Английская Википедия:Corona Australis

Corona Australis is a constellation in the Southern Celestial Hemisphere. Its Latin name means "southern crown", and it is the southern counterpart of Corona Borealis, the northern crown. It is one of the 48 constellations listed by the 2nd-century astronomer Ptolemy, and it remains one of the 88 modern constellations. The Ancient Greeks saw Corona Australis as a wreath rather than a crown and associated it with Sagittarius or Centaurus. Other cultures have likened the pattern to a turtle, ostrich nest, a tent, or even a hut belonging to a rock hyrax.

Although fainter than its northern counterpart, the oval- or horseshoe-shaped pattern of its brighter stars renders it distinctive. Alpha and Beta Coronae Australis are the two brightest stars with an apparent magnitude of around 4.1. Epsilon Coronae Australis is the brightest example of a W Ursae Majoris variable in the southern sky. Lying alongside the Milky Way, Corona Australis contains one of the closest star-forming regions to the Solar System—a dusty dark nebula known as the Corona Australis Molecular Cloud, lying about 430 light years away. Within it are stars at the earliest stages of their lifespan. The variable stars R and TY Coronae Australis light up parts of the nebula, which varies in brightness accordingly.

Name

The name of the constellation was entered as "Corona Australis" when the International Astronomical Union (IAU) established the 88 modern constellations in 1922.^[1]^[2] In 1932, the name was instead recorded as "Corona Austrina" when the IAU's commission on notation approved a list of four-letter abbreviations for the constellations.^[3] The four-letter abbreviations were repealed in 1955.^[4] The IAU presently uses "Corona Australis" exclusively.Шаблон:Sfn

Characteristics

Corona Australis is a small constellation bordered by Sagittarius to the north, Scorpius to the west, Telescopium to the south, and Ara to the southwest. The three-letter abbreviation for the constellation, as adopted by the International Astronomical Union in 1922, is "CrA".Шаблон:Sfn The official constellation boundaries, as set by Belgian astronomer Eugène Delporte in 1930, are defined by a polygon of four segments (illustrated in infobox). In the equatorial coordinate system, the right ascension coordinates of these borders lie between Шаблон:RA and Шаблон:RA, while the declination coordinates are between −36.77° and −45.52°.Шаблон:Sfn Covering 128 square degrees, Corona Australis culminates at midnight around the 30th of JuneШаблон:Refn and ranks 80th in area.Шаблон:Sfn Only visible at latitudes south of 53° north,Шаблон:Sfn Corona Australis cannot be seen from the British Isles as it lies too far south,Шаблон:Refn but it can be seen from southern EuropeШаблон:Refn and readily from the southern United States.Шаблон:Refn

Features

Шаблон:See also

Файл:Constellation Corona Australis.jpg

The constellation Corona Australis as it can be seen by the naked eye

While not a bright constellation, Corona Australis is nonetheless distinctive due to its easily identifiable pattern of stars,Шаблон:Sfn which has been described as horseshoe-Шаблон:Refn or oval-shaped.Шаблон:Refn Though it has no stars brighter than 4th magnitude, it still has 21 stars visible to the unaided eye (brighter than magnitude 5.5).Шаблон:Sfn Nicolas Louis de Lacaille used the Greek letters Alpha through to Lambda to label the most prominent eleven stars in the constellation, designating two stars as Eta and omitting Iota altogether. Mu Coronae Australis, a yellow star of spectral type G5.5III and apparent magnitude 5.21,Шаблон:Sfn was labelled by Johann Elert Bode and retained by Benjamin Gould, who deemed it bright enough to warrant naming.Шаблон:Sfn

