Crux


Crux is a constellation centred on four stars in the southern sky in a bright portion of the Milky Way. It is among the most easily distinguished constellations as its hallmark 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 Latin for cross, 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 α Crucis, its brightest and most southerly member. There follow four less dominant stars which appear clockwise and in order of lessening magnitude: β Crucis, γ Crucis, δ Crucis and ε 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 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 on its western border. To the southeast figures a large, relatively near 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 Ancient Greeks, where Ptolemy 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 CE, the stars in the constellation we now call 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. Others argue that Dante's description was allegorical, and that he almost certainly did not know about the constellation.
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. However, Cadamosto's accompanying diagram was inaccurate. Historians generally credit João Faras for being the first European to depict it correctly. Faras sketched and described the constellation in a letter written on the beaches of Brazil on 1 May 1500 to the Portuguese monarch.
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.
Another early modern description clearly describing Crux as a separate constellation is attributed to Andrea Corsali, 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.
Emery Molyneux and Petrus Plancius have also been cited as the first uranographers 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. The constellation was later adopted by Jakob Bartsch in 1624 and Augustin Royer in 1679. Royer is sometimes wrongly cited as initially distinguishing Crux.

Characteristics

Crux is bordered by the constellations Centaurus 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. 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 right ascension coordinates of these borders lie between and, while the declination 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, Crux is circumpolar and thus always appears in the sky.
Crux is sometimes confused with the nearby False Cross 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 Diamond Cross.

Visibility

Crux is easily visible from the southern hemisphere at practically any time of year. It is also visible near the horizon from tropical latitudes of the northern hemisphere for a few hours every night during the northern winter and spring. For instance, it is visible from Cancun or any other place at latitude 25° N or less at around 10 pm at the end of April. 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

In the Southern Hemisphere, the Southern Cross is frequently used for navigation in much the same way that Polaris is used in the Northern Hemisphere. Projecting a line from γ to α Crucis 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 Alpha Centauri to Beta Centauri, which are stars at an alike declination to Crux and of a similar width as the cross, but higher magnitude.
Argentine gauchos are documented as using Crux for night orientation in the Pampas and Patagonia.
Alpha and Beta Centauri are of similar declinations 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 Musca is fairly easily recognised immediately beneath Crux.

Circumscribed limits around apparent 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.

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.
There is also a fifth star, that is often included with the Southern Cross.
There are several other naked-eye stars within the borders of Crux, especially:
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, 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. 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 Zeta, Lambda and both the components of the visual double star, Mu.

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:
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..

Visible objects beyond the Local Arm

Crux is backlit by the multitude of stars of the Scutum-Crux Arm Arm of the Milky Way. As to the local radial quarter of the galaxy, this is the main inner arm.
Part-obscuring this is:
A key feature of the Arm mentioned relatively near to our position is:
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 Samoa. 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 Londrina and several Argentine provincial flags and emblems. The flag of the Mercosur trading zone displays the four brightest stars. Crux also appears on the Brazilian coat of arms and,, on the cover of Brazilian passports.
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. All coins of the series of the Brazilian real 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".
The Cross gets a mention in the lyrics of the Brazilian National Anthem : "A imagem do Cruzeiro resplandece".
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 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."
"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 Eureka Flag. 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 New Caledonia, and also on the blue diamond of the 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 .
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 is a Catholic fraternal order throughout Australia.

In non-Western astronomy

In Australian Aboriginal astronomy, Crux and the Coalsack mark the head of the 'Emu in the Sky' in several Aboriginal cultures, while Crux itself is said to be a possum sitting in a tree, a representation of the sky deity Mirrabooka, a stingray, or an eagle. Two Pacific constellations also included Gamma Centauri. Torres Strait Islanders in modern-day Australia saw Gamma Centauri as the handle and the four stars as the trident of Tagai's Fishing Spear. The Aranda people of central Australia saw the four Cross stars as the talon of an eagle and Gamma Centauri as its leg.
Various peoples in the East Indies 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. 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 Javanese people of Indonesia called this constellation Gubug pèncèng or lumbung, because the shape of the constellation was like that of a raking hut.
The Southern Cross together with μ Crucis is one of the asterisms used by Bugis sailors for navigation, called bintoéng bola képpang, meaning "incomplete house star"
The Māori name for the Southern Cross is Māhutonga and it is thought of as the anchor of Tama-rereti's waka, while the Pointers are its rope. In Tonga it is known as Toloa ; it is depicted as a duck flying south, with one of his wings wounded because Ongo tangata threw a stone at it. The Coalsack is known as Humu, because of its shape. In Samoa the constellation is called Sumu because of its rhomboid shape, while α and β Centauri are called Luatagata, just as they are in Tonga. The peoples of the Solomon Islands saw several figures in the Southern Cross. These included a knee protector and a net used to catch Palolo worms. Neighboring peoples in the Marshall Islands saw these stars as a fish.
In Mapudungun, the language of Patagonian Mapuches, the name of the Southern Cross is Melipal, which means "four stars". In Quechua, the language of the Inca civilization, Crux is known as "Chakana", which means literally "stair", but carries a deep symbolism within Quechua mysticism. Alpha and Beta Crucis make up one foot of the Great Rhea, a constellation encompassing Centaurus and Circinus along with the two bright stars. The Great Rhea was a constellation of the Bororo 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 Alpha and Beta Centauri. The rhea's body is marked by the four main stars of Crux, while its head is Gamma Centauri and its feet are the bright stars of Musca. The Bakairi 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 in Lupus, the bright stars of Musca, Beta and the optical double star Delta1,2 Chamaeleontis: and some of the stars of Volans, and Mensa. The 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.
Among Tuaregs, the four most visible stars of Crux are considered iggaren, i.e. four Maerua crassifolia trees. 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.