Hydrus is a small
constellation in the deep
southern sky
The southern celestial hemisphere, also called the Southern Sky, is the southern half of the celestial sphere; that is, it lies south of the celestial equator. This arbitrary sphere, on which seemingly fixed stars form constellations, app ...
. It was one of twelve constellations created by
Petrus Plancius
Petrus Plancius (; 1552 – 15 May 1622) was a Dutch-Flemish astronomer, cartographer and clergyman. He was born as Pieter Platevoet in Dranouter, now in Heuvelland, West Flanders. He studied theology in Germany and England. At the age of 24 he ...
from the observations of
Pieter Dirkszoon Keyser
Pieter Dirkszoon Keyser (occasionally Petrus Theodorus; – 11 September 1596) was a Dutch navigator and celestial cartographer who mapped several constellations on the southern celestial hemisphere.
Voyages and star observation
Little is ...
and
Frederick de Houtman
Frederick de Houtman ( – 21 October 1627) was a Dutch explorer, navigator, and colonial governor who sailed on the first Dutch expedition to the East Indies from 1595 until 1597, during which time he made observations of the southern ce ...
and it first appeared on a 35-cm (14 in) diameter celestial globe published in late 1597 (or early 1598) in Amsterdam by Plancius and
Jodocus Hondius. The first depiction of this constellation in a celestial atlas was in
Johann Bayer's
Uranometria
''Uranometria'' is a star atlas produced by Johann Bayer. It was published in Augsburg in 1603 by Christoph Mangle (''Christophorus Mangus'') under the full title ''Uranometria: omnium asterismorum continens schemata, nova methodo delineata, a ...
of 1603. The French explorer and astronomer
Nicolas Louis de Lacaille
Abbé Nicolas-Louis de Lacaille (; 15 March 171321 March 1762), formerly sometimes spelled de la Caille, was a French astronomer and geodesist who named 14 out of the 88 constellations. From 1750 to 1754, he studied the sky at the Cape of Goo ...
charted the brighter
stars and gave their
Bayer designations in 1756. Its name means "male water snake", as opposed to
Hydra, a much larger constellation that represents a female water snake. It remains below the horizon for most
Northern Hemisphere
The Northern Hemisphere is the half of Earth that is north of the Equator. For other planets in the Solar System, north is defined as being in the same celestial hemisphere relative to the invariable plane of the solar system as Earth's Nort ...
observers.
The brightest star is the 2.8-
magnitude
Magnitude may refer to:
Mathematics
*Euclidean vector, a quantity defined by both its magnitude and its direction
*Magnitude (mathematics), the relative size of an object
*Norm (mathematics), a term for the size or length of a vector
*Order of ...
Beta Hydri
Beta Hydri (β Hyi, β Hydri) is a star in the southern circumpolar constellation of Hydrus. (Note that Hydrus is not the same as Hydra.) With an apparent visual magnitude of 2.8, this is the brightest star in the constellation. Based u ...
, also the closest reasonably bright star to the
south celestial pole. Pulsating between magnitude 3.26 and 3.33,
Gamma Hydri
γ Hydri, Latinised as Gamma Hydri, is a solitary, red-hued star in the constellation Hydrus. It has an apparent visual magnitude of 3.26, making it easily visible to the naked eye at night. Based upon an annual parallax shift of 15.24&n ...
is a variable
red giant 60 times the diameter of the
Sun
The Sun is the star at the center of the Solar System. It is a nearly perfect ball of hot plasma, heated to incandescence by nuclear fusion reactions in its core. The Sun radiates this energy mainly as light, ultraviolet, and infrared radi ...
. Lying near it is
VW Hydri
VW Hydri is a dwarf nova of the SU Ursae Majoris type in the deep southern constellation Hydrus; a star system that consists of a white dwarf and another generally cool star. It is one of the brightest dwarf novae systems in the sky. These system ...
, one of the brightest
dwarf nova
A U Geminorum-type variable star, or dwarf nova (pl. novae) is one of several types of cataclysmic variable star, consisting of a close binary star system in which one of the components is a white dwarf that accretes matter from its companion. Dwa ...
e in the heavens. Four star systems in Hydrus have been found to have
exoplanets to date, including
HD 10180
HD 10180, also designated 2MASS J01375356-6030414, is a Sun-like star in the southern constellation Hydrus that is notable for its large planetary system. Since its discovery, at least six exoplanets have been observed orbiting it, and ...
