Of all known multiple star systems consisting of at least three stars, probably the finest and most celebrated of all is Epsilon Lyrae (ε Lyr). This system, also known as the "Double Double" offers something for everyone from naked-eye observers to those with large telescopes.
Epsilon Lyrae is located in the constellation of Lyra, close to bright star, Vega (mag. 0.0). For Northern Hemisphere observers, Vega appears high in the sky during the summer months. Epsilon Lyrae is positioned about 1.5 degrees northeast of this star. At first glance, mag. +3.9, Epsilon Lyrae doesn't appear very remarkable. However, on further inspection you may notice a close double star of two almost identical white components. This pair of stars, named Epsilon1 Lyrae and Epsilon2 Lyrae, have a separation of 208 arc seconds with a position angle of 172 degrees. It's often said if you can split the famous Mizar / Alcor pair in Ursa Major with the naked eye then you have good eyesight. With a separation of 708 arc seconds the Mizar / Alcor pair is a piece of cake to split compared to the much tighter Epsilon1 / Epsilon2 Lyrae pair. Split the latter and you need not worry, your eyesight is of the highest order.
Even if you can't split Epsilon Lyrae with the naked eye it's easy with binoculars. The northern star of the pair is Epsilon1, the southern star, Epsilon2. In addition, both stars are doubles themselves hence the nickname, the "Double Double". A small 80mm refractor at about 120x magnification will show the four components. In larger instruments, such as 200m (8-inch) reflectors, the view is similar to smaller scopes except the pairs appear brighter and easier to split. All four stars are off white in colour.
The component stars of Epsilon1 are of magnitudes +5.15 and +6.10, separated by 2.3 arc seconds at a position angle of 347 degrees. The two stars of Epsilon2 are fractionally further apart at 2.4 arc seconds with magnitudes of +5.25 and +5.38. The current position angle of these stars is 79 degrees. All four stars are gravitationally bound and it's estimated that the two components of Epsilon1 take 1,200 years to complete one orbit, compared to 585 years for the stars of Epsilon2. The two pairs themselves are separated by 0.16 light-years, but at such a distance they take thousands of years to orbit each other.
The Epsilon Lyrae system is located 162 light-years from Earth. An observer at one pair of the stars would see the other pair shining with the light of a quarter Moon, less than a degree apart. In 1985, a fifth component of the system orbiting one of the Epsilon2 stars was detected by speckle interferometry. In addition, there are some other nearby stars that may also be members.
Epsilon Lyrae Data Table
|Epsilon1 Lyrae||Epsilon2 Lyrae|
|Flamsteed||4 Lyr||5 Lyr|
|RA (J2000)||18h 44m 20s||18h 44m 23s|
|DEC (J2000)||+39d 40m 12s||+39d 36m 46s|
|Other Designation||WDS 18443+3940|
|Component Stars||A and B||C and D|
|Component Stars Mag.||A = +5.15, B = +6.10||C = +5.25, D = +5.38|
|Component Stars Separation (arc seconds)||AB = 2.3||CD = 2.4|
|Component Stars Position Angle (degrees)||AB = 347||CD = 79|
|Epsilon1 Lyrae / Epsilon2 Lyrae Separation (arc seconds)||AB / CD = 208|
|Epsilon1 Lyrae / Epsilon2 Lyrae Position Angle (degrees)||AB / CD = 172|