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Perseus


Transit Date of principal star:
12 November


With a father like Zeus, it's no wonder Perseus became one of antiquity's most notable characters. Even his name ("per Zeus") identifies his lineage.

Zeus had fallen in love with Danae, the beautiful daughter of Acrisius, king of Argos. An oracle had predicted that Danae would some day bore a son who would kill the king, so Acrisius hid her in a bronze (or ivory) tower. But Zeus knew of her beauty, and one day he changed himself into a shower of gold dust and visited Danae's cell.

When the child Perseus was born, Acrisius put him and his mother in a wooden chest and threw it into the sea. The wooden chest floated to the island of Seriphos, where the fisherman Dictys rescued it. He took them to his brother Polydectes (or Polydeuces), who happened to be the king of Seriphos. Polydectes raised Perseus to manhood.

Perseus grew to found the city state of Mycenae, on the Peloponnesian peninsula, and become its first king. At least this is the myth. In reality, that city was founded at about 3000 BC, and ca 1650 BC to 1400 BC the Mycenaean civilisation was one of the most brilliant in all of Greece, until its sudden collapse ca 1300 BC.

As for Perseus, he is mostly remembered for one series of adventures: the killing of the Gorgon Medusa and the rescue of Andromeda.

The Gorgons were three sisters: Euryale ("wide roaming"), Stheino ("strong"), and Medusa ("cunning one"). They were originally very beautiful but Medusa committed an indiscretion with Poseidon one night in a temple of Athene. This goddess was so enraged over the sacrilege that she changed Medusa into a hideous monster with huge teeth and protruding tongue, claws in place of hands, snakes in place of tresses, large wings, and a look that would turn anyone into stone.

Needless to say, Medusa wasn't terribly popular. Indeed, her head became the ultimate prize; anyone who could chop it off would be an instant hero. But none were foolish enough to try. Until Perseus one day made a casual promise to Polydectes.

The thing was, Polydectes wanted to marry Perseus' mother Danae, but the king tried to keep his wishes secret by telling Perseus that he wished to take Hippodameia as a wife. Perseus had suspected the king of lusting after his mother, so he was quite relieved, so relieved he told him "If you wish to marry Hippodameia, I will do anything you ask of me. Even offer you the head of the Gorgon Medusa as a wedding present." "Fine," said Polydectes, "that would be a very nice gift indeed".

Athene had been listening; this was the moment she had been waiting for: someone to strike back at her worst enemy. Athene brought Perseus to Samos, where the Gorgons were living, and she showed him an image of the three, so he could distinguish amongst them. Then she warned Perseus to look at the reflection, never the face, lest he be turned to stone. So saying, Athene gave Perseus a brightly shining shield.

Perseus had more help in his quest for the Gorgon's head. Hermes gave him a sickle, but the most important items he got for himself: the winged sandals, the helmet that would make him invisible, and the magic wallet (to put the severed head in). To make a rather long story a little shorter, he managed to steal these items from the Stygian Nymphs, in the bowels of the earth, where they lived. Thus armed, Perseus set out to kill Medusa.

Perseus came across the three Gorgons asleep. Looking at his shield, he carefully studied each figure, making sure it was Medusa who would feel the blade of his sickle. Quickly then he sliced off Medusa's head and threw it into the magic wallet.

The winged horse Pegasus instantly flew out of her body. He too had been conceived by Poseidon in the temple of Athene, but Poseidon had chosen not let Pegasus come into the world, to placate the goddess. At Medusa's death, Pegasus was now free.

The Gorgon sisters frantically looked for the killer of Medusa, but the helmet worn by Perseus rendered him invisible.

With the winged sandals, Perseus made his escape. Again, to shorten the story considerably, he soon came across Andromeda, naked and chained to a rock for a terrible sea monster. Perseus quickly made a deal with Cepheus and Cassiopeia; for rescuing the maiden he would then win her hand.

After killing the sea monster, and rescuing Andromeda, Cassiopeia changed her mind about Perseus marrying her daughter. In the battle that followed, Perseus had to resort to desperate measures. He took the head of Medusa out of the magic wallet and brandished it. Instantly the warring parties, including both mum and dad, were turned to stone.

