Crux

Coordinates: Sky map 12h 30m 00s, −60° 00′ 00″
Source: Wikipedia, the free encyclopedia.
For other uses, see Crux (disambiguation). "Southern Cross" redirects here. For other uses, see Southern Cross (disambiguation).
Crux
Constellation
Acrux (α Cru) (0.87m)
Messier objects0
Meteor showersCrucids
Bordering
constellations		Centaurus
Musca
Visible at latitudes between +20° and −90°.
Best visible at 21:00 (9 p.m.) during the month of May.

Crux (

apparent visual magnitude
brighter than +2.8. It has attained a high level of cultural significance in many Southern Hemisphere states and nations.

Blue-white

ε Crucis (Ginan) also lies within the cross asterism. 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 Milky Way.

Crux contains four Cepheid variables, each visible to the naked eye under optimum conditions. Crux also contains the bright and colourful open cluster known as the Jewel Box (NGC 4755) on its eastern border. Nearby to the southeast is a large dark nebula spanning 7° by 5° known as the Coalsack Nebula, portions of which are mapped in the neighbouring constellations of Centaurus and Musca.

History

The bright stars in Crux were known to the

precession of the equinoxes gradually lowered the stars below the European horizon, and they were eventually forgotten by the inhabitants of northern latitudes.[3] By 400 AD, the stars in the constellation now called Crux never rose above the horizon throughout most of Europe. Dante 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 Divine Comedy.[4][5] His description, however, may be allegorical, and the similarity to the constellation a coincidence.[6]

Depiction of the Crux by João Faras in May 1500

The 15th century Venetian navigator Alvise Cadamosto made note of what was probably the Southern Cross on exiting the Gambia River in 1455, calling it the carro dell'ostro ("southern chariot"). However, Cadamosto's accompanying diagram was inaccurate.[7][8] Historians generally credit João Faras[a] 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.[9][10]

Explorer Amerigo Vespucci seems to have observed not only the Southern Cross but also the neighboring Coalsack Nebula on his second voyage in 1501–1502.[11]

Another early modern description clearly describing Crux as a separate constellation is attributed to Andrea Corsali, an Italian navigator who from 1515 to 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.[12][13]

Emery Molyneux and Petrus Plancius 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 Petrus Plancius and Jodocus Hondius in 1598 and 1600. Its stars were first catalogued separately from Centaurus by Frederick de Houtman in 1603.[14] The constellation was later adopted by Jakob Bartsch in 1624 and Augustin Royer in 1679. Royer is sometimes wrongly cited as initially distinguishing Crux.[2]

Characteristics

Southern Cross from New Zealand

Crux is bordered by the constellations Centaurus (which surrounds it on three sides) on the east, north and west, and Musca to the south. Covering 68 square degrees and 0.165% of the night sky, it is the smallest of the 88 constellations.[15] The three-letter abbreviation for the constellation, as adopted by the International Astronomical Union in 1922, is "Cru".[16] The official constellation boundaries, as set by Belgian astronomer Eugène Delporte in 1930, are defined by a polygon of four segments. In the equatorial coordinate system, the right ascension coordinates of these borders lie between 11h 56.13m and 12h 57.45m , while the declination coordinates are between −55.68° and −64.70°.[17] Its totality figures at least part of the year south of the 25th parallel north.[18][b]

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

Diamond Cross
.

Visibility

Deep exposure of Crux, Coalsack Nebula, and IC 2944

Crux is easily visible from the

Cancun or any other place at latitude 25° N or less at around 10 pm at the end of April.[19][18]
There are 5 main stars. Due to precession, Crux will move closer to the South Pole in the next millennia, up to 67 degrees south declination for the middle of the constellation. However, by the year 14,000 Crux will be visible for most parts of Europe and continental United States which will extend to North Europe by the year 18,000 as it will be less than 30 degrees south declination.

Use in navigation

Locating the south celestial pole

In the

Pampas and Patagonia
.

Alpha and Beta Centauri are of similar declinations (thus distance from the pole) and 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 lie between Crux and the pole itself, although the constellation Musca is fairly easily recognised immediately south of Crux.[20]

Bright stars

Down to apparent magnitude +2.5 are 92 stars that shine the brightest as viewed from the Earth. Three of these stars are in Crux making it the most densely populated as to those stars (this being 3.26% of these 92 stars, and in turn being 19.2 times more than the expected 0.17% that would result on a homogenous distribution of all bright stars and a randomised drawing of all 88 constellations, given its area, 0.17% of the sky).

Features

Stars

Further information: List of stars in Crux
The constellation Crux as it can be seen by the naked eye
Crux with clouds, from Cape Town

Within the constellation's borders, there are 49 stars brighter than or equal to apparent magnitude 6.5.[c][18] The four main stars that form the asterism are Alpha, Beta, Gamma, and Delta Crucis.

