Crux

Crux

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List of stars in Crux
Abbreviation:	Cru
Genitive:	Crucis
Symbolism:	Southern Cross
Right ascension:	12.5 h
Declination:	−60°
Area:	68 sq. deg. (88th)
Main stars:	4
Bayer/Flamsteed stars:	19
Stars with known planets:	1
Bright stars:	4
Nearby stars:	0
Brightest star:	Acrux (α Cru) (0.87m)
Nearest star:	η Cru (64.2 ly)
Messier objects:	0
Meteor showers:	Crucids
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 (pronounced /ˈkrʌks/, Latin: cross), commonly known as the Southern Cross, is the smallest of the 88 modern constellations, but nevertheless one of the most distinctive. It is surrounded on three sides by the constellation Centaurus, and to the south lies Musca. Ancient Greeks originally considered Crux to be part of Centaurus; however, the precession of the equinoxes gradually lowered these stars below the European horizon, and they were eventually forgotten at northern latitudes. (At the latitude of Athens in 1000 BC, Crux was clearly visible, though low in the sky; ^[1] by AD 400, most of the constellation never rose above the horizon for Athenians. ^[2]).

Notable features

With the lack of a significant pole star in the southern sky (Sigma Octantis is closest to the pole, but is too faint to be useful for the purpose), two of the stars of Crux (Alpha and Gamma, Acrux and Gacrux respectively) are commonly used to mark south. Following the line defined by the two stars for approximately 4.5 times the distance between them leads to a point close to the Southern Celestial Pole.

Alternatively, if a line is constructed perpendicularly between Alpha Centauri and Beta Centauri, the point where the above line and this line intersect marks the Southern Celestial Pole. The two stars are often referred to as the "Pointer Stars" or "White Pointers", allowing people to easily find the top of Crux.

Contrary to popular belief, Crux is not opposite to Ursa Major. In fact, in tropical regions both Crux (low in the south) and Ursa Major (low in the north) can be seen in the sky from April to June. Crux is exactly opposite to Cassiopeia on the celestial sphere, and therefore it cannot be in the sky with the latter at the same time. For locations south of 34°S, Crux is circumpolar and thus always visible in the night sky.

Crux is sometimes confused with the nearby False Cross by stargazers. The Southern Cross is somewhat kite-shaped, and it has a fifth star (ε Crucis). The False Cross is diamond-shaped, somewhat dimmer on average, does not have a fifth star and lacks the two "Pointer Stars".

Named Stars

• α is named Acrux, a concatenation of "Alpha" and "Crux"
• β is named Becrux a concatenation of "Beta" and "Crux" and is also named after the Mimosa plant
• γ is named Gacrux, a concatenation of "Gamma" and "Crux"

Notable deep sky objects

The Coalsack Nebula is the most prominent dark nebula in the skies, easily visible to the naked eye as a big dark patch in the southern Milky Way.

Another deep sky object within Crux is the Open Cluster NGC 4755, better known as the Jewel Box or Kappa Crucis Cluster, that was discovered by Nicolas Louis de Lacaille in 1751-1752. It lies at a distance of about 7,500 light years and consists of approximately 100 stars spread across an area of about 20 light-years square.

Three of the five main Southern Cross stars—–Acrux, Mimosa, and Delta Crucis—–are co-moving B-type members of the Scorpius-Centaurus Association, the nearest OB association to the Sun^[3]. 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^[4][5].

History

The Southern Cross, appearing on a number of flags and insignia.

Amerigo Vespucci mapped Alpha Centauri and Beta Centauri as well as the stars of modern Crux on his expedition to South America in 1501. The separation of Crux to be a separate constellation is generally attributed to the French astronomer Augustin Royer in 1679. Other historians attribute the invention of Crux to Petrus Plancius in 1613, and document that the constellation was later published by Jakob Bartsch in 1624. However, Crux had already been a well known southern asterism at least four centuries before it was promoted to an official constellation and published in the seventeenth century.

A CTX image of crux.

Crux is important in Australian Aboriginal Astronomy. It, 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 stone image of the constellation has also been left at the archaeological site of Machu Picchu, Peru.

In 1893, Australian Poet Banjo Paterson wrote : The English flag may flutter and wave, where the world wide oceans toss, but the flag the Australian dies to save, is the flag of the Southern Cross.

Flags and symbols that incorporate Crux

Main article: Southern Cross Flag

The five brightest stars of Crux (α, β, γ, δ, and ε Crucis) appear on the flags of Australia, Brazil, New Zealand (epsilon omitted), Papua New Guinea, and Samoa, and also the Australian States and Territories of Victoria, the Australian Capital Territory, the Northern Territory, as well as the flag of Magallanes Region of Chile, and several Argentine provincial flags and emblems (e.g., Tierra del Fuego and Santa Cruz). The flag of the Mercosur trading zone displays the four brightest stars (epsilon omitted). Crux also appears on the Brazilian coat of arms. The five stars are also in the logo of an Brazilian soccer team called Cruzeiro Esporte Clube. A stylized version of Crux appears on the 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 the blue diamond of the U.S. 1st Marine Division, which fought on the Southern Hemisphere islands of Guadalcanal and New Britain.

•  Australia
•  Brazil
•  New Zealand
•  Niue
•  Papua New Guinea
•  Samoa
•  Tokelau

Other names for Crux

Crux is clearly visible above the aurora australis in this photograph taken from Dunedin, New Zealand. The red giant Gacrux is clearly a different colour to the other three main stars, which are blue-white

• In ancient Hindu astrology, the modern Crux is referred to as "Trishanku".
• The Māori name for Crux is "Te Punga" - "the anchor". It is thought of as anchor of Tama-rereti's waka (the Milky Way), where the Pointers are its rope.
• In Tonga it is known as Toloa — duck; it is a duck flying over, heading south, and one of his wings (δ) is wounded because Ongo tangata — 2 men — α and Β Centauri threw a stone at it. The Coalsack is known as Humu — triggerfish, because of its shape.^[6]
• Among Tuaregs, the 4 most visible stars of Crux are considered iggaren, i.e. four Maerua crassifolia trees.
• In Indonesia and Malaysia, it is known as Buruj Pari (The Stingray).
• In Mapudungun, the language of Patagonian Mapuches, the name of Crux is Melipal, which means "four stars".
• In Quechua, the language of the Inca civilization, Crux is known as "Chakana", which means literally "stair" (chaka, bridge, link; hanan, high, above), but carries a deep symbolism within Quechua mysticism.^[7].

References

External links

• Letter of Andrea Corsali 1516-1989: with additional material ("the first description and illustration of the Southern Cross, with speculations about Australia ...") digitised by the National Library of Australia.
• The Deep Photographic Guide to the Constellations: Crux.
• The Cambridge Guide to the Constellations, Michael E. Bakich, Cambridge University Press, 1995, pg. 85.
• Universe: The Definitive Visual Dictionary, Robert Dinwiddie et al, DK Adult Publishing, (2005), pg. 396.
• Ian Ridpath and Wil Tirion (2007). Stars and Planets Guide, Collins, London. ISBN 978-0007251209. Princeton University Press, Princeton. ISBN 978-0691135564.
• Southern Cross Starry Night Photography.
• Star Tales – Crux
• Finding the South Pole in the sky
• Southern Cross in Te Ara - the Encyclopedia of New Zealand