Acrux is the brightest
star
A star is an astronomical object comprising a luminous spheroid of plasma (physics), plasma held together by its gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked ...
in the southern
constellation
A constellation is an area on the celestial sphere in which a group of visible stars forms Asterism (astronomy), a perceived pattern or outline, typically representing an animal, mythological subject, or inanimate object.
The origins of the e ...
of
Crux
Crux () is a constellation of the southern sky that is centred on four bright stars in a cross-shaped asterism commonly known as the Southern Cross. It lies on the southern end of the Milky Way's visible band. The name ''Crux'' is Latin for c ...
. It has the
Bayer designation α Crucis, which is
Latinised to Alpha Crucis and abbreviated Alpha Cru or α Cru. With a combined
visual 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 +0.76, it is the
13th-brightest star in the
night sky
The night sky is the nighttime appearance of celestial objects like stars, planets, and the Moon, which are visible in a clear sky between sunset and sunrise, when the Sun is below the horizon.
Natural light sources in a night sky include ...
. It is the most southerly star of the
asterism known as the Southern Cross and is the southernmost
first-magnitude star, 2.3 degrees more southerly than
Alpha Centauri. This system is located at a distance of 321
light-year
A light-year, alternatively spelled light year, is a large unit of length used to express astronomical distances and is equivalent to about 9.46 trillion kilometers (), or 5.88 trillion miles ().One trillion here is taken to be 1012 ...
s 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 ...
.
[
To the naked eye Acrux appears as a single star, but it is actually a multiple star system containing six components. Through optical ]telescope
A telescope is a device used to observe distant objects by their emission, absorption, or reflection of electromagnetic radiation. Originally meaning only an optical instrument using lenses, curved mirrors, or a combination of both to observe ...
s, Acrux appears as a triple star
A star system or stellar system is a small number of stars that orbit each other, bound by gravitational attraction. A large group of stars bound by gravitation is generally called a '' star cluster'' or '' galaxy'', although, broadly speak ...
, whose two brightest components are visually separated by about 4 arcseconds and are known as Acrux A and Acrux B, α1 Crucis and α2 Crucis, or α Crucis A and α Crucis B. Both components are B-type star
A B-type main-sequence star (B V) is a main-sequence (hydrogen-burning) star of spectral type B and luminosity class V. These stars have from 2 to 16 times the mass of the Sun and surface temperatures between 10,000 and 30,000 K. B-type star ...
s, and are many times more massive and luminous than the Sun. α1 Crucis is itself a spectroscopic binary
A binary star is a system of two star, stars that are gravity, gravitationally bound to and in orbit around each other. Binary stars in the night sky that are seen as a single object to the naked eye are often resolved using a telescope as separa ...
with components designated α Crucis Aa (officially named Acrux, historically the name of the entire system) and α Crucis Ab. Its two component stars orbit every 76 days at a separation of about 1 astronomical unit
The astronomical unit (symbol: au, or or AU) is a unit of length, roughly the distance from Earth to the Sun and approximately equal to or 8.3 light-minutes. The actual distance from Earth to the Sun varies by about 3% as Earth orbits t ...
(AU).[ ]HR 4729
HR 4729 (HD 108250) is a multiple star system located about from the Sun in the constellation of Crux and part of the asterism known as the Southern Cross. It is a close companion of α Crucis and sometimes called α Crucis C.
Nomenc ...
, also known as Acrux C, is a more distant companion, forming a triple star through small telescopes. C is also a spectroscopic binary, which brings the total number of stars in the system to at least five.
Nomenclature
''α Crucis'' (Latinised to ''Alpha Crucis'') is the system's Bayer designation; ''α1'' and ''α2 Crucis'', those of its two main components stars. The designations of these two constituents as ''Acrux A'' and ''Acrux B'' and those of ''A's'' components—''Acrux Aa'' and ''Acrux Ab''—derive from the convention used by the Washington Multiplicity Catalog
A star system or stellar system is a small number of stars that orbit each other, bound by gravitational attraction. A large group of stars bound by gravitation is generally called a ''star cluster'' or ''galaxy'', although, broadly speaking, ...
(WMC) for multiple star systems, and adopted by 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 ...
(IAU).