, which could bear up to nine planetary companions.
History
![Johann Bayer - Uraniometria - Southern Birds](https://upload.wikimedia.org/wikipedia/commons/b/b5/Johann_Bayer_-_Uraniometria_-_Southern_Birds.jpg)
Hydrus was one of the twelve constellations established by the Dutch astronomer
Petrus Plancius
Petrus Plancius (; 1552 – 15 May 1622) was a Dutch-Flemish astronomer, cartographer and clergyman. He was born as Pieter Platevoet in Dranouter, now in Heuvelland, West Flanders. He studied theology in Germany and England. At the age of 24 he ...
from the observations of the southern sky by the Dutch explorers
Pieter Dirkszoon Keyser
Pieter Dirkszoon Keyser (occasionally Petrus Theodorus; – 11 September 1596) was a Dutch navigator and celestial cartographer who mapped several constellations on the southern celestial hemisphere.
Voyages and star observation
Little is ...
and
Frederick de Houtman
Frederick de Houtman ( – 21 October 1627) was a Dutch explorer, navigator, and colonial governor who sailed on the first Dutch expedition to the East Indies from 1595 until 1597, during which time he made observations of the southern ce ...
, who had sailed on the first Dutch trading expedition, known as the ''
Eerste Schipvaart'', to the
East Indies
The East Indies (or simply the Indies), is a term used in historical narratives of the Age of Discovery. The Indies refers to various lands in the East or the Eastern hemisphere, particularly the islands and mainlands found in and around ...
. It first appeared on a 35-cm (14 in) diameter celestial globe published in 1598 in Amsterdam by Plancius with
Jodocus Hondius. The first depiction of this constellation in a celestial atlas was in the German cartographer
Johann Bayer's ''
Uranometria
''Uranometria'' is a star atlas produced by Johann Bayer. It was published in Augsburg in 1603 by Christoph Mangle (''Christophorus Mangus'') under the full title ''Uranometria: omnium asterismorum continens schemata, nova methodo delineata, a ...
'' of 1603. De Houtman included it in his southern star catalogue the same year under the Dutch name ''De Waterslang'', "The Water Snake", it representing a type of snake encountered on the expedition rather than a mythical creature.
The French explorer and astronomer
Nicolas Louis de Lacaille
Abbé Nicolas-Louis de Lacaille (; 15 March 171321 March 1762), formerly sometimes spelled de la Caille, was a French astronomer and geodesist who named 14 out of the 88 constellations. From 1750 to 1754, he studied the sky at the Cape of Goo ...
called it ''l’Hydre Mâle'' on the 1756 version of his
planisphere
In astronomy, a planisphere () is a star chart analog computing instrument in the form of two adjustable disks that rotate on a common pivot. It can be adjusted to display the visible stars for any time and date. It is an instrument to assist ...
of the southern skies, distinguishing it from the feminine
Hydra. The French name was retained by
Jean Fortin in 1776 for his ''Atlas Céleste'', while Lacaille
Latin
Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through the power of the ...
ised the name to Hydrus for his revised ''Coelum Australe Stelliferum'' in 1763.
Characteristics
Irregular in shape,
Hydrus is bordered by
Mensa to the southeast,
Eridanus to the east,
Horologium and
Reticulum
Reticulum is a small, faint constellation in the southern sky. Its name is Latin for a small net, or reticle—a net of crosshairs at the focus of a telescope eyepiece that is used to measure star positions. The constellation is best viewed b ...
to the northeast,
Phoenix
Phoenix most often refers to:
* Phoenix (mythology), a legendary bird from ancient Greek folklore
* Phoenix, Arizona, a city in the United States
Phoenix may also refer to:
Mythology
Greek mythological figures
* Phoenix (son of Amyntor), a ...
to the north,
Tucana
Tucana (The Toucan) is a constellation of stars in the southern sky, named after the toucan, a South American bird. It is one of twelve constellations conceived in the late sixteenth century by Petrus Plancius from the observations of Pieter D ...
to the northwest and west, and
Octans
Octans () is a faint constellation located in the deep Southern Sky. Its name is Latin for the eighth part of a circle, but it is named after the octant, a navigational instrument. Devised by French astronomer Nicolas Louis de Lacaille in 1752 ...
to the south; Lacaille had shortened Hydrus' tail to make space for this last constellation he had drawn up.
