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 (credit:- ESO Digitized Survey)

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.

Finder Chart for Epsilon Lyrae (credit:- freestarcharts)

Finder Chart for Epsilon Lyrae - pdf format (credit:- freestarcharts)

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.

Sketch of Epsilon Lyrae - 80mm refractor 120x (credit:- freestarcharts)

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 LyraeEpsilon2 Lyrae
HD173582173607
HIP9191991926
SAO6731067315
Flamsteed4 Lyr5 Lyr
ConstellationLyraLyra
RA (J2000)18h 44m 20s18h 44m 23s
DEC (J2000)+39d 40m 12s+39d 36m 46s
Apparent Mag.+4.67+4.59
Distance (light-years)162162
Spectral typeF1VA8Vn
Other DesignationWDS 18443+3940 
Component StarsA and BC and D
Component Stars Mag.A = +5.15, B = +6.10C = +5.25, D = +5.38
Component Stars Separation (arc seconds)AB = 2.3CD = 2.4
Component Stars Position Angle (degrees)AB = 347CD = 79
Epsilon1 Lyrae / Epsilon2 Lyrae Separation (arc seconds) AB / CD = 208 
Epsilon1 Lyrae / Epsilon2 Lyrae Position Angle (degrees) AB / CD = 172 

Sky Highlights - September 2017

Opposition
Neptune reaches opposition on September 5th

The Planets
This Month's Guide

Algol Minima
Algol eclipse dates and times for September

Northern Hemisphere
Evening
West:- Jupiter (mag. -1.7)
Southwest:- Saturn (mag. +0.5)
East:- Neptune (mag. +7.8)
Midnight
South:- Neptune
East:- Uranus (mag. +5.7)
Morning
West:- Neptune
South:- Uranus
East:- Venus (mag. -3.9), Mars (mag. +1.8) (from second week), Mercury (mag. +0.5 to -1.3) (from second week)

Southern Hemisphere
Evening
West:- Jupiter
Northwest:- Saturn
East:- Neptune
Midnight
West:- Saturn
North:- Neptune
Northeast:- Uranus
Morning
West:- Neptune
Northwest:- Uranus
Northeast:- Venus
East:- Mars (end of month)

Deep Sky

Small telescopes:-
Messier 13 - M13 - Great Hercules Globular Cluster
Messier 92 - M92 - Globular Cluster
Messier 11 - M11 - The Wild Duck Cluster (Open Cluster)
Messier 7 - M7 - The Ptolemy Cluster (Open Cluster)
Messier 6 - M6 - The Butterfly Cluster (Open Cluster)
Messier 4 - M4 - Globular Cluster
Messier 8 - M8 - Lagoon Nebula (Emission Nebula)
Messier 16 - M16 - Eagle Nebula (Emission Nebula with Open Cluster)
Messier 20 - M20 - Trifid Nebula (Emission and Reflection Nebula)

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