Enjoying EarthSky? Subscribe.

102,550 subscribers and counting ...

By in
| Constellations on Jun 07, 2012

Libra? Here’s your constellation

In skylore, Libra the Scales is an age-old symbol of divine justice, harmony and balance. Plus its two brightest stars have the coolest of all star names.

Obi-Wan Kenobi of Star Wars movie fame. His name rhymes with the names of the constellation Libra's two brightest stars. This image, from a poster, via Wikimedia Commons.

The zodiacal constellation Libra the Scales is a fixture of the evening sky during a Northern Hemisphere summer (Southern Hemisphere winter). It’s not the most flamboyant constellation of the Zodiac. But you can find Libra fairly easily in a dark sky using two bright stars, Spica and Antares, as guides. Using these two bright stars, you’ll be searching for two fainter stars in Libra, which, by the way, have two of the best star names in the sky.

These two stars in Libra sit about midway between Spica and Antares. The stars are Zubenelgenubi and Zubeneschamali, and they mark Libra’s place in the heavens. Zuben … what? Click the links below to hear pronunciations of these star names, which many have noticed sound a lot like Obi-Wan Kenobi, one of only four characters to appear in all six Star Wars films. Did George Lucas use these stars as inspiration for the character’s name? It would be interesting to know.

Zubenelgenubi: Alpha star of Libra the Scales

Zubeneschamali: Green star?

As seen from Earth, the sun passes in front of the constellation Libra from about October 30 until November 22 every year. This is probably at odds with what you read on the horoscope page, which probably places the sun in Libra from around September 23 to October 22. Keep in mind that astrologers are referring to the sign Libra. We’re talking about the constellation Libra.

This year, in 2014, you can use the planet Saturn to find the constellation Libra the Scales. Saturn will be out all night long, in May 2014 and almost all night long in June 2014.

This year, in 2014, you can use the planet Saturn to find the constellation Libra the Scales. Saturn will be out all night long, in May 2014 and almost all night long in June 2014.

In any year, you can find the constellation Libra between the stars Antares and Spica. But in 2014, the planet Saturn acts as your guide to this fairly faint constellation.

In any year, you can find the constellation Libra between the stars Antares and Spica. But in 2014, the planet Saturn acts as your guide to this fairly faint constellation.

Yes, there is a difference between a constellation and a sign. A constellation of the Zodiac depicts a section of the starry sky. But the sign Libra refers to the sun’s place with respect to the September equinox. Simply put, the sun enters the sign Libra on the September equinox, and stays within the sign Libra for the month following the Northern Hemisphere’s autumnal equinox. In our day, the September equinox sun actually shines in front of the constellation Virgo, but the sign Libra.

Virgo? Here’s your constellation

Be that as it may, the star Zubenelgenubi sits almost exactly on the ecliptic – the sun’s yearly path in front of the background stars. At present, the sun has its annual conjunction with the Libra star Zubenelgenubi on or near November 7, or about midway between the September equinox and the December solstice.

What is the ecliptic?

Sky chart of the constellation Libra

The constellation Libra the Scales and its brightest stars Zubenelgenubi and Zubeneschamali. Image credit: Wikimedia Commons

However, the conjunction date of the sun and Zubenelgenubi changes over the long course of time. Over three thousand years ago, the sun and Zubenelgenubi were in conjunction on the Northern Hemisphere’s autumnal equinox (Southern Hemisphere’s spring equinox). Yet, over three thousand 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).

Irrespective 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.

Libra in history and myth

Several thousands of years ago – around 2,000 B.C. – the ancient Babylonians apparently associated this constellation with scales or a balance. Quite possibly, this association was made because the sun on the autumn 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 harken 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.”

At the return of the golden age, the goddess Astraea will dispense justice and weigh the souls of men. Image credit: Wikipedia Commons

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.

Bottom line: Libra the Scales – a constellation of the Zodiac – can be found in the evening sky during Northern Hemisphere summer (Southern Hemisphere winter). It’s situated between two bright stars, Spica and Antares. Libra’s two brightest stars are Zubenelgenubi and Zubeneschamali, whose names rhyme with Obi-Wan Kenobi of the movie Star Wars.