Our view of the stars as single points of light in the night sky is somewhat deceptive. Astronomers who scan the sky nightly with their telescopes have found that about one-third of all the stars we can see are double stars.
In such a binary star system, two stars revolve around their common center of gravity, some very slowly, others quite rapidly. Many star systems even contain multiple stars, some forming double-double stars and even more complex arrangements.
The evening sky contains many excellent examples of double-star and multiple-star systems. Albireo, for instance, is considered by many to be the finest double star to view through a small telescope. Located in the constellation of Cygnus, Albireo marks the beak of the swan. A small telescope or even a pair of binoculars readily splits Albireo into two tiny points of light—the brighter one a rich yellowish-orange, the other a deep azure blue. Because these two stars are estimated to be over 400 billion miles apart, astronomers once believed that they were merely an optical double and did not in fact orbit around a common center of gravity. We now know they are a true double-star system, with an orbital period on the order of 100,000 years.
Nearby to the west is the small constellation of Lyra in which you'll find Epsilon Lyrae, better known as the "double-double" star. Exceptionally good vision on a clear, dark night will reveal Epsilon as two tiny stars—designated Epsilon 1 and Epsilon 2. The space between the two is a mere 3.5 arc minutes, approximately one-ninth the apparent diameter of the full moon, and probably right at the limit of perfect vision. Binoculars, however, will clearly separate the two stars, and a 3-inch telescope will show you that each of these two stars are themselves double stars, as was first discovered in 1779 by Sir William Herschel.
So there, in what appears as a single speck of light in the sky, we have a system of four stars in a complicated orbital arrangement. The two stars that make up Epsilon 1 take at least several hundred years to orbit each other, the stars that comprise Epsilon 2 appear to have an even longer period of nearly one thousand years, and all the while, the pairs themselves appear to be revolving about a common center of gravity with a period that is probably on the order of one million years.