Libra is a constellation in the southern hemisphere. Its name means "weighing scales" in Latin. Ancient Sumerians called the constellation Zib-ba An-na, meaning "the balance of heaven." For a time, the constellation was represented by scorpion claws because of an error in translation of the Arabic word "zubana" and Akkadian word "zibanitu," both of which can stand for "weighing scale" as well as "scorpion." (In ancient times, scales had a shape similar to that of a scorpion hung upside down.) As a result, the constellation was known as Chelae Scorpionis ("claws of a scorpion") and was not identified with scales until the 1st century BC, in ancient Rome.
Romans considered it to be a favourable constellation because they believed that the Moon was in Libra when the city was founded. Today, Libra is depicted as the scales held by Astraea (Dike), the Greek goddess of justice, associated with the neighbouring
constellation Virgo. The Chinese called the constellation Show Sing, "the Star of Longevity," in ancient times, but later renamed it to Tien Ching, "the Celestial Balance.“
The Libra constellation occupies an area of 538 square degrees and contains three stars with known planets. It can be seen at latitudes between +65° and -90° and is best visible at 9 p.m. during the month of June. In sidereal astrology, the Sun appears to be passing through Libra between October 16 and November 15, while in tropical astrology, it is considered to be in Libra between September 23 and October 23.
Libra is a relatively faint constellation, without any stars of first magnitude. The brightest stars –
[5064]-
[5048] alpha,
[5047] beta,
[5052] gamma and
[5049] sigma Librae – form a quadrangle in the sky. With an apparent magnitude of 2.7,
[5047] beta Librae is the brightest star in the constellation. It is a blue dwarf approximately 160 light-years distant. The star is also known as Zubeneschamali ("the northern claw") and Lanx Australis ("the southern scale" of the balance).
[5052] gamma Librae is a magnitude 4 star also known as Zuben-el-Akrab ("shears of the scorpion").
[5049] sigma Librae is a red giant also known as Brachium ("arm"), Cornu ("horn") and Zubenalgubi ("southern claw"). It used to be part of the constellation Scorpius and had the designation gamma Scorpii before being assigned to Libra in the 19th century.
[5064]-
[5048] alpha Librae, also known as Zubenelgenubi ("southern claw") and Kiffa Australis ("southern pan" of the scales), is the second brightest star in the constellation. It is binary star lying about 77 light-years from the Sun.
Libra does not contain any bright galaxies, but there is one that may be of interest to observers that can be spotted in a large telescope, lying next to
[5047] beta Librae. It is the barred spiral galaxy NGC 5885, with a magnitude of 11.7.
Libra is home to Gliese 581 c, the first extrasolar planet discovered orbiting its parent star, the red dwarf Gliese 581, within the star’s habitable zone. The Earth-like planet was found in 2007. Another planet orbiting the same star, Gliese 581 e is the smallest mass extrasolar planet discovered orbiting a normal star.
Libra belongs to the Zodiac family of constellations, along with
Leo,
Virgo,
Scorpius,
Sagittarius,
Capricornus,
Aquarius,
Pisces,
Aries,
Taurus,
Gemini and
Cancer.
Constellations directly bordering Libra are
Serpens Caput,
Virgo,
Hydra,
Centaurus,
Lupus,
Scorpius and
Ophiuchus.