Visible at latitudes between +20° and −90°. Best visible at 21:00 (9 p.m.) during the month ofMay.
Crux (/krʌks/) is aconstellation of thesouthern sky that is centred on four bright stars in across-shapedasterism commonly known as theSouthern Cross. It lies on the southern end of theMilky Way's visible band. The nameCrux is Latin for cross. Even though it is thesmallest of all88 modern constellations, Crux is among the most easily distinguished as its four main stars each have anapparent visual magnitude brighter than +2.8. It has attained a high level of cultural significance in many Southern Hemisphere states and nations.
Blue-whiteα Crucis (Acrux) is the most southerly member of the constellation and, at magnitude 0.8, the brightest. The three other stars of the cross appear clockwise and in order of lessening magnitude:β Crucis (Mimosa),γ Crucis (Gacrux), andδ Crucis (Imai).ε Crucis (Ginan) also lies within the cross asterism. Many of these brighter stars are members of theScorpius–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 fourCepheid variables, each visible to the naked eye under optimum conditions. Crux also contains the bright and colourfulopen cluster known as theJewel Box (NGC 4755) on its eastern border. Nearby to the southeast is a largedark nebula spanning 7° by 5° known as theCoalsack Nebula, portions of which are mapped in the neighbouring constellations ofCentaurus andMusca.
The bright stars in Crux were known to theAncient Greeks, wherePtolemy regarded them as part of the constellationCentaurus.[1][2] They were entirely visible as far north asBritain in the fourth millennium BC. However, theprecession 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 anasterism of four bright stars in the southern sky in hisDivine Comedy.[4][5] His description, however, may be allegorical, and the similarity to the constellation a coincidence.[6]
The 15th century Venetian navigatorAlvise Cadamosto made note of what was probably the Southern Cross on exiting theGambia River in 1455, calling it thecarro dell'ostro ("southern chariot"). However, Cadamosto's accompanying diagram was inaccurate.[7][8] Historians generally creditJoão 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]
ExplorerAmerigo 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 toAndrea Corsali, an Italian navigator who from 1515 to 1517 sailed to China and theEast Indies in an expedition sponsored byKing 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 andPetrus Plancius have also been cited as the firsturanographers (sky mappers) to distinguish Crux as a separate constellation; their representations date from 1592, the former depicting it on hiscelestial 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 ofPetrus Plancius andJodocus Hondius in 1598 and 1600. Its stars were first catalogued separately from Centaurus byFrederick de Houtman in 1603.[14] The constellation was later adopted byJakob Bartsch in 1624 andAugustin Royer in 1679. Royer is sometimes wrongly cited as initially distinguishing Crux.[2]
Crux is bordered by the constellationsCentaurus (which surrounds it on three sides) on the east, north and west, andMusca 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 theInternational Astronomical Union in 1922, is "Cru".[16] The official constellation boundaries, as set by Belgian astronomerEugène Delporte in 1930, are defined by a polygon of four segments. In theequatorial coordinate system, theright ascension coordinates of these borders lie between11h 56.13m and12h 57.45m, while thedeclination coordinates are between −55.68° and −64.70°.[17] Its totality figures at least part of the year south of the25th parallel north.[18][b]
In tropical regions Crux can be seen in the sky from April to June. Crux is exactly opposite toCassiopeia on the celestial sphere, and therefore it cannot appear in the sky with the latter at the same time. In this era, south ofCape Town,Adelaide, andBuenos Aires (the34th parallel south), Crux is circumpolar and thus always appears in the sky.
Crux is sometimes confused with the nearbyFalse Cross asterism by stargazers. The False Cross consists of stars in Carina and Vela, 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 dimmerDiamond Cross.
Crux is easily visible from thesouthern hemisphere, south of 35th parallel at practically any time of year as circumpolar. It is also visible near the horizon fromtropical latitudes of thenorthern hemisphere for a few hours every night during the northern winter and spring. For instance, it is visible fromCancun 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 toprecession, 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 the continental United States. Its visibility will extend to North Europe by the year 18,000 when it will be less than 30 degrees south declination.