[ Covering 243 square degrees and 0.589% of the night sky, it ranks 61st of the 88 constellations in size.] The three-letter abbreviation for the constellation, as adopted by the International Astronomical Union
The International Astronomical Union (IAU; french: link=yes, Union astronomique internationale, UAI) is a nongovernmental organisation with the objective of advancing astronomy in all aspects, including promoting astronomical research, outreac ...
in 1922, is "Hyi". The official constellation boundaries, as set by Belgian astronomer Eugène Delporte
Eugene is a common male given name that comes from the Greek εὐγενής (''eugenēs''), "noble", literally "well-born", from εὖ (''eu''), "well" and γένος (''genos''), "race, stock, kin".equatorial coordinate system
The equatorial coordinate system is a celestial coordinate system widely used to specify the positions of celestial objects. It may be implemented in spherical or rectangular coordinates, both defined by an origin at the centre of Earth, a fu ...
, the right ascension coordinates of these borders lie between and , while the declination coordinates are between −57.85° and −82.06°. As one of the deep southern constellations, it remains below the horizon at latitudes north of the 30th parallel in the Northern Hemisphere
The Northern Hemisphere is the half of Earth that is north of the Equator. For other planets in the Solar System, north is defined as being in the same celestial hemisphere relative to the invariable plane of the solar system as Earth's Nort ...
, and is circumpolar at latitudes south of the 50th parallel in the Southern Hemisphere. Herman Melville
Herman Melville ( born Melvill; August 1, 1819 – September 28, 1891) was an American novelist, short story writer, and poet of the American Renaissance period. Among his best-known works are ''Moby-Dick'' (1851); ''Typee'' (1846), a rom ...
mentions it and Argo Navis
Argo Navis (the Ship Argo), or simply Argo, is one of the 48 Ptolemy's constellations, now a grouping of three IAU constellations. It is formerly a single large constellation in the southern sky. The genitive is "Argus Navis", abbreviated "Arg" ...
in ''Moby Dick
''Moby-Dick; or, The Whale'' is an 1851 novel by American writer Herman Melville. The book is the sailor Ishmael's narrative of the obsessive quest of Ahab, captain of the whaling ship ''Pequod'', for revenge against Moby Dick, the giant whit ...
'' "beneath effulgent Antarctic Skies", highlighting his knowledge of the southern constellations from whaling voyages. A line drawn between the long axis of the Southern Cross
Crux () is a constellation of the southern sky that is centred on four bright stars in a cross-shaped asterism commonly known as the Southern Cross. It lies on the southern end of the Milky Way's visible band. The name ''Crux'' is Latin for ...
to Beta Hydri
Beta Hydri (β Hyi, β Hydri) is a star in the southern circumpolar constellation of Hydrus. (Note that Hydrus is not the same as Hydra.) With an apparent visual magnitude of 2.8, this is the brightest star in the constellation. Based u ...
and then extended 4.5 times will mark a point due south. Hydrus culminates at midnight around 26 October.[
]
Features
Stars
Keyzer and de Houtman assigned fifteen stars to the constellation in their Malay and Madagascan vocabulary, with a star that would be later designated as Alpha Hydri
Alpha Hydri, Latinized from α Hydri, is the second brightest star in the southern circumpolar constellation of Hydrus. It is readily visible to the naked eye with an apparent visual magnitude of +2.9. It is sometimes informally known ...
marking the head, Gamma the chest and a number of stars that were later allocated to Tucana, Reticulum, Mensa and Horologium marking the body and tail. Lacaille charted and designated 20 stars with the Bayer designations Alpha through to Tau in 1756. Of these, he used the designations Eta, Pi and Tau twice each, for three sets of two stars close together, and omitted Omicron and Xi. He assigned Rho to a star that subsequent astronomers were unable to find.
Beta Hydri, the brightest star in Hydrus, is a yellow star of apparent magnitude
Apparent magnitude () is a measure of the brightness of a star or other astronomical object observed from Earth. An object's apparent magnitude depends on its intrinsic luminosity, its distance from Earth, and any extinction of the object's ...