The historical name ''Acrux'' for ''α1 Crucis'' is an " Americanism" coined in the 19th century, but entering common use only by the mid 20th century. In 2016, 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 ...
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 catalog and standardize proper names for stars. The WGSN states that in the case of multiple stars
A star system or stellar system is a small number of stars that orbit each other, bound by gravitational attraction. A large group of stars bound by gravitation is generally called a ''star cluster'' or ''galaxy'', although, broadly speaking, ...
the name should be understood to be attributed to the brightest component by visual brightness. The WGSN approved the name ''Acrux'' for the star ''Acrux Aa'' on 20 July 2016 and it is now so entered in the IAU Catalog of Star Names.
Since Acrux is at −63° declination
In astronomy, declination (abbreviated dec; symbol ''δ'') is one of the two angles that locate a point on the celestial sphere in the equatorial coordinate system, the other being hour angle. Declination's angle is measured north or south of the ...
, making it the southernmost first-magnitude star, it is only visible south of latitude
In geography, latitude is a coordinate that specifies the north– south position of a point on the surface of the Earth or another celestial body. Latitude is given as an angle that ranges from –90° at the south pole to 90° at the north pol ...
27° North. It barely rises from cities such as Miami
Miami ( ), officially the City of Miami, known as "the 305", "The Magic City", and "Gateway to the Americas", is a East Coast of the United States, coastal metropolis and the County seat, county seat of Miami-Dade County, Florida, Miami-Dade C ...
, United States
The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 states, a federal district, five major unincorporated territorie ...
, or Karachi
Karachi (; ur, ; ; ) is the most populous city in Pakistan and 12th most populous city in the world, with a population of over 20 million. It is situated at the southern tip of the country along the Arabian Sea coast. It is the former cap ...
, Pakistan
Pakistan ( ur, ), officially the Islamic Republic of Pakistan ( ur, , label=none), is a country in South Asia. It is the world's List of countries and dependencies by population, fifth-most populous country, with a population of almost 24 ...
(both around 25°N) and not at all from , United States
The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 states, a federal district, five major unincorporated territorie ...
, or Cairo
Cairo ( ; ar, القاهرة, al-Qāhirah, ) is the capital of Egypt and its largest city, home to 10 million people. It is also part of the largest urban agglomeration in Africa, the Arab world and the Middle East: The Greater Cairo metro ...
, Egypt
Egypt ( ar, مصر , ), officially the Arab Republic of Egypt, is a transcontinental country spanning the northeast corner of Africa and southwest corner of Asia via a land bridge formed by the Sinai Peninsula. It is bordered by the Mediter ...
(both about 30°N). Because of Earth's axial precession
In astronomy, axial precession is a gravity-induced, slow, and continuous change in the orientation of an astronomical body's rotational axis. In the absence of precession, the astronomical body's orbit would show axial parallelism. In particu ...
, the star was visible to ancient Hindu
Hindus (; ) are people who religiously adhere to Hinduism.Jeffery D. Long (2007), A Vision for Hinduism, IB Tauris, , pages 35–37 Historically, the term has also been used as a geographical, cultural, and later religious identifier for ...
astronomers in India
India, officially the Republic of India (Hindi: ), is a country in South Asia. It is the seventh-largest country by area, the second-most populous country, and the most populous democracy in the world. Bounded by the Indian Ocean on the so ...
who named it ''Tri-shanku''. It was also visible to the ancient Romans
In modern historiography, ancient Rome refers to Roman people, Roman civilisation from the founding of the city of Rome in the 8th century BC to the collapse of the Western Roman Empire in the 5th century AD. It encompasses the Roman Kingdom ...
and Greeks
The Greeks or Hellenes (; el, Έλληνες, ''Éllines'' ) are an ethnic group and nation indigenous to the Eastern Mediterranean and the Black Sea regions, namely Greece, Cyprus, Albania, Italy, Turkey, Egypt, and, to a lesser extent, oth ...
, who regarded it as part of the constellation of Centaurus
Centaurus is a bright constellation in the southern sky. One of the largest constellations, Centaurus was included among the 48 constellations listed by the 2nd-century astronomer Ptolemy, and it remains one of the 88 modern constellations. ...
.
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 ...
