Intro and Visual description
Hydra the Water Snake is the largest and longest of the constellations, stretching from Cancer to Libra. Several constellations and asterisms ride on its back; from head to tail they are Sextans the Sextant, Crater the Cup, Corvus the Crow, and Noctua the Owl.
Hydra's brightest star is Alphard, which has an orangish tint.
Origin and History
Hydra is included in the ancient star catalogs of Eudoxos of Knidos, Aratos of Soli, and Ptolemy.
Skylore, Literature and Culture
Hercules was sent to kill Hydra, a sea monster which possessed the terrifying ability, whenever a head was cut off, to grow two heads in its place.
Cicero, De natura deorum, II.110, trans. of Phenomena by Aratos of Soli (ca. 220 B.C.):
Here Hydra rises from the nether realms,
And in her midmost coil the Wine-bowl (Crater) gleams,
While pressing at her tail the feathered Crow (Corvus)
Pecks with his beak; and here, hard by the Twins,
The Hound’s forerunner, in Greek named Prokyon.