2.8, lying 24 light-years from Earth. It has about 104% of the mass of the Sun and 181% of the Sun's radius, with more than three times the Sun's luminosity. The spectrum
A spectrum (plural ''spectra'' or ''spectrums'') is a condition that is not limited to a specific set of values but can vary, without gaps, across a continuum. The word was first used scientifically in optics to describe the rainbow of colors i ...
of this star matches a stellar classification of G2 IV, with the luminosity class
In astronomy, stellar classification is the classification of stars based on their spectral characteristics. Electromagnetic radiation from the star is analyzed by splitting it with a prism or diffraction grating into a spectrum exhibiting the ...
of 'IV' indicating this is a subgiant star
A subgiant is a star that is brighter than a normal main-sequence star of the same spectral class, but not as bright as giant stars. The term subgiant is applied both to a particular spectral luminosity class and to a stage in the evolution o ...
. As such, it is a slightly more evolved
Evolution is change in the heritable characteristics of biological populations over successive generations. These characteristics are the expressions of genes, which are passed on from parent to offspring during reproduction. Variation ...
star than the Sun, with the supply of hydrogen fuel at its core
Core or cores may refer to:
Science and technology
* Core (anatomy), everything except the appendages
* Core (manufacturing), used in casting and molding
* Core (optical fiber), the signal-carrying portion of an optical fiber
* Core, the centra ...
becoming exhausted. It is the nearest subgiant star to the Sun and one of the oldest stars in the solar neighbourhood. Thought to be between 6.4 and 7.1 billion years old, this star bears some resemblance to what the Sun may look like in the far distant future, making it an object of interest to astronomers.[ It is also the closest bright star to the south celestial pole.]
Located at the northern edge of the constellation and just southwest of Achernar is Alpha Hydri
Alpha Hydri, Latinized from α Hydri, is the second brightest star in the southern circumpolar constellation of Hydrus. It is readily visible to the naked eye with an apparent visual magnitude of +2.9. It is sometimes informally known ...
, a white sub-giant star of magnitude 2.9, situated 72 light-years from Earth. Of spectral type F0IV, it is beginning to cool and enlarge as it uses up its supply of hydrogen. It is twice as massive and 3.3 times as wide as the Sun and 26 times more luminous. A line drawn between Alpha Hydri and Beta Centauri
Beta Centauri is a triple star system in the southern constellation of Centaurus. It is officially called Hadar (). The Bayer designation of Beta Centauri is Latinised from β Centauri, and abbreviated Beta Cen or β Cen. The sys ...
is bisected by the south celestial pole.[
In the southeastern corner of the constellation is ]Gamma Hydri
γ Hydri, Latinised as Gamma Hydri, is a solitary, red-hued star in the constellation Hydrus. It has an apparent visual magnitude of 3.26, making it easily visible to the naked eye at night. Based upon an annual parallax shift of 15.24&n ...
, a red giant of spectral type M2III located 214 light-years from Earth. It is a semi-regular variable star, pulsating between magnitudes 3.26 and 3.33. Observations over five years were not able to establish its periodicity
Periodicity or periodic may refer to:
Mathematics
* Bott periodicity theorem, addresses Bott periodicity: a modulo-8 recurrence relation in the homotopy groups of classical groups
* Periodic function, a function whose output contains values tha ...
. It is around 1.5 to 2 times as massive as our Sun, and has expanded to about 60 times the Sun's diameter. It shines with about 655 times the luminosity of the Sun. Located 3° northeast of Gamma is the VW Hydri
VW Hydri is a dwarf nova of the SU Ursae Majoris type in the deep southern constellation Hydrus; a star system that consists of a white dwarf and another generally cool star. It is one of the brightest dwarf novae systems in the sky. These system ...
