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Balancing Planets

December 29, 2017

The planets Mars and Jupiter execute a pincer maneuver as the old year ends and the new one begins: They bracket one of the ancient claws of Scorpius. Jupiter looks like a brilliant star in the southeast at dawn, with fainter Mars to its upper right. And just below Mars is Zubenelgenubi, the second-brightest star of Libra.

Libra represents a set of balance scales. But the name “Zubenelgenubi” comes from an ancient Arabic phrase that means “the southern claw.” That tells us that when the scorpion was first drawn, thousands of years ago, the star represented one of its claws.

Centuries later, though, the claws were separated from Scorpius, and the stars were assigned to the new constellation Libra. That may have been because the Sun appeared against those stars at the time of the fall equinox, a time of equal daylight and darkness — a “balance” in the sky.

Zubenelgenubi consists of two widely separated stars. Both of them are visible through binoculars. But each of the stars is in fact a pair of stars on its own, making four stars in all.

The stars in each pair are quite close together. But the two pairs are separated by more than 5,000 times the distance from Earth to the Sun. At that range, it takes more than 200,000 years for the two pairs to orbit each other.

So if you’re up and about at dawn tomorrow, look for the scorpion’s ancient claw close to two bright planets in the dawn sky — a beautiful decoration for any year.


Script by Damond Benningfield

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