Corvus (constellation)

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Corvus
Constellation
Corvus
Abbreviation Crv
Genitive Corvi
Pronunciation /ˈkɔːrvəs/,
genitive /ˈkɔːrv/
Symbolism the Crow/Raven
Right ascension 12
Declination −20
Family Hercules
Quadrant SQ3
Area 184 sq. deg. (70th)
Main stars 4
Bayer/Flamsteed
stars
10
Stars with planets 3
Stars brighter than 3.00m 3
Stars within 10.00 pc (32.62 ly) 1
Brightest star γ Crv (Gienah) (2.59m)
Nearest star Ross 695
(28.99 ly, 8.89 pc)
Messier objects 0
Meteor showers Corvids
Eta Corvids
Bordering
constellations
Virgo
Crater
Hydra
Visible at latitudes between +60° and −90°.
Best visible at 21:00 (9 p.m.) during the month of May.

Corvus is a small constellation in the Southern Celestial Hemisphere. Its name means "raven" in Latin. One of the 48 constellations listed by the 2nd-century astronomer Ptolemy, it depicts a raven that has been associated with the god Apollo and is perched on the back of Hydra the water snake. The four brightest stars, Gamma, Delta, Epsilon, and Beta Corvi form a distinctive quadrilateral in the night sky.

With an apparent magnitude of 2.59, Gamma Corvi—also known as Gienah—is the brightest star in the constellation. It is an aging blue giant around 4 times as massive as the Sun. The young star Eta Corvi has been found to have two debris disks. Three star systems have exoplanets, and a fourth planetary system is unconfirmed. TV Corvi is a dwarf nova—a white dwarf and brown dwarf in very close orbit.

History and mythology[edit]

Corvus, Crater, and other constellations seen around Hydra in Urania's Mirror (1825).

In the Babylonian star catalogues dating from at least 1100 BCE, what later became Corvus was known as the Babylonian Raven (MUL.UGA.MUSHEN). It was similarly placed sitting on the tail of the Serpent (Greek Hydra). The Babylonian constellation was sacred to Adad, the god of rain and storm; in the second Millennium it would have risen just before the start of the autumnal rainy season. John H. Rogers suggests that Corvus and Crater marked the gate to the Underworld.[1] These two constellations, along with the eagle Aquila and the fish Piscis Austrinus, were introduced to the Greeks around 500 BCE.[2]

One myth associated with Corvus is that of Apollo and Coronis. Coronis had been unfaithful to her lover, who learned this information from a pure white crow. Apollo then turned its feathers black in a fit of rage.[3] Another legend associated with Corvus is that a crow stopped on his way to fetch water for Apollo, in order to eat figs. Instead of telling the truth to Apollo, he lied and said that a snake, Hydra, kept him from the water, while holding a snake in his talons as proof. Apollo saw this to be a lie, however, and flung the crow (Corvus), cup (Crater), and the snake (Hydra) into the sky. He further punished the wayward bird by making sure that it would forever be thirsty, both in real life and in the heavens, where the Cup is barely out of reach.[3]

Equivalents[edit]

In Chinese astronomy, the stars of Corvus are located within the Vermilion Bird of the South (南方朱雀, Nán Fāng Zhū Què).[4] The four main stars depict a chariot, Zhen, which is the 28th and final lunar mansion, while Alpha and Eta mark the linchpins for the wheels, and Zeta is Changsha, a coffin.[5] In Indian astronomy, the five main stars of Corvus represent a hand or fist and correspond to the Hastā, the 13th nakshatra or lunar mansion.[6]

Corvus was recognized as a constellation by several Polynesian cultures. In the Marquesas Islands, it was called Mee; in Pukapuka, it was called Te Manu, and in the Society Islands, it was called Metua-ai-papa.[7] To Torres Strait Islanders, Corvus was the right hand (holding kupa fruit) of the huge constellation Tagai, a man fishing.[8]

The Bororo people of Mato Grosso in central Brazil regarded the constellation as a land tortoise Geriguigui,[9] while the Tucano people of the northwestern Amazon region saw it as an egret.[10] To the Tupi people of São Luís Island in Brazil, Corvus was seen as a grill or barbecue—seychouioura, on which fish were grilled. However, the depiction could have also referred to the Great Square of Pegasus.[11]

Characteristics[edit]

Covering 183 square degrees and hence 0.446% of the sky, Corvus ranks 70th of the 88 constellations in area.[12] It is bordered by Virgo to the north and east, Hydra to the south, and Crater to the west. The three-letter abbreviation for the constellation, as adopted by the International Astronomical Union in 1922, is 'Crv'.[13] The official constellation boundaries, as set by Eugène Delporte in 1930,[a] are defined by a polygon of six segments (illustrated in infobox). In the equatorial coordinate system, the right ascension coordinates of these borders lie between 11h 56m 22s and 12h 56m 40s, while the declination coordinates are between −11.68° and −25.20°.[15] Its position in the Southern Celestial Hemisphere means that the whole constellation is visible to observers south of 65°N.[12][b]

Features[edit]

The constellation Corvus as it can be seen by the naked eye.

