Libra (constellation)

Libra (constellation)

Overview
Libra is a constellation
Constellation
In modern astronomy, a constellation is an internationally defined area of the celestial sphere. These areas are grouped around asterisms, patterns formed by prominent stars within apparent proximity to one another on Earth's night sky....

 of the zodiac
Zodiac
In astronomy, the zodiac is a circle of twelve 30° divisions of celestial longitude which are centred upon the ecliptic: the apparent path of the Sun across the celestial sphere over the course of the year...

. Its name is Latin
Latin
Latin is an Italic language originally spoken in Latium and Ancient Rome. It, along with most European languages, is a descendant of the ancient Proto-Indo-European language. Although it is considered a dead language, a number of scholars and members of the Christian clergy speak it fluently, and...

 for weighing scales, and its symbol is (Unicode
Unicode
Unicode is a computing industry standard for the consistent encoding, representation and handling of text expressed in most of the world's writing systems...

 ). It is fairly faint, with no first magnitude
Apparent magnitude
The apparent magnitude of a celestial body is a measure of its brightness as seen by an observer on Earth, adjusted to the value it would have in the absence of the atmosphere...

 star
Star
A star is a massive, luminous sphere of plasma held together by gravity. At the end of its lifetime, a star can also contain a proportion of degenerate matter. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth...

s, and lies between Virgo
Virgo (constellation)
Virgo is one of the constellations of the zodiac. Its name is Latin for virgin, and its symbol is . Lying between Leo to the west and Libra to the east, it is the second largest constellation in the sky...

 to the west and Scorpius
Scorpius
Scorpius, sometimes known as Scorpio, is one of the constellations of the zodiac. Its name is Latin for scorpion, and its symbol is . It lies between Libra to the west and Sagittarius to the east...

 to the east.

]

The brightest stars in Libra form a quadrangle
Quadrilateral
In Euclidean plane geometry, a quadrilateral is a polygon with four sides and four vertices or corners. Sometimes, the term quadrangle is used, by analogy with triangle, and sometimes tetragon for consistency with pentagon , hexagon and so on...

:
  • α Librae
    Alpha Librae
    Alpha Librae is the second brightest star in the constellation Libra . It has the traditional name Zubenelgenubi. The name, from Arabic الزبن الجنوبي , means "southern claw" and was coined before Libra was recognized as distinct from Scorpius...

    , Zubenelgenubi ("southern claw"), a visual binary;
  • β Librae
    Beta Librae
    Beta Librae is the brightest star in the constellation Libra. It has the traditional name Zubeneschamali and the Latin name Lanx Borealis...

    , Zubeneschamali ("northern claw");
  • γ Librae
    Gamma Librae
    Gamma Librae is a star in the constellation Libra. It has the traditional name Zuben-el-Akrab, meaning "Shears of the Scorpion". The name is a modification of the Arabic al-Zuban al-Aqrab...

    , Zubenelakrab ("scorpion's claw");
  • σ Librae
    Sigma Librae
    Sigma Librae is a star in the constellation Libra. It has the traditional names Brachium , Cornu , and Zubenalgubi ....

    , Brachium, an eclipsing variable.


σ Librae was formerly known as γ Scorpii despite being well inside the boundaries of Libra.
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Encyclopedia
Libra is a constellation
Constellation
In modern astronomy, a constellation is an internationally defined area of the celestial sphere. These areas are grouped around asterisms, patterns formed by prominent stars within apparent proximity to one another on Earth's night sky....

 of the zodiac
Zodiac
In astronomy, the zodiac is a circle of twelve 30° divisions of celestial longitude which are centred upon the ecliptic: the apparent path of the Sun across the celestial sphere over the course of the year...

. Its name is Latin
Latin
Latin is an Italic language originally spoken in Latium and Ancient Rome. It, along with most European languages, is a descendant of the ancient Proto-Indo-European language. Although it is considered a dead language, a number of scholars and members of the Christian clergy speak it fluently, and...

 for weighing scales, and its symbol is (Unicode
Unicode
Unicode is a computing industry standard for the consistent encoding, representation and handling of text expressed in most of the world's writing systems...