Stars

Шаблон:See also The only star in the constellation to have received a name is Alfecca Meridiana or Alpha CrA. The name combines the Arabic name of the constellation with the Latin for "southern".Шаблон:Sfn In Arabic, Alfecca means "break", and refers to the shape of both Corona Australis and Corona Borealis.Шаблон:Sfn Also called simply "Meridiana",Шаблон:Sfn it is a white main sequence star located 125 light years away from Earth,Шаблон:Sfn with an apparent magnitude of 4.10 and spectral type A2Va.Шаблон:Sfn A rapidly rotating star, it spins at almost 200 km per second at its equator, making a complete revolution in around 14 hours.Шаблон:Sfn Like the star Vega, it has excess infrared radiation, which indicates it may be ringed by a disk of dust.Шаблон:Sfn It is currently a main-sequence star, but will eventually evolve into a white dwarf; currently, it has a luminosity 31 times greater, and a radius and mass of 2.3 times that of the Sun.Шаблон:Sfn Beta Coronae Australis is an orange giant 474 light years from Earth.Шаблон:Sfn Its spectral type is K0II, and it is of apparent magnitude 4.11.Шаблон:Sfn Since its formation, it has evolved from a B-type star to a K-type star. Its luminosity class places it as a bright giant; its luminosity is 730 times that of the Sun,Шаблон:Sfn designating it one of the highest-luminosity K0-type stars visible to the naked eye.Шаблон:Sfn 100 million years old, it has a radius of 43 solar radii (Шаблон:Solar radius) and a mass of between 4.5 and 5 solar masses (Шаблон:Solar mass). Alpha and Beta are so similar as to be indistinguishable in brightness to the naked eye.Шаблон:Sfn

Some of the more prominent double stars include Gamma Coronae Australis—a pair of yellowish white stars 58 light years away from Earth, which orbit each other every 122 years. Widening since 1990, the two stars can be seen as separate with a 100 mm aperture telescope;Шаблон:Sfn they are separated by 1.3 arcseconds at an angle of 61 degrees.Шаблон:Sfn They have a combined visual magnitude of 4.2;Шаблон:Sfn each component is an F8V dwarf star with a magnitude of 5.01.Шаблон:Sfn Шаблон:Sfn Epsilon Coronae Australis is an eclipsing binary belonging to a class of stars known as W Ursae Majoris variables. These star systems are known as contact binaries as the component stars are so close together they touch. Varying by a quarter of a magnitude around an average apparent magnitude of 4.83 every seven hours, the star system lies 98 light years away.Шаблон:Sfn Its spectral type is F4VFe-0.8+.Шаблон:Sfn At the southern end of the crown asterism are the stars Eta¹ and Eta² CrA, which form an optical double.Шаблон:Sfn Of magnitude 5.1 and 5.5, they are separable with the naked eye and are both white.Шаблон:Sfn Kappa Coronae Australis is an easily resolved optical double—the components are of apparent magnitudes 6.3 and 5.6 and are about 1000 and 150 light years away respectively.Шаблон:Sfn They appear at an angle of 359 degrees, separated by 21.6 arcseconds.Шаблон:Sfn Kappa² is actually the brighter of the pair and is more bluish white,Шаблон:Sfn with a spectral type of B9V,Шаблон:Sfn while Kappa¹ is of spectral type A0III.Шаблон:Sfn Lying 202 light years away, Lambda Coronae Australis is a double splittable in small telescopes. The primary is a white star of spectral type A2Vn and magnitude of 5.1,Шаблон:Sfn while the companion star has a magnitude of 9.7. The two components are separated by 29.2 arcseconds at an angle of 214 degrees.Шаблон:Sfn

Zeta Coronae Australis is a rapidly rotating main sequence star with an apparent magnitude of 4.8, 221.7 light years from Earth. The star has blurred lines in its hydrogen spectrum due to its rotation.Шаблон:Sfn Its spectral type is B9V.Шаблон:Sfn Theta Coronae Australis lies further to the west, a yellow giant of spectral type G8III and apparent magnitude 4.62.Шаблон:Sfn Corona Australis harbours RX J1856.5-3754, an isolated neutron star that is thought to lie 140 (±40) parsecs, or 460 (±130) light years, away, with a diameter of 14 km.Шаблон:Sfn It was once suspected to be a strange star,Шаблон:Sfn but this has been discounted.Шаблон:Sfn

Corona Australis Molecular Cloud

Файл:Milkyway360-hemispheres-32k m14-g1 Clouds.jpg

The Milky Way as seen by Gaia, with prominent dark features labeled in white, as well as prominent star clouds labeled in black. Corona Australis is on the left bottom center.