In theSouthern Hemisphere, the Southern Cross is frequently used fornavigation in much the same way thatPolaris is used in theNorthern Hemisphere. Projecting a line fromγ toα Crucis (the foot of the crucifix) approximately4+1⁄2 times beyond gives a point close to the Southern Celestial Pole[3] which is also, coincidentally, where intersects a perpendicular line taken southwards from the east–west axis ofAlpha Centauri toBeta Centauri, which are stars at an alike declination to Crux and of a similar width as the cross, but higher magnitude.[20]Argentinegauchos are documented as using Crux for night orientation in thePampas andPatagonia.
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 constellationMusca is fairly easily recognised immediately south of Crux.[20]
Down to apparent magnitude +2.5 are 92 starsthat 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).
The constellation Crux as it can be seen by the naked eyeCrux with clouds, from Cape Town
Within the constellation's borders, there are 49 stars brighter than or equal toapparent magnitude 6.5.[c][18] The four main stars that form the asterism are Alpha, Beta, Gamma, and Delta Crucis.
α Crucis or Acrux is a triple star 321 light-years from Earth. A rich blue in colour, with a visualmagnitude 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.
β Crucis or Mimosa is a blue-hued giant star of magnitude 1.3, and lies 353 light-years from Earth. It is aBeta Cephei-typevariable star with a variation of less than 0.1 magnitudes.[3]
γ Crucis or Gacrux is an opticaldouble star. The primary is a red-hued giant star of magnitude 1.6, 88 light-years from Earth, and is one of the closestred giants to Earth. Its secondary component is magnitude 6.5, 264 light-years from Earth.
δ Crucis (Imai) is a magnitude 2.8 blue-white hued star about 345 light-years from Earth.[3] Like Mimosa it is a Beta Cepheid variable.[15]
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 visualdouble 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]
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 theScorpius–Centaurus association, the nearestOB association to theSun.[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 starsZeta,Lambda and both the components of the visualdouble star,Mu.[26]
BH Crucis, also known as Welch's Red Variable, is aMira 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]
Crux is backlit by the multitude of stars of the Scutum-Crux Arm (more commonly called theScutum-Centaurus Arm) of the Milky Way. This is the main inner arm in the local radial quarter of the galaxy. Part-obscuring this is:
TheCoalsack Nebula lies partially within Crux and partly in the neighboring constellations ofMusca andCentaurus.[3] It is the most prominentdark 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 180parsecs (590 ly) away fromEarth.[34]
A key feature of the Scutum-Crux Arm is:
TheJewel Box, κ Crucis Cluster or NGC 4755, is a small but brightopen 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 1.95kiloparsecs (6,400 ly) from Earth.[3] The cluster was given its name byJohn 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 mostlyblue supergiants, though the cluster contains at least onered 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]
A depiction of The Southern Cross in Mark Twain's 1897 travelogue, "Following the Equator"
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]
Five stars appear in the logo of the Brazilian football teamCruzeiro Esporte Clube and in the insignia of theOrder of the Southern Cross, and the cross has featured as name of the Brazilian currency (thecruzeiro from 1942 to 1986 and again from 1990 to 1994). All coins of the current[update] (1998) series of theBrazilian real display the constellation.
Songs and literature reference the Southern Cross, including the Argentine epic poemMartín Fierro. The Argentinian singerCharly 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 theBrazilian National Anthem (1909): "A imagem do Cruzeiro resplandece" ("the image of the Cross shines").
The Southern Cross is mentioned in theAustralian National Anthem, "Beneath our radiant Southern Cross we'll toil with hearts and hands"
The Southern Cross is also mentioned in theSamoanNational 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 SeriesVictory At Sea contained a musical number entitled "Beneath the Southern Cross".
A stylized version of Crux appears on the AustralianEureka Flag. The constellation was also used on the dark blue, shield-like patch worn by personnel of the U.S. Army'sAmerical Division, which was organized in the Southern Hemisphere, on the island ofNew Caledonia, and also on the blue diamond of theU.S. 1st Marine Division, which fought on the Southern Hemisphere islands ofGuadalcanal andNew Britain.
ThePetersflagge flag of theGerman 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: theReichskolonialbund of 1936–1943 and theFriends of the former German Protectorates [de] (1956/1983 to the present).
ThePersonal 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.
