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Crux is a centred on four stars in the in a bright portion of the . It is among the most easily distinguished constellations as its hallmark (asterism) stars each have an apparent visual magnitude brighter than +2.8, even though it is the smallest of all 88 modern constellations. Its name is for , and it is dominated by a cross-shaped or kite-like asterism that is commonly known as the Southern Cross.

Predominating the constellation is the first-magnitude blue-white star of (Alpha Crucis), its brightest and most southerly member. There follow four less dominant stars which appear clockwise and in order of lessening magnitude: Mimosa (Beta Crucis), (Gamma Crucis), Imai (Delta Crucis) and Ginan (Epsilon Crucis). Many of these brighter stars are members of the Scorpius–Centaurus Association, a large but loose group of hot blue-white stars that appear to share common origins and motion across the southern .

Crux contains four Cepheid variables, each visible to the naked eye under optimum conditions. Crux also contains the bright and colourful known as the Jewel Box (NGC 4755) on its western border. To the southeast figures a large, relatively near spanning 7° by 5° known as the , portions of which are mapped in the neighbouring constellations of and .


History
The bright stars in Crux were known to the , where regarded them as part of the constellation Centaurus. They were entirely visible as far north as Britain in the fourth millennium BC. However, the precession of the equinoxes gradually lowered the stars below the European horizon, and they were eventually forgotten by the inhabitants of northern latitudes. By 400 , the stars in the constellation we now call Crux never rose above the horizon throughout most of Europe. may have known about the constellation in the 14th century, as he describes an asterism of four bright stars in the southern sky in his . Others argue that Dante's description was allegorical, and that he almost certainly did not know about the constellation.

The 15th century Venetian navigator made note of what was probably the Southern Cross on exiting the in 1455, calling it the carro dell'ostro ("southern chariot"). However, Cadamosto's accompanying diagram was inaccurate.. However, no manuscript of Cadamosto's notebook has survived, only the printed version, and the errors in the diagram may be due to the printer's decision. Historians generally credit João FarasJoão Faras was an astronomer and physician of King Manuel I of Portugal who accompanied Pedro Álvares Cabral in the discovery of Brazil in 1500 for being the first European to depict it correctly. Faras sketched and described the constellation (calling it "Las Guardas") in a letter written on the beaches of Brazil on 1 May 1500 to the Portuguese monarch.

Explorer seems to have observed not only the Southern Cross but also the neighboring Coalsack Nebula on his second voyage in 1501–1502.

Another early modern description clearly describing Crux as a separate constellation is attributed to , an Italian navigator who from 1515–1517 sailed to China and the East Indies in an expedition sponsored by King Manuel I. In 1516, Corsali wrote a letter to the monarch describing his observations of the southern sky, which included a rather crude map of the stars around the south celestial pole including the Southern Cross and the two Magellanic Clouds seen in an external orientation, as on a globe.

and have also been cited as the first uranographers (sky mappers) to distinguish Crux as a separate constellation; their representations date from 1592, the former depicting it on his celestial globe and the latter in one of the small celestial maps on his large wall map. Both authors, however, depended on unreliable sources and placed Crux in the wrong position. Crux was first shown in its correct position on the celestial globes of and in 1598 and 1600. Its stars were first catalogued separately from Centaurus by Frederick de Houtman in 1603. The constellation was later adopted by in 1624 and in 1679. Royer is sometimes wrongly cited as initially distinguishing Crux.


Characteristics
Crux is bordered by the constellations (which surrounds it on three sides) on the east, north and west, and to the south. Covering 68 square degrees and 0.165% of the night sky, it is the smallest of the 88 constellations.
(2019). 9781461408307, Springer. .
The three-letter abbreviation for the constellation, as adopted by the International Astronomical Union in 1922, is 'Cru'. The official constellation boundaries, as set by Eugène Delporte in 1930, are defined by a polygon of four segments. In the equatorial coordinate system, the coordinates of these borders lie between and , while the coordinates are between −55.68° and −64.70°. Its totality figures at least part of the year south of the 25th parallel north.

