In The Zone With The Zubes

Libra precedes Scorpius in the evening sky. This map shows the sky facing south around 10-10:30 p.m. now through the end of the month. Libra is a faint, diamond-shaped pattern of stars. Maps created with Stellarium

I love the sound of star names, and two of my favorites are due south at nightfall now through the end of the month. Allow me to introduce Zubenelgenubi and Zubeneschamali. How could anyone resist saying these mellifluous tongue twisters? They’re Libra the Scales’ two brightest stars and known also by their plain vanilla names, Alpha and Beta Librae.

First, let’s pronounce them properly: zoo-BEN-el-je-NEW-bee and zoo-BEN-es-sha-MA-li. Thanks to all the vowels, they’re not as hard to say as they look. They’re also the two stars of Libra’s faint outline you’re likely to see. Both are 3rd magnitude or one level fainter than the stars of the Big Dipper. To find them, face south at nightfall and look for the bright star Spica and planet Saturn. Reach your fist against the sky and look about two fist widths to the left of Spica to spot Zubenelgenubi. Zubeneschamali is a fist to its upper left.

Alpha and Beta Librae, a.k.a. Zubenelgenubi and Zubeneschamali, form part of Libra's balance.

Libra, like its neighbor Scorpius, is one of the zodiac constellations, and the only one that doesn’t represent an animal. Instead its stars suggest a balance or set of scales. Back in the days of ancient Babylon, there was no Libra. The two Zubes were the outstretched claws of the Scorpion. This bit of history is preserved in their names, which translated from the Arabic mean ‘the Northern Claw’ and ‘the Southern Claw’.

Two thousand years ago the sun was in Libra on the first day of fall, and the constellation was re-conceived by the Greeks and Romans as a balance. This is very fitting when you consider that day and night are ‘balanced’ or equal to one another in length on the equinoxes or the first days of spring and fall.

Alpha or Zubenelgenubi is a very nice double star that keen-eyed sky watchers might split using only the naked eye. The companion, called Alpha-1, lies very close northwest of the brighter Alpha-2. Any pair of binoculars will cleave the pair if you’re having difficulty by eyeball alone.

Alpha Librae is a double star easily splittable in binoculars. Credit: AAO/STScI/WikiSky

Although the two are far apart by double star standards, they’re both 77 light years away and moving together through space. 420 billion miles, equal to about 140 times Pluto’s distance from the sun, separate them. Alpha-2, the brighter, has a little secret – it’s double again. The two stars are so close they appear as one even from Alpha-1!

Zubeneschamali is one of the few if not the only naked eye star that some observers see as green. Based on its temperature, it should appear white, but a few observers beg to differ. I’ve always seen it as white or colorless. Take a look yourself the next clear night and tell us what you see.

RCW 120 is a region of hot gas and glowing dust found in the murky interstellar clouds in the constellation Scorpius. The ring of dust is actually glowing in infrared colors that our eyes cannot see, but show up brightly when viewed by Spitzer's infrared detectors. At the center of this ring are a couple of giant stars whose intense ultraviolet light has carved out the bubble. Credit: NASA/JPL-Caltech

Now if you want some real, unequivocal GREEN, take a look at this recent photo from the Spitzer Space Telescope . It’s a ring-shaped nebula some astronomers are likening to the magic green ring wielded by the superhero Green Lantern. The ring is composed of dust and excited to glow by powerful winds and radiation emitted by massive stars in the cloud’s center. Spitzer’s telescope shows the weak infrared (heat) glow of carbon compounds in the ring; the center glows red from light given off by larger, more robust dust grains. This ring’s superpower may lie in its ability to incite the imagination.

3 Responses

      1. caralex

        Those three names have fascinated me since I first taught them to myself at about age 10! I used to recite them to my classmates…who thought I was bonkers!

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