Файл:CentreMilkyWayMap.png

A starchart of night sky towards the Galactic Central area, with the Corona Australis Molecular Cloud at the bottom left marked green.

The Corona Australis Molecular Cloud is a dark molecular cloud just north of Beta Coronae Australis. Illuminated by a number of embedded reflection nebulae Шаблон:Sfn the cloud fans out from Epsilon Coronae Australis eastward along the constellation border with Sagittarius. It contains Шаблон:Solar mass,Шаблон:Sfn Herbig–Haro objects (protostars) and some very young stars,Шаблон:Sfn being one of the closest star-forming regions, 430 light years (130 parsecs) to the Solar System,Шаблон:Sfn at the surface of the Local Bubble. The first nebulae of the cloud were recorded in 1865 by Johann Friedrich Julius Schmidt.Шаблон:Sfn

Файл:R Coronae Australis region.jpg

The R Coronae Australis region. The dust of the cloud is illuminated blue by starlight. Stars that are forming inside the cloud could only be detected by observing at longer wavelengths.

Файл:NGC 6729.jpg

Detail of the star-forming region and Coronet Cluster, with the distinct Herbig–Haro object HH 100/Bernes 158 to the left.

Between Epsilon and Gamma Coronae Australis the cloud consists of the particular dark nebula and star forming region Bernes 157. It is 55 by 18 arcminutes wide and possesses several stars around magnitude 13. These stars are dimmed by up to 8 magnitudes because of the obscuring dust clouds.Шаблон:Sfn At the center of the active star-forming region lies the Coronet cluster (also called R CrA Cluster), which is used in studying star and protoplanetary disk formation.^[5] R Coronae Australis (R CrA) is an irregular variable star ranging from magnitudes 9.7 to 13.9.Шаблон:Refn Blue-white, it is of spectral type B5IIIpe.Шаблон:Sfn A very young star, it is still accumulating interstellar material.Шаблон:Sfn It is obscured by, and illuminates, the surrounding nebula, NGC 6729, which brightens and darkens with it.Шаблон:Refn The nebula is often compared to a comet for its appearance in a telescope, as its length is five times its width.Шаблон:Sfn Other stars of the cluster include S Coronae Australis, a G-class dwarf and T Tauri star.Шаблон:Sfn

Nearby north, another young variable star, TY Coronae Australis, illuminates another nebula: reflection nebula NGC 6726/NGC 6727. TY Coronae Australis ranges irregularly between magnitudes 8.7 and 12.4, and the brightness of the nebula varies with it.Шаблон:Refn Blue-white, it is of spectral type B8e.Шаблон:Sfn The largest young stars in the region, R, S, T, TY and VV Coronae Australis, are all ejecting jets of material which cause surrounding dust and gas to coalesce and form Herbig–Haro objects, many of which have been identified nearby.Шаблон:Sfn

Not part of it is the globular cluster known as NGC 6723, which can be seen adjacent to the nebulosity in the neighbouring constellation of Sagittarius, but is much much further away.Шаблон:Refn

Файл:Localbubble.png

Corona Australis inside the Local Bubble.

Deep sky objects

IC 1297 is a planetary nebula of apparent magnitude 10.7, which appears as a green-hued roundish object in higher-powered amateur instruments.Шаблон:Refn The nebula surrounds the variable star RU Coronae Australis, which has an average apparent magnitude of 12.9Шаблон:Sfn and is a WC class Wolf–Rayet star.Шаблон:Sfn IC 1297 is small, at only 7 arcseconds in diameter; it has been described as "a square with rounded edges" in the eyepiece, elongated in the north–south direction.Шаблон:Sfn Descriptions of its color encompass blue, blue-tinged green, and green-tinged blue.Шаблон:Sfn

