Sunday, April 29, 2007

Hydra is the largest modern constellation but one of the least recognized ones. It is visible this time of year stretching from Cancer in the west to Libra in the east. It takes almost six hours to fully rise. Throughout its course it lays just south of the ecliptic and spans four of the zodiacal constellations. Its only bright star is Alphard which lays just south and a little to the east of the easily visible Regulus in Leo. Alphard (alpha Hydra) is giant orange star of apparent magnitude 2.0, and it is about 85 light years distant. It is from the Arabic and means "the solitary one".
Hydra was one of the 48 constellations recognized by Ptolemy, and its most common mythological reference is to the Hydra of Lerna that Heracles slew as one of his twelve labours. The lair of this water snake was beneath the lake of Lerna in the Argolid where it was reputed to guard an entrance to the underworld. The Hydra was reputedly one of the children of Typhon and Echidna, giants who waged war against the gods of Olympus. Its siblings were the Nemean Lion, the Chimaera and Cerebus. Like Cerebus Hydra was a multi-headed monster who grew two heads back for every one cut off. Heracles was stymied until he asked his nephew Iolaus for help. Iolaus came up with the idea of cauterizing each stump as the head was cut off, thus preventing regrowth. One of the heads, however, was immortal. When Heracles cut that one off he placed the still living head under a great rock where it could do no harm. When Heracles returned to Eurystheus, an agent of Hera who hated Heracles, who had assigned him his labours Eurystheus declared that the help of Iolaus made this labour invalid. Heracles used the poisonous blood from the Hydra applied to an arrow to kill the centaur Nessus as another one of his labours. It was the tainted blood from Nessus' cloak that eventually killed Heracles.
Another version of the origin of Hydra says that Apollo sent his servant the crow (the constellation Corvus) to fetch water in a cup (the constellation Crater), but the crow dallied lazily and brought back the water snake Hydra in the cup as an excuse. Apollo angrily threw the three of them into the sky.

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