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Hydra is the largest of the 88 modern
constellation A constellation is an area on the celestial sphere in which a group of visible stars forms Asterism (astronomy), a perceived pattern or outline, typically representing an animal, mythological subject, or inanimate object. The first constellati ...
s, measuring 1303 square degrees, and also the longest at over 100 degrees. Its southern end borders
Libra Libra generally refers to: * Libra (constellation), a constellation * Libra (astrology), an astrological sign based on the star constellation Libra may also refer to: Arts and entertainment * ''Libra'' (novel), a 1988 novel by Don DeLillo Musi ...
and
Centaurus Centaurus () is a bright constellation in the southern sky. One of the 88 modern constellations by area, largest constellations, Centaurus was included among the 48 constellations listed by the 2nd-century astronomer Ptolemy, and it remains one ...
and its northern end borders
Cancer Cancer is a group of diseases involving Cell growth#Disorders, abnormal cell growth with the potential to Invasion (cancer), invade or Metastasis, spread to other parts of the body. These contrast with benign tumors, which do not spread. Po ...
. It was included among the 48 constellations listed by the 2nd century astronomer
Ptolemy Claudius Ptolemy (; , ; ; – 160s/170s AD) was a Greco-Roman mathematician, astronomer, astrologer, geographer, and music theorist who wrote about a dozen scientific treatises, three of which were important to later Byzantine science, Byzant ...
. Commonly represented as a water snake, it straddles the celestial equator.


History and mythology


Western mythology

The Greek constellation of Hydra is an adaptation of a Babylonian constellation: the MUL.APIN includes a "serpent" constellation (MUL.DINGIR.MUŠ) that loosely corresponds to Hydra. It is one of two Babylonian "serpent" constellations (the other being the origin of the Greek
Serpens Serpens () is a constellation in the northern celestial hemisphere. One of the 48 constellations listed by the 2nd-century astronomer Ptolemy, it remains one of the 88 modern constellations designated by the International Astronomical Union. It ...
), a
mythological hybrid Hybrid beasts are creatures composed of parts from different animals, including humans, appearing in the folklore of a variety of cultures as legendary creatures. In burial sites Remains similar to those of mythological hybrids have been found ...
of serpent, lion and bird. The shape of Hydra resembles a twisting
snake Snakes are elongated limbless reptiles of the suborder Serpentes (). Cladistically squamates, snakes are ectothermic, amniote vertebrates covered in overlapping scales much like other members of the group. Many species of snakes have s ...
, and features as such in some Greek myths. One myth associates it with a water snake that a
crow A crow is a bird of the genus ''Corvus'', or more broadly, a synonym for all of ''Corvus''. The word "crow" is used as part of the common name of many species. The related term "raven" is not linked scientifically to any certain trait but is rathe ...
served
Apollo Apollo is one of the Twelve Olympians, Olympian deities in Ancient Greek religion, ancient Greek and Ancient Roman religion, Roman religion and Greek mythology, Greek and Roman mythology. Apollo has been recognized as a god of archery, mu ...
in a cup when it was sent to fetch water. Apollo saw through the fraud and angrily cast the crow, cup and snake into the sky. It is also associated with the monster Hydra, with its many heads, killed by
Hercules Hercules (, ) is the Roman equivalent of the Greek divine hero Heracles, son of Jupiter and the mortal Alcmena. In classical mythology, Hercules is famous for his strength and for his numerous far-ranging adventures. The Romans adapted the Gr ...
, represented in another constellation. According to legend, if one of the Hydra's heads was cut off, two more would grow in its place. However, Hercules' nephew, Iolaus, seared the necks with a torch to prevent them from growing back and thus enabled Hercules to overcome the Hydra.


