Partner Series
The Cosmic Scales: Spot Libra Constellation in the Night Sky
The constellation Libra, the Scales.
Credit: Stellarium

Here's a trivia question for you. Of the 12 zodiacal signs, only one is an inanimate object. Which is it? 

The answer is the Balance, or Scales, known to horoscope readers everywhere as Libra. I still remember: When I gave my very first lecture at New York's Hayden Planetarium more than three decades ago, one of the senior lecturers was in the darkened sky theater, unbeknownst to me. After I finished my presentation, he approached me. I asked him how I did, and his retort was akin to a reprimand. 

"You referred to the Scales as 'LEE'-brah'; it's 'LY'-brah'!" He then started to walk away, but before I had a chance to recover, he turned back to me and, for good measure, added, "Remember! When you want to borrow a book, you go to a LY'-brary, not a LEE'-brary!" [Facts About the Libra Constellation]

Now, one might argue that we're talking about two completely different things. The English word "library," for example, comes from the Latin word "libraria" ("book"). "Libra" is also a Latin word, meaning "balance." But the World Book Encyclopedia (Field Enterprises Educational Corp.) suggests the pronunciation is LY'-bruh, while The American Heritage Dictionary of the English Language (Houghton Mifflin Co.) says both 'LEE' and 'LY' are acceptable.  

In the sky, Libra really isn't all that much to look at. It's marked by an oblong figure of moderately bright stars; in a way, it sort of resembles a high-flying kite. This week, you'll find Libra almost due south between 10 p.m. and midnight local daylight time. It's really only important because it's part of the zodiac. But Libra could just as well have served as part of the two larger constellations that flank it: the Scorpion to its left, or the Virgin to its right. The Greek poet Aratus, who lived in the third century B.C., knew Libra not as the Scales, but as the claws of Scorpius, the Scorpion. In fact, Libra's two brightest stars still bear their original tongue-twisting Arabic names: Zubenelgenubi and Zubeneschamali, which mean "Southern Claw" and "Northern Claw," respectively. 

Zubenelgenubi is a lovely double star that's easily separated with a simple pair of binoculars. There is a bit of a mystery, however, regarding Zubeneschamali. The ancient Greeks, such as Eratosthenes and Ptolemy, described it as appearing considerably brighter than it does to us today. But no one can explain why this is so. Another mystery is this star's color. Some observers claim that Zubeneschamali shines with a greenish hue, but others disagree. This star's apparent color seems to be strongly subjective. Perhaps you might like to determine this for yourself on the next clear night.

Many years ago, the Fels Planetarium in Philadelphia had an amusing demonstration of how the claws of Scorpius once extended into the region of the sky now occupied by Libra. The Fels staff projected just such a star picture up onto the planetarium dome over the stars of Scorpius and Libra. Then, the lecturer commented that, today, the Scorpion's claws no longer extend as far as they used to, in order to make room for Libra. Then, the lecturer flipped a switch, and the claws retracted back into the current boundaries of Scorpius. What made this funny was that by flicking the switch back and forth, it appeared that Scorpius was doing calisthenics! [Planets, Constellations and Meteors in May 2017 (Skywatching Video)]

Libra also could have been associated with Virgo, representing the scales of the goddess of justice, which Virgo was supposed to represent. 

But Libra's very reason for existence might be to provide the zodiac with 12 signs. There were, after all, 12 months (or moons), so there had to be one sign to represent each month. Perhaps there might have been just four at one time, marking where the equinoxes and solstices occurred — or maybe six, with each sign accounting for two months. But in no way could that number be 11.  

So Libra might have been created for convenience, as a way to round out the zodiacal signs to 12. It first became a separate constellation around the time of the ancient Romans. And the representation of a scale or pan balance might have come out of Libra's position in the night sky long ago. In fact, between the years 2300 B.C. and 700 B.C., the point in the sky where the sun crosses the celestial equator while migrating south to mark the beginning of autumn in the Northern Hemisphere was located within the boundaries of Libra. 

So, quite possibly in this way, Libra might have been intended to symbolize a balance, demonstrating the equality of day and night that occurred when the sun was entering that region of the sky some 30 centuries ago.

Editor's note: If you capture an amazing photo of a night-sky sight and want to share it with Space.com for a story or gallery, please send images and comments in to managing editor Tariq Malik at spacephotos@space.com.

Joe Rao serves as an instructor and guest lecturer at New York's Hayden Planetarium. He writes about astronomy for Natural History magazine, the Farmer's Almanac and other publications, and he is also an on-camera meteorologist for Fios1 News in Rye Brook, New York. Follow us @Spacedotcom, Facebook or Google+. Originally published on Space.com.