Eltanin (Gamma Draconis)
Eltanin (Gamma Draconis) is a star in the constellation Draco, magnitude 2.2.
London’s zenith star — where the hunt for a parallax revealed that Earth is moving.
Eltanin passes almost straight overhead in London, which made it the ideal target for a great prize of 17th- and 18th-century astronomy: measuring a star’s parallax. Robert Hooke tried. In 1728 James Bradley tried too, and failed — but the star’s tiny yearly shifts revealed something else. Bradley had discovered the aberration of light, caused by the Earth’s motion around the Sun. George Airy later called Eltanin “the birth-star of modern astronomy”.
Its name comes from the Arabic for “the great serpent”, and despite its gamma label it is the brightest star in Draco. It is an orange giant about twice the Sun’s mass, some 50 times wider and 600 times as luminous.
Eltanin is heading our way. In about 1.5 million years it will pass much closer and, for a time, become the brightest star in the night sky — nearly as bright as Sirius is now.
Eltanin (Gamma Draconis) is 150 light-years away: the light we see from it set off around 1875, around the time Edison lit his first practical light bulb — the start of light pollution.
Did you know?
- A planet that wasn’t. Regular shifts in its spectrum were once blamed on an orbiting planet. They turned out to come from the star itself — a warning for planet hunters studying other giants, such as Aldebaran.
- Le Guin’s world. Ursula K. Le Guin set her novel Planet of Exile on the third planet of Eltanin.
- The Mother Camels. Arab astronomers saw Eltanin and four neighbours as the Mother Camels, a group later known in Latin as the Quinque Dromedarii.
An orange 2nd-magnitude star, the brightest of the four-star lozenge that forms the head of Draco. Find it north-north-west of Vega; its warm colour contrasts with Vega’s blue-white.
When and where to see it
It is best placed in the evening sky around July, when it crosses the meridian at about 10 pm local time (around midnight in June). It can be seen from everywhere north of 39°S and never sets north of 39°N.
At its highest it stands 89° up from 50°N, 74° up from 35°N, 39° up from the equator, 4° up from 35°S.
Facts
- Type
- Star
- Constellation
- Draco
- Designations
- Gamma Draconis, γ Dra, 33 Dra, HR 6705, HD 164058, HIP 87833
- Magnitude
- 2.2
- Position
- RA 17h 56.6m, Dec +51° 29′ (J2000)
- Spectral type
- K5III
- Colour
- orange-red (B−V 1.53)
- Distance
- 150 light-years
- Discovered
- Known since antiquity
Open AstroPilot to see when Eltanin (Gamma Draconis) is highest tonight from your location, how easy it is with your telescope or binoculars, and an eyepiece view.