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Hydra (constellation): Wikis


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List of stars in Hydra
Abbreviation Hya
Genitive Hydrae
Pronunciation /ˈhaɪdrə/, genitive /ˈhaɪdriː/
Symbolism the sea serpent
Right ascension 8-15 h
Declination −20°
Family Hercules
Quadrant SQ2
Area 1303 sq. deg. (1st)
Main stars 17
Stars with
known planets
Stars brighter than 3m 2
Stars within 10 pc (32.6 ly) 4
Brightest star Alphard (α Hya) (1.98m)
Nearest star LHS 3003
(20.67 ly, 6.34 pc)
Messier objects 3
Meteor showers Alpha Hydrids
Sigma Hydrids
Canis Minor
Lupus (corner)
Visible at latitudes between +54° and −83°.
Best visible at 21:00 (9 p.m.) during the month of April.

Hydra is the largest of the 88 modern constellations, measuring 1303 square degrees. It has a long history, having been included among the 48 constellations listed by the 2nd century astronomer Ptolemy. It is commonly represented as a water snake. In Japanese culture, it is also known as Nuriko, while in Chinese, it is known by the name Willow.


Notable features



Despite its size, Hydra contains only one reasonably bright star, Alphard (α Hya, 30 Hya), which is of apparent magnitude 1.98. Alphard ("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, the lunar zodiacal constellation in Indian astronomy.

R Hydrae is a Mira variable star that ranges in magnitude between 3.5, when it can be visible to the naked eye, to 10.9, when a telescope is required to see it.

There are several double stars of interest in Hydra. Epsilon Hydrae (ε Hya) is a binary star 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, M68 is a globular cluster near M83, and M48 is an open star cluster in the western end of the serpent.


The shape of Hydra resembles a twisting snake, and features as such in some Greek myths. One myth associates it with a water snake that a crow served Apollo 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. The origin of this story is likely to be the juxtaposition of this constellation with those of Crater, and Corvus, in the area of the sky known as the Sea.

The Hydra was also considered to be the Lernaean Hydra (as defeated by Heracles for one of his Twelve Labours) by the Greeks. Its position in the sky (below the ecliptic), together with the constellation Cancer (which lies near its head) may be the origin of parts of the myth.


  • Ian Ridpath and Wil Tirion (2007). Stars and Planets Guide, Collins, London. ISBN 978-0007251209. Princeton University Press, Princeton. ISBN 978-0691135564.

External links

Coordinates: Sky map 10h 00m 00s, −20° 00′ 00″


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