The story of Perseus is quite long so if you prefer to skip to the Astronomical stuff, click here.
The story of Perseus begins as so often with Zeus's lust for a young mortal woman. In this case it was Danae, only child of Akrisios, King of the Argolid. Akrisios had been told by the oracle that Danae would have a son who would kill him, so he locked her away in a dungeon to keep her away from all men. But Zeus came to her is a shower of golden rain through a narrow window and in due course she gave birth to a son, Perseus. Akrisios, refusing to believe that Zeus was the father, locked Danae and the baby in a chest and threw them out to sea. Zeus protected them and directed the chest to drift to the island of Seriphos in the Cyclides where it was caught by Diktys, brother of the local king, Polydektes, and he took Danae and her baby into his home where Perseus grew up uneventfully. But it couldn't last.
Polydektes fell in love with Danae and determined to have her, but the presence of a grown son to protect her was a problem. So he pretended he intended to marry another and was collecting horses as a bridal gift. Perseus bragged that he would even collect the head of the Medusa, the only mortal Gorgon. Since the sight of a Gorgon would turn anyone to stone, Polydektes took him up on the offer satisfied that he would never return. But Perseus was a son of Zeus and so was favoured by help from the gods, in this case by Athene and Hermes. They advised him to seek the help of the Graiai, sisters of the Gorgons, old crones who shared one tooth and one eye between them. At first they were reluctant to help, but Perseus stole their tooth and eye and refused to return them until they told him where to find some nymphs who could help him.
The nymphs provided him with winged sandals, a cap of invisibility, and a special bag in which to carry Medusa's head. In addition, Hermes gave him a sickle of adamant with which to behead her. Perseus had his own shield of polished bronze, so was ready for his task.
He flew on his winged sandals over Ocean to the west to the land of the Gorgons where he found them sleeping. He was careful not to look at them directly but through their reflection in his shield. Athene guided his hand as he swung the scythe and cut off Medusa's head and stuffed it into his bag, and flew off. On his way home he used the head of Medusa twice. When Atlas refused him hospitality he showed him the head and tuned him into Mount Atlas big enough to support the heavens with all its stars. As he passed over Ethiopia, he saw Andromeda chained to the rocks, saved her from the monster in return for her hand in marriage. When this was opposed by Phineus (her uncle) to whom she had been promised, Perseus simply turned Phineus and his supporters to stone. Perseus stayed with Kepheus for a year in which time Andromeda gave birth to a son, Perses. Perseus left his son to be brought up by Kepheus, who had no male heir, and returned to Seriphos where he found his mother and Diktys being persecuted by Polydektes. Perseus found Polydektes and his followers feasting in the palace and revealed the Medusa, turning them all to stone. He made Diktys king in place of Polydektes. His task now over, Perseus returned the sandals, the scythe, and the cap to Hermes, and the head of Medusa to Athene who put it in the centre of her breastplate.
Perseus returned to Argos to introduce Andromeda to his grandfather, Akrisios. However Akrisios remembered the prophesy of the oracle and fled to Larissa. Not knowing this, Perseus also went to Larissa to take part in some games, and he accidentally killed his grandfather whilst throwing the discus. Ashamed to take his rightful place as King of Argos, Perseus exchanged his kingdom with Tiryns. Andromeda bore him a daughter and five more sons. Their great-grandson would be the mighty Herakles. On their deaths, Perseus, Andromeda, Kepheus, and Cassiopeia were all immortalised in the stars.
Although the brightest star is Mirphak (α) of magnitude 1.8, the most interesting star is Algol (β) which is the prototype eclipsing binary. It consists of two stars in close orbit around one another with a period of 2 days 20 hours 48 minutes and 56 seconds. The orbit is such that, as seen from here, one star passes in front of or behind the other, causing a change in the apparent brightness. From this variation it is possible to deduce much about the two stars. The primary is a white star 100 times as luminous as the Sun with a diameter of 4 million kilometres. The secondary is about three times as luminous as the Sun and 5.5 million kilometres in diameter and separated from the primary by 10.5 million kilometres. As the dimmer component passes in front of the brighter star, the combined magnitude drops from 2.1 to 3.4. When it passes behind the primary, the loss of light is less than 0.1 of a magnitude. (There is in fact a third star in the system well away from the eclipsing pair. It is of similar magnitude but separated by only 0.5 arc-sec.) This picture was taken only 1 hour and 19 minutes after Algol was at its minimum and the eclipse lasts a total of 10 hours, so Algol will not have been far from its minimum at the time.
There are four open clusters in the constellation, M34, NGC 869, NGC 884, and Mel 20 of which NGCs 869 and 884 are so close that they make a pretty double cluster. Mel 20 is a very large cluster (185 minutes in diameter) which includes Mirphak.
The picture was taken at 00:45 UT on 7 October 2010 with my Canon 1000D camera with an 18-mm lens at f/4 with an exposure of 30 seconds at ISO 1600. In PhotoImpact, the gamma was increased to 1.7 and the contrast to 30 before removing the background colour caused by light pollution. The size reduced to 16% and the gamma increased again to compensate for the loss caused by the reduction and the final image rendered in monochrome.