Corona Australis

Coordinates: Sky map 19h 00m 00s, −40° 00′ 00″
Source: Wikipedia, the free encyclopedia.
Corona Australis
Constellation
Corona Australis
List of stars in Corona Australis
AbbreviationCrA
Genitive
  • Coronae Australis
Pronunciation
Corona Australids
Bordering
constellations
Visible at latitudes between +40° and −90°.
Best visible at 21:00 (9 p.m.) during the month of August.

Corona Australis is a

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.

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.[5][6] 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on notation approved a list of four-letter abbreviations for the constellations.[7] The four-letter abbreviations were repealed in 1955.[8] The IAU presently uses "Corona Australis" exclusively.[4]

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".[9] 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 17h 58.3m and 19h 19.0m , while the declination coordinates are between −36.77° and −45.52°.[4] Covering 128 square degrees, Corona Australis culminates at midnight around the 30th of June[10] and ranks 80th in area.[11] Only visible at latitudes south of 53° north,[11] Corona Australis cannot be seen from the British Isles as it lies too far south,[12] but it can be seen from southern Europe[13] and readily from the southern United States.[14]

Features

See also: List of stars in Corona Australis
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,

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,[18] was labelled by Johann Elert Bode and retained by Benjamin Gould, who deemed it bright enough to warrant naming.[19]

Stars

See also: List of stars in Corona Australis

The only star in the constellation to have received a name is

bright giant; its luminosity is 730 times that of the Sun,[25] designating it one of the highest-luminosity K0-type stars visible to the naked eye.[1] 100 million years old, it has a radius of 43 solar radii (R☉) and a mass of between 4.5 and 5 solar masses (M☉). Alpha and Beta are so similar as to be indistinguishable in brightness to the naked eye.[25]

Some of the more prominent double stars include

optical double.[32] Of magnitude 5.1 and 5.5, they are separable with the naked eye and are both white.[33] 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.[15] They appear at an angle of 359 degrees, separated by 21.6 arcseconds.[26] Kappa2 is actually the brighter of the pair and is more bluish white,[33] with a spectral type of B9V,[34] while Kappa1 is of spectral type A0III.[35] 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,[36] 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.[26]

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.[39] It was once suspected to be a strange star,[40] but this has been discounted.[39]

Corona Australis Molecular Cloud

star clouds
labeled in black. Corona Australis is on the left bottom center.
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[25] the cloud fans out from Epsilon Coronae Australis eastward along the constellation border with Sagittarius. It contains 7000 M☉,[25] Herbig–Haro objects (protostars) and some very young stars,[41] being one of the closest star-forming regions, 430 light years (130 parsecs) to the Solar System,[42] at the surface of the Local Bubble. The first nebulae of the cloud were recorded in 1865 by Johann Friedrich Julius Schmidt.[43]

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.
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

Coronet cluster (also called R CrA Cluster), which is used in studying star and protoplanetary disk formation.[45] R Coronae Australis (R CrA) is an irregular variable star ranging from magnitudes 9.7 to 13.9.[46] Blue-white, it is of spectral type B5IIIpe.[47] A very young star, it is still accumulating interstellar material.[41] It is obscured by, and illuminates, the surrounding nebula, NGC 6729, which brightens and darkens with it.[46] The nebula is often compared to a comet for its appearance in a telescope, as its length is five times its width.[48] Other stars of the cluster include S Coronae Australis, a G-class dwarf and T Tauri star.[32]

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.[46] Blue-white, it is of spectral type B8e.[49] 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.[50]

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.[51]

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.[52] The nebula surrounds the variable star RU Coronae Australis, which has an average apparent magnitude of 12.9[53] and is a WC class Wolf–Rayet star.[54] 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.[55] Descriptions of its color encompass blue, blue-tinged green, and green-tinged blue.[55]

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,[33] one of which is an elongated elliptical galaxy of classification E4 and the other a lenticular galaxy of classification S0.[56] 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.[57]

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.[33] Halfway between Theta Coronae Australis and Theta Scorpii is the dense globular cluster NGC 6541. Described as between magnitude 6.3[46] and magnitude 6.6,[26] it is visible in binoculars and small telescopes. Around 22000 light years away, it is around 100 light years in diameter.[46] It is estimated to be around 14 billion years old.[58] 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.[59]

Meteor showers

The

Corona Australids are a meteor shower that takes place between 14 and 18 March each year, peaking around 16 March.[60] 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".[61] However, in 1992, astronomers detected a peak rate of 45 meteors per hour.[62] The Corona Australids' rate varies from year to year.[63][64] At only six days, the shower's duration is particularly short,[62] 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.[64] Corona Australid meteors have an entry velocity of 45 kilometers per second.[65] 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.[66]

History

See also:
Corona Australis (Chinese astronomy)
Corona Australis on The Manuchihr Globe, Adilnor Collection, Sweden.

