Alpha Librae (α Librae, abbreviated Alpha Lib, α Lib) is a double star and, despite its ' alpha' designation, it is the second-brightest star system (or star) in the constellation of

Libra Libra generally refers to: * Libra (constellation), a constellation * Libra (astrology), an astrological sign based on the star constellation Libra may also refer to: Arts and entertainment * ''Libra'' (novel), a 1988 novel by Don DeLillo Musi ...

. The two components are designated α¹ Librae and α² Librae. The system bore the traditional name of Zubenelgenubi , though the

International Astronomical Union The International Astronomical Union (IAU; french: link=yes, Union astronomique internationale, UAI) is a nongovernmental organisation with the objective of advancing astronomy in all aspects, including promoting astronomical research, outreac ...

now regards that name as only applying to α² Librae. Alpha² Librae is 0.33 degrees north of the

ecliptic The ecliptic or ecliptic plane is the orbital plane of the Earth around the Sun. From the perspective of an observer on Earth, the Sun's movement around the celestial sphere over the course of a year traces out a path along the ecliptic agains ...

so it can be occulted by the

Moon The Moon is Earth's only natural satellite. It is the fifth largest satellite in the Solar System and the largest and most massive relative to its parent planet, with a diameter about one-quarter that of Earth (comparable to the width of ...

and (very rarely) by

planet A planet is a large, rounded astronomical body that is neither a star nor its remnant. The best available theory of planet formation is the nebular hypothesis, which posits that an interstellar cloud collapses out of a nebula to create a you ...

s. It was occulted by

Venus Venus is the second planet from the Sun. It is sometimes called Earth's "sister" or "twin" planet as it is almost as large and has a similar composition. As an interior planet to Earth, Venus (like Mercury) appears in Earth's sky never f ...

on October 25, 1947; the next occultation by a planet will be by Mercury on 10 November 2052.Peuschel, Marco (2003)
"Astronomische Ereignisse der besonderen Art"
. Retrieved July 10, 2005. Both components are eclipsed ( occulted) by the sun from about 7–9 November. Thus the star can be viewed the whole night, crossing the sky, in early May.

Nomenclature

''α Librae'' ( Latinised to ''Alpha Librae'') is the system's Bayer designation. ''Zubenelgenubi'' , also rendered ''Zuben Elgenubi'', derives from the

Arabic Arabic (, ' ; , ' or ) is a Semitic language spoken primarily across the Arab world.Semitic languages: an international handbook / edited by Stefan Weninger; in collaboration with Geoffrey Khan, Michael P. Streck, Janet C. E.Watson; Walter ...

ّالزُبَانَى الجَنُوبِي ''al-zubānā al-janūbiyy'' "the southern claw", which was coined before Libra was recognized as a constellation distinct from

Scorpius Scorpius is a zodiac constellation located in the Southern celestial hemisphere, where it sits near the center of the Milky Way, between Libra to the west and Sagittarius to the east. Scorpius is an ancient constellation that pre-dates the Gr ...

. The alternative name ''Kiffa Australis'' (''Elkhiffa Australis'') is a partial

Latin Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through the power of the ...

translation of the Arabic ''al-kiffah al-janubiyyah'' ''الكفة الجنوبية'' "southern pan f the scales. Another name used in older astronomy texts, equivalent to "southern pan", was ''Lanx Australis''. In 2016, the

organized a

Working Group on Star Names The International Astronomical Union (IAU) established a Working Group on Star Names (WGSN) in May 2016 to catalog and standardize proper names for stars for the international astronomical community. It operates under Division C – Education ...

(WGSN) to catalogue and standardize proper names for stars. The WGSN approved the name ''Zubenelgenubi'' for ''α² Librae'' on 21 August 2016 and it is now so entered in the IAU Catalog of Star Names. In

Chinese Chinese can refer to: * Something related to China * Chinese people, people of Chinese nationality, citizenship, and/or ethnicity **''Zhonghua minzu'', the supra-ethnic concept of the Chinese nation ** List of ethnic groups in China, people of ...