Various peoples in theEast Indies and Brazil viewed the four main stars as the body of aray.[43] In both Indonesia and Malaysia, it is known asBintang Pari andBuruj Pari,[44] respectively ("ray stars"). This aquatic theme is also shared by an archaic name of the constellation inVietnam, where it was once known assao Cá Liệt (theponyfish star).[45]
TheJavanese people of Indonesia called this constellationGubug pèncèng ("raking hut") orlumbung ("the granary"), because the shape of the constellation was like that of araking hut.[47]
The Southern Cross (α,β,γ andδ Crucis) together withμ Crucis is one of the asterisms used byBugis sailors for navigation, calledbintoéng bola képpang, meaning "incomplete house star"[48]
TheMāori name for the Southern Cross isMāhutonga and it is thought of as the anchor (Te Punga) of Tama-rereti'swaka (theMilky Way), while the Pointers are its rope.[49] InTonga it is known asToloa ("duck"); it is depicted as a duck flying south, with one of his wings (δ Crucis) wounded becauseOngo tangata ("two men",α andβ Centauri) threw a stone at it. The Coalsack is known asHumu (the "triggerfish"), because of its shape.[50] In Samoa the constellation is calledSumu ("triggerfish") because of its rhomboid shape, while α and β Centauri are calledLuatagata (Two Men), just as they are in Tonga. The peoples of theSolomon Islands saw several figures in the Southern Cross. These included a knee protector and a net used to catchPalolo worms. Neighboring peoples in theMarshall Islands saw these stars as a fish.[43]PeninsularMalays also see the likeness of a fish in the Crux, particularly theScomberomorus or its local nameTohok.[44]
InMapudungun, the language of PatagonianMapuches, the name of the Southern Cross isMelipal, which means "four stars". InQuechua, the language of theInca civilization, Crux is known as "Chakana", which means literally "stair" (chaka, bridge, link;hanan, high, above), but carries a deep symbolism within Quechua mysticism.[51] Alpha and Beta Crucis make up one foot of the Great Rhea, a constellation encompassingCentaurus andCircinus along with the two bright stars. The Great Rhea was a constellation of theBororo of Brazil. TheMocoví people of Argentina also saw arhea 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 byAlpha andBeta Centauri. The rhea's body is marked by the four main stars of Crux, while its head isGamma Centauri and its feet are the bright stars ofMusca.[52] TheBakairi people 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 inLupus, the bright stars of Musca,Beta and the optical double starDelta1,2 Chamaeleontis: and some of the stars ofVolans, andMensa.[53] TheKalapalo people ofMato Grosso state in Brazil saw the stars of Crux asAganagi angry bees having emerged from the Coalsack, which they saw as the beehive.[54]
AmongTuaregs, the four most visible stars of Crux are considerediggaren, i.e. fourMaerua crassifolia trees.[55][56][57][58] TheTswana people ofBotswana saw the constellation asDithutlwa, two giraffes – Alpha and Beta Crucis forming a male, and Gamma and Delta forming the female.[59]
^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]
^Objects of magnitude 6.5 are among the faintest visible to the unaided eye in suburban-rural transition night skies.[21]
^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.
^Dekker, Elly (1990).Annals of Science. Vol. 47. pp. 530–533.
^Pasachoff, Jay M (2000).Field Guide to the Stars and Planets. Houghton Mifflin. p. 67.ISBN978-0-395-93431-9.
^abGrainger, DH (1969).Don't die in the Bundu (8th ed.). Cape Town. pp. 84–86.ISBN0-86978-056-5.{{cite book}}: CS1 maint: location missing publisher (link)
^Preibisch, T.; Mamajek, E. (2008). "The Nearest OB Association: Scorpius–Centaurus (Sco OB2)".Handbook of Star-Forming Regions.2: 235.arXiv:0809.0407.Bibcode:2008hsf2.book..235P.
^abNurul Fatini Jaafar (2016). "Kebudayaan Langit Pribumi Malayonesia".Kesturi.26 (2). Akademi Sains Islam Malaysia.doi:10.13140/RG.2.2.24869.55520.
^Huỳnh, Tịnh Của (1895).Đại Nam quấc âm tự vị [Dictionnaire annamite] (in Vietnamese).Nam tào: "tên sao chòm ở phía nam, cũng là sao cá liệt" ... – " the name of a constellation in the south, also known as the ponyfish star."
^Daldjoeni, N. (1984). "Pranatamangsa, the javanese agricultural calendar – Its bioclimatological and sociocultural function in developing rural life".The Environmentalist.4 (S7):15–18.Bibcode:1984ThEnv...4S..15D.doi:10.1007/BF01907286.S2CID189914684.
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