Corona Australis' location near the Milky Way means that galaxies are uncommonly seen. NGC 6768 is a magnitude 11.2 object 35′ south of IC 1297. It is made up of two galaxies merging,Шаблон:Sfn one of which is an elongated elliptical galaxy of classification E4 and the other a lenticular galaxy of classification S0.Шаблон:Sfn IC 4808 is a galaxy of apparent magnitude 12.9 located on the border of Corona Australis with the neighbouring constellation of Telescopium and 3.9 degrees west-southwest of Beta Sagittarii. However, amateur telescopes will only show a suggestion of its spiral structure. It is 1.9 arcminutes by 0.8 arcminutes. The central area of the galaxy does appear brighter in an amateur instrument, which shows it to be tilted northeast–southwest.Шаблон:Sfn

Southeast of Theta and southwest of Eta lies the open cluster ESO 281-SC24, which is composed of the yellow 9th magnitude star GSC 7914 178 1 and five 10th to 11th magnitude stars.Шаблон:Sfn Halfway between Theta Coronae Australis and Theta Scorpii is the dense globular cluster NGC 6541. Described as between magnitude 6.3Шаблон:Refn and magnitude 6.6,Шаблон:Sfn it is visible in binoculars and small telescopes. Around 22000 light years away, it is around 100 light years in diameter.Шаблон:Refn It is estimated to be around 14 billion years old.Шаблон:Refn NGC 6541 appears 13.1 arcminutes in diameter and is somewhat resolvable in large amateur instruments; a 12-inch telescope reveals approximately 100 stars but the core remains unresolved.Шаблон:Sfn

Meteor showers

The Corona Australids are a meteor shower that takes place between 14 and 18 March each year, peaking around 16 March.Шаблон:Refn This meteor shower does not have a high peak hourly rate. In 1953 and 1956, observers noted a maximum of 6 meteors per hour and 4 meteors per hour respectively; in 1955 the shower was "barely resolved".Шаблон:Sfn However, in 1992, astronomers detected a peak rate of 45 meteors per hour.Шаблон:Sfn The Corona Australids' rate varies from year to year.Шаблон:Sfn Шаблон:Sfn At only six days, the shower's duration is particularly short,Шаблон:Sfn and its meteoroids are small; the stream is devoid of large meteoroids. The Corona Australids were first seen with the unaided eye in 1935 and first observed with radar in 1955.Шаблон:Sfn Corona Australid meteors have an entry velocity of 45 kilometers per second.Шаблон:Sfn In 2006, a shower originating near Beta Coronae Australis was designated as the Beta Coronae Australids. They appear in May, the same month as a nearby shower known as the May Microscopids, but the two showers have different trajectories and are unlikely to be related.Шаблон:Sfn

History

Шаблон:See also

Файл:47-Corona-Australis.PNG

Corona Australis on The Manuchihr Globe, Adilnor Collection, Sweden.

Corona Australis may have been recorded by ancient Mesopotamians in the MUL.APIN, as a constellation called MA.GUR ("The Bark"). However, this constellation, adjacent to SUHUR.MASH ("The Goat-Fish", modern Capricornus), may instead have been modern Epsilon Sagittarii. As a part of the southern sky, MA.GUR was one of the fifteen "stars of Ea".Шаблон:Sfn