Stars[edit]

The German cartographer Johann Bayer used the Greek letters Alpha through Eta to label the most prominent stars in the constellation. John Flamsteed gave nine stars Flamsteed designations, while one star he designated in the neighbouring constellation Crater—31 Crateris—ended up in Corvus.[16] Within the constellation's borders, there are 29 stars brighter than or equal to apparent magnitude 6.5.[c][12]

Four principal stars, Delta, Gamma, Epsilon, and Beta Corvi, form a quadrilateral asterism known as "the "Spica's Spanker"[18] or "the Sail".[19][20] Although none of the stars are particularly bright, they lie in a dim area of the sky, rendering the asterism easy to distinguish in the night sky.[21] Gamma and Delta serve as pointers toward Spica. Also called Gienah, Gamma is the brightest star in Corvus at magnitude 2.59.[22] Its traditional name means "wing",[22] the star marking the left wing in Bayer's Uranometria.[16] 154±1 light-years from Earth,[23] it is a blue-white hued giant star of spectral type B8III that is 4.2+0.4
−0.3
times as massive,[24] and 355 times as luminous as the Sun.[22] Around 160+40
−30
million years old,[24] it has exhausted its core hydrogen and begun expanding and cooling as it moves away from the main sequence.[22] A binary star, it has a companion orange or red dwarf star of spectral type K5V to M5V that is about 0.8 times as massive as the Sun.[25] Around 50 astronomical units[d] distant from Gamma Corvi A, it is estimated to complete an orbit in 158 years.[24] Delta Corvi, traditionally called Algorab, is a double star divisible in small amateur telescopes. The primary is a blue-white star of magnitude 2.9, around 87 light-years from Earth.[23] An enigmatic star around 2.7 times as massive as the Sun, it is more luminous (65–70 times that of the Sun) than its should be for its surface temperature of 10,400 K, and hence is either a 3.2 million year-old very young pre-main sequence star that has not settled down to a stable main sequence life stage, or a 260 million year-old star that has begun to exhaust its core hydrogen and expand, cool and shine more brightly as it moves away from the main sequence. Its spectral type is given as A0IV, corresponding with the latter scenario.[26] Warm circumstellar dust—by definition part of its inner stellar system—has been detected around Delta Corvi A.[27] Delta Corvi B is an orange dwarf star of magnitude 8.51 and spectral class K, also surrounded by circumstellar dust. A post T-tauri star, it is at least 650 AU distant from its brighter companion and takes at least 9400 years to complete an orbit.[28] Delta Corvi's common name means "the raven".[3] It is one of two stars marking the right wing.[16] Located 4.5 degrees northeast of Delta Corvi is Struve 1669, a binary star that is divisible into two stars 5.4" apart by small amateur telescopes,[29] 280 light-years from Earth. The pair, both white stars, is visible to the naked eye at magnitude 5.2; the primary is of magnitude 5.9 and the secondary is of magnitude 6.0.[3]

The raven's breast is marked by Beta Corvi,[16] a star of magnitude 2.7 located 146 ± 1 light-years from Earth.[23] Roughly 206 million years old and 3.7 ± 1 times as massive as the Sun, it has exhausted its core hydrogen and expanded and cooled to a surface temperature of around 5,100 K and is now a yellow bright giant star of spectral type G5II.[30] It likely spent most of its existence as a blue-white main sequence star of spectral type B7V.[31] Bearing the proper name of Minkar and marking the raven's nostril is Epsilon Corvi, located some 318 ± 5 light-years from Earth.[23] It is a red giant of spectral type K2III that is around 54 times the Sun's radius and 930 times its luminosity.[32] Around 4 times as massive as the Sun, it spent much of its life as a main sequence star of spectral type B5V.[33] Lying to the south of the quadrilateral between Beta and Epsilon Corvi is the orange-hued 6 Corvi,[21] and ageing giant star of spectral type K1III that is around 70 times as luminous as the Sun.[34] It is 331 ± 10 light-years away from Earth.[23]

