Hydra (constellation)
Encyclopedia
Hydra is the largest of the 88 modern constellation
Constellation
In modern astronomy, a constellation is an internationally defined area of the celestial sphere. These areas are grouped around asterisms, patterns formed by prominent stars within apparent proximity to one another on Earth's night sky....

s, measuring 1303 square degrees. It has a long history, having been included among the 48 constellations listed by the 2nd century astronomer Ptolemy
Ptolemy
Claudius Ptolemy , was a Roman citizen of Egypt who wrote in Greek. He was a mathematician, astronomer, geographer, astrologer, and poet of a single epigram in the Greek Anthology. He lived in Egypt under Roman rule, and is believed to have been born in the town of Ptolemais Hermiou in the...

. It is commonly represented as a water snake
Water snake
Different snakes are called water snakes. Most are colubrids. "Water snake" is also sometimes used as a descriptive term for any snakes that spend a significant time in or near fresh water, such as any species belonging to the family Acrochordidae...

. It should not be confused with the similarly named constellation of Hydrus
Hydrus
Hydrus is a small constellation in the southern sky, created in the sixteenth century. Its name means "male water snake", and it should not be confused with Hydra, a much larger constellation which represents a female water snake.-History:...

.

Stars

Despite its size, Hydra contains only one reasonably bright star
Star
A star is a massive, luminous sphere of plasma held together by gravity. At the end of its lifetime, a star can also contain a proportion of degenerate matter. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth...

, Alphard
Alphard
Alphard is the brightest star in the constellation Hydra. The name Alphard is from the Arabic الفرد , "the solitary one", there being no other bright stars near it. It was also known as the "backbone of the Serpent" to the Arabs. In ancient China it formed part of an asterism called the "red bird"...

 (α Hya, 30 Hya), which is of apparent magnitude
Apparent magnitude
The apparent magnitude of a celestial body is a measure of its brightness as seen by an observer on Earth, adjusted to the value it would have in the absence of the atmosphere...

 1.98. Alphard
Alphard
Alphard is the brightest star in the constellation Hydra. The name Alphard is from the Arabic الفرد , "the solitary one", there being no other bright stars near it. It was also known as the "backbone of the Serpent" to the Arabs. In ancient China it formed part of an asterism called the "red bird"...

 ("the solitary one") is actually a double star. The other main named star in Hydra is Sigma, σ, Hydrae, which also has the name of Minaruja, from the Arabic for snake's nose. At magnitude 4.54, it is rather dim. The head of the snake corresponds to the Āshleshā nakshatra
Nakshatra
Nakshatra is the term for lunar mansion in Hindu astrology. A nakshatra is one of 27 sectors along the ecliptic...

, the lunar zodiacal constellation in Indian astronomy.

R Hydrae
R Hydrae
R Hydrae is a Mira-type variable star in the constellation Hydra.The magnitude of R Hydrae varies over a period of 389 days, between 3.21 and 11.00. The period of R Hydrae changes slowly....

 is a Mira variable
Mira variable
Mira variables , named after the star Mira, are a class of pulsating variable stars characterized by very red colors, pulsation periods longer than 100 days, and light amplitudes greater than one magnitude in infrared and 2.5 magnitude in visual...

 star that ranges in magnitude between 3.5, when it can be visible to the naked eye, to 10.9, when a telescope
Telescope
A telescope is an instrument that aids in the observation of remote objects by collecting electromagnetic radiation . The first known practical telescopes were invented in the Netherlands at the beginning of the 1600s , using glass lenses...

 is required to see it.

There are several double star
Double star
In observational astronomy, a double star is a pair of stars that appear close to each other in the sky as seen from Earth when viewed through an optical telescope. This can happen either because the pair forms a binary star, i.e...

s of interest in Hydra. Epsilon Hydrae
Epsilon Hydrae
Epsilon Hydrae is a Class G5, third-magnitude star in the constellation Hydra. Epsilon Hydrae is a binary star with components of magnitudes 3.3 and 6.8, separated by 2.7 arcseconds...

 (ε Hya) is a binary star
Binary star
A binary star is a star system consisting of two stars orbiting around their common center of mass. The brighter star is called the primary and the other is its companion star, comes, or secondary...

 with components of magnitudes 3.3 and 6.8, separated by 2.7 arcseconds. 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 constellation also contains the radio source Hydra A.

Deep sky objects

Hydra contains three Messier objects. M83, also known as the Southern Pinwheel Galaxy, is located on the border of Hydra and Centaurus
Centaurus
Centaurus is a bright constellation in the southern sky. One of the largest constellations, Centaurus was included among the 48 constellations listed by the 2nd century astronomer Ptolemy, and it remains one of the 88 modern constellations.-Stars:...

, M68
Messier 68
Messier 68 is a globular cluster in the Hydra constellation. It was discovered by Charles Messier in 1780. M68 is at a distance of about 33,000 light-years away from Earth.-External links:* *...

 is a globular cluster
Globular cluster
A globular cluster is a spherical collection of stars that orbits a galactic core as a satellite. Globular clusters are very tightly bound by gravity, which gives them their spherical shapes and relatively high stellar densities toward their centers. The name of this category of star cluster is...

 near M83, and M48
Messier 48
Messier 48 is an open cluster in the Hydra constellation. It was discovered by Charles Messier in 1771.There is actually no cluster in the position indicated by Messier...

 is an open star cluster in the western end of the serpent.

History

The Greek constellation of Hydra is an adaptation of a Babylonian constellation: the MUL.APIN
MUL.APIN
MUL.APIN is the conventional title given to a Babylonian compendium that deals with many diverse aspects of Babylonian astronomy and astrology....

 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
Serpens is a constellation of the northern hemisphere. It was one of the 48 constellations listed by the 2nd century astronomer Ptolemy and it remains one of the 88 modern constellations defined by the International Astronomical Union....

), a mythological hybrid of serpent, lion and bird.

The shape of Hydra resembles a twisting snake
Snake
Snakes are elongate, legless, carnivorous reptiles of the suborder Serpentes that can be distinguished from legless lizards by their lack of eyelids and external ears. Like all squamates, snakes are ectothermic, amniote vertebrates covered in overlapping scales...

, and features as such in some Greek myths. One myth associates it with a water snake that a crow
Crow
Crows form the genus Corvus in the family Corvidae. Ranging in size from the relatively small pigeon-size jackdaws to the Common Raven of the Holarctic region and Thick-billed Raven of the highlands of Ethiopia, the 40 or so members of this genus occur on all temperate continents and several...

 served Apollo
Apollo
Apollo is one of the most important and complex of the Olympian deities in Greek and Roman mythology...

 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.

Equivalents

in Chinese astronomy, the stars that correspond to Hydra are located within the Vermilion Bird and the Azure Dragon. In Japanese
Japanese language
is a language spoken by over 130 million people in Japan and in Japanese emigrant communities. It is a member of the Japonic language family, which has a number of proposed relationships with other languages, none of which has gained wide acceptance among historical linguists .Japanese is an...

 culture
Culture
Culture is a term that has many different inter-related meanings. For example, in 1952, Alfred Kroeber and Clyde Kluckhohn compiled a list of 164 definitions of "culture" in Culture: A Critical Review of Concepts and Definitions...

, the stars are known as Nuriko.

External links

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