Libra (constellation)

From Wikipedia, the free encyclopedia

This article is about the constellation. For other uses, see Libra.

Libra
click for larger image
Abbreviation	Lib
Genitive	Librae
Symbology	the Balance
Right ascension	15 h
Declination	−15°
Area	538 sq. deg. Ranked 29th
Number of main stars	4, 6
Number of stars (Bayer-Flamsteed)	44
Number of stars with planets (BF, variable, other stars)	1, 2
Number of bright stars (magnitude < 3)	2
Number of nearby stars (Distance < 100 ly)	12
Brightest star	Zubeneschamali (β Lib) (App. magnitude 2.6)
Nearest Star	42 Lib (Distance: 66.6 ly)
Meteor showers	May Librids
Bordering constellations	Serpens Caput Virgo Hydra Centaurus (corner) Lupus Scorpius Ophiuchus
Visible at latitudes between +65° and −90° Best visible at 21:00 (9 p.m.) during the month of June

Libra (IPA: /ˈliːbrə/, Latin: balance, symbol , Unicode ♎) is a constellation of the zodiac. It is a fairly inconspicuous constellation and has no star of first magnitude, lying between Virgo to the west and Scorpius to the east. As the names of the brighter stars testify, it was at one point part of Scorpius' claws.

1 Notable features
2 Mythology
3 Stars
4 History
5 External links

[edit] Notable features

The brightest stars in Libra form a rectangle:

α Librae, Zubenelgenubi ("southern claw"), a visual binary;
β Librae, Zubeneschamali ("northern claw");
γ Librae, Zubenelakrab ("scorpion's claw");
σ Librae, an eclipsing variable.

α and β Librae are the scales' balance beam, and γ and σ are the weighing pans.

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).

[edit] Mythology

The constellation, which had originally formed part of the claws of the scorpion (Scorpio), is the youngest of the Zodiac and the only one not to represent a living creature. In later Greek mythology, the constellation, which when considered on its own looks vaguely like a set of scales, was considered to depict the scales held by Astraea (identified as Virgo), the goddess of justice.

Since Libra was originally part of Virgo (as scales), and before that part of Scorpio, it was not a distinct entity for which a zodiac sign was named. Its place may have been taken by Boötes, which is the nearest to the ecliptic. Since the place Boötes should have held on the ecliptic is vacant, it may have, together with Ursa Major, Draco, and Ursa Minor, also in Libra, led to the myth of the apples of the Hesperides, one of The Twelve Labours of Herakles.

[edit] Astrology

Main article: Libra (astrology)

The Western astrological sign Libra of the tropical zodiac (September 23–October 22) differs from the astronomical constellation and the Hindu astrological sign of the sidereal zodiac (October 31–November 22).

In some cosmologies, Libra is associated with the classical element Air, and thus called an Air Sign (with Aquarius and Gemini). It is also one of the four cardinal signs (along with Aries, Cancer, and Capricorn). Librans are the diplomats of the Zodiac. Their polar opposite is Aries. It is the domicile of Venus and the exaltation of Saturn. Each astrological sign is assigned a part of the body, viewed as the seat of its power. Libra rules the lower back and kidneys. The symbol for Libra is the Scales, making it the only sign of this zodiac whose symbol is not a living creature.

[edit] Graphic visualization

Diagram of a fuller way to connect the stars of the constellation Libra: showing the two plates and the beam of the balance.

The stars in the constellation Libra can be connected more fully, graphically showing a balance.

The star beta Librae, of third magnitude, represents the top of the balance. The stars gamma Librae and alpha Librae represent the balance beam: alpha Librae being of third magnitude as well.

The stars upsilon Librae and tau Librae represent the left plate of the balance, whereas the star sigma Librae represents the right plate of the balance. All three of these stars are of the third magnitude.

[edit] Reference

H. A. Rey, The Stars — A New Way To See Them. Enlarged World-Wide Edition. Houghton Mifflin, Boston, 1997. ISBN 0-395-24830-2.

[edit] Stars

Stars with proper names:

(α Lib) Zubenelgenubi [Zuben Elgenubi] or Kiffa Australis [Elkhiffa australis] (8/α¹ Lib, 9/α² Lib) – double 5.15, 2.75

< الزبن الجنوبي az-zuban al-janūbiyy The southern claw (of the scorpion)

< ? al-kiffah al-janūbiyy The southern pan (of the scales)

(27/β Lib) 2.61 Zubeneschamali [Zuben Eschamali, Zuben el Chamali, Zubenesch, Zubenelg] or Kiffa Borealis

< الزبن الشمالي az-zuban aš-šamāliyy The northern claw (of the scorpion)

< ? al-kiffah aš-šamāliyy The northern pan (of the scales)

(38/γ Lib) 3.91 Zuben Elakrab [Zuben (el) Hakrabi, Zuben Hakraki]

< زبن العقرب zuban al-^caqrab The claw of the scorpion

(19/δ Lib) 4.91 Zuben Elakribi or Mulu-lizi (see γ Lib)

(η Lib) 5.41 Zuben Hakrabi [Zuban Alakrab] (see γ Lib)

(21/ν Lib) (or Zuben Hakrabim, see γ Lib) 5.19
(2/σ Lib) 3.29 Brachium or Cornu (or Zuben el Genubi, see α Lib; or Zuben Hakrabi, see γ Lib; or Ankaa, see α Phe) — eclipsing variable

Stars with Bayer designations:

ε Lib 4.92; ζ Lib 5.53; θ Lib 4.13; ι Lib 4.54; κ Lib 4.75; λ Lib 5.04; μ Lib 5.32; ξ¹ Lib 5.78; ξ² Lib 5.48; ο Lib 6.14; τ Lib 3.66; υ Lib 3.60

Stars with Flamsteed designations:

2 Lib 6.22; 4 Lib 5.70; 5 Lib 6.33; 11 Lib 4.93; 12 Lib 5.27; 16 Lib 4.47; 17 Lib 6.61; 18 Lib 5.88; 22 Lib 6.41; 23 Lib 6.47 – has a planet; 25 Lib 6.07; 26 Lib 6.18; 28 Lib 6.16; 30 Lib 6.46; 32 Lib 5.64; 33 Lib 6.69; 34 Lib 5.82; 36 Lib 5.13; 37 Lib 4.61; 41 Lib 5.36; 42 Lib 4.97; 47 Lib 5.95; 48 Lib 4.95; 49 Lib 5.47; 50 Lib 5.53

Other notable stars:

HR 5568

[edit] History

"Scorpion's claws" is zubānā in Arabic and zibanitu in Akkadian. In ancient Mesopotamia a weighing scale was often the arm and the pans without a stand, and to use it it was hung up by a string tied to the midpoint of the arm. A resulting fancied resemblance to a scorpion hung up by the end of its tail resulted in the Akkadian word zibanitu also being used to mean "weighing scale". The constellation was refigured by taking the other meaning of zibanitu.