Libra (constellation)

This article is about the constellation. For other uses, see Libra (disambiguation).

Libra

Constellation
List of stars in Libra
Abbreviation	Lib
Genitive	Librae
Pronunciation	/ˈliːbrə/, genitive /ˈliːbraɪ/
Symbolism	the balance
Right ascension	15 h
Declination	−15°
Quadrant	SQ3
Area	538 sq. deg. (29th)
Main stars	4, 6
Bayer/Flamsteed stars	46
Stars with planets	3
Stars brighter than 3.00m	2
Stars within 10.00 pc (32.62 ly)	5
Brightest star	Zubeneschamali (β Lib) (2.61m)
Nearest star	Gliese 570 (19.20 ly, 5.89 pc)
Messier objects	0
Meteor showers	May Librids
Bordering constellations	Serpens Caput Virgo Hydra Centaurus (corner) Lupus Scorpius Ophiuchus
Visible at latitudes between +65° and −90°. Best visible at 21:00 (9 p.m.) during the month of June.

Libra ( /ˈliːbrə/) is a constellation of the zodiac. Its name is Latin for weighing scales, and its symbol is (Unicode ♎). It is fairly faint, with no first magnitude stars, and lies between Virgo to the west and Scorpius to the east.

Notable features

The constellation Libra as it can be seen with the naked eye. AlltheSky.com

The brightest stars in Libra form a quadrangle:

• α Librae, Zubenelgenubi ("southern claw"), a visual binary;
• β Librae, Zubeneschamali ("northern claw");
• γ Librae, Zubenelakrab ("scorpion's claw");
• σ Librae, Brachium, an eclipsing variable.

σ Librae was formerly known as γ Scorpii despite being well inside the boundaries of Libra. It was not redesignated as σ Librae until 1851 (by Benjamin A. Gould).

Planetary system

Libra is home to the star Gliese 581, which has a planetary system consisting of at least 6 planets, including Gliese 581 g, the best candidate planet for human habitability and extra-solar life yet discovered, Gliese 581 c, the first Earth-like extrasolar planet to be found within its parent star's habitable zone, Gliese 581 d, discovered in 2007 to be another Earth-like planet, and Gliese 581 e, the smallest mass exoplanet orbiting a normal star, all of which are of significance for establishing the likelihood of life outside of the Solar System. The family of candidate habitable planets was extended in late September 2010 to include Gliese 581 g, a tidally locked planet in the middle of the habitable zone, and currently the most likely discovered exoplanet to be capable of supporting life.

History and mythology

Libra as depicted in Urania's Mirror, a set of constellation cards published in London c.1825

Libra was known in Babylonian astronomy as MUL Zibanu ("the scales"), or alternatively as the Claws of the Scorpion. The scales were held sacred to the sun god Shamash, who was also the patron of truth and justice. Since these times, Libra has been associated with law, fairness and civility. In Persian "Zabaneh" or when mispronounced zubānā means "scorpion's claws", and likely similarly in other Semitic languages: this resemblance of words may be why the Scorpion's claws became the Scales.^{[citation needed]} It has also been suggested that the scales are in allusion to the fact that when the sun enters this part of the ecliptic at the autumnal equinox, the days and nights are equal.

Libra is a constellation not mentioned by Eudoxus or Aratus. In Roman mythology, Libra is considered to depict the scales held by Astraea (identified as Virgo), the goddess of justice. Libra is mentioned by Manetho (3rd century B.C.) and Geminus (1st century B.C.), and included by Ptolemy in his 48 asterisms. Ptolemy catalogued 17 stars, Tycho Brahe 10, and Johannes Hevelius 20. it is sad that the huge body of scientific astronomical books of 850 to 1660 AD by famous Persian astronomers are not at all mentioned anywhere- Ref. Beyrouni Razi Nasiruddin Tusi etc. Libra is the only zodiac sign that does not symbolize a living creature.

Astrology

Main article: Libra (astrology)

As of 2002, the Sun appears in the constellation Libra from October 31 to November 22. In tropical astrology, the Sun is considered to be in the sign Libra from September 23 to October 22, and in sidereal astrology, from October 16 to November 15.

Visualizations

Traditionally, α and β Librae are considered to represent the scales' balance beam, and γ and σ are the weighing pans.

H.A. Rey has suggested a way to connect the stars more fully to graphically show a balance. Beta Librae represents the top of the balance, Gamma Librae and Alpha Librae represent the balance beam. Upsilon Librae and Tau Librae represent the left plate of the balance, while Sigma Librae represents the right plate. All these stars are of the third magnitude.

Namesakes

USS Libra (AKA-12) was a United States navy ship named after the constellation.

Citations

For Zabana or Zabaneh see Dictionary encyclopedia by Ustad Dehkhoda.

References

• H. A. Rey, The Stars — A New Way To See Them. Enlarged World-Wide Edition. Houghton Mifflin, Boston, 1997. ISBN 0-395-24830-2.
• Ian Ridpath and Wil Tirion (2007). Stars and Planets Guide, Collins, London. ISBN 978-0007251209. Princeton University Press, Princeton. ISBN 978-0691135564.

External links

• The Deep Photographic Guide to the Constellations: Libra
• Libra constellation
• Star Tales – Libra