, (), meaning ''

Root In vascular plants, the roots are the organs of a plant that are modified to provide anchorage for the plant and take in water and nutrients into the plant body, which allows plants to grow taller and faster. They are most often below the su ...

'', refers to an asterism consisting of α² Librae, ι Librae, γ Librae and β Librae. Consequently, the

Chinese name Chinese names or Chinese personal names are names used by individuals from Greater China and other parts of the Chinese-speaking world throughout East and Southeast Asia (ESEA). In addition, many names used in Japan, Korea and Vietnam are ofte ...

for α² Librae itself is (), "the First Star of Root".香港太空館 - 研究資源 - 亮星中英對照表
, Hong Kong Space Museum. Accessed on line November 23, 2010.

Properties

Alpha Librae is about from the

Sun The Sun is the star at the center of the Solar System. It is a nearly perfect ball of hot plasma, heated to incandescence by nuclear fusion reactions in its core. The Sun radiates this energy mainly as light, ultraviolet, and infrared radi ...

. The two brightest components of Alpha Librae form a double star moving together through space as

common proper motion This glossary of astronomy is a list of definitions of terms and concepts relevant to astronomy and cosmology, their sub-disciplines, and related fields. Astronomy is concerned with the study of celestial objects and phenomena that originate outsid ...

companions. The brightest member, α² Librae, is itself a spectroscopic binary system. The second member, α¹ Librae, is separated from the primary system by around . It too is a spectroscopic binary with an orbital period of 5,870 days and an angular separation of 0.383 arcseconds; equal to about 10 AU. The system may have a fifth component, the star KU Librae at a separation of 2.6°, thus forming a hierarchical quintuple star system. KU Lib shares a similar motion through space to the Alpha Librae system, but is separated from the other stars by about a

parsec The parsec (symbol: pc) is a unit of length used to measure the large distances to astronomical objects outside the Solar System, approximately equal to or (au), i.e. . The parsec unit is obtained by the use of parallax and trigonometry, an ...

. It is sufficiently close to be gravitationally bound to the other members, but has a substantially different metallicity. The two brightest members of Alpha Librae are separated in the sky by an

angular distance Angular distance \theta (also known as angular separation, apparent distance, or apparent separation) is the angle between the two sightlines, or between two point objects as viewed from an observer. Angular distance appears in mathematics (in par ...

of 231" (3'51"). The

position angle In astronomy, position angle (usually abbreviated PA) is the convention for measuring angles on the sky. The International Astronomical Union defines it as the angle measured relative to the north celestial pole (NCP), turning positive into the ...

of the companion is 314 degrees. The brighter of the two is a white star of

spectral type In astronomy, stellar classification is the classification of stars based on their spectral characteristics. Electromagnetic radiation from the star is analyzed by splitting it with a prism or diffraction grating into a spectrum exhibiting the ...

A3, with an

apparent magnitude Apparent magnitude () is a measure of the brightness of a star or other astronomical object observed from Earth. An object's apparent magnitude depends on its intrinsic luminosity, its distance from Earth, and any extinction of the object's ...

of 2.8. Its companion is a type F4 star of apparent brightness 5.2. They are probably members of the

Castor Moving Group The Castor Moving Group, or Castor stream, is a moving group of stars sharing similar velocities and directions. The stars that have been identified as part of the group include Castor, Fomalhaut, Vega, α Cephei and α Librae. While the rep ...

of stars that have a similar motion through space and share a common origin some 200 million years ago.

References

External links

*Kaler, Jim (2004)
"STARS: Zubenelgenubi"
Retrieved July 10, 2005. * {{DEFAULTSORT:Alpha Librae Librae, Alpha Binary stars Libra (constellation) A-type subgiants F-type main-sequence stars Zubenelgenubi Castor Moving Group Librae, 08 9 072603 22 5530 1 130819 41 BD-15 3965 Am stars

Nomenclature

Properties

See also

References

External links