Libra: The Scales of Justice in the Sky

Libra is the only zodiac constellation that represents an inanimate object rather than a living creature. These celestial scales sit between Virgo and Scorpius, and its stars were historically considered the claws of the scorpion before being separated into their own constellation. Though relatively faint, Libra has a distinctive diamond shape and carries rich cultural associations with balance and justice. Locate it with StarGlobe.

How to Find Libra

Libra occupies a position along the ecliptic between the bright stars Spica in Virgo and Antares in Scorpius. Look roughly midway between these two landmarks during late spring or early summer evenings. The constellation's main stars form a lopsided diamond or rectangle.

The two brightest stars, Zubenelgenubi and Zubeneschamali, have names that betray the constellation's origin as part of Scorpius. Zubenelgenubi means "the southern claw" and Zubeneschamali means "the northern claw" in Arabic. These two stars form the beam of the scales, with fainter stars hanging below like pans.

The Stars of Libra

Zubeneschamali (Beta Librae) is the brightest star in the constellation at magnitude 2.6. It is a blue-white star about 185 light-years from Earth. Some observers report seeing a faint green tint to this star, which would make it one of the very few stars with a perceptible green color to the naked eye, though this observation is debated.

Zubenelgenubi (Alpha Librae) is a wide double star at magnitude 2.75. Binoculars easily split it into two components: a brighter white star and a fainter yellowish companion. The pair is about 77 light-years away, and both stars are genuinely gravitationally bound despite their wide separation.

Brachium (Sigma Librae) was historically called Gamma Scorpii before the boundary between the two constellations was redrawn. It is a red giant whose variability can cause it to fluctuate in brightness. Upsilon Librae and Tau Librae complete the main figure of the scales.

Deep Sky Objects

Libra is not particularly rich in bright deep sky objects, as it lies away from the Milky Way's densest regions. However, it contains NGC 5897, a loose globular cluster at a distance of about 40,000 light-years. It is spread over a large area and appears as a faint, diffuse glow in telescopes, making it a challenging but rewarding target for experienced observers.

Several galaxies lie within Libra's boundaries, including NGC 5792, a barred spiral galaxy visible in larger amateur telescopes. The constellation also hosts Gliese 581, a red dwarf star system about 20 light-years away that attracted considerable attention when several potentially habitable exoplanets were reported orbiting it, though some of these detections have since been questioned.

Mythology and Cultural Heritage

Libra is unique among the zodiac constellations for having been "created" from another constellation. The ancient Greeks did not have a separate Libra; they considered these stars to be the claws of Scorpius. The Romans separated them around the first century BCE, associating the scales with the concept of justice and specifically with Astraea, the goddess of justice, who is represented by neighboring Virgo.

The autumnal equinox occurred in Libra in Roman times, when day and night were perfectly balanced, reinforcing the association with scales and equilibrium. Precession has since moved the equinox point into Virgo, but the symbolic connection between Libra and balance persists.

In Babylonian astronomy, this region was associated with the balance or scales of the god Shamash, the sun god who also served as god of justice. Egyptian tradition connected it to the scales used to weigh the hearts of the dead in the afterlife, adding a spiritual dimension to its significance.

Best Time to Observe

Libra is best observed during June and July evenings, when it transits the meridian for Northern Hemisphere observers. The constellation is moderately low in the southern sky from northern latitudes but is easily visible from most populated areas. From the Southern Hemisphere, Libra rides higher and is well-placed from May through August.

Because Libra lies along the ecliptic, the Moon and planets pass through it regularly. When a bright planet sits among Libra's faint stars, it makes the constellation much easier to identify.

Neighboring Constellations

Virgo lies to the west, and Scorpius to the east. Ophiuchus borders Libra to the north, and Hydra and Centaurus lie to the south. Lupus sits to the southeast. The transition from Libra to Scorpius along the ecliptic is one of the most distinctive in the zodiac, as the faint scales give way to the dramatic bright curve of the scorpion. Trace this transition with StarGlobe.

Quick Facts

Libra covers 538 square degrees, ranking 29th in size. It has no Messier objects, and its brightest star, Zubeneschamali, shines at magnitude 2.6. The constellation's right ascension ranges from about 14h 22m to 16h 02m, and its declination spans from about -1 to -30 degrees. The ecliptic passes through the constellation, making it a frequent host to planets and the Moon.