, a dwarf nova
A U Geminorum-type variable star, or dwarf nova (pl. novae) is one of several types of cataclysmic variable star, consisting of a close binary star system in which one of the components is a white dwarf that accretes matter from its companion. Dwa ...
of the SU Ursae Majoris type. It is a close binary
Binary may refer to:
Science and technology Mathematics
* Binary number, a representation of numbers using only two digits (0 and 1)
* Binary function, a function that takes two arguments
* Binary operation, a mathematical operation that ta ...
system that consists of a white dwarf
A white dwarf is a stellar core remnant composed mostly of electron-degenerate matter. A white dwarf is very dense: its mass is comparable to the Sun's, while its volume is comparable to the Earth's. A white dwarf's faint luminosity comes ...
and another star, the former drawing off matter from the latter into a bright accretion disk. These systems are characterised by frequent eruptions and less frequent supereruptions. The former are smooth, while the latter exhibit short "superhumps" of heightened activity. One of the brightest dwarf novae in the sky, it has a baseline magnitude of 14.4 and can brighten to magnitude 8.4 during peak activity.[ ]BL Hydri BL (or similar) may refer to:
Arts and entertainment
* BL Publishing, a division of the wargames manufacturing company, Games Workshop
* '' Boston Legal'', a US legal comedy drama
* Boys' love, Japanese term for female-oriented fiction featuring ...
is another close binary system composed of a low-mass star and a strongly magnetic white dwarf. Known as a polar
Polar may refer to:
Geography
Polar may refer to:
* Geographical pole, either of two fixed points on the surface of a rotating body or planet, at 90 degrees from the equator, based on the axis around which a body rotates
* Polar climate, the c ...
or AM Herculis variable, these produce polarized optical and infrared
Infrared (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with wavelengths longer than those of visible light. It is therefore invisible to the human eye. IR is generally understood to encompass wavelengths from around ...
emissions and intense soft and hard X-ray
An X-ray, or, much less commonly, X-radiation, is a penetrating form of high-energy electromagnetic radiation. Most X-rays have a wavelength ranging from 10 picometers to 10 nanometers, corresponding to frequencies in the range 30&nb ...
emissions to the frequency of the white dwarf's rotation period—in this case 113.6 minutes.
There are two notable optical double stars in Hydrus. Pi Hydri, composed of Pi1 Hydri and Pi2 Hydri, is divisible in binoculars. Around 476 light-years distant, Pi1 is a red giant of spectral type M1III that varies between magnitudes 5.52 and 5.58. Pi2 is an orange giant of spectral type K2III and shining with a magnitude of 5.7, around 488 light-years from Earth.
Eta Hydri is the other optical double, composed of Eta1 and Eta2. Eta1 is a blue-white main sequence star of spectral type B9V that was suspected of being variable, and is located just over 700 light-years away. Eta2 has a magnitude of 4.7 and is a yellow giant star of spectral type G8.5III around 218 light-years distant, which has evolved off the main sequence and is expanding and cooling on its way to becoming a red giant. Calculations of its mass indicate it was most likely a white A-type main sequence star for most of its existence, around twice the mass of the Sun. A planet, Eta2 Hydri b, greater than 6.5 times the mass of Jupiter
Jupiter is the fifth planet from the Sun and the largest in the Solar System. It is a gas giant with a mass more than two and a half times that of all the other planets in the Solar System combined, but slightly less than one-thousandth t ...
was discovered in 2005, orbiting around Eta2 every 711 days at a distance of 1.93 astronomical unit
The astronomical unit (symbol: au, or or AU) is a unit of length, roughly the distance from Earth to the Sun and approximately equal to or 8.3 light-minutes. The actual distance from Earth to the Sun varies by about 3% as Earth orbits ...
s (AU).
Three other systems have been found to have planets, most notably the Sun-like star HD 10180
HD 10180, also designated 2MASS J01375356-6030414, is a Sun-like star in the southern constellation Hydrus that is notable for its large planetary system. Since its discovery, at least six exoplanets have been observed orbiting it, and ...
, which has seven planets, plus possibly an additional two for a total of nine—as of 2012 more than any other system to date, including the Solar System. Lying around from the Earth, it has an apparent magnitude of 7.33.
