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, a bird associated with stories about the god Apollo, perched on the back of Hydra the water snake. The four brightest stars, Gamma, Delta, Epsilon, and Beta Corvi, form a distinctive quadrilateral or cross-shape 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 four 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
In the Babylonian star catalogues dating from at least 1100 BCE, what later became known as Corvus was called the Raven (MUL.UGA.MUSHEN). As with more familiar Classical astronomy, it was 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 BCE it would have risen just before the autumnal rainy season. John H. Rogers observed that Hydra signified Ningishzida, the god of the underworld in the Babylonian compendium MUL.APIN. He proposed that Corvus and Crater (along with Hydra) were death symbols and marked the gate to the underworld. These two constellations, along with the eagle Aquila and the fish Piscis Austrinus, were introduced to the Greeks around 500 BCE; they marked the winter and summer solstices respectively. Furthermore, Hydra had been a landmark as it had straddled the celestial equator in antiquity. Corvus and Crater also featured in the iconography of Mithraism, which is thought to have been of middle-eastern origin before spreading into Ancient Greece and Rome.
Corvus is associated with the myth of Apollo and his lover Coronis the Lapith. Coronis had been unfaithful to Apollo; when he learned this information from a pure white crow (or raven in some versions, called Lycius), he turned its feathers black in a fit of rage. Another legend associated with Corvus is that a crow stopped on his way to fetch water for Apollo, 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, realizing this was a lie, flung the crow (Corvus), cup (Crater), and snake (Hydra) into the sky. He further punished the wayward bird by ensuring it would forever be thirsty, both in real life and in the heavens, where the Cup is just out of reach.
In non-Western astronomy In Chinese astronomy, the stars of Corvus are located within the Vermilion Bird of the South (南方朱雀, Nán Fāng Zhū Què). The four main stars depict a chariot, Zhen, which is the 28th and final lunar mansion; Alpha and Eta mark the linchpins for the wheels, and Zeta is Changsha, a coffin. In Indian astronomy, the five main stars of Corvus represent a hand or fist corresponding to the Hasta, the 13th nakshatra or lunar mansion.
Corvus was recognized as a constellation by several Polynesian cultures and used as a guide for ocean navigation. 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. To Torres Strait Islanders, Corvus was the right hand (holding kupa fruit) of the huge constellation Tagai, a man fishing.
The Bororo people of Mato Grosso in central Brazil regarded the constellation as a land tortoise Geriguigui, while the Tucano people of the northwestern Amazon region saw it as an egret. To the Tupi people of São Luís Island in Brazil, Corvus might have been seen as a grill or barbecue—seychouioura, on which fish were grilled. The depiction could have also referred to the Great Square of Pegasus.
Characteristics Covering 184 square degrees and hence 0.446% of the sky, Corvus ranks 70th of the 88 constellations in area. 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". The official constellation boundaries, as set by Belgian astronomer Eugène Delporte in 1930, 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 and , while the declination coordinates are between −11.68° and −25.20°. Its position in the Southern Celestial Hemisphere means that the whole constellation is visible to observers south of 65°N.
Features
Stars
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—lay within Corvus once the constellation boundaries were established in 1930. Within the constellation's borders, there are 29 stars brighter than or equal to apparent magnitude 6.5.
Four principal stars, Delta, Gamma, Epsilon, and Beta Corvi, form a quadrilateral asterism known as "the "Spica's Spanker" or "the Sail". 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. Gamma and Delta serve as pointers toward Spica.
Also called Gienah, Gamma is the brightest star in Corvus at magnitude 2.59. Its traditional name means "wing", the star marking the left wing in Bayer's Uranometria. 154±1 light-years from Earth, it is a blue-white hued giant star of spectral type B8III that is times as massive, and 355 times as luminous as the Sun. Around million years old, it has largely exhausted its core hydrogen and begun expanding and cooling as it moves away from the main sequence. 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. Around 50 astronomical units distant from Gamma Corvi A, it is estimated to complete an orbit in 158 years.
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. An enigmatic star around 2.7 times as massive as the Sun, it is more luminous (65–70 times that of the Sun) than it 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. Warm circumstellar dust—by definition part of its inner stellar system—has been detected around Delta Corvi A. 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. Delta Corvi's common name means "the raven". It is one of two stars marking the right wing. 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, 280 light-years from Earth. The pair, both white stars, are visible to the naked eye at magnitude 5.2; the primary is of magnitude 5.9 and the secondary is of magnitude 6.0.
The raven's breast is marked by Beta Corvi (the proper name is Kraz), a star of magnitude 2.7 located 146 ± 1 light-years from Earth. 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. It likely spent most of its existence as a blue-white main sequence star of spectral type B7V. Bearing the proper name of Minkar and marking the raven's nostril is Epsilon Corvi, located some 318 ± 5 light-years from Earth. It is a red giant of spectral type K2III that is around 54 times the Sun's radius and 930 times its luminosity. Around 4 times as massive as the Sun, it spent much of its life as a main-sequence star of spectral type B5V. Lying to the south of the quadrilateral between Beta and Epsilon Corvi is the orange-hued 6 Corvi, an ageing giant star of spectral type K1III that is around 70 times as luminous as the Sun. It is 331 ± 10 light-years away from Earth.
Named Alchiba, Alpha Corvi is a white-hued star of spectral type F1V and magnitude 4.0, 48.7 ± 0.1 light-years from Earth. 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. According to Bayer's atlas, it lies above the bird's beak.
Marking the raven's right wing is Eta Corvi, a yellow-white main-sequence star of type F2V that is 1.52 times as massive and 4.87 times as luminous as the Sun. It is 59 light-years distant from the Solar System. Two debris disks have been detected orbiting this star, one warm within 3.5 astronomical units and another out at ~150 astronomical units distant. Zeta Corvi marks the raven's neck. It is of apparent magnitude 5.21, separated by 7 arcseconds from the star HR 4691. Located 420 ± 10 light-years distant, 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 disc. 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.
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. On 27 March 1974, the Mariner 10 mission detected emissions in the far ultraviolet from the planet (suggesting a satellite), but they were found to emanate from the star. 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. The primary is around 15.5 times as massive as the Sun and 52262 times as luminous.