Hydra, the water snake, is the largest constellation in the sky. It lies in the southern hemisphere, stretched across 102.5°.
Hydra’s head is located south of the constellation Cancer and its tail lies between Centaurus and Libra. The constellation was first catalogued by the Greek astronomer Ptolemy in the 2nd century. It represents the Lernaean Hydra from the Greek myth of Heracles’ Twelve Labours. Sometimes it is taken to represent the water snake from the myth about the crow that tried to trick the god Apollo by blaming the snake for its tardiness in fetching the god some water.
Notable deep sky objects in Hydra include the open cluster Messier 48, the globular cluster Messier 68, the Southern Pinwheel Galaxy (Messier 83), the Hydra Cluster of galaxies, Tombaugh’s Globular Cluster (NGC 5694), the Ghost of Jupiter nebula, and the spiral galaxy ESO 510-G13.
FACTS, LOCATION & MAP
Hydra is the largest of the 88 constellations. It occupies an area of 1303 square degrees in the night sky. The constellation lies in the second quadrant of the southern hemisphere (SQ2) and can be seen at latitudes between +54° and -83°. The neighboring constellations are Antlia, Cancer, Canis Minor, Centaurus, Corvus, Crater, Leo, Libra, Lupus, Monoceros, Puppis, Pyxis, Sextans and Virgo.
Hydra belongs to the Hercules family of constellations, along with Aquila, Ara, Centaurus, Corona Australis, Corvus, Crater, Crux, Cygnus, Hercules, Lupus, Lyra, Ophiuchus, Sagitta, Scutum, Sextans, Serpens, Triangulum Australe and Vulpecula.
Hydra contains three Messier objects: Messier 48 (M48, NGC 2548), Messier 68 (M68, NGC 4590), and Messier 83 (Southern Pinwheel Galaxy, M83, NGC 5236). It has 13 stars with known planets. The brightest star in Hydra constellation is Alphard, Alpha Hydrae, with an apparent magnitude of 1.98. There are two meteor showers associated with the constellation: the Alpha Hydrids and the Sigma Hydrids.
MYTH
Hydra constellation as depicted by the Greeks is an adaptation of the Babylonian constellation MUL.DINGIR.MUŠ, which was one of the two Babylonian constellations that represented a serpent and loosely corresponded to Hydra. The other constellation corresponded to the Greek constellation Serpens. The Babylonian constellation represented a mythological hybrid of a serpent, bird and lion.
Hydra constellation is usually associated with the second of Heracles’ labours in Greek mythology. Hydra was a giant multi-headed creature fathered by the monster Typhon and Echidna, who was half-woman, half-serpent. The dragon Ladon, that guarded the garden of the Hesperides, was Hydra’s brother. The dragon, also killed by Heracles, is represented by the constellation Draco, while the hero is commemorated by the constellation Hercules.
In mythology, Hydra had nine heads and one of them was immortal. The celestial Hydra is depicted with only one head, presumably the immortal one.
The monster lived near the town of Lerna, where it ravaged the land and killed cattle. Heracles, faced with a difficult task, first shot flaming arrows into the Hydra’s lair and smoked it out. Then he fought with it, smashing the creature’s heads one by one with his club. Every time he smashed one, two new heads would grow in its place. While the two fought, Heracles was distracted by a crab, which crawled out of the swamp and attacked his foot. Heracles killed the crab and Hera, a sworn enemy of his, placed it among the stars as the constellation Cancer.
Heracles was able to defeat the Hydra when his charioteer Iolaus helped him by burning the stumps of each head that Heracles struck off, and eventually Heracles cut off the immortal head and buried it under a rock. He dipped his arrows in Hydra’s poisonous blood, which would eventually lead to his own death.
In a different myth, the constellation Hydra is associated with the water snake on which Apollo’s crow blamed its tardiness. The god had sent the bird, represented by the constellation Corvus, to fetch him some water in a cup. The cup is associated with the constellation Crater. The crow was distracted by a fig tree and stopped to feast. When it finally returned to Apollo, it said the water snake was to blame, but the god saw through the bird’s lie and punished it by placing it into the sky. Apollo also turned the water snake and the cup into constellations. In the sky, the water snake (Hydra) eternally prevents the crow (Corvus) from drinking out of the cup (Crater).
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