Star Constellation Facts: Libra, the Scales

Star Constellation Facts: Libra, the Scales
Alexander Jamieson’s Celestial Atlas (1822)

Libra is a faint constellation that is the 29th biggest in the night sky, and the only zodiac sign not to represent a living creature. Instead, Libra is depicted in the heavens as “weighing scales” placed next to the hand of its neighbouring constellation Virgo, a goddess of justice who had scales as an emblem of her office. The measuring symbol for pounds (“lb”) is an abbreviation of the word Libra.

Represents: Weighing Scales

The constellation’s association with scales is thought to have originated in ancient Babylonia around 2000 BC, where Libra was called ZIB.BA.AN.NA (“the balance of heaven”). In ancient Greece, Libra was considered to be part of the constellation Scorpius, and represented the creature’s claws, and was noted as such by Ptolemy in his astronomical catalogue Almagest around AD 150. During the reign of Roman dictator Julius Caesar, however, the constellation Libra was created, and was envisioned as scales held by Astraea, the goddess of justice, although its two brightest stars still retained their original names; Zubeneschamali (The Northern Claw), and Zubenelgenubi (The Southern Claw).

Location: Southern Constellation

Libra is a southern sky constellation that can be seen by observers located between latitudes of +65° and -90°, although in the northern hemisphere it is best seen in spring and summer, and in the southern hemisphere from autumn to winter. The constellation’s most luminous stars form a quadrangular pattern that can be found between Virgo to its north-west, and Scorpius to its south-east, by using their brightest stars, Spica and Antares respectively as guides. Other neighbouring constellations include Centaurus, Hydra, Ophiuchus, Serpens Caput, and Lupus.

Notable Stars: 2nd Magnitude or Fainter

Libra takes up a 538 sq/deg area of the sky, with the constellation’s “scale” shape formed by the stars Alpha and Beta Librae that form the “cross-beam”, and the stars Gamma and Sigma Librae that represent the “weighing pans.”

Libra Virgo Scorpius

Zubeneschamali (Beta Librae), the most luminous star in Libra, is located about 185 light years away, and shines with an apparent magnitude of 2.61. The star is a blue-white dwarf (B8 V) around 5 times as big as the Sun, and at least 130 times as luminous. It is also a fast rotator, with a rotational velocity of about 250 km/sec at its equator. Beta Librae is thought to be binary star, since small, periodic variations in brightness have been observed, but to date, no companion has been identified.

– Zubenelgenubi (Alpha Librae), the second most luminous star in Libra, is a binary system found 75 light years from our solar system that shines with an apparent magnitude of 5.153. Alpha Librae forms the primary pair of the system, and both stars are thought to be members of the Castor Moving Group of stars, since they share a common proper motion, which implies a common origin about 200 million years ago.

Other stars of interest in Alpha Librae includes the blue supergiant 48 Librae, the blue-white dwarf stars Tau Librae and Zuben Elakribi (Delta Librae); the yellow dwarf stars 23 Librae and HD 141937; the orange giant stars Upsilon Librae, Gamma Librae, Zuben Elakrab, and Theta Librae; and the red giant Brachium, and the red dwarf star Gliese 581.

Contains Oldest Known Star

Methuselah (HD 140283) is located 190 light years from the Sun, and is a seventh magnitude star that is currently in its pre-red giant phase. It is also the oldest known star, with an estimated age of about 14.46 billion years, give or take 800 million years or so. At first glance, the star’s age seems to contradict the age of the Universe, which is estimated to be about 13.77 billion years old, but the huge uncertainties in the ages of both the star and the Universe means that there is no real conflict. Methuselah consists almost entirely of hydrogen and helium, with only trace amounts of heavy atoms, which means that the star is among the oldest surviving second-generation stars.

Notable Objects: Few Celestial Objects

Libra contains no Messier objects, or any other notable deep-sky objects (DSOs) for that matter, apart the globular cluster NGC 5897, that is 170 light years wide, 24,000 light years distant, and shines with an apparent magnitude of 8.5. In Libra can also be found the barred spiral galaxies NGC 5792 and NGC 5885; and the lenticular galaxy NGC 5890. All these objects, however, can only be seen in large telescopes.

Meteor Showers: May Librids

The only meteor shower associated with Libra, the May Librids, has a very short duration period that runs from May 1st to 9th, with its peak on the 6th, during which time a maximum of 2 to 6 meteors per hour can be seen.

Planets: 3 Stars with Planets

Of the three stars in Libra with confirmed planets, one of the most interesting is Gliese 581, a red dwarf star some 20 light years away. It has more than four confirmed planets, including Gliese 581, which is located in the star’s habitable zone, and is now considered one of the most promising planet yet discovered for extra-solar life or human habitability.

Astrology: Sept 23 to Oct 23

At that time of its creation in Babylon, the Sun’s position in front of the constellation’s stars marked the start of the autumnal equinox, during which time the day and night, being weighed, would be found equal. However, with precession over time the Sun has now moved south of the ecliptic into Virgo, which currently marks the autumn equinox

Date of Birth: Sept 23 to Oct 23
Sign Ruler: Venus
Element: Air
Birth Stone: Coral, Amber
Metal: Quicksilver
Color: Brown
Characteristics: Idealistic, fair-minded, strong social skills, charming, artistic
Compatibility: Aquarius, Gemini and Libra

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