Even though Johann Bayer gave Thuban the designation Alpha, its apparent magnitude of 3.65 means it is 3.7 times fainter than the brightest star in the constellation, Gamma Draconis (Eltanin), whose apparent magnitude is 2.24.
α Draconis (Latinised to Alpha Draconis) is the star's Bayer designation.
The traditional name Thuban is derived from the Arabic Arabic: ثعبان thuʿbān 'snake'. It is sometimes known as the Dragon's Tail and as Adib. In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN) to catalog and standardize proper names for stars. The WGSN's first bulletin of July 2016 included a table of the first two batches of names approved by the WGSN; which included Thuban for this star. It is now so entered in the IAU Catalog of Star Names.
In Chinese, 紫微右垣 (Zǐ Wēi Yòu Yuán), meaning Right Wall of Purple Forbidden Enclosure, refers to an asterism consisting of Alpha Draconis, Kappa Draconis, Lambda Draconis, 24 Ursae Majoris, 43 Camelopardalis, Alpha Camelopardalis and BK Camelopardalis. Consequently, Alpha Draconis itself is known as 紫微右垣一 (Zǐ Wēi Yòu Yuán yī, English: the First Star of Right Wall of Purple Forbidden Enclosure.), representing 右樞 (Yòushū), meaning Right Pivot. 右樞 (Yòushū) is westernized into Yu Choo by R.H. Allen with the same meaning.
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