Corona Australis may have been recorded by ancient

Ea".[67]

In the 3rd century BC, the Greek didactic poet Aratus wrote of, but did not name the constellation,[68] 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.[69] Ascribing 13 stars to the constellation,[10] he named it Στεφάνος νοτιος (Stephanos notios), "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.[70] Similarly, the Romans called Corona Australis the "Golden Crown of Sagittarius".[71] It was known as Parvum Coelum ("Canopy", "Little Sky") in the 5th century.[72] The 18th-century French astronomer Jérôme Lalande gave it the names Sertum Australe ("Southern Garland")[70][72] 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.[70] Sometimes, Corona Australis was not the wreath of Sagittarius but arrows held in his hand.[72]

Johann Bode

Corona Australis has been associated with the myth of

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.[73]

In

Black Tortoise of the North (北方玄武, Běi Fāng Xuán Wǔ).[74] 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.[75] Arabic names for Corona Australis include Al Ķubbah "the Tortoise", Al Ĥibā "the Tent" or Al Udḥā al Na'ām "the Ostrich Nest".[70][72] 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.[70]

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.[76]

The indigenous

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.[79] On the island of Futuna, the figure of Corona Australis was called Tanuma and in the Tuamotus, it was called Na Kaua-ki-Tonga.[80]

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

See also

References

Citations

  1. ^ a b c Bagnall 2012, p. 170.
  2. ^ "Corona". Merriam-Webster.com Dictionary., "Australis". Merriam-Webster.com Dictionary..
  3. ^ "Corona Australis". Dictionary.com Unabridged (Online). n.d.
  4. ^ a b c d IAU, The Constellations, Corona Australis.
  5. ^ Proceedings of the 1st General Assembly. Transactions of the International Astronomical Union. Vol. 1. Rome. 1922. p. 158.
  6. ^ Ridpath, Ian. "IAU constellation list 1". Retrieved 2017-01-06.
  7. doi:10.1017/S0251107X00016631
    .
  8. ^ Ridpath, Ian. "IAU constellation list 2". Retrieved 2017-01-06.
  9. ^ Russell 1922, p. 469.
  10. ^ a b c Malin & Frew 1995, p. 218
  11. ^ a b Ridpath, Constellations.
  12. ^ Moore & Tirion 1997, p. 164
  13. ^ Moore 2005, p. 202
  14. ^ Moore, Stargazing 2000, p. 86
  15. ^ a b c d e Ridpath & Tirion 2017, pp. 126–127.
  16. ^ Falkner 2011, p. 100
  17. ^ Bakich 1995, p. 130.
  18. ^ SIMBAD Mu Coronae Australis.
  19. ^ Wagman 2003, pp. 114–115.
  20. ^ Allen 1963, pp. 172–173.
  21. ^ a b c Kaler, Alfecca Meridiana.
  22. ^ SIMBAD Alpha Coronae Australis.
  23. ^ Royer, Zorec & Gómez 2007, p. 463.
  24. ^ SIMBAD Beta Coronae Australis.
  25. ^ a b c d Kaler, Beta Coronae Australis.
  26. ^ a b c d Moore & Rees 2011, p. 413.
  27. ^ SIMBAD LTT 7565.
  28. ^ SIMBAD HR 7226.
  29. ^ SIMBAD HR 7227.
  30. ^ Kaler, Epsilon Coronae Australis.
  31. ^ SIMBAD Epsilon Coronae Australis.
  32. ^ a b c Motz & Nathanson 1991, pp. 254–255.
  33. ^ a b c d Streicher 2008, pp. 135–139.
  34. ^ SIMBAD HR 6953.
  35. ^ SIMBAD HR 6952.
  36. ^ SIMBAD Lambda Coronae Australis.
  37. ^ SIMBAD Zeta Coronae Australis.
  38. ^ SIMBAD Theta Coronae Australis.
  39. ^ a b Ho Wynn C. G. et al. 2007.
  40. ^ Drake, Jeremy J. et al. 2002.
  41. ^ a b Malin 2010.
  42. ^ Reipurth 2008, p. 735.
  43. ^ Steinicke 2010, p. 176.
  44. ^ Bakich 2010, p. 266.
  45. S2CID 119208696
    .
  46. ^ a b c d e O'Meara 2002, pp. 164–165, 271–273, 311
  47. ^ SIMBAD R Coronae Australis.
  48. ^ Bakich Podcast & 25 June 2009.
  49. ^ SIMBAD TY Coronae Australis.
  50. ^ Wang et al. 2004.
  51. ^ Coe 2007, p. 105
  52. ^ Griffiths 2012, p. 132
  53. ^ Moore, Data Book 2000, pp. 367–368.
  54. ^ SIMBAD RU Coronae Australis.
  55. ^ a b Bakich 2010, p. 270.
  56. ^ NASA/IPAC NGC 6768.
  57. ^ Bakich Podcast & 18 August 2011.
  58. ^ O'Meara 2011, p. 322
  59. ^ Bakich Podcast & 5 July 2012.
  60. ^ Sherrod & Koed 2003, p. 50
  61. ^ Weiss 1957, p. 300.
  62. ^ a b Rogers & Keay 1993, p. 274.
  63. ^ Weiss 1957, p. 302.
  64. ^ a b Ellyett & Keay 1956, p. 479.
  65. ^ Jenniskens 1994, p. 1007.
  66. ^ Jopek et al. 2010, p. 871–872.
  67. ^ Rogers 1998, p. 19.
  68. ^ Bakich 1995, p. 83.
  69. ^ Ridpath, Star Tales Corona Australis.
  70. ^ a b c d e Allen 1963, pp. 172–174.
  71. ^ Simpson 2012, p. 148.
  72. ^ a b c d Motz & Nathanson 1988, p. 254.
  73. ^ Staal 1988, pp. 232–233.
  74. ^ AEEA 2006.
  75. ^ Porter1996, pp. 35–36
  76. ^ Lloyd 1873.
  77. ^ Hamacher & Frew 2010.
  78. ^ Hamacher & 28 March 2011.
  79. ^ Staal 1988, pp. 223–224.
  80. ^ Makemson 1941, p. 281.

Sources

Online sources

SIMBAD

External links

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Corona Australis (category)

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