You are here


July 14, 2013

A scorpion’s claw consists of two parts, allowing the nasty little critter to grab its prey. And so it is in the sky, with the star that represents one of the claws of Scorpius. Zubenelgenubi, the southern claw, consists of two widely separated components, both of which are visible through binoculars.

Zubenelgenubi is actually a member of the constellation Libra, the balance scales. But Libra’s brightest stars have kept ancient names that refer to them as the claws of the scorpion, which is next door to Libra. The other is Zubeneschamali, the northern claw.

There’s more to Zubenelgenubi than even your binoculars can reveal. Each of the two visible stars is in fact a pair of stars on its own, for a total of four stars in all.

The stars in each pair are quite close together. But the two pairs are far apart — more than 5,000 times the distance from Earth to the Sun. At that range, it takes more than 2,000 centuries for the two pairs to complete a single orbit around each other.

There’s evidence that Zubenelgenubi has one more member — a star known as KU Librae. It’s three light-years away from the others, so it might not be bound to them. But it appears to be the same age and composition, it’s about the same distance from Earth, and it moves along with the others — perhaps extending the reach of the scorpion’s claw.

Look for Zubenelgenubi in the south as night falls, to the upper right of orange Antares, the bright heart of the scorpion.


Script by Damond Benningfield, Copyright 2013

Get Premium Audio

Listen to today's episode of StarDate on the web the same day it airs in high-quality streaming audio without any extra ads or announcements. Choose a $8 one-month pass, or listen every day for a year for just $30.