, (, "Cross
A cross is a geometrical figure consisting of two intersecting lines or bars, usually perpendicular to each other. The lines usually run vertically and horizontally. A cross of oblique lines, in the shape of the Latin letter X, is termed a sa ...
"), refers to an asterism consisting of Acrux, Mimosa
''Mimosa'' is a genus of about 590 species of herbs and shrubs, in the mimosoid clade of the legume family Fabaceae. The generic name is derived from the Greek word (''mimos''), an "actor" or "mime", and the feminine suffix -''osa'', "resembl ...
, Gamma Crucis and Delta Crucis
Delta Crucis or δ Crucis, also identified as Imai (), is a star in the southern constellation of Crux, and is the faintest of the four bright stars that form the prominent asterism known as the Southern Cross. This star has an apparent ...
. Consequently, Acrux itself is known as (, "the Second Star of Cross").
This star is known as ''Estrela de Magalhães'' ("Star of Magellan
Ferdinand Magellan ( or ; pt, Fernão de Magalhães, ; es, link=no, Fernando de Magallanes, ; 4 February 1480 – 27 April 1521) was a Portuguese explorer. He is best known for having planned and led the 1519 Spanish expedition to the East ...
") in Portuguese
Portuguese may refer to:
* anything of, from, or related to the country and nation of Portugal
** Portuguese cuisine, traditional foods
** Portuguese language, a Romance language
*** Portuguese dialects, variants of the Portuguese language
** Portu ...
.
Stellar properties
The two components, α1 and α2 Crucis, are separated by 4 arcseconds
A minute of arc, arcminute (arcmin), arc minute, or minute arc, denoted by the symbol , is a unit of angular measurement equal to of one degree. Since one degree is of a turn (or complete rotation), one minute of arc is of a turn. The ...
. α1 is magnitude 1.40 and α2 is magnitude 2.09, both early class B stars, with surface temperatures of about 28,000 and , respectively. Their luminosities are 25,000 and 16,000 times that of the Sun. α1 and α2 orbit over such a long period that motion is only barely seen. From their minimum separation of 430 astronomical units, the period is estimated to be around 1,500 years.
α1 is itself a spectroscopic binary star
A binary star is a system of two stars that are gravitationally bound to and in orbit around each other. Binary stars in the night sky that are seen as a single object to the naked eye are often resolved using a telescope as separate stars, in wh ...
, with its components thought to be around 14 and 10 times the mass of the Sun
The solar mass () is a standard unit of mass in astronomy, equal to approximately . It is often used to indicate the masses of other stars, as well as stellar clusters, nebulae, galaxies and black holes. It is approximately equal to the mass ...
and orbiting in only 76 days at a separation of about . The masses of α2 and the brighter component α1 suggest that the stars will someday explode as supernova
A supernova is a powerful and luminous explosion of a star. It has the plural form supernovae or supernovas, and is abbreviated SN or SNe. This transient astronomical event occurs during the last evolutionary stages of a massive star or when ...
e. Component Ab may perform electron capture in the degenerate O+Ne+Mg core and trigger a supernova explosion,[ otherwise it will become a massive white dwarf.]
Photometry with the TESS Tess or TESS may refer to:
Music
* Tess (band), a Spanish pop band active from 2000 to 2005
* TESS (musician), a UK musician
Film and theatre
* ''Tess'' (1979 film), a 1979 film adaptation of '' Tess of the d'Urbervilles''
* ''Tess'' (2016 film ...
satellite has shown that one of the stars in the α Crucis system is a β Cephei variable Beta Cephei variables, also known as Beta Canis Majoris stars, are variable stars that exhibit small rapid variations in their brightness due to pulsations of the stars' surfaces, thought due to the unusual properties of iron at temperatures of 200, ...
, although α1 and α2 Crucis are too close for TESS to resolve and determine which one is the pulsator.[
Rizzuto and colleagues determined in 2011 that the α Crucis system was 66% likely to be a member of the Lower Centaurus–Crux sub-group of the Scorpius–Centaurus association. It was not previously seen to be a member of the group.]
The cooler, less-luminous B-class star HR 4729
HR 4729 (HD 108250) is a multiple star system located about from the Sun in the constellation of Crux and part of the asterism known as the Southern Cross. It is a close companion of α Crucis and sometimes called α Crucis C.
Nomenc ...
