Constellation
Perseus
Perseus is the northern constellation of the hero who saved Andromeda, still holding the head of Medusa, marked by the winking star Algol.
The myth
Perseus is the hero who killed the gorgon Medusa, whose gaze turned anyone who met it to stone, and who then rescued the princess Andromeda from a sea monster on his way home. In the sky he still carries Medusa’s severed head, marked by the star Algol.
The demon star
Algol, the head of Medusa, is one of the strangest stars you can watch with the naked eye. Every two days and twenty one hours it noticeably fades for a few hours, then brightens back. We now know it is two stars, one eclipsing the other. The ancients did not, yet culture after culture gave it an uneasy name. Ours comes from the Arabic for the ghoul. Its regular dimming was first timed properly in 1783 by John Goodricke, a young deaf astronomer in York, who also suggested the eclipse explanation.
How to find it
Perseus lies along the Milky Way between the W of Cassiopeia and the bright golden star Capella. Its stars make a rough, curved Y, with the hero’s body sweeping out from the point where Algol sits. Autumn and winter evenings are best from the northern hemisphere. Between Perseus and Cassiopeia, binoculars show the Double Cluster, two rich star clusters side by side, one of the finest sights in the northern sky.
The Perseids
Every August the Perseid meteor shower seems to pour out of this constellation. On a dark night near the peak you can see dozens of meteors an hour, and the shower has been watched for close to two thousand years. In parts of Europe the August meteors were called the tears of St Lawrence, because they peak close to his feast day on 10 August.
A star you can find in your chart
By Hali’s 2026 star positions Algol sits at 26 degrees of the sign Taurus, and the Sun passes it around 17 May each year. Ptolemy gave the gorgon’s head the nature of Saturn and Jupiter, and later astrologers made Algol the most feared star in the sky, tied to violence and losing one’s head. Modern fixed star astrologers usually read it more kindly, as raw intensity and the nerve to face what others avoid.
Common confusions
Perseus is not a zodiac constellation, though Algol sits at a zodiac degree by longitude. And Algol is not dangerous. It is two ordinary stars that happen to line up with us, and its winking is pure geometry.
Questions
Why does Algol change brightness?
Algol is really two stars orbiting each other. Every two days and twenty one hours one passes in front of the other and the star visibly dims for a few hours. The ancients could see the change without understanding it, and named it the ghoul.
Are the Perseids named after Perseus?
Yes. The Perseid meteor shower, which peaks every August, appears to radiate from this constellation. The meteors are really dust from Comet Swift Tuttle burning up in our atmosphere, and Perseus is just the direction they seem to come from.
Sources: Standard references, Greek myth and star name scholarship. Hali star positions for 2026.