In tropical regions Crux can be seen in the sky from April to June. Crux is exactly opposite to Cassiopeia on the celestial sphere, and therefore it cannot appear in the sky with the latter at the same time. In this era, south of Cape Town, Adelaide and Buenos Aires (the 34th parallel south), Crux is circumpolar and thus always appears in the sky.

Crux is sometimes confused with the nearby by stargazers. The False Cross is larger and dimmer, does not have a fifth star, and lacks the two prominent nearby "Pointer Stars". Between the two is the even larger and dimmer .


Visibility
Crux is easily visible from the southern hemisphere at practically any time of year. It is also visible near the horizon from of the northern hemisphere for a few hours every night during the northern winter and spring. For instance, it is visible from or any other place at latitude 25° N or less at around 10 pm at the end of April.
(2019). 9780395934319, Houghton Miflin.
There are 5 main stars. Due to , Crux will move closer to the South Pole in the next millennia, up to 67 degrees south declination for the middle of the constellation. But in AD 18000 or BC 8000 Crux will be and was less than 30 degrees south declination making it visible in Northern Europe. Even by AD 14000, it will be visible for most parts of Europe and the whole United States.


Use in navigation
In the Southern Hemisphere, the Southern Cross is frequently used for navigation in much the same way that is used in the Northern Hemisphere. Projecting a line from to (the foot of the crucifix) approximately times beyond gives a point close to the Southern Celestial Pole which is also, coincidentally, where intersects a perpendicular line taken southwards from the east-west axis of to , which are stars at an alike declination to Crux and of a similar width as the cross, but higher magnitude.
9780869780565
are documented as using Crux for night orientation in the and .

Alpha and Beta Centauri are of similar declinations (thus distance from the pole) are often referred as the "Southern Pointers" or just "The Pointers", allowing people to easily identify the Southern Cross, the constellation of Crux. Very few bright stars of importance lie between Crux and the pole itself, although the constellation is fairly easily recognised immediately beneath Crux.


Features

Stars
Within the constellation's borders, there are 49 stars brighter than or equal to apparent magnitude 6.5. The four main stars that form the asterism are Alpha, Beta, Gamma, and Delta Crucis.
  • or Alpha Crucis is a triple star 321 light-years from Earth. A rich blue in colour, with a visual magnitude 0.8 to the unaided eye, it has two close components of a similar magnitude, 1.3 and 1.8 respectively, plus another much wider component of the 5th magnitude. The two close components are resolved in a small amateur telescope and the wide component is readily visible in a pair of binoculars.
  • Mimosa or Beta Crucis is a blue-hued giant star of magnitude 1.3, and lies 353 light-years from Earth. It is a -type with a variation of less than 0.1 magnitudes.
  • or Gamma Crucis is an optical . The primary is a red-hued giant star of magnitude 1.6, 88 light-years from Earth, and is one of the closest to Earth. Its secondary component is magnitude 6.5, 264 light-years from Earth.
  • Imai (Delta Crucis) is a magnitude 2.8 blue-white hued star about 345 light-years from Earth. Like Mimosa it is a Beta Cepheid variable.

There is also a fifth star, that is often included with the Southern Cross.

  • Ginan (Epsilon Crucis) is an orange-hued giant star of magnitude 3.6, 228 light-years from Earth.

There are several other naked-eye stars within the borders of Crux, especially:

  • is a visual 125 light-years from Earth. The primary is an orange-hued giant of magnitude 4.6 and the secondary at magnitude 9.5.

  • or Mu1,2 Crucis is a wide double star where the components are about 370 light-years from Earth. Equally blue-white in colour, the components are magnitude 4.0 and 5.1 respectively, and are easily divisible in small amateur telescopes or large binoculars.


Scorpius–Centaurus Association members
Unusually, a total of 15 of the 23 brightest stars in Crux are spectrally blue-white B-type stars. Among the five main bright stars, Imai, and probably Acrux and Mimosa, are each likely co-moving B-type members of the Scorpius–Centaurus Association, the nearest OB association to the . They are among the highest-mass stellar members of the Lower Centaurus-Crux subgroup of the association, with ages of roughly 10 to 20 million years. Other members include the blue-white stars , and both the components of the visual , .


Variable stars
Crux contains many . It boasts four that may all reach naked eye visibility.