Mythology and equivalents in other cultures

In
Chinese astronomy Astronomy in China has a long history stretching from the Shang dynasty, being refined over a period of more than 3,000 years. The Ancient China, ancient Chinese people have identified stars from 1300 BCE, as Chinese star names later categori ...
, the stars that correspond to Hydra are located within the
Vermilion Bird The Vermilion Bird ( zh, c=朱雀, p=Zhūquè) is one of the Four Symbols of the Chinese constellations. According to Wuxing (Chinese philosophy), Wu Xing, the Taoism, Taoist five elemental system, it represents the Fire (Wu Xing), Fire element, ...
and the
Azure Dragon The Azure Dragon ( zh, c=青龍, p=Qīnglóng) is one of the Dragon King, Dragon Gods who represent the mount or Chthonic deities, chthonic forces of the Wufang Shangdi, Five Regions' Highest Deities (). It is also one of the Four Symbols o ...
. The head of Hydra was collectively known as "Min al Az'al," meaning "belonging to the uninhabited spot" in
Arabic Arabic (, , or , ) is a Central Semitic languages, Central Semitic language of the Afroasiatic languages, Afroasiatic language family spoken primarily in the Arab world. The International Organization for Standardization (ISO) assigns lang ...
.


Features


Stars

Despite its size, Hydra contains only one moderately bright
star A star is a luminous spheroid of plasma (physics), plasma held together by Self-gravitation, self-gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked eye at night sk ...
,
Alphard Alphard (), designated Alpha Hydrae (α Hydrae, abbreviated Alpha Hya, α Hya), is the brightest star in the constellation of Hydra. It is a single giant star, cooler than the Sun but larger and more luminous. It is about 177 light-year ...
, designated Alpha Hydrae. It is an
orange giant A giant star has a substantially larger radius and luminosity than a main-sequence (or ''dwarf'') star of the same surface temperature. They lie above the main sequence (luminosity class V in the Yerkes spectral classification) on the Hertzspr ...
of magnitude 2.0, 177 light-years from Earth. Its traditional name means "the solitary one".Ridpath, Ian. Star Tales Hydra.
Retrieved 2018-12-28.
Beta Hydrae Beta Hydrae, Latinized from β Hydrae, is a double star in the equatorial constellation of Hydra. Historically, Beta Hydrae was designated 28 Crateris, but the latter fell out of use when the IAU defined the permanent constel ...
is a blue-white star of magnitude 4.3, 365 light-years from Earth. Gamma Hydrae is a
yellow giant A giant star has a substantially larger radius and luminosity than a main-sequence (or ''dwarf'') star of the same surface temperature. They lie above the main sequence (luminosity class V in the Yerkes spectral classification) on the Hertzspru ...
of magnitude 3.0, 132 light-years from Earth. Hydra has one bright
binary star A binary star or binary star system is a system of two stars that are gravitationally bound to and in orbit around each other. Binary stars in the night sky that are seen as a single object to the naked eye are often resolved as separate stars us ...
,
Epsilon Hydrae Epsilon Hydrae (ε Hydrae, abbreviated Epsilon Hya, ε Hya) is a multiple star system of a combined third magnitude in the constellation of Hydra. Based upon parallax measurements obtained during the Hipparcos mission, it is located ro ...
, which is difficult to split in amateur telescopes; it has a period of 1000 years and is 135 light-years from Earth. The primary is a yellow star of magnitude 3.4 and the secondary is a blue star of magnitude 6.7. However, there are several dimmer double stars and binary stars in Hydra.
27 Hydrae 27 Hydrae is a triple star system system in the equatorial constellation of Hydra, located 222 light years away from the Sun. It is visible to the naked eye as a faint, orange-hued star with a combined apparent visual magnitude of ...
