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July 13, 2013

Most of the constellations of the zodiac represent living things — from the twins of Gemini to the lion of Leo. The exception is Libra, which represents a balance scale. At the time Libra was named, the Sun passed across its stars at the time of the autumnal equinox, when night and day are of roughly equal length — a type of celestial balance.

But Libra’s two most prominent stars have a “living” connection. Their names refer to the claws of next-door Scorpius, the scorpion.

Scorpius itself is low in the south as night falls. Its curved shape is pretty easy to pick out, with the bright orange star Antares at its heart. Fainter Libra is to its upper right, with the “claw” stars extending up and away from the scorpion’s flat head.

The brighter of the claws is at the top: Zubeneschamali, from an Arabic name that means the northern claw.

Zubeneschamali is in the top few percent of stars in the galaxy. It’s more than three times as massive as the Sun, several times wider, and more than a hundred times brighter. That makes it easily visible even though it’s more than 180 light-years away.

The star is just a fraction of the Sun’s age. And even though it’s much bigger than the Sun, it won’t live anywhere near as long. Heavier stars burn their nuclear fuel in a hurry, so they shine brightly but burn out in a hurry. So Zubeneschamali will live only a few percent as long as the Sun will.

We’ll talk about the southern claw — Zubenelgenubi — tomorrow.


Script by Damond Benningfield, Copyright 2013

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