Meet Libra the Scales, a zodiacal constellation

Twilight background with star chart for Libra shaped like a wide triangle with two trailing lines.
Libra the Scales is a zodiac constellation home to 2 stars with pleasing names: Zubeneschamali and Zubenelgenubi. Chart via EarthSky.

Look for the constellation Libra the Scales on Northern Hemisphere summer evenings (Southern Hemisphere winter evenings). It’s not the most flashy constellation of the zodiac. But its two brightest stars have the best star names: Zubenelgenubi and Zubeneschamali. The names rhyme with Obi-Wan Kenobi of “Star Wars.”

Here’s how to pronounce Zubeneschamali

Here’s how to pronounce Zubenelgenubi

You can find Libra easily in a dark sky. On the chart below, notice Libra’s place with respect to another even brighter star, red Antares, Heart of the Scorpion in the constellation Scorpius. The Scorpion has a distinctive shape. And Antares is noticeable for being bright, and red, and for twinkling fiercely. Find Antares … and Libra will be nearby.

Star chart with stars in black on white with blue line of ecliptic running across.
In Libra, Zubenelgenubi is a bit fainter than Libra’s other bright star Zubeneschamali. But it lies nearly on the ecliptic, or pathway of the sun, moon and planets. That might be why the ancient stargazers gave Zubenelgenubi the alpha designation within this constellation. Image via International Astronomical Union/ Sky and Telescope/ Wikimedia Commons (CC BY 3.0).

Libra and the ecliptic

Libra is a constellation of the zodiac. So you know to look for it along the sun’s path across our sky. This path is the ecliptic. As seen from Earth, the sun passes in front of the constellation Libra from about October 30 until November 22 every year.

Libra’s star Zubenelgenubi sits almost exactly on the ecliptic. At present, the sun has its annual conjunction with Zubenelgenubi on or near November 7, or about midway between the September equinox and the December solstice.

But, as with all things heavenly, the conjunction date of the sun and Zubenelgenubi changes over the long course of time.

More than 3,000 years ago, the sun and Zubenelgenubi were in conjunction on the Northern Hemisphere’s autumnal equinox (Southern Hemisphere’s spring equinox). Over 3,000 years into the future, the sun and Zubenelgenubi will be in conjunction on the December solstice (Northern Hemisphere’s winter solstice or Southern Hemisphere’s summer solstice).

Regardless of which constellation provides a backdrop for the sun on the September equinox, the sun is said to be at the first point of the sign Libra when it the crosses the celestial equator going from north to south.

Read more: what’s the difference between a sign and a constellation?

Antique colored etching of ancient balance scales with 2 golden dishes sprinkled with labeled stars.
The constellation Libra from Urania’s Mirror, a boxed set of 32 constellation cards printed about 1825. Image via Wikipedia (public domain).

Libra in history and myth

Several thousand years ago – around 2,000 BCE – the ancient Babylonians apparently associated this constellation with scales or a balance. Quite possibly, they made this association because the sun on the autumnal equinox shone in front of the stars of Libra at that time. It’s at the equinox that the world realizes its seasonal and temporal balance between the extremes of heat and cold, and with day and night of equal length all over the globe. Metaphorically, Libra the Scales serves as an age-old symbol of divine justice, harmony and balance.

In contrast to their Babylonian forebears, the ancient Greeks seemed to regard Libra as the outstretched claws of the constellation Scorpius the Scorpion. In fact, the names for Libra’s two brightest stars are Arabic terms that hearken back to these olden times when Scorpius reigned as a double or super constellation. Zubenelgenubi translates into the southern claw of the Scorpion and Zubeneschamali into the northern claw of the Scorpion.

The Romans, though inheriting much of the Greek tradition, again revived Libra as the only inanimate constellation of the zodiac. In Roman thought, the constellation Virgo is the embodiment of Astraea, the Starry Goddess, holding Libra, the Scales of Justice.

Astrologers regard Libra as the second air sign, ruled over by the planet Venus. Although astronomy and astrology have been intertwined historically, they are now regarded as separate disciplines. Astrology assumes the positions of heavenly bodies have certain influences over human affairs which most modern-day astronomers regard as unfounded.

Marble relief sculpture of sitting woman in Grecian garb holding a set of scales.
According to mythology, at the return of the golden age the goddess Astraea will dispense justice and weigh the souls of men. Image via Wikipedia (GFDL 1.2).

More constellations of the zodiac

Taurus the Bull
Gemini the Twins, home to 2 bright stars
Cancer the Crab and its Beehive Cluster
Leo the Lion and its backward question mark
Virgo the Maiden in northern spring skies
Libra the Scales, a zodiacal constellation
Scorpius, a summertime delight
Sagittarius the Archer and its famous Teapot
Capricornus the Sea-goat has an arrowhead shape
Aquarius? Here’s your constellation
Pisces the Fish, 1st constellation of the zodiac
Say hello to Aries the Ram
Born under the sign of Ophiuchus?

Bottom line: Find the zodiacal constellation Libra the Scales in the evening sky during Northern Hemisphere summer (Southern Hemisphere winter) near the bright red star Antares.

Read more: M5, in Libra, your new favorite globular cluster

June 25, 2024

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