is a triple star with two components visible in binoculars and three visible in small amateur telescopes. The primary is a white star of magnitude 4.8, 244 light-years from Earth. The secondary, a binary star, appears in binoculars at magnitude 7.0 but is composed of a magnitude 7 and a magnitude 11 star; it is 202 light-years from Earth. 54 Hydrae is a binary star 99 light-years from Earth, easily divisible in small amateur telescopes. The primary is a yellow star of magnitude 5.3 and the secondary is a purple star of magnitude 7.4. N Hydrae (N Hya) is a pair of stars of magnitudes 5.8 and 5.9. Struve 1270 (Σ1270) consists of a pair of stars, magnitudes 6.4 and 7.4. The other main named star in Hydra is Sigma Hydrae (σ Hydrae), which also has the name of Minchir, from the
Arabic Arabic (, , or , ) is a Central Semitic languages, Central Semitic language of the Afroasiatic languages, Afroasiatic language family spoken primarily in the Arab world. The International Organization for Standardization (ISO) assigns lang ...
for snake's nose. At magnitude 4.54, it is rather dim. The head of the snake corresponds to the
Āshleshā Ashlesha (Sanskrit: आश्लेषा or ''Āśleṣā'') (Tibetan: སྐར་མ་སྐག), also known as Ayilyam in Tamil language, Tamil and Malayalam (Tamil: ஆயில்யம், Malayalam: ആയില്യം, ''Āyilyaṃ'') ...
Nakshatra Nakshatra () is the term for Lunar mansion in Hindu astrology and Buddhist astrology. A nakshatra is one of 27 (sometimes also 28) sectors along the ecliptic. Their names are related to a prominent star or asterisms in or near the respective s ...
, the lunar zodiacal constellation in Indian astronomy. The name of Nakshatra (Ashlesha) became the proper name of Epsilon Hydrae since 1 June 2018 by IAU. Hydra is also home to several
variable star A variable star is a star whose brightness as seen from Earth (its apparent magnitude) changes systematically with time. This variation may be caused by a change in emitted light or by something partly blocking the light, so variable stars are ...
s.
R Hydrae R Hydrae, abbreviated R Hya, is a single star in the equatorial constellation of Hydra, about 2.7° to the east of Gamma Hydrae. It is a Mira-type variable that ranges in apparent visual magnitude from 3.5 down to 10.9 over a period ...
is a
Mira variable Mira variables (named for the prototype star Mira) are a class of pulsating stars characterized by very red colours, pulsation periods longer than 100 days, and amplitudes greater than one magnitude in infrared and 2.5 magnitude at visual wave ...
star 2000 light-years from Earth; it is one of the brightest Mira variables at its maximum of magnitude 3.5. It has a minimum magnitude of 10 and a period of 390 days. V Hydrae is an unusually vivid red variable star 20,000 light-years from Earth. It varies in magnitude from a minimum of 9.0 to a maximum of 6.6. U Hydrae is a semi-regular variable star with a deep red color, 528 light-years from Earth. It has a minimum magnitude of 6.6 and a maximum magnitude of 4.2; its period is 115 days. Hydra includes GJ 357, an M-type main sequence star located only 31 light-years from the Solar System. This star has three confirmed exoplanets in its orbit, one of which, GJ 357 d, is considered to be a "Super-Earth" within the circumstellar habitable zone. The constellation also contains the radio source Hydra A galaxy as well as nearby
WISE 0855−0714 WISE 0855−0714 (full designation WISE J085510.83−071442.5, or W0855 for short) is a sub-brown dwarf of Y dwarf, spectral class Y4, located from the Sun in the constellation Hydra (constellation), Hydra. It is the fourth-List of ne ...
brown dwarf being the closest (sub)stellar object of the constellation.