  • ranges from magnitude 5.34 to 5.58 over 3.3428 days,
  • ranges from 6.32 to 6.83 over 6.73331 days,
  • ranges from 6.22 to 6.92 over 4.68997 days,
  • ranges from 6.4 to 7.23 over 5.82575 days.

Other well studied variable stars includes:

  • and Theta2 Crucis, that are both Beta Cepheid type variable stars.

  • , also known as Welch's Red Variable, is a that ranges from magnitude 6.6 to 9.8 over 530 days. Discovered in October 1969, it has become redder and brighter (mean magnitude changing from 8.047 to 7.762) and its period lengthened by 25% in the first thirty years since its discovery.


Host star exoplanets in Crux
The star HD 106906 has been found to have a planet—HD 106906 b—that has a larger orbit than any other discovered to date.


Deep-sky objects
Crux is placed in a bright part of the Milky Way, and features many deep-sky objects within its boundaries. The most well known of them include:

  • The is the most prominent in the skies, and is easily visible to the naked eye as a prominent dark patch in the southern Milky Way. It can be found 6.5° southeast from the centre of Crux or 3° east from Acrux. It large area covers about 7° by 5°, and is away from . Not all of the nebula is in the borders of Crux; some of it is technically in the constellations of , .

  • The Jewel Box, Kappa Crucis Cluster or NGC 4755, is a small but bright that appears as a fuzzy star to the naked eye and is placed very close to the westernmost boundary of Crux: about 1° southwest of Mimosa. The combined or total magnitude is 4.2 and it lies at a distance of from Earth. The cluster was given its name by , based on the range of colours visible throughout the star cluster in his telescope. About seven million years old, it is one of the youngest open clusters in the Milky Way, and it appears to have the shape of a letter 'A'. The Jewel Box Cluster is classified as Shapley class 'g' and Trumpler class 'I 3 r -' cluster; it is a very rich, centrally-concentrated cluster detached from the surrounding star field. It has more than 100 stars that range significantly in brightness. The brightest cluster stars are mostly , though the cluster contains at least one . Kappa Crucis is a true member of the cluster that bears its name, and is one of the brighter stars at magnitude 5.9.


Cultural significance
The most prominent feature of Crux is the distinctive asterism known as the Southern Cross. It has great significance in the cultures of the southern hemisphere, particularly of Australia and New Zealand.


Flags and symbols
Several southern countries and organisations have traditionally used Crux as a national or distinctive symbol. The four or five brightest stars of Crux appear, heraldically standardised in various ways, on the flags of Australia, Brazil, New Zealand, Papua New Guinea and . They also appear on the flags of the Australian state of Victoria, the Australian Capital Territory, the Northern Territory, as well as the flag of Magallanes Region of Chile, the flag of (Brazil) and several provincial flags and emblems (for example, Tierra del Fuego and Santa Cruz). The flag of the trading zone displays the four brightest stars. Crux also appears on the Brazilian coat of arms and, , on the cover of Brazilian passports.

A Cross also gets a mention in the lyrics of the Brazilian National Anthem (1909): " A imagem do Cruzeiro resplandece" ("the image of the Cross shines"). Five stars appear in the logo of the Brazilian football team Cruzeiro Esporte Clube and in the Brazilian coat of arms, and the cross has featured as name of the Brazilian currency (the cruzeiro from 1942 to 1986 and again from 1990 to 1994). All coins of the (1998) series of the display the constellation.

Songs and literature reference the Southern Cross, including the Argentine epic poem Martín Fierro. The Argentinian singer Charly García says that he is "from the Southern Cross" in the song "No voy en tren".

"Southern Cross" is a single released by Crosby, Stills and Nash in 1981. It reached #18 on Billboard Hot 100 in late 1982.

The Order of the Southern Cross is a Brazilian order of chivalry awarded to "those who have rendered significant service to the Brazilian nation".

In "O Sweet Saint Martin's Land", the lyrics mention the Southern Cross: Thy Southern Cross the night.

A stylized version of Crux appears on the Australian . The constellation was also used on the dark blue, shield-like patch worn by personnel of the U.S. Army's Americal Division, which was organized in the Southern Hemisphere, on the island of , and also on the blue diamond of the U.S. 1st Marine Division, which fought on the Southern Hemisphere islands of and .

