Constellation Hydra (Female Water Snake)

Hydra: IAU Constellation Map [150]


With an area of 1303 square degrees, Hydra is the largest and with around seven hours in right ascension (105 °) also the longest constellation in the sky. However, due to the numerous faint stars, it is difficult to identify. In addition to Alphard, the brightest star that represents the heart of the water snake, only the head consisting of a group of six stars is easy to find. The head of the Hydra is south of Cancer. The body plunges under the equator and winds east, south of Sextans, Crater, Corvus, Virgo to the Libra, where the tail can be found. Alphard culminates around midnight on February 9th. [9, 15]

Stars with Proper Names [154]
α Hya Alphard, Alfard, Alphart, Kalbelaphard, Cor Hydrae
σ Hya Al Minliar Al Shuja, Minchir
Data for constellation Hydra [150]
IAU NameHydra
IAU GenitiveHydrae
IAU Abbr.Hya
English NameFemale Water Snake
Opposition21 February
Season (47° N)January … April
Right Ascension08h 10m 56s … 15h 02m 31s
Declination-35° 41' 38" … +06° 37' 49"
Area1303 deg2
Neighbours (N↻)Crt, Sex, Leo, Cnc, CMi, Mon, Pup, Pyx, Ant, Cen, Lup, Lib, Vir, Crv

Deep-Sky Object Descriptions


Mythology and History

In the case of the northern water snake, two different images from Greek mythology overlap.

The first picture shows the rather harmless water snake from the story of the raven: The raven was sent by Apollo to fetch fresh spring water with a golden cup. Instead, he feasted on figs and carried the water snake in his claws on his return as an alleged reason for his delay. In order to remind everyone of this crime, the raven with its cup and water snake were put on display in the sky.

The water serpent Heracles dealt with was of a completely different kind: in a swamp near Lerna, a lake and a town on the coast of Argo, lived an unspeakably dangerous and hideous beast. This snake is said to have had several heads. It should have been five, but some also speak of six, nine, even fifty or a hundred heads, but in any case the head in the middle was invulnerable. It was terrible when these hideous mouths - whether the snake was asleep or awake - let out a putrid breath, a breath, the poison of which was deadly. No sooner did a death-defying man cut off the head of the monster than two new heads grew out of the spot, which were even more terrifying. Eurystheus, king of Argos, commissioned Heracles in his second task to kill this lernean water snake.

Constellation Hydra
Constellation Hydra: Illustration from «Uranometria» by Johann Bayer, copper engraving by Alexander Mair, 1603 [28]

So Heracles went out and his nephew Iolaos, a skilled Calydonian hunter, went with him. First he tried to drive the snake out of its lair with incendiary arrows, then he tried to kill it with the gigantic club, but unsuccessfully. Even the razor-sharp sickle sword did not help much, because every head grew back - not just once, but twice. Heracles sent Iolaos into the forest to light a fire so that incendiary torches could be brought. He pressed the torches onto the freshly made wounds and prevented them from growing again. This attack would almost have been thwarted, because Hera hated the illegitimate son of her husband Zeus from the bottom of her heart and sent a large cancer that stabbed the hero in the heel in this dangerous situation. But Heracles trampled on the animal and flung it away. He and his nephew finally beheaded the snake completely and thus freed the city of Lerna from great danger. Heracles then dipped his arrowheads in the poisonous blood that oozed from the serpent's necks. From then on, his arrows were even more dangerous than they were before.

The northern water snake is also known as the female water snake and the large water snake and also has the Latin names Hydra, Hydra et Crater or Hydra et Corvus. The constellation Faelis, Felis or Cat used to exist south of the Northern Water Snake, but is no longer recognized today. [20]


  • [9] «Drehbare Sternkarte SIRIUS» von H. Suter-Haug; Hallwag-Verlag, Bern
  • [15] «Hartung's Astronomical Objects for Southern Telescopes» by David Malin and David J. Frew; Melbourne University Press 1995; ISBN 0-522-84553-3
  • [20] «Sternbilder und ihre Mythen» von Gerhard Fasching; Zweite, verbesserte Auflage; Springer Verlag Wien, New York; ISBN 3-211-82552-5 (Wien); ISBN 0-387-82552-5 (New York)
  • [28] «Uranometria omnium asterismorum continens schemata, nova methodo delineata aereis laminis expressa» Johann Bayer, Augsburg, 1603; DOI:10.3931/e-rara-309
  • [150] IAU: The Constellations, 11. Oktober 2020;
  • [154] Yale Bright Star Catalog, 15. Oktober 2020;