Star Tales – Hydra

Hydra is the largest of the 88 constellations, winding a quarter of the way around the sky. Its head is south of the constellation Cancer, the Crab, while the tip of its tail lies between Libra, the Scales, and Centaurus, the Centaur. Yet for all its size there is nothing prominent about Hydra. Its only star of note is second-magnitude Alphard, a name that comes from the Arabic al-fard appropriately meaning ‘the solitary one’.

The water-snake features in two legends. First, and most familiar, the Hydra was the creature that Heracles fought and killed as the second of his famous labours. The Hydra was a multi-headed creature, the offspring of the monster Typhon and the half-woman, half-serpent called Echidna. Hydra was thus the brother of the dragon that guarded the golden apples, commemorated in the constellation Draco. Hydra reputedly had nine heads, the middle one of which was immortal. (In the sky, though, it is shown with one head only – perhaps this is the immortal one.)

Hydra lived in a swamp near the town of Lerna, from where it sallied forth over the surrounding plain, eating cattle and ravaging the countryside. Its breath and even the smell of its tracks were said to be so poisonous that anyone who breathed them died in agony.

Heracles rode up to the Hydra’s lair in his chariot and fired flaming arrows into the swamp to force the creature into the open, where he grappled with it. The Hydra wrapped itself around one of his legs; Heracles smashed at its heads with his club but no sooner had one head been destroyed than two grew in its place. To add to Heracles’s worries, a huge crab scuttled out of the swamp and attacked his other foot, but Heracles stamped on the crab and crushed it. The crab is commemorated in the constellation Cancer.

Heracles called for help to his charioteer Iolaus who burned the stump of each head as soon as it was struck off to prevent others growing in its place. Finally Heracles cut off the immortal head of the Hydra and buried it under a heavy rock by the roadside. He slit open the body of the Hydra and dipped his arrows in its poisonous gall.

Hydra winds across the pages of John Flamsteed’s Atlas Coelestis. On its back are Corvus and Crater, associated with it in legend.

A second legend associates the water-snake with the constellations of the Crow (Corvus) and the Cup (Crater) that lie on its back. In this story, the crow was sent by Apollo to fetch water in the bowl, but loitered to eat figs from a tree. When the crow eventually returned to Apollo it blamed the water-snake for blocking the spring. But Apollo knew that the crow was lying, and punished him by placing him in the sky, where the water-snake eternally prevents him from drinking out of the bowl.

In Chinese astronomy, Hydra contained three constellations after which lunar mansions were named. First of these was Liu, also the name of the 24th lunar mansion. Liu consisted of the stars we visualize as the head of Hydra (Theta, Omega, Zeta, Rho, Epsilon, Delta. Sigma and Eta Hydrae). Liu means willow, a traditional symbol of mourning and of rebirth. The constellation was also said to represent the chef of the celestial kitchen. To the south of Liu was a ring of fainter stars forming Waichu, a kitchen, possibly for preparing sacrifices. South again of Waichu was a single star (probably 12 Hydrae) called Tianji, representing an assessor who decided whether animals were old enough to be sacrificed. This is another example, common in the Chinese sky, of several constellations in one area forming a seasonal theme.

The second Chinese constellation in present-day Hydra with an eponymous lunar mansion (the 25th) was Xing, which consisted of a chain of stars centred on Alpha Hydrae (Alphard); the chain started at Iota Hydrae in the north and ended at 26 Hydrae in the south. Xing marked the neck of the Red Bird and Alphard itself was known as Niao, the Bird Star. The third Chinese constellation within modern Hydra to give its name to a lunar mansion (the 26th) was Zhang, a name meaning an outstretched net, possibly for catching birds in flight. It consisted of six stars including Lambda, Mu and Upsilon-1 Hydrae. Zhang was also seen as the bow of an archer, who was represented by the stars of neighbouring Crater. Closer to the tail of Hydra, Gamma and Pi Hydrae formed Ping, a flat plain for carriage driving.