Perseus took his new bride back to Seriphos, where a new threat greeted him. Danae, his mother, had fled to a temple to avoid marrying Polydectes. The king was hosting a banquet; Perseus entered the palace and announced that he had brought the marriage gift, as promised. So saying, he showed them the Gorgon's head, turning the entire banquet party to stone. (The island of Seriphos contains a group of boulders which some still believe to be the petrified remains of the banquet.)

Some time later a discus flung by Perseus during some funeral games struck his grandfather, Acrisius, and killed him, thus fulfilling the prophecy, to the shame and sorrow of Perseus himself.


Perseus isn't a very clear asterism; some forms of the constellation have a straight line from alpha to theta, perhaps indicating Perseus' sword or sickle that he used to kill the Medusa.

However, as far back as Ptolemy's time, Perseus was seen as holding the head of Medusa, with Algol (beta Persei) being the "evil eye" of the Gorgon.

Perseus' stars are fairly bright. A good many of them go under other than Bayer names; several are notable binaries. There are also a few fine deep sky objects.


Double stars:

[See the Binocular Section link below for updates on the following data.]
Epsilon Persei is rather difficult because of the dim companion: 2.9, 8.1; PA 10, separation 8.8".

Zeta Persei is a multiple system, also with faint companions:

AB: 2.9, 9.5; 208 and separation 12.9".
C is a dim 11.3, PA 286 and separation 32.8";
D is 9.5, 195, 94.2".

Eta Persei is a fixed triple system; AB are yellow and blue.

AB: 3.8, 8.5; PA 300, separation 28.3".
C: 9.8; 268, separation 66.6".

Struve 331 is a splendid fixed binary: 5.4, 6.8; PA 85, separation 12.1".

It's found midway on a line between gamma Persei and tau Persei and just a bit south.

h1123 is a fine wide binary in the middle of M34: 8.5, 8.5; PA 248, separation 20.0".


Variable stars:

Perseus had many types of variable stars, many of which are too small to notice. Below are some of the more obvious examples.

Beta Persei (Algol) is a notable EA type eclipsing binary, changing from 2.12 to 3.39 every 2.8673 days (2d, 20h 48m 56s) as the companion eclipses the primary. The eclipse lasts roughly ten hours.

The name itself, Al Ghul, means "Mischief Maker"; it is sometimes called Ras Algol, Ra's al Ghul, "The Demon's Head".

This is a very bright white star, and the first eclipsing binary every discovered, in 1669 (thus giving the name "Algol variable" to this type of star). However the theory itself of an eclipsing binary being responsible for the variations in visual magnitude had to wait until 1783; this theory was only proved correct in 1889.

The whole system is a bit more complicated than one star occulting another. A third component, Algol C, orbits both A and B about every 1.86 years, and even more companions have been proposed, but not proven.

R Persei is a long-period variable, 8.1 to 14.8 every 209.89 days. The next maximum is scheduled for mid May 1997 (then that December). In 2000 the maximum should occur the last week of October.

S Persei is an SRc type variable, 7.9 to 12 every 822 days (2.25 years). The next maximum should occur in the last half of October, 1998.


Deep Sky Objects:

M34 (NGC 1039) is a fine open cluster containing about eighty stars. The cluster is considered about 100 million years old.

The cluster is about five degrees WNW of Algol (beta Persei), or more precisely twenty-seven arc minutes west of Algol and two degrees north.
NGC 869 and NGC 884 form the well known "Double Cluster", two open star clusters side by side, easily seen by naked eye or binoculars.

The clusters are both considered babies, 869 only being about 6.5 million years old, and 884 about 11-12 million years old.

The easiest way to find them is to form a triangle, using gamma Andromedae and alpha Persei. Then the northern point becomes the twin clusters.

NGC 1499, The California Nebula, is a gaseous nebula one degree north of zeta Persei, and stretching itself in an east-west direction. Unfortunately it is extremely faint and difficult to view. In fact binoculars might afford the best chance.


The Perseid Meteor Showers

This meteor shower is active every year from late July to late August, primarily in the Northern Hemisphere. Peak showers occur on either 12 August or 13 August with about a meteor every minute at its peak.

These showers derive from the Swift-Tuttle comet, which has an 130-year orbit.


For a more detailed appreciation of Perseus, visit the Binocular Section.


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All files associated with The Constellations Web Page are
Richard Dibon-Smith.