How the Ancient Egyptians understood the 'Demon Star' 3,200 years ago - and their calculations have helped solve a modern dilemma



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.

Not only that, their specific calculations have helped support a scientific line of inquiry which only emerged just a few years ago.



The binary system - two stars which rotate around each other - was first noted in modern astronomy by a John Goodricke, back in 1783.

He spotted how Algol - also known as the Demon Star - appeared to decrease in brightness for a few hours every 2.87 days, and was the first to theorise that this was two stars blocking each other's light in relation to Earth.

Or we thought he was the first - it turns out the Egyptians apparently had this all figured 3,000 years earlier.

The Algol binary stars slowly rotate each other in this artist's impression: The two stars - both about twice the mass of the sun - rotate around each other and swap material

Written in the skies: Algol's position is shown within the Perseus constellation

The Egyptians were huge star-gazers, taking copious and accurate notes about changes in the heavens, and using these to form predictions about lucky and unlucky parts of the day.



When Finnish researchers studied the Cairo Calendar, a badly-damaged but readable calendar highlighting the good and bad days of a year in 1200BC, they came to some startling observations.

For the Egyptions not only made observations, they made conclusions and calculations to figure out the inner mechanisms of the stars for their charts.

Two cycles were spotted in the Cairo Calendar. One lasted 29.6 days - almost exactly that of the lunar cycle.

And the other was 2.85 days - which researchers from the University of Helsinki in Finland ascribe to the Algol system.

And as the Egyptians made very specific calculations, their figures appear to have solved a very modern puzzle.

As the two stars rotate, their perceived brightness from the Earth takes a big dip every 2.85 days

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.

The Algo system has now been confirmed as a tertiary system - three stars in total.

The third star is much further out from the other two, with Algo A and B rotating around each other at a gap of about half the distance from the Earth to the Sun, and Algo C almost six times further away.

However the introduction of the third star - and the theory that the first two transfer matter between them - led scientists to believe their rotation would be slowing down over time.

With only 200 years since the first modern calculation of a rotation period of 2.867 Earth days, the theory could not be tested.