The Petersflagge flag of the German East Africa Company of 1885–1920, which included a constellation of five white five-pointed Crux "stars" on a red ground, later served as the model for symbolism associated with generic German colonial-oriented organisations: the Reichskolonialbund of 1936–1943 and the (1956/1983 to the present).

Southern Cross station is a major rail terminal in Melbourne, Australia.

The Personal Ordinariate of Our Lady of the Southern Cross is a personal ordinariate of the Roman Catholic Church primarily within the territory of the Australian Catholic Bishops Conference for groups of Anglicans who desire full communion with the Catholic Church in Australia and Asia.

The Knights of the Southern Cross (KSC) is a Catholic fraternal order throughout Australia.


In non-Western astronomy
In Australian Aboriginal astronomy, Crux and the mark the head of the 'Emu in the Sky' (which is seen in the dark spaces rather than in the patterns of stars) in several Aboriginal cultures,Norris, R. (2007): The Emu in the Sky Australian Aboriginal Astronomy website. Retrieved 2 May 2013. while Crux itself is said to be a sitting in a tree ( of the region of northwestern Victoria), a representation of the sky deity Mirrabooka (Quandamooka people of Stradbroke Island), a stingray ( of ), or an eagle ( of the ).Musgrave, I.: May sky guide: The Eta Aquarid meteor shower, constellations and planets ABC News, 2 May 2016. Retrieved 2 May 2016. Two Pacific constellations also included . Torres Strait Islanders in modern-day Australia saw Gamma Centauri as the handle and the four stars as the of Tagai's Fishing Spear. The of central Australia saw the four Cross stars as the talon of an and Gamma Centauri as its leg.

Various peoples in the and Brazil viewed the four main stars as the body of a ray. In both Indonesia and Malaysia, it is known as Bintang Pari and Buruj Pari respectively ("ray stars")

The of Indonesia called this constellation Gubug pèncèng ("raking hut") or lumbung ("the granary"), because the shape of the constellation was like that of a .

The Māori name for the Southern Cross is Te Punga ("the "). It is thought of as the anchor of Tama-rereti's waka (the ), while the Pointers are its rope. In it is known as Toloa ("duck"); it is depicted as a duck flying south, with one of his wings () wounded because Ongo tangata ("two men", α and β Centauri) threw a stone at it. The Coalsack is known as Humu (the ""), because of its shape. In Samoa the constellation is called Sumu ("triggerfish") because of its rhomboid shape, while α and β Centauri are called Luatagata (Two Men), just as they are in Tonga. The peoples of the saw several figures in the Southern Cross. These included a knee protector and a net used to catch . Neighboring peoples in the saw these stars as a fish.

In , the language of Patagonian , the name of the Southern Cross is Melipal, which means "four stars". In Quechua, the language of the civilization, Crux is known as "", which means literally "stair" ( chaka, bridge, link; hanan, high, above), but carries a deep symbolism within Quechua mysticism. Acrux and Mimosa make up one foot of the Great Rhea, a constellation encompassing and along with the two bright stars. The Great Rhea was a constellation of the of Brazil. The Mocoví people of Argentina also saw a rhea including the stars of Crux. Their rhea is attacked by two dogs, represented by bright stars in Centaurus and Circinus. The dogs' heads are marked by and . The rhea's body is marked by the four main stars of Crux, while its head is and its feet are the bright stars of . The of Brazil had a sprawling constellation representing a bird snare. It included the bright stars of Crux, the southern part of Centaurus, Circinus, at least one star in Lupus, the bright stars of Musca, Beta and the optical double star Delta1,2 Chamaeleontis: and some of the stars of , and Mensa. The of state in Brazil saw the stars of Crux as Aganagi angry bees having emerged from the Coalsack, which they saw as the beehive.

(1987). 9780816510221, University of Arizona Press. .

Among , the four most visible stars of Crux are considered iggaren, i.e. four Maerua crassifolia trees. The of saw the constellation as Dithutlwa, two giraffes – Acrux and Mimosa forming a male, and Gacrux and Imai (Delta Crucis) forming the female.


See also


Notes
Citations

Sources


External links

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