mardi 23 septembre 2008


Perseus is one of the most famous Greek heroes. The characters in the story of Perseus are represented by six constellations that occupy a substantial part of the sky. The constellation depicting Perseus lies in a prominent part of the Milky Way, which is perhaps why Aratus termed him ‘dust-stained’.
In Greek myth, Perseus was the son of Danaë, daughter of King Acrisius of Argos. Acrisius had locked Danaë away in a heavily guarded dungeon when an oracle foretold that he would be killed by his grandson. But Zeus visited Danaë in the form of a shower of golden rain that fell through the skylight of the dungeon into her lap and impregnated her. When Acrisius found out, he locked Danaë and the infant Perseus into a wooden chest and cast them out to sea.
Inside the bobbing chest Danaë clutched her child and prayed to Zeus for deliverance from the sea. A few days later, the chest washed ashore on the island of Seriphos, its cargo still alive but starved and thirsty. A fisherman, Dictys, broke the chest open and found the mother and child. Dictys brought up Perseus as his own son.
The brother of Dictys was King Polydectes, who coveted Danaë as a wife. But Danaë was reluctant and Perseus, now grown to manhood, defended her from the king’s advances. Instead, King Polydectes hatched a plan to get rid of Perseus. The king pretended he had turned his attentions to Hippodameia, daughter of King Oenomaus of Elis. King Polydectes asked his subjects, including Perseus, to provide horses for a wedding present. Perseus had no horse to give, nor money to buy one, so Polydectes sent him to bring the head of Medusa the Gorgon.
The Gorgons were three hideously ugly sisters called Euryale, Stheno and Medusa. They were the daughters of Phorcys, a god of the sea, and his sister Ceto. The Gorgons had faces covered with dragon scales, tusks like boars, hands of brass and wings of gold. Their evil gaze turned to stone anyone who set eyes on them. Euryale and Stheno were immortal, but Medusa was mortal. She was distinguishable from the others because she had snakes for hair. In her youth Medusa had been famed for her beauty, particularly that of her hair, but she was condemned to a life of ugliness by Athene in whose temple she had been ravished by Poseidon.
A Gorgon’s head would be a powerful weapon for a tyrannical king to enforce his rule, but King Polydectes probably thought that Perseus would die in his attempt to obtain it. However, the king had reckoned without Perseus’s family connections among the gods. Athene gave him a bronze shield which he carried on his left arm, while in his right hand he wielded a sword of diamond made by Hephaestus. Hermes gave him winged sandals, and on his head he wore a helmet of darkness from Hades that made him invisible.
Under the guidance of Athene, Perseus flew to the slopes of Mount Atlas where the sisters of the Gorgons, called the Graeae, acted as lookouts. The Graeae were poorly qualified for the task, since they had only one eye between the three of them, which they passed to each other in turn. Perseus snatched the eye from them and threw it into Lake Tritonis.
He then followed a trail of statues of men and animals who had been turned to stone by the gaze of the Gorgons. Unseen in his helmet of invisibility, Perseus crept up on the Gorgons and waited until night when Medusa and her snakes were asleep. Looking only at her reflection in his brightly polished shield, Perseus swung his sword and decapitated Medusa with one blow. As Medusa’s head rolled to the ground, Perseus was startled to see the winged horse Pegasus and the armed warrior Chrysaor spring fully grown from her body, the legacy of her youthful affair with Poseidon. (Pegasus is commemorated in a constellation of its own.) Perseus rapidly collected up Medusa’s head, put it in a pouch and flew away before the other Gorgons awoke.
Drops of blood fell from the head and turned into serpents as they struck the sands of Libya below. Strong winds blew Perseus across the sky like a raincloud, so he stopped to rest in the kingdom of Atlas. When Atlas refused him hospitality, Perseus took out the Gorgon’s head and turned him into the range of mountains that now bear his name.
The following morning Perseus resumed his flight with new vigour, coming to the land of King Cepheus whose daughter Andromeda was being sacrificed to a sea monster. Perseus’s rescue of the girl, one of the most famous themes of mythology, is told in detail under the entry for Andromeda. Perseus returned with Andromeda to the island of Seriphos, where he found his mother and Dictys sheltering in a temple from the tyranny of King Polydectes. Perseus stormed into the king’s palace to a hostile reception. Reaching into his pouch, Perseus brought out the head of Medusa, turning Polydectes and his followers to stone. Perseus appointed Dictys king of Seriphos. Athene took the head of Medusa and set it in the middle of her shield.
Incidentally, the prophecy that had started all these adventures – namely, that Acrisius would be killed by his grandson – eventually came to pass during an athletics contest when a discus thrown by Perseus accidentally hit Acrisius, one of the spectators, and killed him. Perseus and Andromeda had many children, including Perses, whom they gave to Cepheus to bring up. From Perses, the kings of Persia were said to have been descended.

In the sky, Perseus lies next to his beloved Andromeda. Nearby are her parents Cepheus and Cassiopeia, as well as the monster, Cetus, to which she was sacrificed. Pegasus the winged horse completes the tableau. Perseus himself is shown holding the Gorgon’s head. The star that Ptolemy called ‘the bright one in the Gorgon head’ is Beta Persei, named Algol from the Arabic ra’s al-ghul meaning ‘the demon’s head’. Algol is the type of star known as an eclipsing binary, consisting of two close stars that orbit each other, in this case every 2.9 days. Algol varies in brightness as the two stars eclipse each other. Its variability was discovered in 1669 by the Italian astronomer Geminiano Montanari.
The brightest star in the constellation, second-magnitude Alpha Persei, has two alternative names. One is Mirphak (or Mirfak), from the Arabic for ‘elbow’. The other name is Algenib from the Arabic meaning ‘the side’, which is where Ptolemy described it as lying. Perseus is depicted holding aloft his sword in his right hand. This hand is marked by what Ptolemy termed a ‘nebulous mass’ – in fact, a twin cluster of stars now called the Double Cluster.

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