 ). It is fairly faint, with no first magnitude
Apparent magnitude
The apparent magnitude of a celestial body is a measure of its brightness as seen by an observer on Earth, adjusted to the value it would have in the absence of the atmosphere...

 star
Star
A star is a massive, luminous sphere of plasma held together by gravity. At the end of its lifetime, a star can also contain a proportion of degenerate matter. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth...

s, and lies between Virgo
Virgo (constellation)
Virgo is one of the constellations of the zodiac. Its name is Latin for virgin, and its symbol is . Lying between Leo to the west and Libra to the east, it is the second largest constellation in the sky...

 to the west and Scorpius
Scorpius
Scorpius, sometimes known as Scorpio, is one of the constellations of the zodiac. Its name is Latin for scorpion, and its symbol is . It lies between Libra to the west and Sagittarius to the east...

 to the east.

Notable features


]

The brightest stars in Libra form a quadrangle
Quadrilateral
In Euclidean plane geometry, a quadrilateral is a polygon with four sides and four vertices or corners. Sometimes, the term quadrangle is used, by analogy with triangle, and sometimes tetragon for consistency with pentagon , hexagon and so on...

:
  • α Librae
    Alpha Librae
    Alpha Librae is the second brightest star in the constellation Libra . It has the traditional name Zubenelgenubi. The name, from Arabic الزبن الجنوبي , means "southern claw" and was coined before Libra was recognized as distinct from Scorpius...

    , Zubenelgenubi ("southern claw"), a visual binary;
  • β Librae
    Beta Librae
    Beta Librae is the brightest star in the constellation Libra. It has the traditional name Zubeneschamali and the Latin name Lanx Borealis...

    , Zubeneschamali ("northern claw");
  • γ Librae
    Gamma Librae
    Gamma Librae is a star in the constellation Libra. It has the traditional name Zuben-el-Akrab, meaning "Shears of the Scorpion". The name is a modification of the Arabic al-Zuban al-Aqrab...

    , Zubenelakrab ("scorpion's claw");
  • σ Librae
    Sigma Librae
    Sigma Librae is a star in the constellation Libra. It has the traditional names Brachium , Cornu , and Zubenalgubi ....

    , 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
Gliese 581
Gliese 581 is a red dwarf star with spectral type M3V, located 20.3 light years away from Earth in the constellation Libra. Its estimated mass is about a third of that of the Sun, and it is the 89th closest known star system to the Sun. Observations suggest that the star has at least six planets:...

, which has a planetary system
Planetary system
A planetary system consists of the various non-stellar objects orbiting a star such as planets, dwarf planets , asteroids, meteoroids, comets, and cosmic dust...

 consisting of at least 6 planets, including Gliese 581 g
Gliese 581 g
Gliese 581 g , also Gl 581 g or GJ 581 g, is a hypothesized extrasolar planet proven nonexistent by the Geneva Team, orbiting the red dwarf star Gliese 581, 20.5 light-years from Earth in the constellation of Libra. It is the sixth planet discovered in the Gliese 581 planetary system and the fourth...

, the best candidate planet for human habitability and extra-solar life yet discovered, Gliese 581 c
Gliese 581 c
Gliese 581 c or Gl 581 c is a planet orbiting the red dwarf star Gliese 581. It is the second planet discovered in the system and the third in order from the star. With a mass at least 5.6 times that of the Earth, it is classified as a super-Earth...

, the first Earth-like extrasolar planet
Extrasolar planet
An extrasolar planet, or exoplanet, is a planet outside the Solar System. A total of such planets have been identified as of . It is now known that a substantial fraction of stars have planets, including perhaps half of all Sun-like stars...

 to be found within its parent star's habitable zone
Habitable zone
In astronomy and astrobiology, a habitable zone is an umbrella term for regions that are considered favourable to life. The concept is inferred from the empirical study of conditions favourable for Life on Earth...

, Gliese 581 d
Gliese 581 d
Gliese 581 d or Gl 581 d is an extrasolar planet orbiting the star Gliese 581 approximately 20 light-years away in the constellation of Libra. It is the third planet discovered in the system and the fifth in order from the star....

