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If you look toward Lyra, the harp, on a dark summer night, you might think you’re seeing double. And if you look with a telescope, you’ll see double double. That’s because one of the constellation’s stars is known as the Double Double. It consists of two pairs of stars that appear to be moving through the galaxy together.
The pairs are known as Epsilon 1 and Epsilon 2 Lyrae. At nightfall, they stand close to the lower left of Vega, one of summer’s brightest stars, which is high in the east. Those with good eyesight can just separate the two pairs, while a telescope splits each pair into its individual stars. Epsilon 2 is about twice as bright as Epsilon 1.
The stars of Epsilon 2 are so far apart that it takes them about 725 years to orbit each other. One of its stars appears to have a companion of its own. It’s so close in, though, that not even the biggest telescopes can spot it.
The stars of Epsilon 1 are a little farther apart. And their combined mass is a little less than those of Epsilon 2. So it takes them more than a thousand years to orbit each other.
The two systems are separated by a trillion miles or more. So it takes hundreds of thousands of years for the two pairs to complete a single orbit around each other. Astronomers need to see a good bit of an orbit to confirm that two objects are bound together. So we can’t be positive that the Double Double really is a single family, moving through the galaxy as one.
Script by Damond Benningfield