Also called Alchiba, Alpha Corvi is a white-hued star of spectral type F1V and magnitude 4.0, 48.7 ± 0.1 light-years from Earth.[23] It exhibits periodic changes in its spectrum over a three-day period, which suggests it is either a spectroscopic binary or (more likely) a pulsating Gamma Doradus-type variable. If the latter is the case, it is estimated to be 1.39 times as massive as the Sun.[35] According to Bayer's atlas, it lies above the bird's beak.[16]

Also marking the raven's right wing is Eta Corvi,[16] a yellow-white main sequence star that is 1.52 times as massive and 4.87 times as luminous as the Sun. It is 59 light-years distant from our Solar System.[36] Two debris disks have been detected orbiting this star, one warm within 3.5 astronomical units and another out at ~150 astronomical units distant.[37][38] Zeta Corvi marks the raven's neck.[16] It is of apparent magnitude 5.21, separated by 7 arcseconds from the star HR 4691.[39] Located 420 ± 10 light-years distant,[23] it is a blue-white Be star of spectral type B8V, the presence of hydrogen emission lines in its spectrum indicating it has a circumstellar disk. These stars may be an optical double or a true multiple star system, with a separation of at least 50,000 astronomical units and the stars taking 3.5 million years to orbit each other. HR 4691 is itself double, composed of an ageing yellow-orange giant whose spectral type has been calculated at K0 or G3, and an F-type main sequence star.[39]

31 Crateris (which was originally placed in Crater by Flamsteed) is a 5.26 magnitude star which was once mistaken for a moon of Mercury. It is in reality a remote binary star system with a hot blue-white star of spectral type B1.5V and a companion about which little is known. The two stars orbit each other every 2.9631 days. The primary is possibly a blue straggler of the Hyades group.[40] The primary is around 15.5 times as massive as the Sun and 52262 times as luminous.[41]

VV Corvi is a close spectroscopic binary, its two component stars orbiting each other with a period of 1.46 days.[42] Both are yellow-white main sequence stars of spectral type F5V, though the primary has begun expanding and cooling as it nears the end of its time on the main sequence.[43] The mass ratio of the two stars is 0.775±0.024.[44] A tertiary companion was discovered during the Two Micron All-Sky Survey.[45] W Corvi is an eclipsing binary that varies in brightness from apparent magnitude 11.16 to 12.5 over 9 hours.[46] Its period has increased by 1/4 second over a century. It is an unusual system in that its two stars are very close to each other yet have different surface temperatures and hence thermal transfer is not taking place as expected.[47] SX Corvi is an eclipsing binary that is also a contact binary also known as a W Ursae Majoris variable. The two component stars orbit closely enough to each other for mass to have been transferred between them—in this case the secondary having transferred a large amount of mass to the primary.[48] RV Corvi is another eclipsing binary. Its brightness varies from apparent magnitude 8.6 to 9.16 over 18 hours.[49] The system is composed of stars of spectral types F0 and G0, which orbit each other every 0.7473 days.[50]

Close to Gamma Corvi and visible in the same binocular field is R Corvi, a long period (Mira) variable star.[51] It ranges in brightness from a magnitude of 6.7 to 14.4 with a period of approximately 317 days.[52] TT Corvi is a Semiregular variable red giant of spectral type M3III and apparent magnitude 6.48 around 923 light years distant.[53] It is around 993 times as luminous as of the Sun.[34] TU Corvi is a Delta Scuti variable—a class of short period (six hours at most) pulsating stars that have been used as standard candles and as subjects to study astroseismology.[54] It varies by 0.025 of a magnitude around apparent magnitude 6.53 over 59 minutes.[55]

Three star systems have confirmed planets. HD 103774 is a young yellow-white main-sequence star of apparent magnitude 7.12 that is 181 ± 5 light-years distant from Earth. It is 1.335 ± 0.03 times as massive and 3.5 ± 0.3 as luminous as the Sun. Variations in its radial velocity showed it was being orbited by a Neptune-sized planet every 5.9 days in 2013.[56] HD 104067 is an orange dwarf of spectral type K2V of apparent magnitude 7.93 that is 69 ± 1 light-years distant from Earth. Around 80% as massive as the Sun, it is orbited by a planet 3.6 times the mass of Neptune every 55.8 days.[57] WASP-83 has a planet around as massive as Saturn that orbits it every 5 days. It was discovered by its transit across the star in 2015.[58] A fourth star system has an unconfirmed planet. HD 111031 is a sunlike star of spectral type G5V located 101 ± 2 light-years distant from Earth.[23]