, discovered in 2007 to be another Earth-like planet, and Gliese 581 e
Gliese 581 e
Gliese 581 e or Gl 581 e is an extrasolar planet found around Gliese 581, an M3V red dwarf star approximately 20.5 light-years away from Earth in the constellation of Libra...

, the smallest mass exoplanet orbiting a normal star, all of which are of significance for establishing the likelihood of life
Extraterrestrial life
Extraterrestrial life is defined as life that does not originate from Earth...

 outside of the Solar System
Solar System
The Solar System consists of the Sun and the astronomical objects gravitationally bound in orbit around it, all of which formed from the collapse of a giant molecular cloud approximately 4.6 billion years ago. The vast majority of the system's mass is in the Sun...

. 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
Habitable zone
In astronomy and astrobiology, a habitable zone is an umbrella term for regions that are considered favourable to life. The concept is inferred from the empirical study of conditions favourable for Life on Earth...

, and currently the most likely discovered exoplanet to be capable of supporting life.

History and mythology


Libra is the only zodiac sign that does not symbolize a living creature. It 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
Shamash
Shamash was a native Mesopotamian deity and the sun god in the Akkadian, Assyrian and Babylonian pantheons. Shamash was the god of justice in Babylonia and Assyria, corresponding to Sumerian Utu...

, who was also the patron of truth and justice. Since these times, Libra has been associated with law, fairness and civility. In Arabic 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.

In Roman mythology
Roman mythology
Roman mythology is the body of traditional stories pertaining to ancient Rome's legendary origins and religious system, as represented in the literature and visual arts of the Romans...

, Libra is considered to depict the scales held by Astraea (identified as Virgo
Virgo (constellation)
Virgo is one of the constellations of the zodiac. Its name is Latin for virgin, and its symbol is . Lying between Leo to the west and Libra to the east, it is the second largest constellation in the sky...

), the goddess of justice.

Astrology



, 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
Libra (astrology)
Libra is the seventh astrological sign in the Zodiac, originating from the constellation of Libra. In astrology, Libra is considered a "masculine", positive sign. It is also considered an air sign and is one of four cardinal signs...

 from September 23 to October 22, and in sidereal astrology
Sidereal astrology
Sidereal and tropical are astronomical terms used to describe two different definitions of a "year". They are also used as terms for two systems of ecliptic coordinates used in 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
Weighing scale
A weighing scale is a measuring instrument for determining the weight or mass of an object. A spring scale measures weight by the distance a spring deflects under its load...

. Beta Librae
Beta Librae
Beta Librae is the brightest star in the constellation Libra. It has the traditional name Zubeneschamali and the Latin name Lanx Borealis...

 represents the top of the balance, Gamma Librae
Gamma Librae
Gamma Librae is a star in the constellation Libra. It has the traditional name Zuben-el-Akrab, meaning "Shears of the Scorpion". The name is a modification of the Arabic al-Zuban al-Aqrab...

 and Alpha Librae
Alpha Librae
Alpha Librae is the second brightest star in the constellation Libra . It has the traditional name Zubenelgenubi. The name, from Arabic الزبن الجنوبي , means "southern claw" and was coined before Libra was recognized as distinct from Scorpius...

 represent the balance beam. Upsilon Librae
Upsilon Librae
Upsilon Librae is a Class K3, fourth-magnitude star in the constellation Libra. Upsilon Librae is a double or multiple stellar system located about 195 light-years from Earth....

 and Tau Librae
Tau Librae
Tau Librae is a Class B2.5, fourth-magnitude star in the constellation Libra. Tau Librae is a stellar system located about 445 light-years from Earth....

 represent the left plate of the balance, while Sigma Librae
Sigma Librae
Sigma Librae is a star in the constellation Libra. It has the traditional names Brachium , Cornu , and Zubenalgubi ....

 represents the right plate. All these stars are of the third magnitude.

Namesakes


USS Libra (AKA-12)
USS Libra (AKA-12)
USS Libra was an named after the constellation Libra. She served as a commissioned ship for 11 years.Libra was laid down as Jean Lykes by Federal Shipbuilding and Drydock Company, Kearny, N.J., under contract for Lykes Brothers Steamship Company, Galveston, Texas; launched 12 November 1941;...

 was a United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...

navy ship named after the constellation.

External links