Deep-sky objects

Hydra contains three
Messier object The Messier objects are a set of 110 astronomical objects catalogued by the French astronomer Charles Messier in his ' (''Catalogue of Nebulae and Star Clusters''). Because Messier was interested only in finding comets, he created a list of th ...
s. M83, also known as the Southern Pinwheel Galaxy, is located on the border of Hydra and
Centaurus Centaurus () is a bright constellation in the southern sky. One of the 88 modern constellations by area, largest constellations, Centaurus was included among the 48 constellations listed by the 2nd-century astronomer Ptolemy, and it remains one ...
, M68 is a
globular cluster A globular cluster is a spheroidal conglomeration of stars that is bound together by gravity, with a higher concentration of stars towards its center. It can contain anywhere from tens of thousands to many millions of member stars, all orbiting ...
near M83, and M48 is an
open star cluster An open cluster is a type of star cluster made of tens to a few thousand stars that were formed from the same giant molecular cloud and have roughly the same age. More than 1,100 open clusters have been discovered within the Milky Way galaxy, and ...
in the western end of the serpent. NGC 3242 is a
planetary nebula A planetary nebula is a type of emission nebula consisting of an expanding, glowing shell of ionized gas ejected from red giant stars late in their lives. The term "planetary nebula" is a misnomer because they are unrelated to planets. The ...
of magnitude 7.5, 1400 light-years from Earth. Discovered in 1785 by
William Herschel Frederick William Herschel ( ; ; 15 November 1738 – 25 August 1822) was a German-British astronomer and composer. He frequently collaborated with his younger sister and fellow astronomer Caroline Herschel. Born in the Electorate of Hanover ...
, it has earned the nickname "Ghost of
Jupiter Jupiter is the fifth planet from the Sun and the List of Solar System objects by size, largest in the Solar System. It is a gas giant with a Jupiter mass, mass more than 2.5 times that of all the other planets in the Solar System combined a ...
" because of its striking resemblance to the giant planet. Its blue-green disk is visible in small telescopes and its halo is visible in larger instruments. M48 (NGC 2548) is an open cluster that is visible to the naked eye under dark skies. Its shape has been described as "triangular"; this 80-star cluster is unusually large, more than half a degree in diameter, larger than the diameter of the full Moon. There are several globular clusters in Hydra. M68 (NGC 4590) is a globular cluster visible in binoculars and resolvable in medium amateur telescopes. It is 31,000 light-years from Earth and of the 8th magnitude. NGC 5694 is a globular cluster of magnitude 10.2, 105,000 light-years from Earth. Also called "Tombaugh's Globular Cluster", it is a Shapley class VII cluster; the classification indicates that it has intermediate concentration at its nucleus. Though it was discovered as a non-stellar object in 1784 by
William Herschel Frederick William Herschel ( ; ; 15 November 1738 – 25 August 1822) was a German-British astronomer and composer. He frequently collaborated with his younger sister and fellow astronomer Caroline Herschel. Born in the Electorate of Hanover ...
, its status as a globular cluster was not ascertained until 1932, when
Clyde Tombaugh Clyde William Tombaugh (; February 4, 1906 – January 17, 1997) was an American astronomer best known for discovering Pluto, the first object to be identified in what would later be recognized as the Kuiper belt, in 1930. Raised on farms in ...
looked at photographic plates taken of the region near Pi Hydrae on 12 May 1931. M83 (NGC 5236), the Southern Pinwheel Galaxy, is an 8th magnitude face-on
spiral galaxy Spiral galaxies form a galaxy morphological classification, class of galaxy originally described by Edwin Hubble in his 1936 work ''The Realm of the Nebulae''
. It is easily observed in skies south of 40°N latitude, found by using 1, 2, 3, and
4 Centauri 4 Centauri is a star in the constellation Centaurus. It is a blue-white B-type subgiant with an apparent magnitude of +4.75 and is approximately 640 light years from Earth. 4 Centauri is a hierarchical quadruple star system. The primar ...
as guide stars. It has been host to six
supernova A supernova (: supernovae or supernovas) is a powerful and luminous explosion of a star. A supernova occurs during the last stellar evolution, evolutionary stages of a massive star, or when a white dwarf is triggered into runaway nuclear fusion ...
e. Large amateur telescopes - above 12 inches
