What’s a Double Double star? Ordinary binoculars show you Epsilon Lyrae as two stars in one. But look more closely. A telescope reveals that each of the two stars in the Epsilon Lyrae system is, in itself, a double star. That’s why Epsilon Lyrae is famous for being the Double Double star, a single point of light to the eye that’s really four stars in one. One stellar pair circles around the other stellar pair in an intricate gravitational dance. Follow the links below to learn more.
How to find Epsilon Lyrae. Epsilon Lyrae is wonderfully easy to find. It’s not as bright as Vega, the constellation Lyra’s brightest star. It’s not far from Vega on the sky’s dome, though, and Lyra’s brightness, plus the distinctive shape of the constellation Lyra (see chart at right), can help you spot Epsilon Lyra.
With the eye, the gap between Vega and Epsilon Lyrae only amounts to the width of your little finger at an arm length away. As a fun bonus, you can see Vega and Epsilon Lyrae in a single binocular field.
You might also find Vega by looking for the brightest star in the famous Summer Triangle asterism. Just remember, Epsilon Lyrae, though not as bright as Vega, shines near this brighter, beacon star.
From our mid-northern latitudes, Epsilon Lyrae and its constellation Lyra the Harp shine for at least part of the night all year round. Epsilon Lyrae graces the nighttime from dusk until dawn on Northern Hemisphere summer nights. It’s high overhead on northern autumn evenings. In northern winter, this star appears both in the northwest sky after dusk, and then in the northeast sky before dawn. When northern spring arrives in March, Epsilon Lyrae rises before midnight, then shines for rest of the night.
Science of a Double Double star. Although Vega and Epsilon Lyrae look like they’re close together in space, they really aren’t. These stars only reside along the same line of sight. Astronomers have determined that Vega is some 25 light-years, whereas Epsilon is over six times farther, at about 160 light-years away.
There are many multiple star systems in the sky, but Epsilon Lyrae is special because it’s so easy – and so satisfying – to see as multiple. You can easily split the widest two components of the Epsilon Lyrae quadruple system with binoculars. You might even be able to split them with the unaided eye under excellent sky conditions. The two primary star systems of Epsilon Lyrae – the two that you see with binoculars – are thought to be 10,000 times the sun-Earth distance apart. They probably take at least a half a million years to revolve around each other.
The component binaries visible through the telescope are much closer together. They’re believed to circle each other in periods of about a thousand years.
And there are even more stars in this system. A fifth star orbits one of the primary pairs; it was first detected in 1986, not with the eye but with speckle imaging. Other nearby stars may also be part of the Epsilon Lyrae system, bringing the system to a total of 10 stars.
Epsilon Lyrae’s position is RA: 18h 44m 18.5s, dec: +39° 40′ 12.4″
Bottom line: Epsilon Lyrae is the sky’s most famous double double star. It’s four stars in all.
Bruce McClure has served as lead writer for EarthSky's popular Tonight pages since 2004. He's a sundial aficionado, whose love for the heavens has taken him to Lake Titicaca in Bolivia and sailing in the North Atlantic, where he earned his celestial navigation certificate through the School of Ocean Sailing and Navigation. He also writes and hosts public astronomy programs and planetarium programs in and around his home in upstate New York.