It's time for part three of the series-within-a-series featuring the myth of Apollon and the raven. The previous parts were the constellation Corvus: the Raven, and the Constellation Crater: the Cup. This third installment is about the longest constellation we still recognize as a constellation today: Hydra, or the sea-serpent.

To recap the story of Apollon and the raven: the raven (or crow) was in service to Apollon, and was sent out on an errant for the Theos. He was asked to bring water to Him, but instead, he paused in his quest. Most commonly it is assumed is that he stopped for a meal of figs. When the raven returned without water, Apollon questioned him. Instead of giving a straight answer, the raven lied, and said he had been kept from the water by a snake. In some accounts, he actually had a snake in his talons as he said this. Apollon, however, saw that the raven was lying, and flung the raven, the krater with which the raven was supposed to collect water, as well as the snake into the sky, where they remain to this day.

Roman author Gaius Julius Hyginus (64 BC - 17 AD) talks about the serpent's continued function in his Astronomica:

"This is the sign on which the Crow sits and over which the Bowl is placed. [...] As long as the figs are ripening, the crow cannot drink, because on those days he has a sore throat. So when the god wished to illustrate the thirst of the crow, he put the bowl among the constellations, and placed the water-snake underneath to delay the thirsty crow. For the crow seems to peck at the end of its tail to be allowed to go over to the bowl." [2.40]

Another hydra the constellation is associated with is the Hydra vanquished by Hēraklēs as his second labour. After his victory over the Nemean lion, Hēraklēs is send off to handle another sticky problem: the Lernaean Hydra, who was raised from the earth by Hera just to end the life of Hēraklēs. The Lernaean Hydra (Λερναία Ὕδρα) was the offspring of Typhon, and layered in the swampy lake of Lerna. He realized he would need help for this labour, and asked it of his nephew Iolaus (Ἰόλαος). Together they devised a plan: Hēraklēs would cut off the heads, and Iolaus would sear the stumps shut, in this way, the heads could not regenerate. When Hēraklēs returns to Eurystheus after completing the labour, the king decrees that, because Hēraklēs could not have completed the labour without the help of Iolaus, the labour will not count against his total, and he will have to do an extra one to fulfill his debt.

On the hydra, Pausanias writes in his 'History of Greece'. He speaks of the birth place of the hydra, and of his alleged number of heads:

"At the source of the Amymone grows a plane tree, beneath which, they say, the hydra (water-snake) grew. I am ready to believe that this beast was superior in size to other water-snakes, and that its poison had something in it so deadly that Heracles treated the points of his arrows with its gall. It had, however, in my opinion, one head, and not several. It was Peisander76 of Camirus who, in order that the beast might appear more frightful and his poetry might be more remarkable, represented the hydra with its many heads." [2.37.4]

Constellations are often associated with the constellations they are surrounded with, and with no constellation this is clearer than with Hydra. Aratos, a Hellenic poet who flourished in Macedonia in the early third century BC, speaks best of Hydra in regards to his surrounding constellations in his 'Phaenomena':

"Another constellation trails beyond, which men call the Hydra. Like a living creature it winds afar its coiling form. Its head comes beneath the middle of the Crab, its coil beneath the body of the Lion, and its tail hangs above the Centaur himself. Midway on its coiling form is set the Crater, and at the tip the figure of a Raven that seems to peck at the coil." [443]

The constellation Hydra is visible at latitudes between +54° and −83°, and best visible at 21:00 (9 p.m.) during the month of April.