Ancient Egyptians Tracked Eclipsing Binary Star Algol

Discovery News (Jennifer Ouellette)

Turn your telescope to the constellation of Perseus and you might note an unusual star called Algol, dubbed the "Demon Star" or the "Raging One." You wouldn't notice anything much different at first, unless you happened to be looking during a window of a few hours -- every 2.867 days -- when Algol's brightness visibly dims.

This unusual feature was first noticed back in 1667 by an astronomer named Geminiano Montanari, and later confirmed -- with a proposed possible mechanism -- in 1783 by John Goodricke, who precisely measured the period of variability: it dims every 2.867 days.

But a new paper by researchers at the University of Helsinki, Finland, claims that the ancient Egyptians may have recorded Algol's periodic variability 3000 years ago, based on their statistical analysis of a bit of papyrus known as the Cairo Calendar.

This isn't the first time people have hypothesized that Algol's variable nature was known prior to its discovery in the 17th century. Certainly it was a familiar object, prominent in mythology and lore. In the second century, Ptolemy referred to Algol as the "Gorgon of Perseus," and associated it with death by decapitation. (In Greek mythology, the hero Perseus slays the snake-headed Gorgon, Medusa, by chopping off her head.)

Science News (Nadia Drake)

The blinking of a distant star may be chronicled in an ancient Egyptian calendar created more than 3,000 years ago to distinguish lucky days from unlucky ones.

Known today as the Demon Star, the three-star system Algol sparkles in the constellation Perseus, near the eye of Medusa’s severed head. Observers on Earth can see Algol twinkling when the two closest members of the system eclipse one another: Every 2.867 days, as the dimmer star crosses between Earth and the brighter star, the Demon Star’s light appears snuffed.

A repeating pattern of similar duration appears in the Cairo Calendar, a roll of papyrus dating to 1271 B.C. that characterizes each day as all good, all bad or a mix. The occurrence of all-good days matches Algol’s brightness fluctuations, researchers from the University of Helsinki report in a paper posted April 30 on arXiv.org.

“They seem to have established rather clearly that there is a periodicity,” astrophysicist Peter Eggleton of Lawrence Livermore National Laboratory in California, says of the team’s analysis of the calendar. “What they haven’t established to my mind is that it is most likely due to a variable star.”