LIBRA

Libra, pronounced as /ˈliːbrə/, is a constellation of the zodiac situated in the Southern celestial hemisphere. Its name, originating from Latin, translates to “weighing scales.” Its ancient astronomical symbol is (♎︎). Although it lacks any first magnitude stars, Libra is characterized by its relatively faint appearance. Positioned between Virgo to the west and Scorpius to the east, the brightest star in this constellation is Beta Librae, also known as Zubeneschamali. Libra is known to host three star systems with planets.

History and mythology

In Babylonian astronomy, Libra was recognized as MUL Zibanu, signifying the “scales” or “balance.” Alternatively, it was referred to as the Claws of the Scorpion. These scales held a sacred significance, representing the domain of the sun god Shamash, who was also the patron of truth and justice.

Ancient Greece also associated Libra with the Scorpion’s Claws. Over time, Libra has been symbolically linked with concepts of law, equity, and civility. In Arabic, “zubānā” translates to “scorpion’s claws,” likely sharing similar meanings in other Semitic languages. This linguistic resemblance may have contributed to the transformation of the Scorpion’s claws into the Scales. Notably, the names of Libra’s two primary stars in Arabic, Zubenelgenubi and Zubeneschamali, mean “southern claw” and “northern claw,” respectively.

There is also a suggestion that the scales allude to the equinox, signifying the moment when the sun enters this part of the ecliptic during the autumnal equinox, resulting in equal durations of day and night. Libra’s historical role as the equinox location led to the name “First Point of Libra” for the equinox, although this alignment shifted due to the precession of the equinoxes around 730 BC.

In ancient Egypt, the three brightest stars in Libra (α, β, and σ Librae) formed a constellation resembling a boat. Interestingly, Libra was not mentioned by Eudoxus or Aratus. It found references in ancient Egyptian records, including Manetho (3rd century B.C.) and Geminus (1st century B.C.), and was later included by Ptolemy in his list of 48 asterisms. While Ptolemy cataloged 17 stars within Libra, Tycho Brahe counted 10, and Johannes Hevelius identified 20. Libra only acquired its status as a constellation during ancient Rome, representing the scales held by Astraea, the goddess of justice, closely associated with Virgo in Greek mythology.

The constellation

Libra is surrounded by neighboring constellations, with Serpens’ head to the north, Virgo to the northwest, Hydra to the southwest, the edge of Centaurus to the southwest, Lupus to the south, Scorpius to the east, and Ophiuchus to the northeast. It occupies an area of 538.1 square degrees, accounting for approximately 1.304% of the night sky, and holds the 29th position among the 88 constellations in terms of size. The three-letter abbreviation assigned to the constellation by the International Astronomical Union in 1922 is “Lib.” The official boundaries of the constellation, as established by Eugène Delporte in 1930, are delineated by a polygon consisting of 12 segments, as illustrated in the infobox. In the equatorial coordinate system, the right ascension coordinates for these borders span from 14h 22m 08.08s to 16h 02m 17.23s, while the declination coordinates range from -0.47° to -30.00°. Libra can be fully observed by skywatchers located south of latitude 60°N.

Planetary systems

Within the boundaries of Libra lies the Gliese 581 planetary system, comprising the star Gliese 581, three confirmed planets, and two planets whose existence is yet to be definitively confirmed. Among these, Gliese 581d and Gliese 581g stand out as potential candidates for hosting life, although there is ongoing debate and uncertainty regarding the existence of Gliese 581g within the scientific community. Gliese 581c is notable for being the first Earth-like exoplanet discovered within the habitable zone of its parent star. Furthermore, Gliese 581e is remarkable as possibly the smallest mass exoplanet known to orbit a regular star to date. These exoplanets hold significant importance in assessing the possibility of extraterrestrial life beyond our Solar System. In late September 2010, the family of potential habitable planets was expanded to include exoplanets orbiting red dwarf stars, prompted by the discovery of Gliese 581g, a tidally locked planet situated squarely within the habitable zone. Studies on weather patterns suggest that tidally locked planets could still offer conditions conducive to supporting life.

Deep-sky objects

Within the boundaries of Libra, you can find the notable presence of NGC 5897, a prominent globular cluster. Situated at a distance of 50,000 light-years from Earth, this cluster is relatively large and shines with an integrated magnitude of 9. Additionally, Libra hosts IC 1059, a galaxy located within the constellation.