“The Demon Star” – Ancient Cairo Calendar Shows Egyptians Discovered the Binary Algol 3200 Years Ago

Algol, aka the Demon Star, is actually a binary star in the Perseus constellation, and has been discovered by a group of Finnish researchers, but startling evidence suggests the ancient Egyptians understood the inner mechanics of a binary star system, spinning through our skies 93 light years away, more than 3,200 years ago. It is one of the best known eclipsing binaries, the first such star to be discovered, and also one of the first (non-nova) variable stars to be discovered.


The eclipses in binary stars give precise information of orbital period changes. Algol brightens and dims every 2.867 days, a phenomenon first described in semi-modern western astronomy by John Goodricke, who wrote about what he saw with the naked eye back in 1783.The irregular orbital period changes of this longest known eclipsing binary continues to puzzle astronomers. The mass transfer between the two members of this binary should cause a long-term increase of the orbital period, but observations over two centuries have not confirmed this effect.

The Finnish reserach team presents evidence indicating that the period of Algol was 2.850 days three millenia ago. For religious reasons, the ancient Egyptians recorded this period into the Cairo Calendar, which describes the repetitive changes of “The Raging one.” Cairo Calendar may be the oldest preserved historical document of the discovery of a variable star.


The data from the Cairo Calendar however describes the binary period as 2.85 days –slightly less than the 2.867 days observed today. The Helsinki team doesn’t believe this difference is due to error, they think it’s because the period has changed over time, and that they say, gives credence to the theory that the Algol binary is actually a three star system as new research suggests:  Beta Persei A, B, and C.

Why is it the Demon Star?

The name Algol translates from the Arabic word for ‘Demon’.

Many of our constellations get their names from Greek heroes, such as Perseus, who tackled the evil, snake-haired monster Medusa, whose very appearance would turn people to stone.

Perseus then took Medusa’s head, slung it on his belt, and defeated the sea monster Cetus by showing him the grisly relic.

For his triumphs, Perseus was immortalised in the stars.

So why is Algos ‘the Demon star? Because the star hangs eternally on Perseus’s belt, ready to turn the next monster into stone.

Source and author: dailygalaxy binary




One response to ““The Demon Star” – Ancient Cairo Calendar Shows Egyptians Discovered the Binary Algol 3200 Years Ago

  1. Incredible story… Thank you so much for sharing it. It is amazing how much seems to be uncovering itself and making so much sense out of what is occurring today in our skies. A bit scary, a bit incredible.