Although we are used to thinking of stars coming as individuals because our own Sun appears to be a lone star, this is not always true. In fact, binary or multiple star systems are very common in the Galaxy; surprisingly, they seem to be more plentiful than single stars such as the Sun.
One excellent example of a multiple star is Epsilon Lyrae, a quadruple system commonly known as the Double-Double.
To the average eye Epsilon Lyrae appears as a single star, but small binoculars or even keen eyesight show it to consist of a wide pair of 5th-magnitude stars. Nothing spectacular until now, but if you use an aperture of at least 3-inches and high power you will find that each star is itself a close double!
These two pairs where first noticed in 1779 by William Herschel, the famous musician turned astronomer. Here is his observing log entry: “A very curious double-double star. At first sight it appears double at some considerable distance, and by attending a little we see that each of the stars is a very delicate double star.”
The northern pair, called Epsilon 1, has a separation of 2.6 arcseconds. The component stars are physically connected and it probably takes something on the order of 1,200 years for them to complete one orbit. Epsilon 2 has a present separation of 2.3 arcseconds, and the two component stars are also physically connected, orbiting once every 600 years.
Besides providing two pairs for the price of one, Lyra’s Double-Double is a fine resolution test for small-aperture scopes. To get accurate results, choose a night with low atmospheric turbulence and try to observe using the highest magnification your scope can give.
Finder map – field width 10 degrees, stars to magnitude 8.5.