VHS 1256-1257 is a brown dwarf of spectral type M7.5 located 41 ± 3 light-years distant from Earth. Around 73 times as massive as Jupiter, it is just under the boundary between brown dwarves and stars. It has a companion that was first identified and documented by the 2MASS survey in 2015. It orbits at a distance of 102 ± 9 AU and has an estimated mass of approximately 11 times Jupiter's,[59] DENIS-P J1228.2-1547 is a system composed of two brown dwarfs orbiting each other. TV Corvi is a dwarf nova composed of a white dwarf and brown dwarf that orbit each other every 90 minutes.[60][61] The system has a baseline magnitude of 17 that brightens periodically to magnitude 12, discovered by Clyde Tombaugh in 1931 and David Levy in 1990 and 2005.[62]

Deep-sky objects[edit]

Corvus contains no Messier objects. It has several galaxies and a planetary nebular observable with amateur telescopes.[63] The center of Corvus is home to a planetary nebula NGC 4361.[63] The nebula itself resembles a small elliptical galaxy and has a magnitude of 10.3, but the magnitude 13 star at its centre gives away its true nature.[51]

The NGC 4038 Group is a group of galaxies across Corvus and Crater. The group may contain between 13 and 27 galaxies. The best-known member is the Antennae peculiar galaxy, located 0.25 north of 31 Crateris.[64] It consists of two interacting galaxies—NGC 4038 and 4039—that appear to have a heart shape as seen from Earth. The name originates from the huge tidal tails that come off the ends of the two galaxies, formed because of the spiral galaxies' original rotation. Both original galaxies were spiral galaxies and are now experiencing extensive star formation due to the interaction of gas clouds. The galaxies are 45 million light-years from Earth and each has multiple ultraluminous X-ray sources, the source of which is unknown. Astronomers theorize that they may be a rare type of x-ray emitting binary stars or intermediate-mass black holes.[65] The Antennae galaxies appear in a telescope at the 10th magnitude.[3] SN 2004gt was a type Ic supernova that erupted on December 12, 2004. The progenitor was not identified from older images of the galaxy, and is either a type WC Wolf-Rayet star with a mass over 40 times that of the Sun, or a star 20 to 40 times as massive as the Sun in a binary star system.[66] SN 2007sr was a Type Ia supernova event that peaked in brightness on December 14, 2007.[67] The galaxy has been identified as a good place to take detailed images in case of further supernovae.[66]

NGC 4027 is another member of the NGC 4038 group, notable for its extended spiral arm. Known as the Ringtail Galaxy, it lies close to 31 Crateris.[64] A barred spiral galaxy, its distorted shape is probably due to a past collision, possibly with the nearby NGC 4027A. NGC 4782 and NGC 4783 are a pair of merging elliptical galaxies in the northeastern part of the constellation, around 200 million light-years distant.[62]

Meteor showers[edit]

Corvus hosts two established meteor showers. Cuno Hoffmeister discovered the Corvids in June 1937.[68] In January 2013, the MO Video Meteor Network published the discovery of the Eta Corvids,[69] their existence later confirmed by data analysis.[70]

Popular culture[edit]

In Action Comics #14 (January 2013), which was published 7 November 2012, Neil Degrasse Tyson appears in the story, in which he determines that Superman's home planet, Krypton, orbited the red dwarf LHS 2520 in the constellation Corvus, 27.1 light-years from Earth. Tyson assisted DC Comics in selecting a real-life star that would be an appropriate parent star to Krypton, and picked the star in Corvus,[71][72] and which is the mascot of Superman's high school, the Smallville Crows.[73]

See also[edit]

Notes[edit]

  1. ^ Delporte had proposed standardising the constellation boundaries to the International Astronomical Union, who had agreed and gave him the lead role[14]
  2. ^ While parts of the constellation technically rise above the horizon to observers between the 65°N and 78°N, stars within a few degrees of the horizon are to all intents and purposes unobservable.[12]
  3. ^ Objects of magnitude 6.5 are among the faintest visible to the unaided eye in suburban-rural transition night skies.[17]
  4. ^ the distance between the Earth and the Sun is one astronomical unit

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External links[edit]

Coordinates: Sky map 12h 00m 00s, −20° 00′ 00″