Eltanin, Etamin
| Right Ascension | 17 : 56 : 36.3 (h:m:s) |
|---|---|
| Declination | +51 : 29 : 20 (deg:m:s) |
| Distance | 100 (ly) |
| Visual brightness | 2.23 (mag) |
| Spectral type | K5III |
Eltanin became famous when in 1728, James Bradley discovered the aberration of light, due to Earth's motion and the finite velocity of light, from observations of this star.
This star is a red giant (its color best indicated by the color index, B-V, of 1.5) at distance 100 light years (according to the Sky Catalogue 2000.0; Michael E. Bakich, in The Cambridge Guide to the Constellations, gives the slightly higher value of 130 light years, others some value between). Therefore, its absolute magnitude is about -0.4 (or up to -0.8), corresponding to a luminosity roughly 100 times that of our sun. Robert Burnham, Jr. mentions measurements of a variablility in a 0.08 magnitudes range. The star shows an annual proper motion of 0.025" and is approaching us at 26 km/sec.
R.G. Aitken lists Gamma Draconis in his New General Catalogue of Double Stars as ADS 10923 with 6 optical companions: B (mag 13.2, separation 20.9", position angle 151 deg), C (12.7, 48", PA 230), D (12.7, 56", PA 14), E (11.7, 97", PA 235), F (11.0, 125", PA 116), and G (11.7, 140", PA 28).
The name Eltanin comes from Arabic and means "The Snake" or "The Dragon." According to R.H. Allen, several temples in ancient Egypt have been oriented toward it, including one in Thebes, the "city of the Dragon". Admiral Smyth (his entry No. 629 in the Bedford Catalog) writes that it may come from arabic "Ras-el-tannin", the Head of the Dragon. He mentions that this star bears the name "Rasaben" in the Alphonsine Tables, and that Scalinger has interpreted it as "Ras-al-thu'ban", or Head of the Devouring Basilisk.