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

  • ε Crucis
    (Ginan) 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:

  • Iota Crucis is a visual double star 125 light-years from Earth. The primary is an orange-hued giant of magnitude 4.6 and the secondary at magnitude 9.5.
  • Mu Crucis 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.[3]

Scorpius–Centaurus association

Unusually, a total of 15 of the 23 brightest stars in Crux are spectrally blue-white B-type stars.[15] Among the five main bright stars, Delta, and probably Alpha and Beta, are likely co-moving B-type members of the Scorpius–Centaurus association, the nearest OB association to the Sun.[22][23] 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.[24][25] Other members include the blue-white stars Zeta, Lambda and both the components of the visual double star, Mu.[26]

Variable stars

Crux contains many variable stars. It boasts four Cepheid variables that may all reach naked eye visibility.

Other well studied variable stars includes:

  • Lambda Crucis and Theta2 Crucis, that are both Beta Cepheid type variable stars.[15]
  • BH Crucis, also known as Welch's Red Variable, is a Mira variable that ranges from magnitude 6.6 to 9.8 over 530 days.[31] 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.[32]

Host star exoplanets in Crux

The star HD 106906 has been found to have a planet—HD 106906 b—that has one of the widest orbits of any currently known planetary-mass companions.[33]

Objects beyond the Local Arm

Crux is backlit by the multitude of stars of the Scutum-Crux Arm (more commonly called the

Scutum-Centaurus Arm
) of the Milky Way. This is the main inner arm in the local radial quarter of the galaxy. Part-obscuring this is:

  • The Coalsack Nebula lies partially within Crux and partly in the neighboring constellations of Musca and Centaurus.[3] It is the most prominent dark nebula 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 α Crucis. Its large area covers about 7° by 5°, and is 180 parsecs (590 ly) away from Earth.[34]

A key feature of the Scutum-Crux Arm is:

  • The Jewel Box, κ Crucis Cluster or NGC 4755, is a small but bright open cluster that appears as a fuzzy star to the naked eye and is very close to the easternmost boundary of Crux: about 1° southeast of Beta Crucis. The combined or total magnitude is 4.2 and it lies at a distance of 1.95 kiloparsecs (6,400 ly) from Earth.[3] The cluster was given its name by John Herschel,[3] based on the range of colours visible throughout the star cluster in his telescope. About seven million years old,[35] 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.[36] The brightest cluster stars are mostly blue supergiants, though the cluster contains at least one red supergiant. Kappa Crucis is a true member of the cluster that bears its name, and is one of the brighter stars at magnitude 5.9.[3]

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, Brazil, Chile and New Zealand.[37]

Flags and symbols

Further information: Flags depicting the Southern Cross
Crux, appearing on a number of flags and insignia

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

Santa Cruz). The flag of the Mercosur trading zone displays the four brightest stars. Crux also appears on the Brazilian coat of arms and, as of July 2015, on the cover of Brazilian passports
.

Five stars appear in the logo of the Brazilian football team

cruzeiro from 1942 to 1986 and again from 1990 to 1994). All coins of the current (1998) series of the Brazilian real
display the constellation.

National Order of the Southern Cross

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".

The Cross gets a mention in the lyrics of the Brazilian National Anthem (1909): "A imagem do Cruzeiro resplandece" ("the image of the Cross shines").

The Southern Cross is mentioned in the Australian National Anthem, "Beneath our radiant Southern Cross we'll toil with hearts and hands"

The Southern Cross features in the coat of arms of

First World War
.

The Southern Cross is also mentioned in the Samoan National Anthem. "Vaai 'i na fetu o lo'u a agiagia ai: Le faailoga lea o Iesu, na maliu ai mo Samoa." ("Look at those stars that are waving on it: This is the symbol of Jesus, who died on it for Samoa.")

The 1952-53 NBC Television Series

Victory At Sea
contained a musical number entitled "Beneath the Southern Cross".

"

Crosby, Stills and Nash
in 1981. It reached #18 on Billboard Hot 100 in late 1982.

"The Sign of the Southern Cross" is a song released by Black Sabbath in 1981. The song was released on the album "Mob Rules".

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

U.S. 1st Marine Division, which fought on the Southern Hemisphere islands of Guadalcanal and New Britain
.

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 Friends of the former German Protectorates [de] (1956/1983 to the present).

Southern Cross station is a major rail terminal in Melbourne, Australia.[38]

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.

Various cultures

In India, there is a story related to the creation of Trishanku Swarga (त्रिशंकु), meaning Cross (Crux), created by Sage Vishwamitra.[39]

In

β Crucis and δ Crucis.[40]

In

Aranda traditions of central Australia, the four Cross stars are the talon of an eagle and Gamma Centauri as its leg.[43]

Various peoples in the

ray.[43] In both Indonesia and Malaysia, it is known as Bintang Pari and Buruj Pari,[44] respectively ("ray stars"). This aquatic theme is also shared by an archaic name of the constellation in Vietnam, where it was once known as sao Cá Liệt (the ponyfish star).[45]

Among

puffer fish) in Waray.[46]

The Javanese people of Indonesia called this constellation Gubug pèncèng ("raking hut") or lumbung ("the granary"), because the shape of the constellation was like that of a raking hut.[47]

