Gamma Draconis

From Wikipedia, the free encyclopedia

**Gamma Draconis**
Observation data Epoch J2000
Constellation (pronunciation)	Draco
Right ascension	17^h 56^m 36.4^s
Declination	+51° 29′ 20.3″
Apparent magnitude (V)	2.24
Characteristics
Spectral type	K5 III
U-B color index	1.87
B-V color index	1.52
Variable type	?
Astrometry
Radial velocity (R_v)	-28 km/s
Proper motion (μ)	RA: -8.52 mas/yr Dec.: -23.05 mas/yr
Parallax (π)	22.10 ± 0.46 mas
Distance	148 ± 3 ly (45.2 ± 0.9 pc)
Absolute magnitude (M_V)	-1.04
Details
Mass	1.7 M_☉
Radius	50 R_☉
Luminosity	600 L_☉
Temperature	4,000 K
Metallicity	?
Rotation	<17 km/s.
Age	? years
Other designations
Etamin, Etanin, Ettanin, Rastaban, Rasaben, Zenith star, 33 Draconis, HR 6705, BD +51°2282, HD 164058, SAO 30653, FK5 676, HIP 87833.

Gamma Draconis (γ Dra / γ Draconis) is a star in the constellation Draco. It has the traditional name Eltanin (also Etamin).

Eltanin is an orange giant of spectral type K5, lying 148 light years away. Despite its Bayer designation of "gamma," it is actually the brightest star in Draco, outshining Rastaban (Beta Draconis) by nearly half a magnitude. In fact, the name "Rastaban" was formerly used for Eltanin, and the two terms share an Arabic root meaning "serpent" or "dragon." Its proximity to the point directly overhead of London has also earned it the name "Zenith Star."

In 1.5 million years, Eltanin will pass within 28 light years of Earth. At this point it will be the brightest star in the night sky, surpassing Sirius.

In 1728, while unsuccessfully attempting to measure the parallax of this star, James Bradley discovered the aberration of light resulting from the movement of the Earth. Bradley's discovery proved Copernicus' theory that the Earth revolved around the Sun.