In the 3rd century BC, the Greek didactic poet Aratus wrote of, but did not name the constellation,Шаблон:Sfn instead calling the two crowns Στεφάνοι (Stephanoi). The Greek astronomer Ptolemy described the constellation in the 2nd century AD, though with the inclusion of Alpha Telescopii, since transferred to Telescopium.Шаблон:Sfn Ascribing 13 stars to the constellation,Шаблон:Refn he named it Στεφάνος νοτιος (Шаблон:Transl), "Southern Wreath", while other authors associated it with either Sagittarius (having fallen off his head) or Centaurus; with the former, it was called Corona Sagittarii.Шаблон:Sfn Similarly, the Romans called Corona Australis the "Golden Crown of Sagittarius".Шаблон:Sfn It was known as Parvum Coelum ("Canopy", "Little Sky") in the 5th century.Шаблон:Sfn The 18th-century French astronomer Jérôme Lalande gave it the names Sertum Australe ("Southern Garland")Шаблон:Sfn Шаблон:Sfn and Orbiculus Capitis, while German poet and author Philippus Caesius called it Corolla ("Little Crown") or Spira Australis ("Southern Coil"), and linked it with the Crown of Eternal Life from the New Testament. Seventeenth-century celestial cartographer Julius Schiller linked it to the Diadem of Solomon.Шаблон:Sfn Sometimes, Corona Australis was not the wreath of Sagittarius but arrows held in his hand.Шаблон:Sfn

Файл:Corona Australis Atlas Coelestis.jpg

Corona Australis depicted in the Uranographia of Johann Bode

Corona Australis has been associated with the myth of Bacchus and Stimula. Jupiter had impregnated Stimula, causing Juno to become jealous. Juno convinced Stimula to ask Jupiter to appear in his full splendor, which the mortal woman could not handle, causing her to burn. After Bacchus, Stimula's unborn child, became an adult and the god of wine, he honored his deceased mother by placing a wreath in the sky.Шаблон:Sfn

In Chinese astronomy, the stars of Corona Australis are located within the Black Tortoise of the North (北方玄武, Běi Fāng Xuán Wǔ).Шаблон:Sfn The constellation itself was known as ti'en pieh ("Heavenly Turtle") and during the Western Zhou period, marked the beginning of winter. However, precession over time has meant that the "Heavenly River" (Milky Way) became the more accurate marker to the ancient Chinese and hence supplanted the turtle in this role.Шаблон:Refn Arabic names for Corona Australis include Al Ķubbah "the Tortoise", Al Ĥibā "the Tent" or Al Udḥā al Na'ām "the Ostrich Nest".Шаблон:Sfn Шаблон:Sfn It was later given the name Al Iklīl al Janūbiyyah, which the European authors Chilmead, Riccioli and Caesius transliterated as Alachil Elgenubi, Elkleil Elgenubi and Aladil Algenubi respectively.Шаблон:Sfn

The ǀXam speaking San people of South Africa knew the constellation as ≠nabbe ta !nu "house of branches"—owned originally by the Dassie (rock hyrax), and the star pattern depicting people sitting in a semicircle around a fire.Шаблон:Sfn

The indigenous Boorong people of northwestern Victoria saw it as Won, a boomerang thrown by Totyarguil (Altair).Шаблон:Sfn The Aranda people of Central Australia saw Corona Australis as a coolamon carrying a baby, which was accidentally dropped to earth by a group of sky-women dancing in the Milky Way. The impact of the coolamon created Gosses Bluff crater, 175 km west of Alice Springs.Шаблон:Sfn The Torres Strait Islanders saw Corona Australis as part of a larger constellation encompassing part of Sagittarius and the tip of Scorpius's tail; the Pleiades and Orion were also associated. This constellation was Tagai's canoe, crewed by the Pleiades, called the Usiam, and Orion, called the Seg. The myth of Tagai says that he was in charge of this canoe, but his crewmen consumed all of the supplies onboard without asking permission. Enraged, Tagai bound the Usiam with a rope and tied them to the side of the boat, then threw them overboard. Scorpius's tail represents a suckerfish, while Eta Sagittarii and Theta Coronae Australis mark the bottom of the canoe.Шаблон:Sfn On the island of Futuna, the figure of Corona Australis was called Tanuma and in the Tuamotus, it was called Na Kaua-ki-Tonga.Шаблон:Sfn

Файл:Regioni celesti scelte - Osc A.png

Main dark nebulae of the Solar apex half of the galactic plane, with the Corona Australis on the right

References

Citations

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Sources

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Online sources

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SIMBAD

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External links

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[2] Шаблон:Cite web

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Английская Википедия:Corona Australis

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