GJ 3021 is a solar twin
Solar may refer to:
Astronomy
* Of or relating to the Sun
** Solar telescope, a special purpose telescope used to observe the Sun
** A device that utilizes solar energy (e.g. " solar panels")
** Solar calendar, a calendar whose dates indica ...
—a star very like our own Sun—around 57 light-years distant with a spectral type G8V and magnitude of 6.7. It has a Jovian planet
The giant planets constitute a diverse type of planet much larger than Earth. They are usually primarily composed of low-boiling-point materials ( volatiles), rather than rock or other solid matter, but massive solid planets can also exist. T ...
companion ( GJ 3021 b). Orbiting about 0.5 AU from its sun, it has a minimum mass 3.37 times that of Jupiter and a period of around 133 days. The system is a complex one as the faint star GJ 3021B orbits at a distance of 68 AU; it is a red dwarf of spectral type M4V.
HD 20003 is a star of magnitude 8.37. It is a yellow main sequence star of spectral type G8V a little cooler and smaller than our Sun around 143 light-years away. It has two planets that are around 12 and 13.5 times as massive as the Earth with periods of just under 12 and 34 days respectively.
Deep-sky objects
Hydrus contains only faint deep-sky object
A deep-sky object (DSO) is any astronomical object that is not an individual star or Solar System object (such as Sun, Moon, planet, comet, etc.). The classification is used for the most part by amateur astronomers to denote visually observed f ...
s. IC 1717 was a deep-sky object discovered by the Danish astronomer John Louis Emil Dreyer
John Louis Emil Dreyer (13 February 1852 – 14 September 1926) was a Danish astronomer who spent most of his career working in Ireland. He spent the last decade of his life in Oxford, England.
Life
Dreyer was born in Copenhagen. His fath ...
in the late 19th century. The object at the coordinate Dreyer observed is no longer there, and is now a mystery. It was very likely to have been a faint comet
A comet is an icy, small Solar System body that, when passing close to the Sun, warms and begins to release gases, a process that is called outgassing. This produces a visible atmosphere or coma, and sometimes also a tail. These phenomena ...
. PGC 6240
PGC 6240, also known as AM 0139-655 or the White Rose Galaxy, is a very large and old galaxy in the southern constellation of Hydrus, about 345 million light years away from Earth.
Appearing like a white rose in the sky, the galaxy has foggy sh ...
, known as the White Rose Galaxy, is a giant spiral galaxy surrounded by shells resembling rose petals, located around 345 million light years from the Solar System. Unusually, it has cohorts of globular clusters of three distinct ages suggesting bouts of post-starburst formation following a merger with another galaxy. The constellation also contains a spiral galaxy, NGC 1511, which lies edge on to observers on Earth and is readily viewed in amateur telescopes.[
Located mostly in ]Dorado
Dorado () is a constellation in the southern sky. It was named in the late 16th century and is now one of the 88 modern constellations. Its name refers to the dolphinfish (''Coryphaena hippurus''), which is known as ''dorado'' in Spanish, altho ...
, the Large Magellanic Cloud extends into Hydrus. The globular cluster NGC 1466 is an outlying component of the galaxy, and contains many RR Lyrae-type variable stars. It has a magnitude of 11.59 and is thought to be over 12 billion years old. Two stars, HD 24188 of magnitude 6.3 and HD 24115 of magnitude 9.0, lie nearby in its foreground. NGC 602 is composed of an emission nebula
An emission nebula is a nebula formed of ionized gases that emit light of various wavelengths. The most common source of ionization is high-energy ultraviolet photons emitted from a nearby hot star. Among the several different types of emissio ...
and a young, bright open cluster
An open cluster is a type of star cluster made of up 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, an ...
of stars that is an outlying component on the eastern edge of the Small Magellanic Cloud, a satellite galaxy
A satellite galaxy is a smaller companion galaxy that travels on bound orbits within the gravitational potential of a more massive and luminous host galaxy (also known as the primary galaxy). Satellite galaxies and their constituents are bound ...
to the Milky Way
The Milky Way is the galaxy that includes our Solar System, with the name describing the galaxy's appearance from Earth: a hazy band of light seen in the night sky formed from stars that cannot be individually distinguished by the naked eye. ...
. Most of the cloud is located in the neighbouring constellation Tucana.
See also
* Hydrus (Chinese astronomy)
References
External links
Chandra information about Hydrus
{{DEFAULTSORT:Hydrus
Southern constellations
Constellations listed by Petrus Plancius
Dutch celestial cartography in the Age of Discovery
Astronomy in the Dutch Republic
1590s in the Dutch Republic