The Southern Cross (

γ and δ Crucis) together with μ Crucis is one of the asterisms used by Bugis sailors for navigation, called bintoéng bola képpang, meaning "incomplete house star"[48]

The

Palolo worms. Neighboring peoples in the Marshall Islands saw these stars as a fish.[43] Peninsular Malays also see the likeness of a fish in the Crux, particularly the Scomberomorus or its local name Tohok.[44]

In

Kalapalo people of Mato Grosso state in Brazil saw the stars of Crux as Aganagi angry bees having emerged from the Coalsack, which they saw as the beehive.[54]

Among Tuaregs, the four most visible stars of Crux are considered iggaren, i.e. four Maerua crassifolia trees.[55][56][57][58] The Tswana people of Botswana saw the constellation as Dithutlwa, two giraffes – Alpha and Beta Crucis forming a male, and Gamma and Delta forming the female.[59]

See also

Notes

  1. ^ João Faras was an astronomer and physician of King Manuel I of Portugal who accompanied Pedro Álvares Cabral in the discovery of Brazil in 1500
  2. ^ While parts of the constellation technically rise above the horizon to observers between 25°N and 34°N, stars within a few degrees of the horizon are to all intents and purposes unobservable.[18]
  3. ^ Objects of magnitude 6.5 are among the faintest visible to the unaided eye in suburban-rural transition night skies.[21]

References

Citations
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  3. ^ a b c d e f g h i Ridpath & Tirion 2017, pp. 134–135.
  4. ^ Dante, Purgatorio, Canto I, lines 22-27, Hollander translation
    "I turned to the right and, fixing my attention
    on the other pole, I saw four stars
    not seen but by those first on earth.
    The very sky seemed to rejoice
    in their bright glittering. O widowed
    region of the north, denied that sight!"
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  7. ^ Cadamosto, A. (c. 1465). Navigatione (1550 Ramusio ed.). p. 116r. We likewise observed ... due south by compass, a constellation of six large bright stars, in the figure of a cross in this form ... we conjectured this to be the southern chariot, but could not expect to observe the principal star, as we had not yet lost sight of the north pole.Cadamosto, A. (c. 1465). Navigatione (1811 Kerr ed.). p. 244.. 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.
  8. ^ Dekker, Elly (1990). Annals of Science. Vol. 47. pp. 530–533.
  9. ^ Revista do Instituto Histórico e Geográfico Brasileiro. Vol. V. Rio de Janeiro. 1843.
  10. ^ Dekker, Elly (1990). Annals of Science. Vol. 47. pp. 533–535.
  11. ^ Dekker, Elly (1990). Annals of Science. Vol. 47. pp. 535–543.
  12. ^ Dekker, Elly (1990). Annals of Science. Vol. 47. pp. 545–548.
  13. ^ "Letter to Giuliano de Medici". State Library of New South Wales. c. 1516. Retrieved 1 February 2018.
  14. ^ "Ian Ridpath's Star Tales – Crux". Retrieved 5 August 2013.
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  17. ^ "Crux, Constellation Boundary". The Constellations. International Astronomical Union. Retrieved 23 June 2014.
  18. ^ a b c d Ian Ridpath. "Constellations 1: Andromeda–Indus". Self-published. Retrieved 23 June 2014.
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  27. ^ Watson, Christopher (4 January 2010). "BG Crucis". AAVSO Website. American Association of Variable Star Observers. Retrieved 12 March 2014.
  28. ^ Watson, Christopher (4 January 2010). "T Crucis". AAVSO Website. American Association of Variable Star Observers. Retrieved 12 March 2014.
  29. ^ Watson, Christopher (4 January 2010). "S Crucis". AAVSO Website. American Association of Variable Star Observers. Retrieved 12 March 2014.
  30. ^ Watson, Christopher (4 January 2010). "R Crucis". AAVSO Website. American Association of Variable Star Observers. Retrieved 12 March 2014.
  31. ^ Otero, Sebastian (6 January 2011). "BH Crucis". AAVSO Website. American Association of Variable Star Observers. Retrieved 23 June 2014.
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  35. ^ "WEBDA Open cluster". Results for NGC 4755. Retrieved 30 April 2019.
  36. ^ Levy 2005, p. 87.
  37. ^ "Story: Southern Cross".
  38. ^ "Southern Cross Railway Station, Victoria – Railway Technology". Railway Technology. Retrieved 2018-04-19.
  39. ^ "Vishwamitra created the parallel universe! PiPa News - PiPa News". 28 May 2022.
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  41. ^ Norris, R. (2007): The Emu in the Sky Australian Aboriginal Astronomy website. Retrieved 2 May 2013.
  42. ^ Musgrave, I.: May sky guide: The Eta Aquarid meteor shower, constellations and planets ABC News, 2 May 2016. Retrieved 2 May 2016.
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  51. ^ "Chakana: Inca Cross". 23 June 2007. Archived from the original on 4 January 2012. Retrieved 9 July 2012.
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  53. ^ Staal 1988, p. 250.
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  59. JSTOR 40979758
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Sources

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