(HD 108250) lies 90 arcseconds away from triple star system α Crucis and shares its motion through space, suggesting it may be gravitationally bound to it, and it is therefore generally assumed to be physically associated. It is itself a spectroscopic binary system, sometimes catalogued as component C (Acrux C) of the Acrux multiple system. Another fainter visual companion listed as component D or Acrux D. A further seven faint stars are also listed as companions out to a distance of about two arc-minutes.
On 2 October 2008, the Cassini–Huygens
''Cassini–Huygens'' ( ), commonly called ''Cassini'', was a space research, space-research mission by NASA, the European Space Agency (ESA), and the Italian Space Agency (ASI) to send a space probe to study the planet Saturn and its system, i ...
spacecraft resolved three of the components (A, B and C) of the multiple star system as Saturn
Saturn is the sixth planet from the Sun and the second-largest in the Solar System, after Jupiter. It is a gas giant with an average radius of about nine and a half times that of Earth. It has only one-eighth the average density of Earth; h ...
's disk occulted it.
In culture
Acrux is represented in the flags of Australia
Australia, officially the Commonwealth of Australia, is a Sovereign state, sovereign country comprising the mainland of the Australia (continent), Australian continent, the island of Tasmania, and numerous List of islands of Australia, sma ...
, New Zealand
New Zealand ( mi, Aotearoa ) is an island country in the southwestern Pacific Ocean. It consists of two main landmasses—the North Island () and the South Island ()—and over 700 smaller islands. It is the sixth-largest island count ...
, Samoa
Samoa, officially the Independent State of Samoa; sm, Sāmoa, and until 1997 known as Western Samoa, is a Polynesian island country consisting of two main islands (Savai'i and Upolu); two smaller, inhabited islands (Manono Island, Manono an ...
and Papua New Guinea
Papua New Guinea (abbreviated PNG; , ; tpi, Papua Niugini; ho, Papua Niu Gini), officially the Independent State of Papua New Guinea ( tpi, Independen Stet bilong Papua Niugini; ho, Independen Stet bilong Papua Niu Gini), is a country i ...
as one of five stars which comprise the Southern Cross
Crux () is a constellation of the southern sky that is centred on four bright stars in a cross-shaped asterism commonly known as the Southern Cross. It lies on the southern end of the Milky Way's visible band. The name ''Crux'' is Latin for ...
. It is also featured in the flag of Brazil
The national flag of Brazil ( pt, bandeira do Brasil), is a blue disc depicting a starry sky (which includes the Southern Cross) spanned by a curved band inscribed with the national motto "''Ordem e Progresso''" ("Order and Progress"), within a ...
, along with 26 other stars, each of which represents a state; Acrux representing the state of São Paulo
São Paulo (, ; Portuguese for 'Saint Paul') is the most populous city in Brazil, and is the capital of the state of São Paulo, the most populous and wealthiest Brazilian state, located in the country's Southeast Region. Listed by the GaWC a ...
. It is also represented (as part of the Southern Cross) on the cover of the current (from 2015) Brazilian passport
The Brazilian passport is the official document for foreign travel issued by the federal government, through the Federal Police.
A new model was officially introduced in July 2015 that complies with both Mercosul and ICAO standards, and bring a ...
.
The Brazilian oceanographic research vessel ''Alpha Crucis'' is named after the star.
See also
* Lists of stars
The following are lists of stars. These are astronomical objects that spend some portion of their existence generating energy through thermonuclear fusion.
By location
* Lists of stars by constellation
By name
* List of traditional star names
...
References
External links
* http://jumk.de/astronomie/big-stars/acrux.shtml
* http://www.daviddarling.info/encyclopedia/A/Acrux.html
{{DEFAULTSORT:Acrux
Crucis, Alpha
Double stars
B-type main-sequence stars
B-type subgiants
Crux (constellation)
Lower Centaurus Crux
Acrux
Acrux is the brightest star in the southern constellation of Crux. It has the Bayer designation α Crucis, which is Latinised to Alpha Crucis and abbreviated Alpha Cru or α Cru. With a combined visual magnitude of +0.76, it is the 1 ...
Triple star systems
6
060718
108248 9
4730 1
Crucis, 26 7
Spectroscopic binaries
Durchmusterung objects