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Constellation Hydra (Sea Serpent)

Constellation Hydra (Sea Serpent)

Southern Hemisphere Northern Hemisphere

Spring Summer

Sea Serpent


With an area of 1,303 square degrees, the Sea Serpent (lat. Hydra) is the largest constellation in the night sky. It's so big that it takes almost seven hours to rise completely in the sky. Nevertheless, it is not very noticeable, only the main star Alphard has a magnitude of two.

How to spot Hydra

The Hydra can be seen for the first time completely in May at midnight. South of the Cancer is the collection of stars located that represent the head of the Hydra. You can find the Cup (lat. Crater) and the Crow (lat. Corvus) close in the north of the constellation. South of the Hydra there are the constellations Centaurus and Compass.


Two tales of Greek mythology are associated with the constellation of Hydra. The first one is about Apollo, who sent his crow with a cup to a spring to bring him water. However, on the way there, the crow was distracted by fruits and therefore fulfilled its mission much later. To appease Apollo, the crow came up with an excuse: At the spring, it found a sea serpent that it first killed and then slandered, claiming that it had blocked the access to the water for days. Apollo, however, recognized the untruthfulness and put the three parties in warning to all liars in the sky.

The more familiar version of the Hydra is associated with the mythical hero Hercules. One of his twelve tasks was to defeat the nine-headed monster of Lerna, the venomous snake Hydra. After Hercules had driven it into its hiding place with burning arrows, he attacked it with his sword. For every head he took off, however, two heads grew. The situation became even more delicate when Hera sent a crab to help Hydra. Eventually, however, Hercules managed to defeat the crab and later Hydra with the help of his nephew Iolaos. At Hera's request, Zeus placed the sea serpent and the crab in the starry sky.