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Libra (constellation)

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Libra is a constellation located in the southern celestial hemisphere. Its name is the Latin word for weighing scales. It occupies 538.1 square degrees of the night sky. This means it covers about 1.304% of the entire sky. It is ranked as the 29th largest of the 88 official constellations.

Libra constellation map
Libra constellation map

Libra is positioned between the constellations Virgo to the west and Scorpius to the east. The International Astronomical Union adopted the three-letter abbreviation "Lib" for this group in 1922. The official boundaries were defined by Eugène Delporte in 1930. These borders form a polygon made of 12 segments.

Libra symbol (fixed width)
Libra symbol (fixed width)

Observing Libra requires looking south of the 60°N latitude line. The constellation is relatively faint for observers. It contains no first magnitude stars, which are the brightest stars in the sky. However, there are 83 stars within its borders that have an apparent magnitude of 6.5 or brighter. The brightest stars in Libra form a distinct quadrangle.

LibraCC
LibraCC

Traditionally, the stars Alpha and Beta Librae represent the balance beam of the scales. The stars Gamma and Sigma Librae are seen as the weighing pans. This geometric arrangement helps astronomers identify the constellation even when the stars appear dim.

Many of the stars in Libra are complex multiple star systems. Alpha Librae, also known as Zubenelgenubi, is a system divisible into two stars when using binoculars. Its primary star, Alpha2 Librae, is a blue-white star with a magnitude of 2.7. The secondary star, Alpha1 Librae, is a white star of spectral type F3V. This star is approximately 74.9 light-years from Earth. The brightest star in the constellation is Beta Librae, or Zubeneschamali. It is a green-tinged star with a magnitude of 2.6. It sits about 160 to 185 light-years away from our solar system.

Sidney Hall - Urania's Mirror - Libra
Sidney Hall - Urania's Mirror - Libra

Other stars in the constellation demonstrate unique physical behaviors. Iota Librae is a complex multiple star located 377 light-years away. It contains both optical and true binary components. Its primary is a blue-white star with a magnitude of 4.5. The secondary star is part of a binary system with two other components. Delta Librae is an Algol-type eclipsing variable star. This means its brightness changes as stars pass in front of one another. It has a period of 2 days and 8 hours.

NGC5885 - SDSS DR14
NGC5885 - SDSS DR14

Another interesting object is FX Librae, which is classified as a shell star. This star rotates at an abnormally high speed. This rapid rotation causes the star to eject gas from its equator.

Libra has a long history in human astronomy and mythology. In ancient Babylon, it was known as MUL Zibanu, meaning the scales or the balance. It was also associated with the Claws of the Scorpion. These scales were considered sacred to the sun god Shamash, the patron of truth and justice. In ancient Greece, the stars were often seen as the claws of a scorpion. This connection is reflected in Arabic names. Zubenelgenubi and Zubeneschamali mean "southern claw" and "northern claw" in Arabic.

Sidney Hall - Urania's Mirror - Libra
Sidney Hall - Urania's Mirror - Libra

Later, in ancient Rome, the constellation came to represent the scales held by Astraea. She was the goddess of justice associated with Virgo.

Astronomers have also found significant deep-sky objects and planetary systems in this region. Libra is home to the Gliese 581 planetary system. This system consists of the star Gliese 581 and three confirmed planets. In 2009, the discovery of Gliese 581e was notable. It was the smallest mass exoplanet known to orbit a normal star at that time. The constellation also contains the NGC 5897 globular cluster. This is a large, loose cluster located 50,000 light-years from Earth.

NGC 5897GCL01a
NGC 5897GCL01a

Additionally, the galaxy IC 1059 can be found within the constellation's borders.

The study of Libra connects various fields of science and history. Its position relative to the sun has historical importance. During the autumnal equinox, the sun enters this part of the ecliptic. This event once earned the location the name "First Point of Libra." However, due to the precession of the equinoxes, this location stopped coinciding with the constellation in 730 BC. Today, Libra remains a vital part of the zodiac. It helps astronomers map the southern celestial hemisphere and understand the movement of stars and planets.

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🖼️ Images & Media (6)
File:Libra symbol (fixed width).svg
Libra symbol (fixed width).svg
File:Libra constellation map.svg
Libra constellation map.svg
File:LibraCC.jpg
LibraCC.jpg
File:NGC5885 - SDSS DR14.jpg
NGC5885 - SDSS DR14.jpg
File:NGC 5897GCL01a.jpg
NGC 5897GCL01a.jpg
File:Sidney Hall - Urania's Mirror - Libra.jpg
Sidney Hall - Urania's Mirror - Libra.jpg
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