Libra means "The Scales" or "Balance", so named because when the zodiac was still in its infancy, some four thousand years ago, the sun passed through this constellation at the autumnal equinox (21 September). At the two equinoxes (Spring and Autumn) the hours of daylight and darkness are equal.
As a symbol for equality, the constellation came to represent Justice in
several middle Eastern cultures. However, the Greeks had a different
perspective; at one time Scorpius, which lies just to the east, was much
larger, and the stars that make up Libra were then known as the Claws of
Eventually, however, these stars of Libra came
to represent the Golden Chariot of Pluto. The story of Pluto's abduction
of Persephone is a widely known Greek myth, perhaps because it has such a
strong astronomical association.
Pluto's (or Hades') Golden Chariot was used whenever the Lord of the
Underworld wished to visit the Upperworld, usually to seduce a nymph.
But when he took Persephone back to Tartarus, the deepest part of Hades,
the Upperworld would change forever.
The name of the ruler of the Underworld was actually Hades. Hades was a
brother of Zeus and of Poseidon; he was usually ignorant of the
happenings of the Upperworld, only emerging rarely from his dark kingdom.
Deep beneath the earth, he owned all its mineral riches, but his favourite
possession was a gift from the Cyclopes: a helmet that rendered him
invisible. (Those familiar with Wagner's Ring Cycle will
recognise the leitmotif, and a number of others in this story of Persephone.)
It was considered imprudent and dangerous to mention the names of certain
gods and goddesses. Thus the Furies, or Cronies, were called Eumenides
(Kindly Ones), and Hades was called Pluto (Rich One).
His golden chariot was pulled by four jet-black horses. While he used the
chariot to periodically visit the Upperworld, in order to seduce a beautiful
nymph, he rarely wished the relationship to last. Until he saw Persephone,
the daughter of Demeter and Zeus.
Demeter was the sister of Zeus and Hades, and one of the most important of
goddesses as she was responsible for Agriculture, and all growing things.
Hades is so enamoured by the beauty of Persephone, he wants her for his
own, so takes her by force down to his kingdom, where she becomes the Queen
of the Underworld.
Demeter mourns for her lost daughter and begs the other gods for help.
So Theseus and Peiritheus (his brother) descend into Hades in search of
Persephone, but are unsuccessful. In fact, they are held captive by
Hades, and Heracles is sent to rescue them. He can only manage to
bring back Theseus; Peiritheus is condemned to remain forever in Hades.
Demeter is so distraught about the loss of her daughter she decides to
forbid any seeds from sprouting. A vast drought spreads throughout the
Upperworld. Zeus becomes vexed, for he is owed a certain tribute, and if
the drought continues his tribute will not be forthcoming.
Some accounts give Zeus a more noble reason for acting on his sister's
behalf: that he empathizes with Demeter and wishes to rectify her loss.
In any event, he convinces his brother Hades to give up Persephone, so
that the Upperworld can again become green and lush.
Hades agrees, provides that Persephone hasn't eaten anything since her
arrival. Alas, she had consumed six pomegranate seeds, so Hades claims she
Zeus will have none of it, and rules that she must forever divide her time
between the Upperworld and the Underworld; four months out of the year she
must stay with her husband, while the rest of the year she may visit her
mother, in the Upperworld.
Thus every year the world retreats briefly into a cold and forbidding
place, until the 21st of March, when Persephone is allowed to emerge
from the Underworld, bringing Spring with her.
The Bayer stars are fairly dim, except for two
two-magnitude stars, alpha2 and beta. The
constellation has several objects of interest, including some fine
double stars and an unusual variable.
Alpha Librae is also known as Zubenelgenubi, a derivation
of an older Arabic name that translates into "Southern Claw" (i.e. of the
Scorpion). The star is a wide binary of unequal stars (see below).
Beta Librae is called Zubeneschamali, "The Northern Claw".
This white star has been described by some to be green in colour; Burnham
points out that truly green stars are close companions to red stars
(such as the companion to Antares), and beta Librae doesn't fit
that category. Still, the impression apparently persists for some
observers; you'll have to decide for yourself.
Double stars in Libra:
Alpha2 and alpha1 Librae form a
very wide double with colour contrast: yellow and pale blue. Note that
alpha2 is the primary: 2.9, 5.3; PA 314, separation 231".
Iota Librae is a multiple system:
The companion iota1a is a rapid binary with a period of 22.35
years, travelling in a retrograde motion.
Iota1B is a fixed wide companion: 4.5, 9.5; PA 111,
Struve 1962 is a fixed pair of equal stars: 6.5, 6.6; PA 188
degrees, separation 11.9".
Variable stars in Libra:
Delta Librae is an Algol-type variable: 4.9-5.9 with a period of
48 Librae (also known as FX Librae) is a noted shell star
that may be dormant for many years, then show rapid activity.
The star has an exceptionally large rotational velocity, and (perhaps as a
consequence) an equatorial ring of gases about twice the diameter of the
star which rapidly expands.
Deep Sky Objects in Libra:
The only notable deep sky object is a rather loose globular cluster of faint
stars: NGC 5897, thought to be about 50,000 light years away. The larger
the telescope, the better the impression.
The cluster is found two degrees southeast of iota Librae.