aperture In optics, the aperture of an optical system (including a system consisting of a single lens) is the hole or opening that primarily limits light propagated through the system. More specifically, the entrance pupil as the front side image o ...
- reveal its spiral arms,
bar Bar or BAR may refer to: Food and drink * Bar (establishment), selling alcoholic beverages * Candy bar ** Chocolate bar * Protein bar Science and technology * Bar (river morphology), a deposit of sediment * Bar (tropical cyclone), a laye ...
, and small, bright nucleus. In a medium-sized amateur instrument, around 8 inches in aperture, the spiral arms become visible under good conditions. It is not perfectly symmetrical in the eyepiece, rather, the northwest side is flattened and the nucleus has a southwest-to-northeast bar. A smaller sister to the Milky Way, it is a
grand design spiral galaxy A grand design spiral galaxy is a spiral galaxy with prominent and well-defined continuous spiral arms, as opposed to multi-arm, patchy and flocculent spirals which have subtler structural features. The spiral arms of a grand design galaxy exten ...
40,000 light-years across. There are many other galaxies located in Hydra. NGC 3314, usually delineated as NGC 3314a and NGC 3314b, is a pair of galaxies that appear superimposed, despite the fact that they are not related or interacting in any way. The foreground galaxy, NGC 3314a, is at a distance of 140 million light-years, and is a face-on spiral galaxy. The background galaxy, NGC 3314b, is an oblique spiral galaxy, and has a nucleus that appears reddened because of NGC 3314a's dusty disk. ESO 510-G13 is a warped
spiral galaxy Spiral galaxies form a galaxy morphological classification, class of galaxy originally described by Edwin Hubble in his 1936 work ''The Realm of the Nebulae''
located 150 million light-years from Earth. Though most galactic disks are flat because of their rate of rotation, their conformation can be changed, as is the case with this galaxy. Astronomers speculate that this is due to interactions with other galaxies. NGC 5068 may be a member of the M83 group, but its identity is disputed. It has a low surface brightness and has a diameter of 4.5 arcminutes. It is not perfectly circular, rather, it is elliptical and oriented on a west-northwest/east-southeast axis. However, it is of fairly uniform brightness throughout. Another notable galaxy is
NGC 4993 NGC 4993 (also catalogued as NGC 4994 in the New General Catalogue) is a lenticular galaxy located about 140 million light-years away in the constellation Hydra (constellation), Hydra. It was discovered on 26 March 1789 by William Herschel and ...
, an elliptical galaxy which was the source of events
GW170817 GW170817 was a gravitational wave (GW) observed by the LIGO and Virgo detectors on 17 August 2017, originating within the shell elliptical galaxy NGC 4993, about 144 million light years away. The wave was produced by the last moments of the in ...
,
GRB 170817A GW170817 was a gravitational wave (GW) observed by the LIGO and Virgo detectors on 17 August 2017, originating within the shell elliptical galaxy NGC 4993, about 144 million light years away. The wave was produced by the last moments of the ins ...
and
SSS17a GW170817 was a gravitational wave (GW) observed by the LIGO and Virgo interferometer, Virgo detectors on 17 August 2017, originating within the shell elliptical galaxy NGC 4993, about 144 million light years away. The wave was produced by the la ...
from the merger of two
neutron star A neutron star is the gravitationally collapsed Stellar core, core of a massive supergiant star. It results from the supernova explosion of a stellar evolution#Massive star, massive star—combined with gravitational collapse—that compresses ...
s.


Meteor showers

The Sigma Hydrids peak on December 6 and are a very active shower. The parent body of the Sigma Hybrids is believed to be Comet Nishimura (C/2023 P1), which was discovered in 2023 by the Japanese astronomical photographer Hideo Nishimur

The Alpha Hydrids are a minor shower that peaks between January 1 and 7.


See also

*
Hydra (Chinese astronomy) The modern constellation Hydra (constellation), Hydra lies across two of the quadrants, symbolized by the Azure Dragon, Azure Dragon of the East (東方青龍, ''Dōng Fāng Qīng Lóng'') and the Vermilion Bird, Vermilion Bird of the South (南方� ...


References


Citations


References

* * * * * Ian Ridpath and Wil Tirion (2007). ''Stars and Planets Guide'', Collins, London. . Princeton University Press, Princeton. . * *


External links


The Deep Photographic Guide to the Constellations: Hydra



Warburg Institute Iconographic Database (medieval and early modern images of Hydra)
{{DEFAULTSORT:Hydra (Constellation) Constellations Constellations listed by Ptolemy Equatorial constellations