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Gamma Virginis

April 4, 2021

Many stars — and perhaps most of them — travel in pairs. The stars are siblings — they were born together, from the same cloud of gas and dust. In most cases, the twin stars aren’t much alike. In a few cases, though, they’re almost identical. One example is Gamma Virginis, one of the brighter stars of Virgo.

Both stars are about half-again the mass of the Sun. They’re also wider and hotter than the Sun. And they’re probably a little more than a billion years old — just a quarter the age of the Sun.

On average, the two stars are separated by about the distance between the Sun and Pluto. Their orbit is quite lopsided, though, so the distance varies by billions of miles.

Tracking that orbit confirmed that the two stars are related, and don’t just happen to line up in the same direction. The fact that the system consists of two stars was discovered in 1689. And by 1803, astronomer William Herschel wrote that the stars were “intimately held together by the bonds of mutual attraction” — the attraction of their gravitational pull.

The stars were closest to each other about 15 years ago — so close that it was nearly impossible to see them as individual stars through most telescopes. But now they’re moving away from each other, making it much easier to see these identical twin stars.

As the sky gets good and dark, Gamma Virginis stands directly above bright Spica, Virgo’s leading light, in the east-southeast. It’s to the right of Spica at first light.

Script by Damond Benningfield

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